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摘要
Two strains, NF4 and NF5, of a yellow-colored gram-negative bacterium were isolated from sediments of Lake Baikal and from old oil sludge of the Nizhnekamsk oil-processing plant. The cells of the strains are ultrasmall coccoids or short rods, measuring 0.2-0.4 x 0.2-0.5 mu m; the average cell volume ranges from 0.004 to 0.04 mu m(3). A considerable proportion (30-60%) of cells have nanometer dimensions (180-300 nm in diameter and 0.004-0.02 mu m(3) in volume). The new isolates are thus among the smallest representatives of presently known free-living ultramicrobacteria. The two studied isolates are gram-negative nonmotile cells possessing a pronounced outer membrane. The cells do not have flagella and are not capable of gliding motility. They divide by constriction, budding, and multiple septation. The multiplicity of reproduction mechanisms results in a high degree of cell polymorphism. The isolates are chemoorganotrophic, aerobic, psychrotolerant, oxidase- and catalase-positive. Their characteristic trait is the absence of extracellular hydrolytic enzymes, such as proteases, lipases, pectinases, and cellulases. Menaquinone MK-6 is the main respiratory quinone; the flexirubin pigment was not detected. The G + C contents of the DNA of strains NF4 and NF5 are 40.8 and 40.5 mol %, respectively. The DNA-DNA hybridization level of strains NF4 and NF5 was close to 100%. Analysis of the 16S rRNA gene sequences and the fatty acid compositions showed that the isolates are most closely related to certain representatives of the genus Chryseobacterium (C. solincola, C. antarcticum, and C. jeonii). However, the differences in the 16S rRNA gene sequences, as well as in the phenotypic properties, such as formation of ultrasmall cells, the absence of extracellular hydrolases, oligotrophy, and the capacity for epibiosis on bacterial cells, suggest that the studied strains belong to a new species of the genus Chryseobacterium. The capacity for epibiosis, i.e., the ability to exist in a tightly adhered state on the surfaces of host Bacillus subtilis cells, is a peculiar trait of the studied isolates. It is assumed that adhesion of the cells of strains NF4 and NF5 (members of the phylum Bacteroidetes) occurs via by the same unique mechanism as the mechanism that we previously described for representatives of Alphaproteobacteria (Kaistia sp., NF1, and NF3), which use polysaccharide chains equipped with sticky granules as trapping and constricting cords.
- 出版日期2011-8
