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Background:Chromohalobacter salexigens synthesizes and accumulates ectoines. Results: High ratio of the anaplerotic and catabolic fluxes involved in ectoines synthesis supports high biosynthetic fluxes at high salinity and leads to metabolite overflow at low salinity. Conclusion: Evolution optimized the metabolism of C. salexigens to support high production of ectoines. Significance: Metabolic adaptations in a compatible solute-accumulating halophile are described for the first time.

SummaryLysine acetylation is a well-established posttranslational modification widely conserved and distributed in bacteria. Although multiple regulatory roles have been proved, little is known about its regulation. Here, we present evidence that the transcription of the Gcn5-like acetyltransferase YfiQ of Escherichia coli (proposed name: PatZ) is regulated by cAMP-CRP and its implications on acetate metabolism regulation. The acetate scavenging acetyl-CoA synthetase (Acs) is regulated at the transcriptional and post-translational levels. Post-translational regulation depends on a protein acetyltransferase (yfiQ) and an NAD + -dependent deacetylase (cobB). We have studied their expression under different environmental conditions. cobB is constitutively expressed from a promoter located upstream nagK. The expression of yfiQ occurs from its own promoter; it is upregulated in the stationary phase and in the presence of non-PTS carbon sources and is positively regulated by cAMP-CRP. Two putative CRP binding sites are necessary for its full activity. Gene deletion revealed that cobB is essential for growth on acetate, yfiQ deletion restoring growth of the cobB mutant. The fine tuning of metabolic enzymes results from the integration of multiple mechanisms, and redundant systems may exist. Despite the existence of divergent catabolite repression systems, this may be a conserved strategy common to both Gram-positive and -negative bacteria.

Acetate is ubiquitously found in natural environments. Its availability in the gut is high as a result of the fermentation of nutrients, and although it is rapidly absorbed by intestinal mucosa, it can also be used as carbon source by some members of gut microbiota. The metabolism of acetate in Escherichia coli has attracted the attention of the scientific community due to its role in central metabolism and its link to multiple physiological features. In this microorganism, acetate is involved directly or indirectly on the regulation of functional processes, such as motility, formation of biofilms, and responses to stress. Furthermore, it is a relevant nutrient in gut, where it serves additional roles, which regulate or, at least, modulate pathophysiological responses of E. coli and other bacteria. Acetate is one of the major by-products of anaerobic (fermenting) metabolism, and it is also produced under fully aerobic conditions. This acetate overflow is recognized as one of the major drawbacks limiting E. coli's productivity in biotechnological processes. This review sums up current knowledge on acetate metabolism in E. coli, explaining the major milestones that have led to deciphering its complex regulation in the K-12 strain. Major differences in the metabolism of acetate in other strains will be underlined, with a focus on strains of biotechnological and biomedical interest.

Background: Acetate metabolism in Escherichia coli plays an important role in the control of the central metabolism and in bioprocess performance. The main problems related to the use of E. coli 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.