The relationship between a coiled morphology and Mbl in alkaliphilic Bacillus halodurans C-125 at neutral pH values

The facultative alkaliphilic Bacillus halodurans C-125 can grow in a pH range from 6.8 to 10.8. The morphology of the cells grown at pH values above 7.5 is rod shaped, whereas, that gown at pH values less than 7.5 is coiled. Cytoplasmic membrane staining revealed that this coiled morphology was formed not by one filamentous cell, but by many chained bent/non-bent cells. Prokaryotic actin and tubulin homologs (MreB, Mbl MreBH, and FtsZ, respectively) are known to function as bacterial cytoskeleton proteins. The transcription levels of ftsZ, mreB, and mreBH genes were hardly affected by growth pH. However, the level of the mbl gene was significantly decreased at neutral pH values. Moreover, the expression level of the Mbl protein at pH 7.0 was about one-fourth of that at pH 10. Immunofluorescence microscopy (IFM) showed that the Mbl protein was localized as a helical structure in the rod-shaped cell grown at pH 10, whereas a helical structure was not observed in the cells grown at pH 7.0. Fluorescent vancomycin staining showed insertion of new peptidoglycan strands of sidewalls occurred in the cells grown at pH 7.0. These data suggested that a decrease in the expression level of the Mbl protein can influence the morphology of B. halodurans C-125 grown at pH 7.0 without influencing insertion of new peptidoglycan strands.