Production of surfactin by Bacillus pumilus UFPEDA 448 in solid-state fermentation using a medium based on okara with sugarcane bagasse as a bulking agent

Abstract We studied the production of surfactin by Bacillus pumilus UFPEDA 448 in solid-state fermentation (SSF), using a medium based on okara with the addition of sugarcane bagasse as a bulking agent. The optimum proportions of okara and sugarcane bagasse were 50% each, by mass. Due to the relatively high production of proteases during SSF, pre-hydrolysis of the okara with a protease did not improve surfactin levels. The optimum temperature for surfactin production was 37 °C, with the incubation temperature affecting the ratios of the various surfactin homologues produced. Cultivation in column bioreactors with forced aeration under optimized conditions gave a surfactin level of 809 mg L −1 of impregnating solution, which corresponds to 3.3 g kg-dry-solids −1 . This is the highest surfactin level that has been produced to date in SSF with a non-recombinant microorganism. The peak O 2 uptake rate was 20 mmol min −1  kg-initial-dry-solids −1 , corresponding to metabolic waste heat production rate of 182 W kg-initial-dry-solids −1 . The tensioactive properties of the surfactin were similar to those reported in the literature for surfactin produced by submerged fermentation. These results suggest that it might be feasible to use SSF to produce surfactin but at large scale special attention will need to be given to heat removal.