Original articleStatistical optimization of antifungal iturin A production from Bacillus amyloliquefaciens RHNK22 using agro-industrial wastes

Biosurfactants are secondary metabolites with surface active properties and have wide application in agriculture, industrial and therapeutic products. The present study was aimed to screen bacteria for the production of biosurfactant, its characterization and development of a cost effective media formulation for iturin A production. A total of 100 bacterial isolates were isolated from different rhizosphere soil samples by enrichment culture method and screened for biosurfactant activity. Twenty isolates were selected for further studies based on their biosurfactant activity [emulsification index (EI%), emulsification assay (EA), surface tension (ST) reduction] and antagonistic activity. Among them one potential isolate Bacillus sp. RHNK22 showed good EI% and EA with different hydrocarbons tested in this study. Using biochemical methods and 16S rRNA gene sequence, it was identified as Bacillus amyloliquefaciens. Presence of iturin A in RHNK22 was identified by gene specific primers and confirmed as iturin A by FTIR and HPLC. B. amyloliquefaciens RHNK22 exhibited good surface active properties and antifungal activity against Sclerotium rolfsii and Macrophomina phaseolina. For cost-effective production of iturin A, 16 different agro-industrial wastes were screened as substrates, and Sunflower oil cake (SOC) was favouring high iturin A production. Further, using response surface methodology (RSM) model, there was a 3-fold increase in iturin A production (using SOC 4%, inoculum size 1%, at pH 6.0 and 37 °C temperature in 48 h). This is the first report on using SOC as a substrate for iturin A production.