Department of Biochemistry, Microbiology and Biotechnology

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Abundance and diversity of microalgae in freshwater eutrophic systems of Namibia and optimization of lipid and biomass production in Nannochloropsis Limnetica
(University of Namibia, 2017) Garus-Oas, Carol H.
Namibia is one of the driest countries in Sub-Saharan Africa, and man-made dams play an important role on salvaging water. These dams are however periodically frequented by microalgae blooms that pose devastating effects on the water quality, making water treatment processes troublesome and cost prohibitive. However, these unicellular organisms can be exploited in various ways especially when cultivated in controlled and closed systems under optimal conditions of light, temperature, pH and nutrient concentrations. Biomass can be optimized to produce proteins that can be a source of fertilizers, while lipids can be extracted to refine into various hydrocarbons such as biodiesel and bioethanol. It is therefore essential to study the dynamics of these microalgae and provide necessary guidelines on how to utilize them. The first objective of the current study was to assess the seasonal relative genera abundance, diversity, richness and eveness of microalgae in three fresh water eutrophic systems in central Namibia. The hypothesis was to seek whether there is no significant difference in the seasonal relative genera abundance of microalgae per dam in three freshwater eutrophic systems of Namibia namely, Goreangab dam, Von Bach dam and Swakoppoort dam. Microalgae were enumerated with the use of a haemocytometer and identified to genus level during the dry and the wet seasons. Environmental parameters such as turbidity, pH, temperature, dissolved oxygen, macronutrients (i.e. phosphates, nitrates and ammonia) and dam water volumes, were also measured during this time to assess how they are correlated to the relative genera abundance per dam. All statistical analyses were performed using the SPSS software package (IBM statistics Version 23) and differences in data were considered significant at p < 0.05. The Shannon-Weiner diversity index was applied to calculate the microalgae diversity per dam. Evenness Index (J’) and Margalef’s Index (d) was used to calculate the species evenness and species richness, respectively per dam. Results revealed that seasonal relative genera abundance was not normally distributed (p = 0.000) per dam. Von Bach dam seasonal relative genera abundance was statistically not significant (p = 1.000). Goreangab dam seasonal relative genera abundance was statistically not significant (p = 0.652) and Swakoppoort dam relative genera abundance was statistically not significant (p = 0.444). Data presentation of relative genera abundance showed Chlorophyceae as the most dominant class followed by Cyanophycea for Swakoppoort and Von Bach dams for both seasons. Chlorophyceae was the most abundant microalgae class in Goreangab dam during the dry season, while Florideophyceae and Cyanophycea were the second most abundant classes during the wet season. Microcystis was the most abundant genus for Swakoppoort and Goreangab dams during dry and wet seasons. However, in Von Bach dam Aulacoseira was the most abundant microalgae. The Shannon-Weiner diversity index showed that Von Bach dam had the highest diversity of 3.21 followed by Goreangab dam (2.32) and the lowest diversity was found in Swakoppoort dam (2.13). Species evenness varied between 0.46 - 0.65 for Swakoppoort and Goreangab dams, but was higher for Von Bach dam (0.72 - 0.97). Species richness calculated with the Margaleff’s index was around 1 for all the dams and throughout all the seasons, except for Swakoppoort dam during the dry season where it was 1.5. According to the statistical analysis performed, all of the environmental parameters measured for all the dams during the dry and wet seasons were not normally distributed (p = 0.000). Correlation tests showed that all the environmental parameters captured during the time for all the dams were not statistically significant (p > 0.05). According to the literature review, the higher relative abundance of the class Chlorophycea observed during the time of sampling for the current study was due to their higher growth rates. The higher relative abundance of the genera Microcystis was due to their physiological advantage (i.e. nitrogen fixing, surface to volume ratios, intracellular gas vesicles for buoyancy and slimy undulation to enable photomovement) over other microalgae identified during the time of sampling. Microcystis was prominent mostly in Goreangab dam which was characterized by optimum combination of environmental factors such temperature, pH levels and high macronutrients when compared to the other dams. The current study recommends assessment of microalgae diversity and abundance over a one year period with sampling at least every second week. It will be essential to also study other macro-and micronutrients, trace elements, chlorophyll a along with their cumulative effects on microalgae composition. Furthermore, the study advises assessment of topography and mechanical extractions for water transfer on microalgae composition. Moreover, a variety of mesh sizes will constitute a more diversified pool of microalgae to study. The second objective of the study was to optimize the neutral intracellular lipid and biomass production in Nannochloropsis limnetica under variant nitrate concentrations in highly controlled conditions in lab-scaled bioreactors over duration of 14 days. The hypothesis was to seek whether there was no significant difference in growth rate, biomass and neutral intracellular lipid productivity of Nannochloropsis limnetica in “normal nitrate” (3.53 M), “nitrate replete” (7.06 M), “moderate nitrate deplete” (1.765 M), and “high nitrate deplete” (0.8825 M) cultivated under the same conditions of light, pH, temperature and CO2 concentration. The parameters measured throughout this process include optical density to measure growth rates, gravimetrical measurements of bio dry mass/biomass (BDM), ion chromatography measurements for ions, pH as well as sterility tests. All statistical analyses were performed using the SPSS software package (IBM statistics Version 23) and differences in data were considered significant at p < 0.05. During the main-cultivation of Nannochloropsis limnetica, growth was observed in a characteristic pattern consisting of lag, exponential, stationary and declining phases. The growth rates across all of the Flasks during the main-cultivation were not normally distributed (p = 0.012). The statistical tests showed that they were statistically significant (p = 0.001). Bio dry mass increased linearly over time for all of the Flasks from 0 day-1 to the highest on 14 day-1 at the end of the experiment. Bio dry mass was normally distributed (p = 0.055). The statistical test showed that it was statistically not significant (p = 0.939). Bio dry mass and growth rates were moderate and positively correlated and statistically not significant (rs (8) = 0.529, p = 