Molecular Microbiology, September 2003, Vol.49(6), pp.1671-1683
The differentiating bacterium produces two different cell types at each cell division, a motile swarmer cell and an adhesive stalked cell. The stalked cell harbours a stalk, a thin cylindrical extension of the cell surface. The tip of the stalk is decorated with a holdfast, an adhesive organelle composed at least in part of polysaccharides. The synthesis of the stalk and holdfast occur at the same pole during swarmer cell differentiation. Mutations in the gene cluster had been shown to disrupt the attachment of the holdfast to the tip of the stalk, but the role of individual genes was unknown. We used fusions of various DNA fragments from the region to show that these genes form an operon. In order to analyse the relative contribution of the different genes to holdfast attachment, mutations were constructed for each gene. was not required for holdfast attachment or binding to surfaces. The and mutants shed some holdfast material into the surrounding medium and were partially deficient in binding to surfaces. Unlike and mutants, mutants were still able to form rosettes efficiently. Cells with insertions in were unable to bind to surfaces, and lectin binding studies indicated that the mutants had the strongest holdfast shedding phenotype. We determined that HfaB and HfaD are membrane‐associated proteins and that HfaB is a lipoprotein. Purification of stalks and cell bodies indicated that both HfaB and HfaD are enriched in the stalk as compared to the cell body. These results suggest that HfaB and HfaD, and probably HfaA, serve to anchor the holdfast to the tip of the stalk.
Bacterial Adhesion ; Bacterial Proteins -- Metabolism ; Caulobacter Crescentus -- Cytology ; Membrane Proteins -- Metabolism;