The QseB/QseC Signaling Affects Initiation Of Chromosomal Replication And Cell Motility In Escherichia Coli

The Escherichia coli two-component system, QseB/QseC signaling regulates expressions of more than 50 genes encoding flagellar proteins and proteins associated with virulence. In this work, we found that absence of the qseB gene led to an early initiation of chromosomal replication in a manner of medium-independent, the early initiation was shown to be reversed by ectopic expression of QseB from a plasmid pqseB. Further, absence of the qseB gene resulted in an increase of DnaA concentration and the purified QseB protein did not interact with the oriC DNA in vitro. The early initiation was also found in the AqseC mutant cells. These results indicate that absence of the QseB/QseC signaling increases concentration of DnaA and the later subsequently triggers the early initiation of replication. Interestingly, absence of the fliM, fliQ, fliP or fliO gene which is target of QseB protein delayed initiation of replication. Further, we observed that absence of QseB/QseC signaling did not but of flagelar genes affected cell size, indicating that cell motility affects cell division. Flourescene microscope analysis showed that the QseC protein localized at cell membrane while QseB was in cytosol.Cell motility was largely increased in the absence of qseB gene, which was reversed by ectopic expression of the QseB protein. However, cell motility was significantly decreased in AqseC cells as well as in AflhDC cells, indicating QseC signaling, FlhD and FlhC transcription factor are required for normal cell motility. As expected, absence of flagellar genes led to a decrease in cell motility.Immunoprecipitation with GFP-QseB suggested that QseB could interact with the DnaK chaperone protein and FtsZ cell division protein in vitro. Indeed, bacterial two-hybrid analysis indicated that QseB interacted with DnaK and FtsZ in vivo. Further analysis showed that absence of DnaK or partial inactivation of FtsZ decreased cell motility. It is most likely that the QseB/QseC signaling indirectly affects initiation of replication through changing DnaA synthesis, cell division by interacting with FtsZ, and the cell motility by interacting with DnaK.