Identification of facultatively alkaliphilic Bacillus sp strain YN-2000 and its fatty acid composition and cell-surface aspects depending on culture pH

Facultatively alkaliphilic Bacillus sp. strain YN-2000 was isolated from an indigo ball. Although the strain has been extensively investigated as a re presentative strain of alkaliphilic bacillus, its taxonomic position is not yet known. Morphological, biochemical, and physiological characteristics a nd chemotaxonomic properties indicated that the strain was closely related to Bacillus cohnii; this was confirmed by the high homology of the 16S rRNA sequence and the construction of a phylogenetic tree on the basis of the 1 6S rRNA sequence and DNA-DNA relatedness data. Strain YN-2000 contained a l arger amount of unsaturated fatty acids compared with Bacillus subtilis and the obligate alkaliphile, Bacillus alcalophilus, regardless of its culture pH. When the cells were grown at pH 10, the unsaturated fatty acid content and anteiso-/iso-branched fatty acid ratio became lower than those at pH 7 . This result suggests that membrane fluidity decreases when the cells are grown at pH 10 compared to those of pH 7. In the cells of strain YN-2000 gr own at pH 10, the cell-surface aspect was rougher, the cell shape was longe r, and the cell-surface layer was thicker compared with those of the cells grown at pH 7. The cell-surface structural change might be related to adapt ation to an alkaline environment.