Genomes to Life Contractor-Grantee Workshop III
February 6-9, 2005, Washington, D.C.
Microbial Genomics
85
Dynamics and Control of Biofilms of the Oligotrophic Bacterium Caulobacter crescentus
Alfred M. Spormann (spormann@stanford.edu )and Plamena Entcheva-Dimitrov
Stanford University, Stanford, CA
Caulobacter crescentus is an oligotrophic α-proteobacterium with a complex cell cycle involving sessile stalked and piliated, flagellated swarmer cells. Because the natural lifestyle of C. crescentus intrinsically involves a surface-associated, sessile state, we investigated the dynamics and control of C. crescentus biofilms developing on glass surfaces in a hydrodynamic system. In contrast to biofilms of the well studied Pseudomonas aeruginosa, E. coli, and Vibrio cholerae, C. crescentus CB15 cells form biphasic biofilms, consisting predominantly of a cell monolayer biofilm and a biofilm containing densely-packed, mushroom-shaped structures. Based on comparisons between the C. crescentus strain CB15 wild type and its holdfast (hfsA, ∆CC0095), pili (∆pilA-cpaF::Ωaac3), motility (motA), flagellum (flgH) mutants and a double mutant lacking holdfast and flagellum (hfsA; flgH), a model for biofilm formation in C. crescentus is proposed: For both biofilm forms, the holdfast structure at the tip of a stalked cell is crucial for mediating the initial attachment. Swimming motility by means of the single polar flagellum enhances initial attachment and enables progeny swarmer cells to escape from the monolayer biofilm. The flagellum structure contributes also to maintaining the mushroom structure. Type IV pili enhance but are not absolutely required for the initial adhesion phase. However, pili are essential for forming and maintaining the well-defined three-dimensional mushroom-shaped biofilm. The involvement of pili in mushroom architecture is a novel function for type IV pili in C. crescentus. These unique biofilm features demonstrate a spatial diversification of the C. crescentus population into a sessile, as ‘stem cells’ acting subpopulation (monolayer biofilm), which generates progeny cells capable of exploring the aqueous, oligotrophic environment by swimming motility, and a subpopulation accumulating in large mushroom structures.
* Presenting author