0.077). Relative fluorescence data recorded for all the Flasks was the highest only on the first couple of days during the lag phase and decelerated towards the end of the cultivation period. Therefore, there was no lipid accumulation. The relative fluorescence data captured for neutral intracellular lipid analysis showed that during the cultivation process all of the data were not normally distributed (p = 0.000). Statistical analysis showed it to be statistically significant (p = 0.112). Correlation tests performed between BDM and lipids was strong and negatively correlated and statistically significant (rs (8) = -0.765, p = 0.004). The relationship between lipids and growth rates was moderate, negatively correlated and statistically not significant (rs (8) = -0.501, p = 0.087). The highest growth rates were under “moderate nitrate deplete” at 6 days-1, 11.32 hours at 16.11 OD. The highest BDM value (7780 mg/L) was also captured for “moderate nitrate deplete” at 14 days-1, 19.47 hours at 60.27 mg/L nitrate. The highest relative fluorescence (neutral intracellular lipid content) was captured under “nitrate replete” at 2.387 % at 1 day-1, 6.28 hours and 2550.439 mg/L nitrate. The main-cultivation addressed the hypotheses set out. The study was successful in that it exponentially optimized the biomass production of Nannochloropsis limnetica in each of the four Flasks during the main-cultivation. These results suggest elaborate research on the biomass composition for various outputs such as proteins, lipids, carbohydrates, pigments et cetera. It was discovered during the current study that the various nitrate concentrations did not optimize lipid productivity. Therefore, it is proposed that other macronutrients such as phosphate concentrations along with variables such as light intensity and CO2 be manipulated for lipid optimization. Furthermore, in future studies, the Nile red method should be used in conjunction with other conventional gravimetric methods for lipid quantification and validation for the N.limnetica.
Abundance, species composition and diversity of small mammals and the prevalence and intensity of infestation of associated fleas (Siphonaptera) across an altitudinal gradient along the Ugab river, Namibia
(University of Namibia, 2021) Frans, Alma Inga
The objectives of the study were to determine and compare the abundance, species composition and diversity of small mammals and the associated fleas and to determine and compare the prevalence and intensity of infestation of fleas across an altitudinal gradient along the Ugab River, Namibia. Three sampling sites at different altitudes were selected, Outjo (high altitude site) at about 1300 m above sea level (a.s.l.), Vingerklip (middle altitude site) at about 1000 m a.s.l. and Brandberg (low altitude site) at 400 m a.s. l. Small mammals were trapped in January (hot wet season) and May (cold dry season) in 2018. A total of 159 small mammals belonging to seven rodents and two insectivore species were trapped during the entire study. Small mammals trapped included: Namaqua rock mouse (Micaelamys namaquensis), Natal multimammate rat (Mastomys natalensis), Red rock rat (Aethomys chrysophilus), lesser Red musk shrew (Crocidura hirta), pouched mouse (Saccostomus campestris), bushveld gerbil (Gerbiliscus leucogaster), black-tailed tree rat (Thallomys nigricauda), Acacia rat (Thallomys paedulcus) and bushveld elephant shrew (Elephantulus intufi). The abundance, species composition and diversity of small mammal hosts were not significantly different among the sampling sites during the two seasons (hot wet and cold dry seasons). A total of 139 fleas were collected from small mammals during the study. Three flea species were recorded from small mammal hosts during the study, namely: Xenopsylla cheopis, Xenopsylla brasiliensis and Listropsylla dorripae. The overall intensity of flea infestation (median) per host was not significantly different among the three sampling sites during the hot wet and the cold dry season. Overall infestation prevalence of fleas for the three sites during the hot wet season revealed no significant difference. However, the infestation prevalence of fleas of small mammals was significant among the three sites during the cold dry season. Altitude affects vegetation structure and cover, which in turn affect the small mammal and flea communities. Altitude also affects several climatic factors (temperature, rainfall, humidity), which affect small mammal and flea communities.
Abundance, structure and uses of Baobab (Adansonia Digitata L.) populations in omusati region, Namibia
(2015) Munyebvu, Faith
This study sought to determine the biology and the uses of baobab (Adansonia digitata L.) populations in Outapi and Onesi constituencies in Omusati Region, Namibia. As one of the important Non-Timber Forest Products (NTFPs)-providing species of ecological and socio-economic significance, there is need to have a better understanding of the biology and local uses of the species before its full potential and sustainable harvesting is realized. A comparison of densities, distribution patterns, structure, phenology, stem conditions and uses of baobabs between the two constituencies was done. Field data collection was conducted in April 2014. Road transects were used to sample baobabs in the two sites by purposively choosing the next road to gain access to the next focal tree. Circular plots with a radius of 30m from the edge of the canopy of each focal tree were demarcated. In each plot, diameter at breast height (dbh) of adult and sub-adult trees, height of adults, sub-adults and saplings and their stem conditions, number of fruits on each fruiting baobab tree, the Global Positioning System (GPS) waypoints and coordinates and the land-use types where baobabs occurred were recorded. The results revealed that there was no significant difference in the baobab densities (χ2=2, df=1, p>0.05) and median fruit abundance (U=5550.5, p>0.05) between Outapi and Onesi constituencies. The Chi-square tests detected significant differences in the dbh-size classes (χ2=33.038, df=8, p<0.001) and height classes (χ2=16.295, df=4, p<0.05) between the two study sites. The bell-shaped distribution curve in dbh size-classes in the two sites showed poor recruitment. Onesi constituency had 77% damaged stems compared to 50% in Outapi constituency (χ2=22.705, df=2, p<0.001). Onesi villagers make use of the baobab tree more extensively than Outapi residents (χ2=31.022, df=9, p<0.001). Some of the common uses of baobabs in both study sites include human and livestock consumption and treating various ailments. Poor seedling survival resulting primarily from herbivory, human activities and climate variability hampers baobab recruitment. Considering the poor recruitment due to the above factors, the potential for commercialization of baobabs in the region may not be viable. Therefore, active planting in undisturbed areas, protection of seedlings from livestock coupled with community awareness are vital to ensure recruitment so that effective commercialization and subsistence use is realized and sustainable.
