An insight into the role of phosphotransacetylase (<it>pta</it>) and the acetate/acetyl-CoA node in <it>Escherichia coli</it>

• Main Authors: Iborra José L, Bernal Vicente, Renilla Sergio, Pastor José M, Castaño-Cerezo Sara, Cánovas Manuel
• Format: Article
• Language: English
• Published: BMC 2009-10-01
• Series: Microbial Cell Factories
• Online Access: http://www.microbialcellfactories.com/content/8/1/54

<p>Abstract</p> <p>Background</p> <p>Acetate metabolism in <it>Escherichia coli </it>plays an important role in the control of the central metabolism and in bioprocess performance. The main problems related to the use of <it>E. coli </it>as cellular factory are i) the deficient utilization of carbon source due to the excretion of acetate during aerobic growth, ii) the inhibition of cellular growth and protein production by acetate and iii) the need for cofactor recycling (namely redox coenzymes and free CoASH) to sustain balanced growth and cellular homeostasis.</p> <p>Results</p> <p>This work analyzes the effect of mutations in the acetate excretion/assimilation pathways, acetyl-CoA synthethase (<it>acs</it>) and phosphotransacetylase (<it>pta</it>), in <it>E. coli </it>BW25113 grown on glucose or acetate minimal media. Biomass and metabolite production, redox (NADH/NAD⁺) and energy (ATP) state, enzyme activities and gene expression profiles related to the central metabolism were analyzed. The <it>knock-out </it>of <it>pta </it>led to a more altered phenotype than that of <it>acs</it>. Deletion of <it>pta </it>reduced the ability to grow on acetate as carbon source and strongly affected the expression of several genes related to central metabolic pathways.</p> <p>Conclusion</p> <p>Results showed that <it>pta </it>limits biomass yield in aerobic glucose cultures, due to acetate production (overflow metabolism) and its inefficient use during glucose starvation. Deletion of <it>pta </it>severely impaired growth on acetate minimal medium and under anaerobiosis due to decreased acetyl-coenzyme A synthethase, glyoxylate shunt and gluconeogenic activities, leading to lower growth rate. When acetate is used as carbon source, the joint expression of <it>pta </it>and <it>acs </it>is crucial for growth and substrate assimilation, while <it>pta </it>deletion severely impaired anaerobic growth. Finally, at an adaptive level, <it>pta </it>deficiency makes the strain more sensitive to environmental changes and de-regulates the central metabolism.</p>