CcpA-Independent Regulation of Expression of the Mg²⁺-Citrate Transporter GenecitMby Arginine Metabolism inBacillus subtilis

Abstract

Transcriptional regulation of the Mg2؉ -citrate transporter, CitM, the main citrate uptake system of Bacillus subtilis, was studied during growth in rich medium. Citrate in the growth medium was required for induction under all growth conditions. In Luria-Bertani medium containing citrate, citM expression was completely repressed during the exponential growth phase, marginally expressed in the transition phase, and highly expressed in the stationary growth phase. The repression was relieved when the cells were grown in spent Luria-Bertani medium. The addition of a mixture of 18 amino acids restored repression. L-Arginine in the mixture appeared to be solely responsible for the repression, and ornithine appeared to be an equally potent repressor of citM expression. Studies of mutant strains deficient in RocR and SigL, proteins required for the expression of the enzymes of the arginase pathway, confirmed that uptake into the cell and, most likely, conversion of arginine to ornithine were required for repression. Arginine-mediated repression was independent of a functional CcpA, the global regulator protein in carbon catabolite repression (CCR). Nevertheless, CCR-mediated repression was the major mechanism controlling the expression during exponential growth, while the newly described, CcpA-independent arginine-mediated repression was specifically apparent during the transition phase of growth.

Catabolite Repression and Activation in Bacillus subtilis : Dependency on CcpA, HPr, and HprK

“…(x) Effects of hprK mutations alter growth independently of their effects on CR (22). (xi) Several reports have demonstrated the existence of CcpA-independent CR in B. subtilis (7,8,64,73,78,80). All of these observations suggest that multiple mechanisms of CR/CA in B. subtilis exist, and that the CcpA-dependent mechanism shown in Fig.…”

Functional characterization and Me2+ ion specificity of a Ca2+–citrate transporter from Enterococcus faecalis

“…This may be the reason for the strict regulation of expression of the transporter, which involves a number of regulatory systems. Expression is repressed by carbon catabolite repression [15] and by arginine metabolism [16], and induced by a two‐component sensory system [15,17]. Moreover, the expression of the latter is itself under control of carbon catabolite repression [18].…”

Catabolite repression of the citST two-component system in Bacillus subtilis

“…CitM is a secondary transporter that catalyzes proton motive force driven transport of citrate when it is complexed to Mg 2+ , but also to the divalent metal ions Zn 2+ , Co 2+ and Ni 2+ (Krom et al , 2000). Transcription of the citM gene is repressed in the presence of several carbon sources (glucose, glycerol, inositol) by carbon catabolite repression (CCR) and by the nitrogen source arginine by an unknown mechanism (Warner et al , 2000, 2003).…”