Enhanced production of recombinant aspartase of Aeromonas media NFB-5 in a stirred tank reactor

Aspartase gene (aspA) from Aeromonas media NFB-5 was cloned and expressed in Escherichia coli BL21 using pET21b(+) expression vector. Maximum production of aspartase was obtained at shake-flask after 5 h of IPTG (1.5 mM) induction at 37 °C and by supplementing the media with KH2PO4 (0.3%, w/v) and K2HPO4 (0.3%, w/v). Further production was investigated at a laboratory scale stirred tank reactor using response surface methodology (RSM). Agitation (130–270 rpm), aeration (0.30–1.70 vvm) and IPTG induction time (3–7 h) was optimized. Optimal levels of agitation (250 rpm), aeration (1.25 vvm) and induction time (6 h) were determined by statistical analysis of the experimental data. More than 7-fold increase in recombinant aspartase (1234 U/g wet weight) was observed than the parent strain (172 U/g wet wt). Homogenized immobilized permeabilized recombinant cells (566 mg/g wet cells) produced more l-aspartic acid as compared to permeabilized recombinant free cells (154 mg/g wet cells).