Age determination and growth rate of the northern Benguela saddine (Sardinops sagax)
(2015) Malakia, Maria
The main objective of this study was to determine sardine age by counting rings on otoliths and to analyse the length, age and growth through regression and Von Bertalanffy Growth models. Otoliths amounting to 826 pairs were collected from the annual sardine research survey of the Ministry of Fisheries and Marine Resources in October 2013. A total of 713 sardine otoliths were mounted on black Perspex plates and aged by means of counting rings using a Zeiss microscope at a magnification of 22x. A micrometer (4 epu = 1 mm) was used to measure the radius and distance of rings from the nucleus on each otolith. In total, six age groups were represented in the sample, including, zero, one year, two years, three years, four years and five year age groups. The one year old age class was the dominant age group. Mean lengths at age were determined for each age group and were as follows: Zero age group had a mean length of 13.8 cm, one year olds were 16.8 cm, two year olds were 19.6 cm, three year olds were 21.4 cm, four year olds 22.4 cm and mean length for the five year age group was 23.4 cm. All these lengths were significantly different from each other, except the four and five year age groups. Fish length and otolith radius relationship was strong (r = 0.75, p < 0.05). The estimated parameters for the Von Bertalanffy Growth model were: = 26.6 cm, K = 0.28, and t0 = 2.69. Growth rate of females (K = 0.2256) was lower than males (K = 0.3188).
Aloe Zebrina Baker
(2010) Ndeunyema, Nghitoolwa E.
Analysis of antibacterial activity of Terminalia Sericea and Combretum Imberbe two combretaceae species from Namibia
(University of Namibia, 2019) Mapiye, Samson
The study was conducted to investigate the antibacterial activities of stem and leaves from Terminalia sericea and the live and dead bark from Combretum imberbe. The aqueous and organic crude extracts of the two plants were tested on Gram-negative bacteria Escherichia coli, Shigella sonnei, Serratia marcescens, Helicobacter pylori and Gram-positive bacteria Enterococcus faecalis, Staphylococcus aureus and Clostridium perfringens using the disk diffusion method. All the crude extracts exhibited activity against the tested bacteria species except for extracts from C. imberbe (dead bark). Organic extracts had high activity with minimum inhibitory concentration (MIC) values of 0.1mg/ml for all plant parts against S. aureus , S. marcescens, and H. pylori whilst the aqueous extracts from T. sericea (stem and leaves) and C. imberbe (live bark) had MIC values of 1mg/ml all against S. marcescens and H. pylori. Fractions from the two plants were obtained by vacuum liquid chromatography (VLC) using different solvents with increasing polarity. The organic extract fractions from both plants were observed to have good activity against two of the seven bacterial species that were tested. The dead bark plant extracts from C. imberbe had MIC value of 10mg/ml with 100% Ethyl acetate extracts against the bacteria H. pylori. T. sericea leaf extracts had MIC value of 0.01mg/ml against H. pylori in 100% MeOH fractions whilst the stem extracts had activity at 0.01mg/ml against E. faecalis in 100% Acetone fractions. The results indicate that the two plants have good antibacterial activity hence further research is needed to isolate and identify active compounds which can be developed into effective drugs.
An analysis of antibacterialactivity of Terminalia Sericea and Combretum Imerbe two comretaceae species from Namibia
(University of Namibia, 2019) Samson, Mapiye
The study was conducted to investigate the antibacterial activities of stem and leaves from Terminalia sericea and the live and dead bark from Combretum imberbe. The aqueous and organic crude extracts of the two plants were tested on Gram-negative bacteria Escherichia coli, Shigella sonnei, Serratia marcescens, Helicobacter pylori and Gram-positive bacteria Enterococcus faecalis, Staphylococcus aureus and Clostridium perfringens using the disk diffusion method. All the crude extracts exhibited activity against the tested bacteria species except for extracts from C. imberbe (dead bark). Organic extracts had high activity with minimum inhibitory concentration (MIC) values of 0.1mg/ml for all plant parts against S. aureus , S. marcescens, and H. pylori whilst the aqueous extracts from T. sericea (stem and leaves) and C. imberbe (live bark) had MIC values of 1mg/ml all against S. marcescens and H. pylori. Fractions from the two plants were obtained by vacuum liquid chromatography (VLC) using different solvents with increasing polarity. The organic extract fractions from both plants were observed to have good activity against two of the seven bacterial species that were tested. The dead bark plant extracts from C. imberbe had MIC value of 10mg/ml with 100% Ethyl acetate extracts against the bacteria H. pylori. T. sericea leaf extracts had MIC value of 0.01mg/ml against H. pylori in 100% MeOH fractions whilst the stem extracts had activity at 0.01mg/ml against E. faecalis in 100% Acetone fractions. The results indicate that the two plants have good antibacterial activity hence further research is needed to isolate and identify active compounds which can be developed into effective drugs.
