Effective production of recombinant esterase in Bacillus brevis using a pH-controlled fed-batch culture

Abstract

An automated two-component substrate (polypepton plus glucose) feeding strategy with a pH-stat modal fed-batch culture using a high pH limit was developed to effectively produce esterase from a protein-hyperproducing Bacillus brevis HPD31 harboring the plasmid pHSC131 which carries the Bacillus stearothermophilus esterase gene. Highest activity of the secreted esterase (34 U/ml) was obtained when the concentrations of polypepton and glucose in the nutrient feed solution were 250 g/l and 41.60 g/l, respectively. The absence and excessive amount of glucose in the nutrient feed solution were ineffective for extracellular esterase production because without glucose cell growth was minimal while excessive amount of glucose flavored cell growth at the expense of esterase production. The feed rate, automatically controlled by a direct signal of pH change, at 0.30 ml/pulse was found optimum for extracellular esterase secretion. The activity of the secreted esterase was increased more than eight times from 4 U/ml in the conventional batch culture to 34 U/ml obtained in this studs. The esterase productivity was likewise increased more than three-fold.