Increased phenylalanine production by growing and nongrowing Escherichia coli strain CWML2

Chemostat selection at low dilution rate in glycerol-limited minimal medium was previously employed to isolate the mutant Escherichia coli strain CWML2 which exhibits shorter lag phases, decreased acetate production, and higher specific growth rates and biomass yields in batch culture (Weikert, C.; Sauer, U.; Bailey, J. E. Microbiology 1997, 143, 1567-1574). In this study, CWML2 was analyzed for its biochemical production capabilities in batch culture and under nongrowing conditions. Both CWML2 and MG1655 were transformed with plasmid pSY130-14, which encodes feedback resistant mutants of the enzymes chorismate mutase P-prephenate synthase and 3-hydroxy-d-arabinoheptulosonate-7-phosphate dehydratase, to enable phenylalanine production. In batch culture, transformed CWML2 produced twice as much phenylalanine as did MG1655:pSY130-14. In contrast to the reference strain, substantial growth-independent production of phenylalanine was calculated for CWML2:pSY130-14 by using Luedeking-Piret kinetic analysis. Over a period of 30 h, nongrowing cells of CWML2:pSY130-14 exhibited a 2.5-fold higher specific phenylalanine production rate. The apparent capability of E. coli CWML2 to partly uncouple metabolic activity from growth suggests a potentially general advantage of this class of modified hosts for production of biochemicals.