A Comparative Analysis: Molecular Mechanisms of Carbon Catabolite Repression in Bacteria

In the environment, bacteria often encounter a mixture of different carbon sources (C-sources) that can potentially be used. However, their uptake and utilization are selective and controlled in a hierarchical order by a complex regulatory pathway named carbon catabolite repression (CCR). Currently, two major types of CCR mechanisms have been described: (<i>a</i>) In <i>Escherichia coli, Bacillota</i> (formerly <i>Firmicutes</i>) and <i>Vibrio</i>, CCR depends on the phosphorylation state of the components of the phosphoenolpyruvate-sugar phosphotransferase system (PTS) and their subsequent regulatory activity, and (<i>b</i>) in pseudomonads, transcripts under CCR control are repressed by the posttranscriptional regulators Hfq and Crc. The repressive effect is antagonized by Hfq- and Crc-titrating RNAs (e.g., CrcZ, CrcY, and CrcX) that are expressed in response to the preference for C-sources. In addition, the importance of CCR as a sensor linking carbon availability with the regulation of virulence, chemotaxis, quorum sensing, and antibiotic susceptibility is addressed in this article.