The Transcription Factor Mlc Promotes Vibrio cholerae Biofilm Formation through Repression of Phosphotransferase System Components

The phosphoenol phosphotransferase system (PTS) is a multicomponent signal transduction cascade that regulates diverse aspects of bacterial cellular physiology in response to the availability of high-energy sugars in the environment. Many PTS components are repressed at the transcriptional level when the substrates they transport are not available. InEscherichia coli, the transcription factor Mlc (form akesl argec olonies) represses transcription of the genes encoding enzyme I (EI), histidine protein (HPr), and the glucose-specific enzyme IIBC (EIIBCGlc ) in defined media that lack PTS substrates. When glucose is present, the unphosphorylated form of EIIBCGlc sequesters Mlc to the cell membrane, preventing its interaction with DNA. Very little is known aboutVibrio cholerae Mlc. We found thatV. cholerae Mlc activates biofilm formation in LB broth but not in defined medium supplemented with either pyruvate or glucose. Therefore, we questioned whetherV. cholerae Mlc functions differently thanE. coli Mlc. Here we have shown that, likeE. coli Mlc,V. cholerae Mlc represses transcription of PTS components in both defined medium and LB broth and thatE. coli Mlc is able to rescue the biofilm defect of aV. cholerae Δmlc mutant. Furthermore, we provide evidence that Mlc indirectly activates transcription of thevps genes by repressing expression of EI. Because activation of thevps genes by Mlc occurs under only a subset of the conditions in which repression of PTS components is observed, we conclude that additional inputs present in LB broth are required for activation ofvps gene transcription by Mlc.