Transcriptome analysis of a shikimic acid producing strain of Escherichia coli W3110 grown under carbon- and phosphate-limited conditions

Abstract

Shikimic acid, which is produced in the aromatic amino acid pathway in plants and microorganisms, is an industrially interesting chiral starting material for the synthesis of many chemical substances, e.g. the influenza medicine Tamiflu. When produced by genetically modified Escherichia coli it has previously been found that carbon-rich conditions (e.g. phosphate-limitation) favors production of shikimic acid over shikimate pathway by-products, whereas the situation is the opposite at carbon-(glucose-) limited conditions. In the present study, gene expression patterns of the shikimate producing strain W3110.shik1 (W3110 with aroL deletion and plasmid-overexpressed aroF) and the wild type strain W3110 grown under carbon- and phosphate-limited (carbon-rich) chemostat conditions (D=0.23h(-1)) were analyzed. The study suggests that the by-product formation under carbon-limitation is explained by a set of upregulated genes coupled to the shikimate pathway. The genes, ydiB, aroD and ydiN, were strongly induced only in carbon-limited W3110.shik1. Compared to W3110 the lg(2)-fold changes were: 6.25 (ydiB); 3.93 (aroD) and 8.18 (ydiN). In addition, the transcriptome analysis revealed a large change in the gene expression when comparing phosphate- to carbon-limitation, which to a large part could be explained by anabolic-catabolic uncoupling, which is present under phosphate-limitation but not under carbon-limitation. Interestingly, there was also a larger difference between the two strains under carbon-limitation than under phosphate-limitation. The reason for this difference is interpreted in terms of starvation for aromatic amino acids under carbon-limitation which is relieved under phosphate-limitation due to an upregulation of aroK and aroA.