Analysis of food safety and food handling knowledge among street food vendors in selected local food markets in Windhoek
(University of Namibia, 2022) Ngalangi, Paulus
Contaminated food leads to foodborne disease outbreaks (FDO) that cause millions of deaths among people every year. In Namibia, many low and middle-income consumers use street-vended foods (SVF) with compromised quality of raw materials, degraded handling and storage conditions that do not meet food safety standards. Therefore, this study was conducted by means of a descriptive, cross-sectional study of six Windhoek locations of Okuryangava, Katutura, Klein Windhoek, Kleine Kuppe, Prosperita, and Otjomuise. Food samples were purchased for laboratory analysis to determine pH, moisture and total plate count (TPC). Systems-Theoretic Accident Models and Processes (STAMP) was adopted, informed by data gathered based on event chain models drawn from street food handlers (SFH). Food-handlers were knowledgeable about the need for hygienic practices such as hand washing (94.6%), and cleaning of utensils (83.5%). Knowledge on food pathogens revealed that 72.1% did not know food pathogens such as Salmonella, Listeria, Campylobacter, and E. coli, meanwhile, only 28.4% did not know that parasites, fungi, and viruses act as agents to cause food poisoning. There is a none-consistent pattern of SFH knowledge with regard to hygienic practices during food handling and processing. pH values were lower (3.21±0.29) for liquid beverage than all solid foods that ranged from 6.81±0.10 to 7.54±0.16. The moisture percentage was higher (90.97±0.85) for liquid beverage than all solid foods that ranged from 37.66±1.20 to 63.28±0.89. High TPC of 5.28±0.49 Log CFU/g was detected in matangara, followed by sausage (5.06±0.99), kapana (3.07±0.47), and oshifima (2.66±1.99). STAMP with ready to use scenarios was introduced to deal with accidents that lead to FDO. Moreover, an assessment of the potency and appropriateness of food preservation methods and preservatives are ii recommended. A robust food safety regulatory regime, including a strong component of food safety training for contamination prevention should be pursued and is recommended for SVF handlers
Analysis of seasonal variation in dietary composition and behaviour of wild chacma baboons (Papio ursinus) in two habitats of different human influence around windhoek, central Namibia
(University of Namibia, 2024) Mukuve, Bernhard Z.M.
Diet composition of an organism gives a holistic picture of what an organism forages on in its environment to maximize energy intake for all its essential activities that contribute to survival and successful reproduction. Chacma baboons have the ability to modify their broad omnivorous diet and behavior under changing environmental and climatic conditions. However, the ever-increasing environmental and anthropogenic pressures on baboon populations are likely to affect both the diet composition and foraging behavior of these animals. Moreover, Namibia being one of the driest countries in the Sub Saharan Africa, and coupled with accelerated anthropogenic changes, baboon populations, especially those thriving in and around the city of Windhoek are facing constant threats of habitat destruction and fragmentation due to the rapid expansion of the city and are under pressure to adapt to these changes in order to survive. With limited research carried out on primates in the central highlands of Namibia, this study was carried out in an effort to bridge the knowledge gap and obtain insight into the influence humans have on the ecology of these primates around the city of Windhoek. The study investigated the activity budget and diet of the baboons using data collected from two contrasting habitats (Dobra and farm Krumhuk) that are influenced by human activities. A total of 166 baboons were observed during 2 seasons (wet & dry) at two sites using a focal animal method. Forty-nine (49) scat samples were collected between the seasons, separated in the laboratory, weighed, and placed into four categories (fruits and seeds, roots, stems, and leaves, invertebrates, and others). Results showed that baboons consumed plant materials more than any other food type and that they maintained their diet profile across the seasons. Furthermore, their behavior was found to be reactional to seasonal changes. The study further confirmed the ii broad diet and selectivity that exists in the so-called “generalist diet” of these well documented old-world monkeys while also providing an alternative method to enhance scat analysis techniques in the laboratory. The study noted that the human-disposed food waste, stable and constant water supply, preserved wild flora and minimal disturbance regimes around human settlements, all contribute to increased contact with humans
Analysis of short tandem repeat loci for forensic use in Namibia
(University of Namibia, 2020) Lukas, Ann-Angelique
In the genetics section of the forensics laboratory, in Windhoek, Namibia, forensic DNA (deoxyribonucleic acid) typing has become an integral part of establishing familial relations as well as providing weight to evidence during criminal investigations. Currently, there is limited existing knowledge regarding the ethnic and racial genetic diversity of the Namibian population. In the present study, biological samples from 150 individuals from three racial groupings selected for the paper were used to generate a reference DNA database. The data was analysed at 21 short tandem repeat (STR) loci to observe the genetic variation between individuals of different racial groupings. In order to obtain the STR profiles, the Globalfiler Express kit from Life Technologies was used. The extracted samples were amplified and detected by the Genetic Analyser 3500 as STR profiles, with its recommended allelic ladder. Allele frequencies from the STR profiles were used to evaluate the forensic efficiency parameters such as the power of discrimination (PD), power of exclusion (PE) and the expected heterozygosity (He). Locus point SE33 exhibited the highest polymorphism and was the most informative during the study, whereas TPOX and D13S317 were the least informative. The findings in this study would be useful in assisting the Namibian legal system as well as other relevant bodies in human identification. The findings provided a method for characterizing the genetic structure of the Namibian population and suggested valuable information required to generate a standard online reference DNA database, thus motivate population studies on the Y-chromosome and mitochondrial DNA which could be useful in human identification of complex cases.
Analysis of the mycochemicals components of the indigenous Namibian Ganoderma mushrooms
(2012) Shikongo, Laimy T.
Abstract provided by author
Analysis of the Namib and Kalahari dune sand deposits in Namibia and their application in Potasium Sillicates synthesis
(University of Namibia, 2017) Nuumbembe, Wilhelm P.
