Coordinated expression of acetyl CoA synthetase and the operon enzymes in in preparation for adaptation to acetate.

Successful adaptation of to constant environmental challenges demands the operation of a wide range of regulatory control mechanisms, some of which are global, while others are specific. Here, we show that the ability of acetate-negative phenotype strains of devoid of acetate kinase (AK) and phosphotransacetylase (PTA) to assimilate acetate when challenged at the end of growth on acetogenic substrates is explicable by the co-expression of acetyl CoA-synthetase (AcCoA-S) and acetate permease (AP). Furthermore, mRNA transcript measurements for , together with the enzymatic activities of their corresponding enzymes, acetyl CoA synthetase (AcCoA-S) and isocitrate lyase (ICL), clearly demonstrate that the expression of the two enzymes is inextricably linked and triggered in response to growth rate threshold signal (0.4 h± 0.03: n4). Interestingly, further restriction of carbon supply to the level of starvation led to the repression of (AcCoA-S), (AK) and (PTA). Further, we provide evidence that the reaction sequence catalysed by PTA, AK and AcCoA-S is not in operation at low growth rates and that the reaction catalysed by AcCoA-S is not merely an ATP-dissipating reaction but rather advantageous, as it elevates the available free energy (Δ°) in central metabolism. Moreover, the transcriptomic data reinforce the view that the expression of PEP carboxykinase is essential in gluconeogenic phenotypes.