Phylogenetic Identification of DNase Secreting Soil Bacteria Antagonistic to Fungus Aspergillus

Contamination of major cash crops by mycotoxigenic fungi in developing countries, including India, is becoming one of the major areas of concern. Continual use of synthetic pesticides to fulfil the increasing demand for consumption of major legumes has negative impact on human health and has major environmental risks associated with it. Microbes living in vicinity to these mycotoxin producing fungi have been found to be a promising substitute against harmful pesticides. The main objective of the present work was to isolate the bacterial strain which has a promising potential to act as an antagonist against the fungal pathogen Aspergillus which is considered to secrete Aflatoxin, the most potent mycotoxin. Large number of bacteria were isolated randomly from the rhizosphere of groundnut crop sown in Jamia Hamdard (New Delhi, India) randomly by serial dilution method, and screened for their antagonistic effect against fungus Aspergillus. Initial screening results show that, 14 of the isolates exhibit promising antagonism on dual culture media. Optimization of growth conditions was carried out at different pH, temperature and salt (NaCl) concentration. In vitro antagonism assay comprising of mycelial inhibition assay on to PDA using the scale of 1-4 (where 1 indicates bacterial colony completely overgrown by fungi, 2 indicates overgrown but bacterial colony visible, 3 indicates growth of fungus to the edge of the bacterial colony and 4 indicates inhibition zone) and inhibition of mycelial growth as observed by a significant drop on mycelial dry weight by co-inoculation of bacterial culture with fungal spores in M1 media. One of the bacterial isolates MAK603 exhibiting the maximum antagonistic effect was selected after optimization for further studies. The mechanism of action of MAK603 was studied in vitro for the production of hydrolytic enzymes. Phylogenetic analysis using 16 S rDNA amplification was carried out to establish its identity.