Tepidicella baoligensis sp. nov., A Novel Member of Betaproteobacterium Isolated from an Oil Reservoir.

A Gram-negative, non-pigmented, aerobic bacterium, designated strain B18-50T was isolated from oil-well production water in Baolige oilfield, China. The strain was able to grow at pH 6.5-10.5 (optimum at pH 7.5-8.5), in 0-3% (w/v) NaCl (optimum at 0-0.5%, w/v) and at 20-60 °C (optimum at 45 °C). Cells of the isolate were motile with a single polar flagellum and non-spore-forming rods. Organic acids and amino acids were used as carbon and energy sources, but sugars and polyols were not assimilated. The major cellular fatty acids were C16:0, C16:1ω6c/ω7c, and C18:1ω7c. Ubiquinone 8 was the predominant respiratory quinone. The major polar lipids consisted of phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol. The genomic DNA G+C content of the isolate was 62.8 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain B18-50T was most closely related to Tepidicella xavieri DSM 19605T (97.5% similarity). Comparative analysis of genotypic and phenotypic features indicate that strain B18-50T represents a novel species of the genus Tepidicella, for which the name Tepidicella baoligensis sp. nov. is proposed. The type strain is B18-50T (= CGMCC 1.13575T = KCTC 62779T).

The biophysics of a critical phenomenon: colonization and sedimentation of the photosynthetic bacteria Rubrivivax gelatinosus.

In response to environmental changes, the photosynthetic bacterium Rubrivivax gelatinosus (Rvx.) can switch from a planktonic lifestyle to a phototrophic biofilm. Like in critical phenomena, the colonization and sedimentation of the cells is abrupt and hard to predict causally, and the underlying biophysics of the mechanisms involved is not known. Herein, we report basic experimental observations and quantitative explanations as keys to understanding microbial turnover of aggregates. (1) The moment of sedimentation can be controlled by the height of the tube of cultivation, by the concentrations of externally added Ficoll (a highly branched polymer) and/or of internally produced polysaccharides (constituents of the biofilm). (2) The observed translational diffusion coefficient of the planktonic bacteria is the sum of diffusion coefficients coming from random Brownian and twitching movements of the bacteria and amounts to 14 (µm)2/s. (3) This value drops hyperbolically with the association number of the cell aggregates and with the concentration of the exopolysaccharides in the biofilm. In the experiments described herein, their effects could be separated. (4) The critical conditions of colonization and sinking of the cells will be achieved if the height of the tube meets the scale height that is proportional to the ratio of the diffusion coefficient and the net mass of the bacterium. The decisive role of the web-like structure of a biofilm, the organization of bacteria from loose cooperativity to solid aggregation, and the possible importance of similar controls in other phototrophic microorganisms are discussed.