The Relationship of Sulfhydryl and Disulfide Constituents of Bacillus cereus to Radioresistance

Sulfhydryl (SH) and disulfide (SS) levels in vegetative cells and spores of Bacillus cereus were studied in attempts to explain the biochemical basis for increased radioresistance of mature spores. Insight into this mechanism was facilitated by the use of an organic sulfurrequiring auxotrophic mutant. The determination of SH and SS was carried out on intact organisms polarographically by estimation of unreacted MeHgI, a reagent specific for SH groups. This reagent was made accessible to cells by treating them for 24 hours in the presence of 8 M urea. Results of various analyses of the wild-type strains agreed with published findings of Vinter, namely, that radioresistance increased with progressive spore maturity, and that spores had extremely low, or no, SH content. Mutant spore did not reflect a progressive radioresistance with maturation. In addition, it was noted that, when the mutant was grown on three different levels of cystine or cysteine, spores with greatest radioresistance were formed on highest amino acid concentration. However, this work failed to establish a direct relationship between disulfide content and radioresistance similar to that predicted by Vinter. Instead it was found that an increased SS/SH ratio accompanied the development of radioresistance in any cell sample. (auth)