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/

Transcription of the cob/pdu regulon of Salmonella typhimurium is acti vated by the PocR regulatory protein in response to 1,2-propanediol (1 ,2-PDL) in the environment. Nutritional analysis and DNA sequencing co nfirmed that a strain defective in expression of the cob/pdu regulon i n response to I,2-PDL lacked a functional gshA gene, gshA encodes gamm a-glutamylcysteine synthetase (L-glutamate:L-cysteine gamma-ligase [AD P forming]; EC 6.3.2.2), the enzyme that catalyzes the first step in t he synthesis of glutathione (GSH). The DNA sequence of gshA was partia lly determined, and the location of gshA in the chromosome was establi shed by two-factor crosses. P22 cotransduction of gshA with nearby mar kers showed 21% linkage to sri and 1% linkage to hyd; sri was 9% cotra nsducible with hyd. In light of these data, the gene order gshA sri hy d 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 aerobi cally and anaerobically grown cells. 1,2-PDL-dependent transcription o f cob/pdu was studied by using M. Casadaban's Mu-lacZ fusions. In aero bically grown cells, transcription of a cbi-lacZ fusion (the cbi genes are the subset of cob genes that encode functions needed for the synt hesis of the corrin ring) was I-fold lower and transcription of a pdu- lacZ fusion was 10-fold lower in a gshA mutant than in the wild-type s train. Expression of the cob/pdu regulon in response to 1,2-PDL was re stored when GSH was included in the medium. In anaerobically grown cel ls, 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 use d 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 I,2- PDL, ethanolamine, or propionate as a carbon and energy source. The de fect in ethanolamine utilization appears to be at the level of ethanol amine ammonia-lyase activity, not at the transcriptional level. Possib le roles for GSH in ethanolamine, 1,2-PDL, and propionate catabolism a re proposed and discussed.