Silica sand is a main component in the synthesis of potassium silicates that are commonly used as binding, coating, and adhesives agents. Physical and chemical properties of the sand particles such as grain size, mineralogical and geochemical compositions, determine the viability of sand in the synthesis of potassium silicates. This study analysed sand samples from dunes in the Namib and Kalahari deserts in order to 1) evaluate their suitability in potassium silicate synthesis as well as to 2) synthesize potassium silicate and characterize microstructural and chemical properties of the potassium silicate. Sand grains were analysed and characterized using the following techniques: mechanical sieves, ICP-EOS/MS spectrometry, and X-ray diffractometry. Synthesized potassium silicate was characterized using techniques of XRD, ICP-OES, and SEM-EDX. The dunes sand grain sizes range from 45 – 2000 μm, with 98 % of the Namib dune sand are distributed in the grain size range 63 – 500 μm and only 60% of the Kalahari dune sand are distributed in the similar grain size range, while the other 20 % is confined in the 45 -63 μm grain size range and the other 20 % confined in the grain size 500 - 2000 μm. Quartz is the dominant mineral in all sand samples and feldspar minerals were observed only in the Namib dune sand samples. High SiO2 contents 93-99 % and 85-88 % were observed in the Kalahari dune sands and in the Namib dune sands, respectively. In contrast, oxides (Al2O3+Fe2O3+K2O+Na2O) contents are relatively high in the Namib dune sands (9-11%) compare to the Kalahari dune sands (0.9-2%). Similarly, trace elements and REE such as Rb, Sr, Ba, Y, Zr, La, V, Cr, Ce, and Nd are present in higher contents in the Namib dune sands compare to the Kalahari dune sands. Chemical index of alteration (CIA) values are high in Kalahari dune sands (76-82 %), compare to values in the Namib dune sands (58-59%). Finer and well-sorted grains, geochemical and mineralogical compositions of the Kalahari dune sands are attributed to long distance aeolian transportation, intense weathering and sediment recycling processes, whereas for the Namib dune sand, coarser and well-sorted grains and the presence of feldspars are ascribed to fluvial transportation by the Orange River as well as marine, and short aeolian transportation and a moderate degree of weathering. An amorphous potassium silicate glass with a 4.24 SiO2/K2O molar ratio and a dense, uniform surface morphology based on ESEM micrographs is reported in this study. SiO2/K2O molar ratio correlates with the concentrations of Si, K, and Al recorded by EDX point analysis. The concentrations of SiO2, K2O and Al2O3 were determined as 71.67±0.21 wt.%, 26.56±1.75 wt.% and 1.76±0.01 wt. %, respectively, resulting in a silicate glass composition of K2Si2O5. In view of specification and requirements of silica sand as raw material in the synthesis of potassium silicate such as high SiO2, low contents of Al2O3, K2O, Fe2O3 and Na2O, low contents of refractory and heavy minerals, it is recommended that Kalahari sand deposits are suitable for exploitation in the development of silicate glasses. In contrast, the Namib dune sands with high contents of Al2O3, K2O, and Na2O can be considered in the processing and manufacturing of other sand type products such as refractory sand, foundry sand, coal-washing sand and metallurgical sand.
Anopheles vectors species composition, their biting cycle and role of human behaviour in Malaria transmission in an endemic region from Namibia
(University of Namibia, 2021) Mwema, Tabeth
Any vector control effort aimed at reducing malaria burden should be based on an understanding of the malaria vectors’ populations, distribution, and behaviours as they relate to both transmission and response to interventions in place. It is well documented that the composition of malaria vectors changes over time but there has not been up-to-date information about that in Namibia. This study aimed to determine the population dynamics of Anopheline vectors and climatic factors that affect their distribution. It also described their biting behaviour and human social activities and behaviours that might expose them to mosquito bites. To address these objectives, human landing catches were conducted hourly from 19:00 hrs – 07:00 hrs indoors and outdoors for eight consecutive days during 2018/2019 and 2019/2020 malaria seasons in Shadikongoro village, Kavango East region. Mosquitoes collected were identified to species level using both morphological and molecular tools. Concurrently, data on which housing structures offered a high risk of mosquito bites was observed. Meteorological data from the Namibia Meteorological Centre was collected and used to determine the relation between these factors and mosquito abundance. A total of 1958 mosquitoes collected. Of these, 1190 were collected in 2018/19 and 768 in 2019/20. Species identification confirmed the presence of Anopheles arabiensis, An. gambiae s.s. and An. funestus s.s. In the 2018/2019 malaria season, An. arabiensis was the most abundant species, predominating both indoors (n = 334) and outdoors (n = 625). Anopheles funestus s.s was the least abundant species with 10 mosquitoes collected indoors and only one outdoors. During the 2019/2020 season, only An. arabiensis was collected. The statistical comparison showed a difference in species abundance between the two sampling periods (X2 = 24.0, p < 0.008). In the 2018/19 malaria season, both An. arabiensis and An. gambiae s.s. preferred biting outdoors (X2 = 32, p < 0.001; X2 = 25.9, p < 0.001, respectively) than indoors while An. funestus s.s. preferred biting indoors (X2 = 1532.719, p < 0.001). In the 2018/2019 and 2019/2020 malaria seasons, sleeping indoors was associated with a higher risk of mosquito bites (2018/19: OR = 0.62, 95% CI: 0.17 – 0.91, p = 0.02; 2019/2020: OR = 0.32, 95% CI: 0.07 – 1.06, p = 0.008). In 2019/2020, outdoor chatting (OR = 0.70, 95% CI: 0.31 – 1.58, p = 0.01) was a risk factors for mosquito bites. The risk of being bitten by mosquitoes in traditional houses was significantly higher (RR = 0.79, 95% CI: 01.23–6.56, p = 0.001) than in modern (RR = 0.48, 95% CI: 0.07–0.93, p = 0.012) and zinc (RR = 0.15, 95% CI: 0.04–0.63, p<0.06) houses. In 2018/2019, only rainfall had a significant effect on overall abundance (Coeff = 0.33, 95% CI: 0.31 – 1.58, p = 0.01) while in 2019/2020, only temperature had an effect (Coeff = 0.6, 95% CI: 0.12 – 0.88, p = 0.01) on abundance. Given this evidence, there is a need to provide interventions targeting both indoor and outdoor mosquito biting such as mosquito nets and spatial insect repellents, respectively. Mosquitoes are still abundant even when there is no rainfall. Therefore, it is important to spray insecticides that last throughout the year.
