Metabolic flux analysis of Escherichia coli expressing the Bacillus subtilis acetolactate synthase in batch and continuous cultures

Metabolically engineered Escherichia coli expressing the B. subtilis acetol actate synthase has shown to be capable of reducing acetate accumulation. T his reduction subsequently led to a significant enhancement in recombinant protein production. The main focus of this study is to systematically exami ne the effect of ALS in the metabolic patterns of E. coli in batch and cont inuous culture. The specific acetate production rate of a strain carrying t he B. subtilis als gene is 75% lower than that of the control strain (host carrying the control plasmid pA-CYC184) in batch cultures. The ALS strain i s further demonstrated to be capable of maintaining a reduced specific acet ate production rate in continuous cultures at dilution rates ranging from 0 .1 to 0.4 h(-1). In addition, this ALS strain is shown to have a higher ATP yield and lower maintenance coefficient. The metabolic flux analysis of ca rbon flux distribution of the central metabolic pathways and at the pyruvat e branch point reveals that this strain has the ability to channel excess p yruvate to the much less toxic compound, acetoin. (C) 1999 John Wiley & Son s, Inc.