Activation and regeneration of whole cell biocatalysts: Initial and periodic induction behavior in starvedEscherichia coli after immobilization in thin synthetic films

Abstract

Activation and regeneration of whole cell biocatalytic activity via initial and subsequent induction of the lacZ gene was investigated in starved Escherichia coli using a novel synthetic biofilm. Stationary-phase bacteria were entrapped in 10-80 mum thick multi-layer films, where a copolymer of acrylic and vinyl acetate was the immobilization matrix. The E. coli were placed in a defined starvation medium containing essentially no nitrogen or carbon source and induced initially using lactose or isopropylthiogalactoside (IPTG). Subsequent inductions were performed with IPTG. Comparison studies with suspended bacteria showed that when IPTG was the initial inducing agent, induction kinetics are linear for both immobilized and suspended cells. After induction with lactose, however, a lag time is noted for suspended cells, but not for E. coli in the biofilm. Biocatalytic activity was successfully regenerated by re-inducing starved suspended cells 1-3 days after an initial induction with lactose. This regeneration was demonstrated in the synthesis of additional active beta-galactosidase. However, immobilized cells could be re-induced for at least 17 days after the initial induction, and viability in the synthetic biofilms remained greater than 90%, demonstrating that periodic induction is a valuable method for extending the life of whole cell biocatalysts.