Transcriptional analysis and adaptive evolution of Escherichia coli strains growing on acetate
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- Rajaraman, E., Agarwal, A., Crigler, J. et al. Appl Microbiol Biotechnol (2016) 100: 7777. doi:10.1007/s00253-016-7724-0
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Eighteen strains of Escherichia coli were compared for maximum specific growth rate (μMAX) on 85 mM acetate as the sole carbon source. The C strain ATCC8739 had the greatest growth rate (0.41 h−1) while SCS-1 had the slowest growth rate (0.15 h−1). Transcriptional analysis of three of the strains (ATCC8739, BL21, SMS-3-5) was conducted to elucidate why ATCC8739 had the greatest maximum growth rate. Seventy-one genes were upregulated 2-fold or greater in ATCC8739, while 128 genes were downregulated 2-fold or greater in ATCC8739 compared to BL21 and SMS-3-5. To generate a strain that could grow more quickly on acetate, ATCC8739 was cultured in a chemostat using a progressively increasing dilution rate. When the dilution rate reached 0.50 h−1, three isolated colonies each grew faster than ATCC8739 on 85 mM acetate, with MEC136 growing the fastest with a growth rate of 0.51 h−1, about 25 % greater than ATCC8739. Transcriptional analysis of MEC136 showed that eight genes were downregulated 2-fold or greater and one gene was upregulated 2-fold or greater compared to ATCC8739. Genomic sequencing revealed that MEC136 contained a single mutation, causing a serine to proline change in amino acid 266 of RpoA, the α subunit of the RNA polymerase core enzyme. The 260–270 amino acid region of RpoA has been shown to be a key region of the protein that affects the interaction of the α subunit of the RNA polymerase core enzyme with several global transcriptional activators, such as CRP and FNR.