Transcriptional analysis and adaptive evolution of Escherichia coli growing on acetate
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Acetate is an unavoidable degradation product in biomass hydrolysis which inhibits microbial production of biochemicals. Acetate can be selectively removed from mixture of sugars and acetate using substrate-selective degradation. This research focuses on improving the growth of E. coli on acetate which in turn will help improve the substrate-selective degradation. In a first study, eighteen strains of E. coli were compared for maximum specific growth rate (µMAX) on acetate. We observed that ATCC8739 had the greatest growth rate growth rate (0.405 h-1) while SCS-1 had the slowest growth rate (0.153 h-1). Gene expressions of ATCC8739, SMS-3-5 and BL21 were compared determine why ATCC8739 grows fastest on acetate. From the results, we observed that folK of the folate biosynthesis pathway had atleast 2-fold greater expression in ATCC8739 in comparison with the other strains. Also, genes of phenylacetate degradation pathway were more than 2-fold upregulated in ATCC8739 than SMS-3-5 and BL21. These results might explain why ATCC8739 grows faster than other strains on acetate. An A-stat process was carried out to evolve ATCC8739 for a faster growth on acetate. Three colonies isolated from the A-stat at 0.50 h-1 had a greater maximum specific growth rate than the parent strain ATCC8739. Specifically, the MEC136 isolate had a maximum specific growth rate of 0.51 h-1 on acetate. Transcriptome comparison between MEC136 and the parent strain revealed that 10 genes were atleast 2-fold downregulated in MEC136 and 1 gene was 2-fold upregulated in MEC136. Therefore, the MEC136 can be used to improve the substrate selective degradation method.