Subtilosin A production by Bacillus subtilis KATMIRA1933 and colony morphology are influenced by the growth medium

Bacillus subtilis KATMIRA1933, cultured in modified MRS (de Man, Rogosa, and Sharpe) broth without peptone (animal-free [AF]-MRS), produced subtilosin A at levels similar to, or even higher, than when cultured in MRS broth with peptone. AF-MRS medium contained 2.5 % (w/v) Martone or 2.5 % (w/v) cottonseed hydrolysate instead of peptone and 0.25 % (w/v) bacteriological grade yeast extract instead of normal yeast extract. An increase in cell numbers, accompanied by an increase in subtilosin activity, was recorded when cells were grown in AF-MRS supplemented with 0.4 % (w/v) K 2 HPO 4 and 0.02 % (w/v) MgSO 4 . Subtilosin production increased from 30 arbitrary units (AU) mL −1 in a static culture to 320 AU mL −1 when cells were agitated on an orbital shaker at 300 rpm. A further increase in subtilosin production, from 150 AU mL −1 to 240 AU mL −1 , was recorded when cells were cultured in AF-MRS supplemented with 2.0 % (w/v) amylopectin or 2.0 % (w/v) maltodextrin. Slightly higher cell densities were recorded in the presence of maltodextrin. Two colony types, one with a flat (“typical”), sprawling morphology and the other elevated (“atypical”), were isolated from cells grown in AF-MRS broth. Higher subtilosin levels (213 AU mL −1 ) were recorded from cells grown in AF-MRS broth supplemented with MgSO 4 as compared to cells grown in the absence of MgSO 4 (150 AU mL −1 ).