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Solid substrate motility and phototaxis of the alpha-proteobacterium Rhodobacter capsulatus

University of British Columbia

The work in this thesis reports the first discovery of flagellum-independent motility in Rhodobacter capsulatus, a purple photosynthetic bacterium. Furthermore, while aqueous swimming motility using a flagellum had been documented, the occurrence of movement over solid and semi-solid substrates had not been reported in R. capsulatus. This motility was found to be affected by the physical and chemical composition of the translocation surface. While motility was reduced under anaerobic (dark) conditions, it did not require oxygen. Cells appeared to respond to multiple stimuli, and were able to move both as coordinated masses and individual cells. Coordinated movements did not require any of the known cell-to-cell communication mechanisms. Movements were influenced by light such that cells usually moved toward a light source over a broad region of the visible spectrum, and this movement appeared to be a genuine phototaxis. A direct linkage between photoresponsive movement and photosynthesis was ruled out, because the photosynthetic reaction center was not required for movement toward white light. Photoresponsive movement occurred independently of the photoactive yellow protein, but appeared to require the bacteriochlorophyll and/or carotenoid pigments. Motility was mediated by flagellum-dependent and flagellum-independent contributions. Flagellum-dependent contributions were responsible for dispersive semi-random movements while flagellum-independent contributions resulted in linear, directed movements. Analysis of several strains indicated that flagellum-independent motility is widespread throughout R. capsulatus. This motility appears to be mediated by a gliding mechanism, perhaps involving the deposition of exopolysaccharide to achieve coordinated cell taxis.

Text

2011-02-23

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/31666

Microbiology and Immunology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/