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

► Expression conditions for recombinant aspartase from Aeromonas media NFB-5 were optimized. ► Optimization of process parameters for recombinant aspartase production at bioreactor level. ► Permeabilization of recombinant cells to investigate its effect on l-aspartic acid production. ► Permeabilized free recombinant cells and homogenized immobilized cells were compared for l-aspartic acid production. 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 5h of IPTG (1.5mM) 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 (130–270rpm), aeration (0.30–1.70vvm) and IPTG induction time (3–7h) was optimized. Optimal levels of agitation (250rpm), aeration (1.25vvm) and induction time (6h) were determined by statistical analysis of the experimental data. More than 7-fold increase in recombinant aspartase (1234U/g wet weight) was observed than the parent strain (172U/g wet wt). Homogenized immobilized permeabilized recombinant cells (566mg/g wet cells) produced more l-aspartic acid as compared to permeabilized recombinant free cells (154mg/g wet cells).