FIG. 6.

HCl resistance of YH221 spores. (A) Low- and high-Si spores were prepared from 50-h cultures, washed two times with sterilized water, and suspended in 0.2 N HCl. Viability was determined as described in the text. Symbols: closed circles, high-Si spores; open circles, low-Si spores. Data represent the means and standard deviations of the results of at least three independent experiments. (B) Effect of Si content in YH221 spores on survival rate after HCl treatment. YH221 spores containing different amounts of silicate were prepared. The viability of the spores after a 2-h incubation in 0.2 N HCl was determined.