Sci. STKE, 22 July 2003
MICROBIOLOGY Polarity in Bacterial Cell Division
The flagellar bacteria Caulobacter crescentus are polarized prokaryotes, and cell division produces asymmetric daughter cells. Lam et al. investigated how the response regulator DivK contributes to this polarized cell-division process. DivK localization is dynamic during the cell cycle. DivK starts out diffusely localized in G1, accumulates at the old pole during the stalked stage (which is the beginning of S phase, the DNA replication stage of the cell cycle), partially migrates to the new pole during the predivisional stage, and is finally released only from the new pole during G2 in the swarmer cell. Mutation of the DivK phosphorylation site in a green fluorescent protein-tagged version of DivK (DivK-GFP) prevented its redistribution, which confirmed the importance of phosphorylation in regulating accumulation at the poles. In a genetic complementation assay, DivK phosphorylation was also shown to be essential for cell viability. Expression of a histidine kinase-deficient version of tagged DivJ, a histidine kinase suggested to be responsible for DivK phosphorylation, showed that kinase activity was not essential for DivJ localization to the old pole or recruitment of wild-type DivK to the old pole, but that DivK did not subsequently accumulate at the new pole. A nonphosphorylatable mutant of DivK was not recruited to the old pole; thus, a second kinase appears to phosphorylate DivK before its interaction with DivJ. At the new pole, release of DivK during G2 requires PleC, which is another histidine kinase that may serve as a phosphatase in vivo. Mutation of a residue required for kinase activity resulted in the loss of release of DivK from the new pole. The authors propose that phosphorylated DivK accumulates at the old pole in response to accumulation of DivJ at the old pole; DivJ then phosphorylates DivK, increasing the concentration of phosphorylated DivK. Phosphorylated DivK migrates to the new pole, where PleC dephosphorylates DivK, leading to its release from the pole in the daughter swarmer cell. Surprisingly, even nonpolarized bacteria have homologs to DivK, and monitoring of a GFP-tagged version of Sinorhizobium meliloti DivK indicated that even nonpolarized bacteria have polarized accumulation of DivK during cell division that is dependent on phosphorylation of DivK.
H. Lam, J.-Y. Matroule, C. Jacobs-Wagner, The asymmetric spatial distribution of bacterial signal transduction proteins coordinates cell cycle events. Dev. Cell 5, 149-159 (2003). [Online Journal]
Citation: Polarity in Bacterial Cell Division. Sci. STKE 2003, tw284 (2003).
Science Signaling. ISSN 1937-9145 (online), 1945-0877 (print). Pre-2008: Science's STKE. ISSN 1525-8882