Global analyses of transcriptomes and proteomes of a parent strain and an L-threonine-overproducing mutant strain

We compared the transcriptome, proteome, and nucleotide sequences between the parent strain Escherichia coli W3110 and the L-threonine-overproducing mutant E. coli TF5015. DNA macroarrays were used to measure mRNA levels for all of the genes of E. coli, and two-dimensional gel electrophoresis was used to compare protein levels. It was observed that only 54 of 4,290 genes (1.3%) exhibited differential expression profiles. Typically, genes such as aceA, aceB, icdA, gltA, glnA, leu operon, proA, thrA, thrC, and yigJ, which are involved in the glyoxylate shunt, the tricarboxylic acid cycle, and amino acid biosynthesis (L-glutamine, L-leucine, proline, and L-threonine), were significantly upregulated, whereas the genes dadAX, hdeA, hdeB, ompF, oppA, oppB, oppF, yfiD, and many ribosomal protein genes were downregulated in TF5015 compared to W3110. The differential expression such as upregulation of thr operon and expression of yigJ would result in an accumulation of L-threonine in TF5015. Furthermore, two significant mutations, thrA345 and ilvA97, which are essential for overproduction Of L-threonine, were identified in TF5015 by the sequence analysis. In particular, expression of the mutated thrABC (pATF92) in W3110 resulted in a significant incremental effect on L-threonine production. Upregulation of aceBA and downregulation of b1795, hdeAB, oppA, and yfiD seem to be linked to a low accumulation of acetate in TF5015. Such comprehensive analyses provide information regarding the regulatory mechanism of L-threonine production and the physiological consequences in the mutant stain.