Si content of various Bacillus spores. The amounts of silicate per spore were measured for B. subtilis 168, B. cereus NBRC15305, B. thuringiensis NBRC101235, B. mycoides NBRC101228, B. megaterium NBRC15308, and the bacteria isolated in this study (YH64 and YH221). Data represent the means and standard deviations of the results of three independent experiments.