Glutathione is required for maximal transcription of the cobalamin biosynthetic and 1,2-propanediol utilization (cob/pdu) regulon and for the catabolism of ethanolamine, 1,2-propanediol, and propionate in Salmonella typhimurium LT2

Abstract

Transcription of the cob/pdu regulon of Salmonella typhimurium is activated by the PocR regulatory protein in response to 1,2-propanediol (1,2-PDL) in the environment. Nutritional analysis and DNA sequencing confirmed that a strain defective in expression of the cob/pdu regulon in response to 1,2-PDL lacked a functional gshA gene. gshA encodes ␥-glutamylcysteine synthetase (L-glutamate:L-cysteine ␥-ligase [ADP forming]; EC 6.3.2.2), the enzyme that catalyzes the first step in the synthesis of glutathione (GSH). The DNA sequence of gshA was partially determined, and the location of gshA in the chromosome was established by two-factor crosses. P22 cotransduction of gshA with nearby markers showed 21% linkage to srl and 1% linkage to hyd; srl was 9% cotransducible with hyd. In light of these data, the gene order gshA srl hyd is suggested. The level of reduced thiols in the gshA strain was 87% lower than the levels measured in the wild-type strain in both aerobically and anaerobically grown cells. 1,2-PDL-dependent transcription of cob/pdu was studied by using M. Casadaban's Mu-lacZ fusions. In aerobically grown cells, transcription of a cbi-lacZ fusion (the cbi genes are the subset of cob genes that encode functions needed for the synthesis of the corrin ring) was 4-fold lower and transcription of a pdu-lacZ fusion was 10-fold lower in a gshA mutant than in the wild-type strain. Expression of the cob/pdu regulon in response to 1,2-PDL was restored when GSH was included in the medium. In anaerobically grown cells, cbi-lacZ transcription was only 0.4-fold lower than in the gshA ؉ strain; pdu-lacZ transcription was reduced only by 0.34-fold, despite the lower thiol levels in the mutant. cobA-lacZ transcription was used as negative control of a gene whose transcription is not controlled by the PocR/1,2-PDL system; under both conditions, cobA transcription remained unaffected. The gshA mutant strain was unable to utilize 1,2-PDL, ethanolamine, or propionate as a carbon and energy source. The defect in ethanolamine utilization appears to be at the level of ethanolamine ammonia-lyase activity, not at the transcriptional level. Possible roles for GSH in ethanolamine, 1,2-PDL, and propionate catabolism are proposed and discussed.In Salmonella typhimurium, the cobalamin biosynthetic operon (cob) and the 1,2-propanediol (1,2-PDL) utilization (pdu) genes are coregulated at the transcriptional level in response to 1,2-PDL in the environment (9, 33). This induction requires the PocR protein (9, 33), a transcriptional activator with homology to the AraC protein (11,36). Adenosylcobalamin serves as a cofactor for the first enzyme in the 1,2-PDL degradation pathway (21).The cob and the pdu operons are located at min 41 on the chromosome and are transcribed divergently from each other (21). The intervening DNA between cob and pdu contains the pocR gene (9,11,33), which is transcribed in the same direction as the cob operon (9).In this paper, we report the isolation and characterization of a mutant strain of S. typhimurium (JE2546) w...

Diverse Bacterial Microcompartment Organelles

“…Subsequently, propionaldehyde is depleted by conversion to propionate and 1-propanol, at which time growth of Salmonella resumes, with propionate and 1-propanol serving as the carbon and energy sources (22,24). The aldehyde toxicity model is further supported by the findings that polA (DNA repair polymerase) and gsh (glutathione biosynthesis) mutants are unable to grow on 1,2-PD or ethanolamine (23,102). Thus, several lines of evidence support the idea that the Pdu MCP functions to mitigate propionaldehyde toxicity (Fig.…”

Bacterial Microcompartments

“…The first model, and the one that is supported by the largest body of experimental evidence for the Pdu BMC, suggests that the BMC shell acts as a diffusional barrier to propionaldehyde and prevents leakage of this intermediate into the cytoplasm, where its relatively high reactivity could have deleterious effects on other cellular components (7,57). The analogous function of the EutBMCs would be to contain acetaldehyde until it is further metabolized to acetyl-CoA by acetaldehyde dehydrogenase (EutE (65)) in the BMC interior prior to entry into the central metabolism, or converted to acetyl-phosphate by a phosphotransacetylase (EutD (9, 64)) (10) (Figure 2c).…”

From food to cell: nutrient exploitation strategies of enteropathogens

“…Glutathione is necessary for maximal transcription of cob/pdu when Salmonella enterica sv. Typhimurium grows aerobically, possibly by protecting proteins in the microcompartment from damage by aldehydes (Rondon et al, 1995). In this enteropathogen, the expression of pdu (and the genes for cobalamin synthesis) seems to be regulated in a coordinated manner by the DNA-binding protein PocR, whose activity depends on the presence of 1,2-propanediol (Rondon & Escalante-Semerena, 1992.…”