The Effect of pH on Growth of Clostridium botulinumType A and Expression of bontAand botRDuring Different Growth Stages

AbstractIn this study, the effects of pH on the growth, relative expressions of bontAand botRgenes, and neurotoxin formation of foodborne pathogens Clostridium botulinumtype A were systematically studied throughout its growth stage. As in the previous reports, no C. botulinumgrowth was observed at extremely acidic pH. However, the effect of alkaline pH on the growth and neurotoxin production of C. botulinumwas first revealed in this study. The maximum growth rate at pH 9.0 was similar to that at other pH values, although the lag phase at pH 9.0 was 16 h longer than that at pH 8.0. The peak of bontAmRNA expression at pH 9.0 was only 15.5% compared with that at pH 7.0. However, the neurotoxin concentration quantified in the cultures did not differ significantly. BotRis a known regulatory protein of bontA. The quantitative relationship between bontAand botRat different growth stages was first determined in this study. The mRNA levels of bontAwere found to be positively correlated with those of botR, and the ratio of the mRNA transcript varied with pH. All these findings provide important physiological information on C. botulinumand thereby contribute to the improvement of food safety.