Active “Par”-titioning of Bacterial Chemotaxis Proteins

Science Signaling  26 Jul 2011:
Vol. 4, Issue 183, pp. ec206
DOI: 10.1126/scisignal.4183ec206

Localization of proteins to specific subcellular domains is an important aspect of the spatial-temporal regulation of bacterial processes, such as cell division and chemotaxis. Cell pole–anchored partitioning (Par) systems comprising a Walker-type ATPase (ParA) and a centromere-binding protein (ParB) facilitate chromosome segregation in several species of rod-shaped bacteria, including Vibrio cholerae. Ringgaard et al. identified a ParA homolog (VC2061) encoded by a gene in the chemotaxis operon of V. cholerae. Genes encoding ParA-like proteins were also identified in the chemotaxis operons of other bacteria with polar flagella and thus named ParC. Fluorescently tagged proteins indicated that ParC localized to distinct foci at one or both poles of V. cholerae cells, with younger (shorter) cells containing a single focus and older (longer) cells containing bipolar foci. The cell cycle–dependent ParC redistribution from a single flagellated pole to both the “old” and “new” poles did not require ParA1, nor was it dependent on the prior arrival of ParB1 at the new cell pole. Static and time-lapse fluorescence microscopy revealed that release of a portion of ParC from the first, “old” cell pole and its recruitment to the second, “new” cell pole preceded the appearance of two other proteins encoded by the main V. cholerae chemotaxis operon, the adaptor protein CheW1 and the response regulator CheY3. Moreover, in a V. cholerae strain lacking parC (ΔparC), a greater percentage of cells contained randomly localized foci of fluorescently tagged CheW1 or CheY3 in comparison to wild-type cells, which had polar accumulation of these two proteins. Also, cell division occurred before bipolar localization of CheW1 and CheY3 had been established. The CheW1 and CheY3 mislocalization phenotype in ΔparC cells was rescued by expression of wild-type fluorescently tagged ParC, but not by two ParC mutants containing single amino acid substitutions in the putative Walker-A ATP-binding pocket expected to inhibit ATPase activity. Because the ParC ATPase activity mutants were themselves mislocalized, these results suggest that catalytic activity is needed for polar localization of ParC and subsequent recruitment of chemotaxis proteins. The ΔparC cells exhibited a reduced swarming ability in soft agar in comparison with wild-type V. cholerae cells. These ΔparC cells also exhibited an altered propensity for linear motility in that, in comparison with wild-type cells, they displayed a counterclockwise-biased flagellar rotation and reversed direction less frequently. A mouse model for studying cholera indicated that the reduced chemotactic capacity of the ΔparC strain resulted in an enhanced capacity to colonize proximal parts of the small intestine in comparison with wild-type V. cholerae, which mainly colonizes the middle and distal parts of the small intestine.

S. Ringgaard, K. Schirner, B. M. Davis, M. K. Waldor, A family of ParA-like ATPases promotes cell pole maturation by facilitating polar localization of chemotaxis proteins. Genes Dev. 25, 1544–1555 (2011). [Abstract] [Full Text]