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

Abstract

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) K₂HPO₄ and 0.02 % (w/v) MgSO₄. 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 MgSO₄ as compared to cells grown in the absence of MgSO₄ (150 AU mL⁻¹).