Faculty of Agriculture, Engineering and Natural Sciences

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Browsing Faculty of Agriculture, Engineering and Natural Sciences by Subject "Actinobacteria"

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    In vitro antimicrobial and antioxidant potential of endophytic actinobacteria associated with Harpagophytum procumbens [Burch.] DC ex Meissn.: An ethno medicinal plant of Southern Africa
    (University of Namibia, 2021) Lang, Magdalena Elizabeth
    The present study was designed to determine the taxonomic diversity, metabolic activity, structure elucidation, and screening of genes involved in antimicrobial and antioxidant activity of the endophytic actinobacteria associated with Harpagophytum procumbens. Six lateral tubers collected from the Hardap (A) and Khomas (B) regions were used. After primary screening, 23 of 140 isolate extracts of ethyl acetate, chloroform and methanol were tested for their antimicrobial potential against 8 microorganisms and their MIC was determined. The ethyl acetate extracts produced significantly better results in all tests (P = 0.000). Ethyl acetate extracts of isolate B44 (Curtobacterium sp.) demonstrated a significant broad-spectrum potential against 7 out of 8 of the test organisms. The 23 isolates were identified by using 16S rRNA sequencing and phylogenetic analyses and were taxonomically grouped into 6 families and 7 genera: Streptomyces (̴52%), Agromyces (̴4%), Nocardiopsis (̴4%), Rubrobacter (̴4%), Patulibacter (̴13%), Rhodococcus (̴4%), Curtobacterium (̴4%) and 3 unidentified strains (̴13%). PKS-I (found in 61% of isolates) and NRPS (found in 13% of isolates) gene clusters were also amplified. From the four antioxidant tests carried out, ethyl acetate extracts of A36 (Streptomyces sp.) had the highest phenolic content (1.993 ± 0.004) and total antioxidant activity (0.258±0.001), B12 (Streptomyces sp.) had the highest radical scavenging activity (95%), while B43 (unidentified) had the highest total reducing power (0.849 ± 0.003). Ethyl acetate solvent extracts tested for their ability to protect DNA from degradation found that 61% of the extracts had DNA damage protection potential. When testing for industrially important enzymes, 74% tested positive for urease, 83% for gelatin degradation, 74% for protease, 65% for starch degradation, 48% for indole-acetic acid, and 96% for catalase. Furthermore, optimal growth conditions for antimicrobial production of the best overall performing strains (B12, B44 and A65) were evaluated and a multiple regression analysis was carried out (F(6,1451) = 293.036, p = 0.000, R2 = 0.548). GC/MS analysis was carried out on extracts B12, B44 and A65 and compounds were tentatively identified as alkanes (56%) and unknown compounds (37%), with B12 and A65 also containing octadecenamide. From the present study, it is possible to conclude that these endophytic actinobacteria associated with H. procumbens could be a promising source of bioactive compounds and warrant further studies.