| dc.description.abstract | Fungi are eukaryotic microorganisms that have simple multicellular or unicellular cell
structures. They are distributed in terrestrial soils, forests, aquatic habitats and in extreme
environments with high ambient salts, temperature, pH and pressure. Fungi from extreme
environments are potential sources of novel biocatalysts for example antimicrobial agents
that can help solve the rising cases of drug resistance. However, the diversity of fungi
recovered and described from less studied environments such as the soda lakes is quite
low as compared to the soil ecosystem. Very few haloalkaliphic fungi have been recovered
from hypersaline environments. In this study, we explored the cultivable fungal diversity
in Lake Magadi and their ability to produce secondary metabolites. Dilution plate
technique was used to isolate fungi from soda lake soils using alkaline media (Potato
dextrose agar, Malt extract agar, Oatmeal agar and Sabouraud dextrose agar) prepared
using sterilized lake water from the lake. Unique isolates were selected based on
morphological features and subjected to physiological tests to determine their ability to
grow at different pH, temperature and salts ranges. Molecular characterization was done
by analysis (BLAST) of the amplified conserved regions of 18SrDNA followed by
phylogeny. Ability of the isolates to utilize different carbon sources was tested on media
supplemented with different substrates (starch, cellulose, casein, lignin, pectin, xanthan,
chitin, Tween 20). Antimicrobial screening was done using both crude and cell free
extracts to determine the ability of the isolates to produce metabolites (comparison of
mean diameter of inhibition zones) that can be used to control both human pathogens and
agricultural pathogens. The test pathogens included human pathogens Staphylococcus
aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Salmonella spp.,
Shigella spp. and Candida albicans which were laboratory isolates and plant pathogens
Epicoccum sorghinum strain JME-11, Alternaria tenuissima, Didymella glomerata,
Schizophyllum commune isolate ScGD28, Phoma destructiva, Cladosporium halotolerans
CBS 119416, Aspergillus fumigatus EG11-4 and Dickeya dianthicola (field isolates). In
total, 52 isolates were recovered from the study having different pigmentations. Their
physiology depicted actual characteristic of haloalkaliphilic environments as the fungi
tolerated extreme pH of up to 10 and salts (15-20%) and some grew at 35-40ºC. Sequence
analysis indicated that the isolates were affiliated to 18 different genera with Aspergillus,
Penicillium, Phoma, Cladosporium, and Acremonium. Substrate utilization tests showed
that the different isolates produced proteases, chitinases, cellulases, amylases, pectinases
and lipases. Isolates 2M, 59M, 69M, 87M, 100M, 111M and 113M were outstanding as
they produced more than four enzymes. Results from the antimicrobial screening showed
one isolate (11M from Site 3 soil) with 99% affiliation to Penicillium chrysogenum CBS
306.48 was able to inhibit major enteric bacteria and plant pathogenic fungi. Similar
studies on saline environments have reported the phylum Ascomycota as the dominant
fungal group and all the genera recovered in this study are classified in the same phylum.
Antimicrobial from the fungal isolates provide a basis for pharmacological research since
they can further be purified to obtain compounds that can be used as antibiotics or
biopesticide against human and plant pathogens respectively. This can provide a solution
to the rising problem of antibiotic resistance and pesticide resistance. | en_US |
