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: (a) In Escherichia coli, Bacillota (formerly Firmicutes) and Vibrio, CCR depends on the phosphorylation state of the components of the phosphoenolpyruvate-sugar phosphotransferase system (PTS) and their subsequent regulatory activity, and (b) 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.