Synergetic antimicrobial activity of bioactive secondary metabolites from endophytic Fungi and actinobacteria associated with Cassia Abbreviata oli. Subsp. Beareana (Holmes) Brenan
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Date
2025
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University of Namibia
Abstract
This study was designed to investigate antimicrobial activities in both axenic and
interkingdom microbial fermentations of fungal and bacteria strains associated with
the roots of a medicinal plant Cassis abbreviata. A diverse range of microorganisms,
including Streptomyces, Patulibacter, Nocardiopsis, Rhodococcus, Curtobacterium,
Bacillus cereus, Aspergillus, Paecilomyces, Trichoderma, Curvularia, and Epicoccum,
were isolated the roots of Cassis abbreviata. PKS-I and NRPS gene clusters were also
amplified. Isolates possessing at least one of these biosynthetic genes exhibited activity
against at least more than one of the tested pathogens. The ethyl acetate extracts
antimicrobial potential from 21- and 28-days incubation was evaluated against Listeria
monocytogenes, Mycobacterium avium, Staphylococcus aureus, Shigella sonnei,
Salmonella typhi, Escherichia coli and Candida albicans using the disk diffusion
method. Statistical analysis showed no significant difference in inhibition zones
between the two culture techniques (p = 0.124). However, notable extracts emerged;
the 28- days fermented axenic extracts of Bacillus cereus and Trichoderma
longibrachiatum and their 21- days co-culture extract showed significant good result
against all test pathogens (p= 0.00). T. longibrachiatum and the co-culture extracts
demonstrated a significant broad-spectrum potential against all test pathogens, with
the co-culture demonstrating the highest zones of inhibition. Moreover, B. cereus
extract inhibited only bacterial indicator microorganisms. Secondary metabolites from
T. longibrachiatum and the 21- days co-culture extracts of Bacillus cereus and
Trichoderma longibrachiatum were confirmed with TLC, which revealed the presence
of alkaloids, flavonoids and phenols. Additionally, terpenoids were detected in the coculture extract only. The synergistic effect of combining the co-culture extract of 21-
day incubation of B. cereus and T. longibrachiatum with the antibiotic nitrofurantoin,
ii
was demonstrated. It was observed that the inhibitory effect of both nitrofurantoin and
the co-culture extract on the pathogen reduced by eight-fold. These results indicate
that the endophytic fungi and bacteria from the C. abbreviata could be a potential
source for bioactive antimicrobial compounds
Description
A thesis submitted in fulfilment of the requirements for the Degree of Master of Science in Microbiology
Keywords
Biosynthetic Genes Clusters, Co-culture, C. abbreviata, Fungi, Bacteria, Antimicrobial, Endophytes, Medicinal plants, Secondary metabolites, Namibia, University of Namibia