Abstract
BackgroundRegulation of sulphur metabolism in Corynebacterium glutamicum ATCC 13032 has been studied intensively in the last few years, due to its industrial as well as scientific importance. Previously, the gene cg0156 was shown to belong to the regulon of McbR, a global transcriptional repressor of sulphur metabolism in C. glutamicum. This gene encodes a putative ROK-type regulator, a paralogue of the activator of sulphonate utilisation, SsuR. Therefore, it is an interesting candidate for study to further the understanding of the regulation of sulphur metabolism in C. glutamicum.ResultsDeletion of cg0156, now designated cysR, results in the inability of the mutant to utilise sulphate and aliphatic sulphonates. DNA microarray hybridisations revealed 49 genes with significantly increased and 48 with decreased transcript levels in presence of the native CysR compared to a cysR deletion mutant. Among the genes positively controlled by CysR were the gene cluster involved in sulphate reduction, fpr2 cysIXHDNYZ, and ssuR. Gel retardation experiments demonstrated that binding of CysR to DNA depends in vitro on the presence of either O-acetyl-L-serine or O-acetyl-L-homoserine. Mapping of the transcription start points of five transcription units helped to identify a 10 bp inverted repeat as the possible CysR binding site. Subsequent in vivo tests proved this motif to be necessary for CysR-dependent transcriptional regulation.ConclusionCysR acts as the functional analogue of the unrelated LysR-type regulator CysB from Escherichia coli, controlling sulphide production in response to acceptor availability. In both bacteria, gene duplication events seem to have taken place which resulted in the evolution of dedicated regulators for the control of sulphonate utilisation. The striking convergent evolution of network topology indicates the strong selective pressure to control the metabolism of the essential but often toxic sulphur-containing (bio-)molecules.
Highlights
Regulation of sulphur metabolism in Corynebacterium glutamicum ATCC 13032 has been studied intensively in the last few years, due to its industrial as well as scientific importance
2.1 The Corynebacterium glutamicum mutant CR030 with a deleted cg0156 gene can no longer grow with sulphate or sulphonates as sole source of sulphur The transcriptional regulator McbR, discovered by Rey et al [6], was shown to act as the global repressor of sulphur metabolism in Corynebacterium glutamicum ATCC 13032 [7]
Despite being somewhat similar to NagC [21] and Mlc from Escherichia coli, the function of Cg0156 could not be inferred based on sequence similarity alone
Summary
Regulation of sulphur metabolism in Corynebacterium glutamicum ATCC 13032 has been studied intensively in the last few years, due to its industrial as well as scientific importance. The gene cg0156 was shown to belong to the regulon of McbR, a global transcriptional repressor of sulphur metabolism in C. glutamicum This gene encodes a putative ROK-type regulator, a paralogue of the activator of sulphonate utilisation, SsuR. One focus of this research has been the elucidation of the pathways involved in the metabolism of sulphur-containing amino acids (reviewed in [2]). This is in part due to the ability of C. glutamicum to produce high yields of L-lysine, which shares the precursor L-aspartic acid with L-methionine, and L-serine [3,4], the precursor for L-cysteine biosynthesis. Almost all of the genes involved in the various pathways have been identified in the last few years [2], no production strain is available up to now
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