Transcriptome profiling of sulfur containing amino acid biosynthesis regulator genes and production of L-methionine in escherichia coli

Abstract

It has been reported that the biosynthesis of sulfur containing amino acids, methionine and cysteine, might be regulated by the gene products of metJ and cysB in E. coli. In this study, metJ and cysB genes are disrupted in E. coli, respectively and investigated the change of transcriptome profile compared with that of parent W3110 strain. In metJ mutant strain, genes involved in methionine biosynthesis were found up-regulated as expected. cysB mutant showed very slow growth rate and was not able to grow in minimal medium without L-cysteine. Interestingly, genes directly involved in the cysteine biosynthesis were not significantly affected by cysB disruption. Instead, genes related to redox regulation were mainly affected. Although two mutant strains showed L-methionine overproduction and cysteine auxotrophism, respectively which are opposite effects in cellular metabolism, transcriptome profiles of two mutants largely corresponds with each other. Therefore, this study could be helpful to understand the metabolism of sulfur containing amino acids, and develop the strategy of overproduction of sulfur containing cofactors and metabolites. For over-production of L-methionine in Escherichia coli W3110, one strategy is to redirect carbon flow from phosphoenolpyruvate (PEP) to oxaloacetate. pykA, pykF genes involved in conversion of PEP to pyruvate and ptsG gene which is involved in consumption of PEP for glucose uptake were disrupted. Resulting Escherichia coli W3110GFA strain produced L-methionine 4 times more than wild-type. However, this mutant showed increased production rate of L-phenylalanine and L-tryptophan which is a erythrose-4-phosphate derived amino acids. Simulation using MetaFlux.NET shows that, pentose phosphate pathway (PPP) of Escherichia coli W311OGFA strain is increased significantly which contribute to increase of erythrose-4-phosphate pool and hence explains the increase of L-phenylalanine and L-tryptophan production.