Anti-gonococcal activity of extracts from selected Namibian medicinal plants and computational studies of xerantholide, a neisseria gonorrhoeae inhibitor
(University of Namibia, 2023) Nyambe, Moola M.
Neisseria gonorrhoeae, the causative agent of a sexually transmitted infection, gonorrhea, has developed resistance to all available antibiotics. It is found in humans only and if left untreated can lead to serious complications such as infertility and disseminated gonococcal infections. The search for new effective, affordable, and readily accessible drugs for the treatment of gonorrhea thus continues. Plants have been a good source of structurally diverse lead compounds from which drugs have been developed. Various communities in Namibia commonly use plants in traditional health care for the treatment of sexually transmitted infections (STIs). However, these plants have not yet been evaluated for their anti-gonococcal activity and human safety. Therefore, this study aimed to isolate compounds from plants that are traditionally used to treat gonorrhea, ascertain their anti-gonococcal activity, and elucidate the structures of these compounds in an effort towards searching for selective anti-gonococcal agents. Another aim was to employ computational approaches, including density functional theory (DFT), molecular docking, prediction of activity spectra for substances (PASS) and Quantitative Structure-Property Relationship (QSPR), to model the interaction of xerantholide and its analogues with the active site of Neisseria gonorrhoeae carbonic anhydrase (NgCA) and to investigate the geometry, electronic structure, and biological activity spectra. Agar well diffusion and broth microdilution methods were used to determine the minimum inhibitory concentration (MIC) of extracts. Isolation and characterization of compounds were done using thin layer chromatography (TLC), column chromatography, x-ray diffraction and nuclear magnetic resonance (NMR). Crude extracts from six plants were ii confirmed to have anti-gonococcal activity (MIC 2.5-5.0 mg/mL). Xerantholide, with an MIC50 = 0.095 mg/mL was isolated from Pechuel-loeschea leubnitziae leaves. Molecular docking analysis revealed that xerantholide and its analogues docked with binding affinities ranging from -5.3 to -7.4 kcal/mol and DFT predicted binding energy of -16.5 to – 43.1 kcal/mol for these sesquiterpene lactones. Based on the docking results, binding of these compounds to NgCA involves hydrogen bonding, ligand-metal-acceptor, and hydrophobic interactions. Using QSPR, a six descriptors model with good predictive ability (R = 0.789, R 2 = 0.623, AdjR2 = 0.578, BIC = 241, AIC = 225) was developed. Finally, a PASS analysis showed that these compounds are potential antibacterial agents. The results in this study suggest that the studied sesquiterpene lactones offer potential anti-gonococcal and inhibitory activity towards NgCA, thus further in-vitro studies are recommended.
Antibacterial activities of silver-nanoparticles-titania composite thin films fabricated by the molecular precursor method (MPM)
(University of Namibia, 2019) Joseph, Moses Tuhafeni
Titanium Oxide (TiO2) as a photocatalyst produces free radicals upon receiving light energy; thus, it possesses antibacterial properties. The antibacterial property of silver-nanoparticles-doped TiO2 photocatalysts (Ag-NPs/TiO2) could be further enhanced by visible light illumination, which also widens its practical applications. However, the major limitation of this Ag-NPs/TiO2 composite material is its poor miscibility, which subsequently reduces the antibacterial activities of the material. To overcome this limitation, the Molecular Precursor Method (MPM) was adopted in this study as a synthetic method for the fabrication of Ag-NPs/TiO2 composite thin films with various and unprecedentedly high amounts of Ag-NPs. X-ray Diffraction (XRD) results revealed the presence of metallic Ag and a mixed phase in composite films. For composite films with less Ag content, Field Emission-Scanning Electron Microscopic (FE-SEM) analyses showed well dispensed Ag nanoparticles which appeared uniformly distributed across the films. Particles agglomeration and rough surface morphology were observed in films with high loads of Ag-NPs. Far-reaching absorption across the visible region was observed for composite films and the Surface Plasmon Resonance (SPR) of Ag-NPs is ascribed to the effect. The antibacterial behaviors of resultant films were investigated against a gram negative bacterium, Escherichia coli as a model, both in the dark and under visible light by using the Antibacterial Susceptibility Testing method. Composite films were found to have superior bactericidal activity than either neat TiO2 or Ag-only films, both in the dark and under visible light. Furthermore, films showed enhanced antibacterial activity under visible light than in the dark. In summary, all films exhibited bactericidal effect of different proportions depending on the Ag-NPs content in the titania matrix.
Antibacterial, antioxidant and phytochemical investigation of Acacia Arenaria, Aloe Esculenta and Pechuel-Loeschea Leubnitziae
(University of Namibia, 2017) Ndongo, Daniel
Natural products present in medicinal plants are an important source of therapeutic agents and many research groups are currently screening different biological activities of plants. This study aimed to investigate the antibacterial, antioxidant properties and phytochemical analysis of Acacia arenaria (Fabaceae), Aloe esculenta (Alliaceae) and Pechuel-Loeschea leubnitziae (Asteraceae) that are used in traditional settings. The antimicrobial activity of the methanol-dichloromethane (DCM) (1:1) extracts of these medicinal plants were tested against Shigella sonnei (ATCC 25931), Serratia marcescens (ATCC 8100), Enterococcus faecalis (ATCC 7080) and Alcaligenes faecalis (ATCC 8750). The minimum inhibitory concentration (MIC) of the extracts against afore mentioned microbes were determined. The antioxidant activity of the extracts was determined using α, α-diphenyl-β-picrylhydrazyl (DPPH) radical scavenging and reducing power assays. The phytochemical analysis of A. arenaria, A. esculenta and P. leubnitziae was done using qualitative and quantitative phytochemical analysis. Extracts demonstrated anti-microbial activity against S. sonnei, A. faecalis, E. faecalis and S. marcescens. The best activity was recorded with A. arenaria leaves extract, with MIC values ranging from 0.1 to 5.0 mg/mL against all tested bacteria. All extracts exhibited antioxidant activity for both assay techniques. The antioxidant activity correlated with the quantitative phytochemical presence of phenolic content ranging from 0.5 ± 0.1 to 5.7 ± 0.1 mg of GAE/g extract obtained in the extracts as well as condensed tannins ranging from 0.1 ± 0.0 to 72.6 ± 0.0 mg of TAC/g extract. Qualitative phytochemical analysis showed the presence of steroids, terpenoids, saponins, flavonoids, anthraquinones, coumarins, alkaloids, phenols and tannins. The results obtained in the present study indicated that the leaves, stem and roots of A. esculenta, and A. arenaria, P. leubnitziae are potential sources of natural antioxidants and antimicrobials. Further studies could look into the characterization of the bioactive compounds present in these plants.
