Ericka L. Barrett

Formate dehydrogenase mutants of Salmonella typhimurium: A new medium for their isolation and new mutant classes

SummaryWe have designed a new medium for the differentiation of mutants of Salmonella typhirmurium defective in the ability to reduce nitrate with formate, and have characterized 24 formate dehydrogenase (FDH) mutants isolated on this medium. The mutants were assayed for the ability to use formate to reduce benzyl viologen and phenazine methosulfate, and were mapped by means of conjugation and P22-mediated transduction. Mutants lacking the ability to reduce either dye were found to map at three distinct sites: at a site co-transducible with xyl (presumably fdhA), at a site or sites between 13U and 33U, but not co-transducible with aroA, bio, purB, pyrC, or pyrD (near, but not identical with fdhB), and at a site 10–20% co-transducible with pyrE, for which we suggest the designation fdhC. Six mutant isolates reduced benzyl viologen, but not phenazine methosulfate. They retained the ability to produce nitrite during growth with nitrate. They mapped between 83U and 89U, but no co-transduction was found with metE, glnA, metB, or argH. The combined biochemical and genetic data suggest the existence of a gene in this area which is essential for the reduction of nitrate with formate, but not for formate hydrogenlyase activity or for nitrate reductase activity.

Gram-negative respiratory bacteria which cause ropy milk constitute a distinct cluster within the genusAcinetobacter

Eight strains of Gram-negative respiratory bacteria that produce ropiness in milk were characterized with respect to morphology, physiology, and DNA base composition. All were found to belong to one of the major groups of the genusAcinetobacter. The results of tests for the utilization of 50 different compounds as sole source of carbon and energy were used for a numerical analysis in which 20 strains ofAcinetobacter characterized by other investigators were included. The eight ropy-milk strains, and one previously described, were found to cluster together. The characteristics differentiating the members of this cluster from other strains ofAcinetobacter were determined.

Catabolite repression of thiosulfate reduction bySalmonella typhimurium

The effect of glucose and other carbon sources on thiosulfate reduction and on the expression ofphs bySalmonella typhimurium was examined. Glucose repressed both H2S production from thiosulfate and methyl viologen-linked thiosulfate reductase activity. Cyclic AMP (2 mM) in the growth medium restored both activities. Cyclic AMP was essential for both activities in acya mutant. Glucose and many other sugars repressedphs expression in both Cya+ and Cya−phs::Mu d1(Aprlac) operon fusion mutants. Increasing cyclic AMP to 10 mM increasedphs expression in the presence of some, but not all, sugars. It appears that catabolite repression of thiosulfate reduction inS. typhimurium involves more than a simple requirement for cyclic AMP.