A GENETICAL AND BIOCHEMICAL STUDY OF CHLORATE-RESISTANT MUTANTS OF SALMONELLA-TYPHIMURIUM

S.typhimurium can form nitrate reductase A, chlorate reductase C, thiosulfate reductase, tetrathionate reductase and formic dehydrogenase. None of these enzymes are formed in chlorate-resistant mutants. Conjugation experiments showed the presence of a strong linkage between the chl and gal markers of the bacterial chromosome. By deletion mapping the gene order nic A aro G gal bio chl D uvr B chl A was found. Strains with deletions terminating between bio and uvr B or between uvr B and chl A have a number of aberrant properties. Though resistant against chlorate they reduce nitrate and form gas. After growth with nitrate they form less nitrate reductase than the wild type which may explain the resistance against chlorate. After growth with thiosulfate they form small amounts of thiosulfate reductase and chlorate reductase C. In crosses between an E.coli Hfr chl+ strain and a S.typhimurium chl A strain recombinants were obtained, forming nitrate reductase A and chlorate reductase C. These recombinants do not form gas, which indicates that the chl+ gene from E.coli does not function normally in S.typhimurium. © 1969 Swets & Zeitlinger.