Attachment of the adhesive holdfast organelle to the cellular stalk of Caulobacter crescentus

Abstract

Caulobacters attach to surfaces in the environment via their holdfasts, attachment organelles located at the base of the flagellum in swarmer cells and later at the end of the cellular stalk in the stalked cells which develop from the swarmer cells. There seems to be little specificity with respect to the types of surfaces to which holdfasts adhere. A notable exception is that the holdfast of one cell does not adhere to the cell surface of another caulobacter, except by joining holdfasts, typically forming "rosettes" of stalked cells. Thus, the localized adhesion of the holdfasts to the cells is in some way a specialized attachment. We investigated this holdfast-cell attachment by developing an adhesion screening assay and analyzing several mutants of Caulobacter crescentus CB2A selected to be defective in adhesion. One class of mutants made a normal holdfast by all available criteria, yet the attachment to the cell was very weak, such that the holdfast was readily shed. Another class of mutants made no holdfast at all, but when mixed with a wild-type strain, a mutant of this class participated in rosette formation. The mutant could also attach to the discarded holdfast produced by a shedding mutant. In addition, when rosettes composed of holdfast-defective and wild-type cells were examined, an increase in the number of holdfast-defective cells was correlated with a decrease in the ability of the holdfast material at the center of the rosette to bind colloidal gold particles. Gold particles are one type of surface to which holdfasts adhere well, suggesting that the stalk end and the colloidal gold particles occupy the same sites on the holdfast substance. Taken together, the data support the interpretation that there is a specialized attachment site for the holdfast at the base of the flagellum which later becomes the end of the stalk, but not a specialized region of the holdfast for attachment to this site. Also, attachment to the cell is accomplished by bond formations that occur not only at the time of holdfast production. Thus, we propose that the attachment of the holdfast to the cell is a true adhesion process and that the stalk tip and base of the flagellum must have compositions distinctly different from that of the remainder of the caulobacter cell surface.

In situ cell and glycoconjugate distribution in river snow studied by confocal laser scanning microscopy

“…Examination of cells with colloidal gold labelled lectins was done by electron microscopy (Vasse et al 1984, Morioka et al 1987, Sanford et al 1995, Hood & Schmidt 1996 whereas bacteria stained with fluorescently labelled lectins were observed by epifluorescence microscopy or measured by flow cytometry (Jones et al 1986, YagodaShagam et al 1988, Quintero & Weiner 1995. Lectins were employed in studies of adhesive polymers such as Caulobacter holdfasts (Merker & Smit 1988, Ong et al 1990), bacterial 'footprints' (Neu & Marshal1 1991) and Hyphomonas cell surface structures (Quintero et al 1998). Fluorescent lectins have been suggested to distinguish between Gram-positive and Gram-negative bacteria (Sizemore et al 1990) and between different cell surface mutants of Rhodosporidium (Buck & Andrews 1999).…”

Identification, isolation, and structural studies of extracellular polysaccharides produced by Caulobacter crescentus

“…We also note that we have not in the past had difficulty in labeling the S-layer protein with specific antibodies and colloidal gold labels for electron microscopy (30,38). It may be that highly hydrated neutral polysaccharides, incapable of ion bridging or charge repulsion effects, have little ability to limit access of antibody molecules to the cell surface.…”

“…The methyl glycosides were vacuumdried overnight and then treated with (-)-2-butanolic 1 M HCl (1 ml) for 8 h at 80°C. After the removal of the HCI as before, the residues were vacuum-dried overnight and then treated with hexamethyldisilazane-chlorotrimethylsilanepyridine (0.4 ml, 1:1:5) for 30 Electron microscopy techniques. (i) Thin-section transmission electron microscopy (TEM).…”

“…Clearly, the adhesive holdfast has a primary role, being involved with surface attachment, and we have reported initial analyses for the holdfast of freshwater and marine species (28)(29)(30). The organelle appears to be a complex polysaccharide whose composition varies somewhat between species (26,28 …”

Getting in the Loop: Regulation of Development inCaulobacter crescentus

“…It is unclear if protein components also function within the holdfast, though proteins that anchor the holdfast to the cell have been identified. Mutations in the holdfast attachment genes cause shedding of the holdfast from cells to various degrees (37,127,182,229).…”