Antibacterial, antioxidant and phytochemical investigation of Albizia Anthelmintica leaves, roots and stem bark
(University of Namibia, 2016) Nawinda, Teopolina N.
Albizia anthelmintica belongs to the family Fabaceae. The plant is traditionally used to treat symptoms of microbial infections in both humans and animals. The present study was designed to evaluate the phytochemical content, antibacterial and antioxidant activities of A. anthelmintica leaves, roots and stem bark ethanol extracts. Antibacterial activity was carried out by means of the agar disc diffusion method. The anti-oxidative activities of the extracts were determined by means of ferric reducing antioxidant power (Fe 3+- Fe 2+), phosphomolybdenum reduction and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays and phytochemical screening was used to determine the major classes of compounds present in the specific plant parts. Phytochemical screening revealed the presence of alkaloids, saponins and diterpenes in roots and bark extracts, flavonoids in leaves extract, tannins in roots extracts, and phenolic compounds were detected in all three extracts. The root extract exhibited the highest total phenolic and flavonoid content of 1741.08 ± 0.05 mg GAE/100 g and 366.80 0.02 ± mg QEE/100 g, respectively. The extracts demonstrated dose dependent varying degrees of anti-oxidative efficacy in the phosphomolybdenum reduction, iron (III) reduction and 2,2-diphenyl-1-picrylhydrazyl radical scavenging assays. For the DPPH assay, IC50 values of 0.018 ± 0.01, 0.019 ± 0.01 and 0.024 ± 0.01 mg/mL were obtained for the root, leaf and bark extracts, respectively. All extracts were active against Staphylococcus aureus, Shigella sonnei and Serratia marcescens but did not show activity against Enterococcus faecalis and alcaligenes faecalis. The results from the study show that Albizia anthelmintica extracts possess compounds with antibacterial as well as anti-oxidative properties, making this plant species a good source for potent antibacterial and anti-oxidative agents. The findings of this study will add value to the traditional uses of A. anthelmintica, and conservation is necessary due to the significant medicinal properties demonstrated by the plant.
Anticancer, antioxidant and antimicrobial sreening of extracts from Ziziphus Mucronata, Heliotropium Ciliatum and Gnidia Polycephala from the Oshikoto region of Namibia
(2012) Ilonga, Secilia K.
Plants have long been used to treat ailments such as headaches, stomach-ache, diarrhoea, tumours, wounds and sexually transmitted diseases, just to mention a few. Ziziphus mucronata, Heliotropium ciliatum and Gnidia polycephala are traditionally used to treat tumours and wound-related illnesses. Tumours and persistent wounds can be a sign of cancer. Microbial wound infections can also bring fatal consequences if unattended. This study evaluates the antioxidant, anticancer and antimicrobial potential of extracts of these three plants. The leaves (Z. mucronata) and aerial parts (G. polycephala and H. ciliatum) were collected from Oshikoto region, grinded and sequentially extracted with hexane, dichloromethane, ethanol and methanol. Water extracts were also prepared. The antioxidant potential was evaluated by 1,1-diphenyl-picrylhydrazyl (DPPH) assay whereas the Brine shrimp lethality test (BST), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromine (MTT) assay and APOPercentageTM flow cytometry assay were used to evaluate the anticancer potential of the extracts. The antimicrobial potential of the plant extracts against eight wound pathogens: Candida albicans, Clostridium tetani, Escherichia coli, Methillicin-resistant Staphylococcus aureus, Mycobacterium terrae, Pseudomonas aeruginosa, Staphylococcus epidermidis and Streptococcus A, was evaluated using the broth micro-dilution method. Methanol extracts of Z. mucronata and G. polycephala showed good antioxidant activity, comparable to that of a control, butylated hydroxyl toluene. Dichloromethane and hexane extracts of Z. mucronata and H. ciliatum as well as ethanol extracts of H. ciliatum showed high cytotoxicity, with LC50 values < 250 μg/ mL. Water extracts showed the least cytotoxic activity. In addition, dichloromethane extract of Z. mucronata also demonstrated a broad spectrum antimicrobial activity, obtaining MIC values ≤ 1 mg/ mL against six of the eight tested pathogens. The low toxicity of water extracts of the three plants and the antimicrobial activity recorded validates the use of these extracts in traditional medicine. Some extracts also appears to be good sources of potential antioxidant and anticancer agents. However, more studies are required.
Antimicrobial activity of fungal secondary metabolites isolated from pearl millet on gut microflora
(University of Namibia, 2022) Nghaamwa, Pamela M.N.
