Transcriptome sequencing reveals key metabolic pathways for the synthesis of L-serine from glycerol and glucose in Escherichia coli

In the present study, the ability of Escherichia coli to produce L-serine by fermentation using glycerol and glucose was investigated. The results showed that the maximum accumulation of L-serine in glycerol and glucose medium was 634.37 mg/L and 459.27 mg/L, respectively. Transcriptome sequencing was then applied to explore the reasons for this difference, and showed: (1) A total of 2041 differentially expressed genes (DEGs) were screened, and these DEGs were mainly concentrated in biosynthesis of amino acids and histidine metabolism；(2) In the biosynthesis of amino acids, the key genes (e.g., tdcG、ilvA and tdcB) involved in the degradation of L-serine to pyruvate were significantly down-regulated; (3) The key genes (e.g., ilvB、ilvN and ilvM etc) involved in the degradation of pyruvate to branched-chain amino acids were significantly down-regulated; (4) Many up-regulated genes appeared in the glycine anabolic pathway, which may provide a large number of one-carbon units for the growth of E. coli.; and (5) Transcription levels of regulatory genes in histidine metabolism were down-regulated, which may reduce energy consumption. In summary, the present study provides insight at the genetic level into the construction of high-yielding strains for the efficient use of glycerol for L-serine synthesis.