Hydrodynamic effects on microcapillary motility and chemotaxis assays of Methylosinus trichosporium OB3b.
A study of the random motility and chemotaxis of Methylosinus trichosporium OB3b was conducted by using Palleroni-chamber microcapillary assay procedures. Under the growth conditions employed, this methanotroph was observed qualitatively with a microscope to be either slightly motile or essentially nonmotile. However, the cells did not not respond in the microcapillary assays in the manner expected for nonmotile Brownian particles. As a consequence, several hydrodynamic effects on these Palleroni microcapillary assays were uncovered. In the random-motility microcapillary assay, nondiffusive cell accumulations occurred that were strongly dependent upon cell concentration. An apparent minimal random-motility coefficient (mu) for this bacterial cell of 1.0 x 10(-7) cm2/s was estimated from microcapillary assays. A simple alternative spectrophotometric assay, based upon gravitational settling, was developed and shown to be an improvement over the Palleroni microcapillary motility assay for M. trichosporium OB3b in that it yielded a more-accurate threefold-lower random-motility coefficient. In addition, it provided a calculation of the gravitational-settling velocity. In the chemotaxis microcapillary assay, the apparent chemotactic responses were strongest for the highest test-chemical concentrations in the microcapillaries, were correlated with microcapillary fluid density, and were strongly dependent upon the microcapillary volume. A simple method to establish the maximal concentration of a chemical that can be tested and to quantify any contributions of abiotic convection is described. Investigators should be aware of the potential problems due to density-driven convection when using these commonly employed microcapillary assays for studying cells which have low motilities.
Shonnard
D R
DR
Biomedical Sciences Division, Lawrence Livermore National Laboratory, University of California 94550.
Taylor
R T
RT
Tompson
A
A
Knapp
R B
RB
D001431:Bacteriological Techniques / Q000295:instrumentation; D001673:Biodegradation, Environmental; D002465:Cell Movement; D002633:Chemotaxis / Q000187:drug effects / Q000502:physiology*; D015169:Colony Count, Microbial; D006838:Hydrocarbons / Q000378:metabolism; D008772:Methylococcaceae / Q000187:drug effects / Q000502:physiology*; D010316:Particle Size
D006838:Hydrocarbons