Pearl millet also known as mahangu in Namibia is a crop commonly found regions in the Northern part of Namibia such as Zambezi and Ohangwena region. Pearl millet is a common staple food of a certain percentage of Namibians. Traditional methods used for processing millet comprise of threshing, cleaning, washing, soaking, germination, wet and dry milling and fermentation. The fungal species gain access to grain matrices, depending on the type of environmental conditions certain secondary metabolites are generated this may occur during the pre-harvest, storage, transportation, processing, and marketing stages. Hazardous secondary metabolites with antimicrobial properties for instance polyketide, non-ribosomal peptides, alkaloids, and terpenes are produced by fungi and can cause food poisoning and possibly affect the microflora in the gut. It is important to identify and document whether fungi that produce antimicrobial secondary metabolites are present in mahangu that may affect the microflora. Even though sophisticated machinery exist, traditional methods of food storage and preparation are still being used in certain parts of the country. These traditional methods are seldom done in unhygienic conditions resulting in contamination of the food. The effect of food poisoning by fungi in Namibia is unknown, to the best of my knowledge there are fewer studies in Namibia that focused on the effect of antimicrobial fungi secondary metabolites on the microflora found in the gut. For this reason this study focused on isolating fungal species from pearl millet and testing their antimicrobial ability on four gut microflora E. coli ATCC 33849, K. pneumoniae ATCC BAA- 2146, L. monocytogenes and L. plantarum ATCC 8014. The pearl millet was bought from the local market and serial dilution was performed using distilled water. The solution of pearl millet with a dilution of 1:100 000 was plated on Sabouraud Dextrose Agar, it was then sub cultured until pure fungal isolates was obtained. Fungi were identified on the basis of colony characteristics and microscopic examinations. The following six types of fungi were identified Aspergillus flavus, Aspergillus niger, Saccharomyces sp., Rhodotorula sp., Trichosporon sp. and Saccharomyces sp. Ethyl acetate was used for extraction of the secondary metabolites and agar well diffusion was used to test for ii antimicrobial activity. Then Minimum Inhibitory Concentration was carried out only with fungi which produced zones of inhibition against the selected bacteria, lastly Minimum Bactericidal Concentration was carried out. The analytic test used showed that there was a significant difference in the antimicrobial activity among different fungal species p= 0.019. The fungus A. niger did not show any form of antimicrobial activity while Saccharomyces sp. showed the highest inhibitory effects with a mean value of 12.16 ± 0.21. The fungus A. flavus showed more inhibitory activity against the following bacterial strain L. plantarum, L. monocytogenes and K. pneumoniae at 7.5 mg/ml when MIC was carried out. The extract from A. flavus was the only extract exhibiting bactericidal effects and this was seen against K. pneumoniae and L. plantarum. It is evident that gut microflora can be affected by secondary metabolites of fungi from pearl millet which can lead to detrimental effects in humans. Further studies are required to detect secondary metabolites that could cause harm to the gut microflora also what dosage level is required to cause an effect in vivo on gut microflora.
Antimicrobial and antioxidant activity of crude extracts and fractions from stems and leaves of Tephrosia Lupinifolia
(University of Namibia, 2018) Nanhapo, David
Tephrosia lupinifolia is used traditionally for the treatment of malaria, diarrhea, toothache and tuberculosis. Two flavonoids, lupinifolin and lupinifolinol were previously isolated from the hexane root extract of T. lupinifolia, but there are no reports on phytochemical and pharmacological studies conducted on the stems and leaves of the plant. The purpose of this study was to prepare and fractionate crude extracts from the leaves and stems of T. lupinifolia, and to evaluate their antioxidant as well as antimicrobial activities. Crude extracts were prepared by suspending the powdered plant material in an equivolume mixture of dichloromethane and methanol at room temperature for 48 hours on an orbital shaker. The extracts were then subjected to a combination of trituration, column chromatography and preparative TLC, which yielded nine partially purified fractions as revealed by Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The fractions and crude extracts were tested for antimicrobial activity against one gram-positive bacterium (Staphylococcus aureus), two gram-negative bacteria (Klebsiella pneumonia and Escherichia coli) and one fungal strain (Candida albicans), using the agar disc-diffusion method. The best activity, albeit moderate, was recorded for the crude stem extract with zones of inhibition of 14 and 12 mm against K. pneumonia and C. albicans, respectively. The crude leaf extract displayed equipotent activity against E. coli and C. albicans with zones of inhibition of 10 mm. According to the GC-MS analysis fraction L5, which was obtained by subjecting the crude leaf extract to column chromatography, consisted of 10 compounds and the major compound was tentatively identified as 4-tetradecane. Fraction L6 comprised of four compounds of which two major compounds were tentatively identified as hexadecane and cyclohexanone with the aid of mass spectral libraries. Only fractions S1, S2, S3, L1, L5 and L6 were tested for antioxidant activity using the 2, 2-diphenyl-1-picrylhydrazyl radical (DPPH) assay. The test revealed that S3 showed the highest IC50 value of 23.50 ± 3.28 mg/mL whereas the lowest, and thus the best, antioxidant activity was recorded for fraction L6 with an IC50 of 0.80 + 0.01 mg/mL.Quantitative determination of the total phenolic and total flavonoid contents of the methanolic leaf, root and stem extracts was done using the Folin Ciocalteu method and aluminum chloride complex forming assays, with the results expressed in mg of gallic acid equivalents (GAE)/g of dry weight (DW) and mg of quercetin equivalents (QE)/g DW, respectively. Total phenolic content was recorded as 45.3 mg GAE/g DW for the leaves, 58.3 mg GAE/g DW for the roots and 250.5 mg GAE/g DW for the stems. Flavonoid contents were obtained as 31.8 ±0.032 mg QE/ g DW for the leaves, 13.2 ±0.003 mg of QE/g DW for the roots and 20.3 ±0.013 mg of QE/g DW for the stems. The methanolic stems extract showed the highest total phenolic content whereas the highest total flavonoid content was shown from the methanol leaves extract.

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