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author:("Shi, wenchuan")
1.  Isolation and Characterization of a Suppressor Mutation that Restores Myxococcus xanthus Exopolysaccharide Production 
Microbiology (Reading, England)  2009;155(Pt 11):3599-3610.
SUMMARY
Myxococcus xanthus, a Gram-negative soil bacterium, undergoes multicellular development when nutrients become limiting. Aggregation, which is part of the developmental process, requires the surface motility of this organism. One component of M. xanthus motility, the social (S) gliding motility, enables the movement of cells in close physical proximity. Previous studies demonstrated that the cell-surface associated exopolysaccharide (EPS) is essential for S motility and the Dif proteins form a chemotaxis-like pathway that regulates EPS production in M. xanthus. DifA, a homologue of methyl-accepting chemotaxis proteins (MCPs) in the Dif system, is required for EPS production, S motility and development. In this study, a spontaneous extragenic suppressor of a difA deletion was isolated in order to identify additional regulators of EPS production. The suppressor mutation was found to be a single base-pair insertion in cheW7 at the che7 chemotaxis gene cluster. Further examination indicated that mutations in cheW7 may lead to the interaction of Mcp7 with DifC (CheW-like) and DifE (CheA-like) to reconstruct a functional pathway to regulate EPS production in the absence of DifA. In addition, the cheW7 mutation was found to partially suppress a pilA mutation in EPS production in a difA+ background. Further deletion of difA from the pilA cheW7 double mutant resulted in a triple mutant that produced wild-type levels of EPS, implying that DifA (MCP-like) and Mcp7 compete for interactions with DifC and DifE in the modulation of EPS production.
doi:10.1099/mic.0.031070-0
PMCID: PMC2879065  PMID: 19684067
2.  Genes Involved in the Repression of Mutacin I Production in Streptococcus mutans 
Microbiology (Reading, England)  2009;155(Pt 2):551-556.
Streptococcus mutans is considered a primary pathogen for human dental caries. Its ability to produce a variety of peptide antibiotics called mutacins may play an important role in its invasion and establishment in the dental biofilm. S. mutans strain UA140 produces two types of mutacins, the lantibiotic mutacin I and the non-lantibitoc mutacin IV. In a previous study, we constructed a random insertional-mutation library to screen for genes involved in regulating mutacin I production, and found 25 genes/operons that have a positive effect on mutacin I production. In this study, we continued our previous work to identify genes that are negatively involved in mutacin I production. By using a high phosphate BHI plate that inhibited mutacin I production of the wild-type, we isolated 77 clones that consistently produced mutacin I under repressive conditions. From the 34 clones that we were able to obtain a sequence, 17 unique genes were identified. These genes encompass a variety of functional groups including the central metabolism, surface binding, sugar transport, and unknown functions. Some of the 17 mutations were further characterized and shown to increase mutacin gene expression during growth when it is usually not expressed in the wild-type. These results further demonstrate an intimate and intricate connection between mutacin production and the overall cellular homeostasis.
doi:10.1099/mic.0.021303-0
PMCID: PMC2946218  PMID: 19202103
3.  The response regulator ComE in Streptococcus mutans functions both as a transcription activator of mutacin production and repressor of CSP biosynthesis 
Microbiology (Reading, England)  2007;153(Pt 6):1799-1807.
In Streptococcus pneumoniae, competence and bacteriocin genes are controlled by two two-component systems, ComED and BlpRH, respectively. In Streptococcus mutans, both functions are controlled by the ComED system. Recent studies in S. mutans revealed a potential ComE binding site characterized by two 11 bp direct repeats shared by each of the bacteriocin genes responsive to the competence-stimulating peptide (CSP). Interestingly, this sequence was not found in the upstream region of the CSP structural gene comC. Since comC is suggested to be part of a CSP-responsive and ComE-dependent autoregulatory loop, it was of interest to determine how it was possible that the ComED system could simultaneously regulate bacteriocin expression and natural competence. Using the intergenic region IGS1499, shared by the CSP-responsive bacteriocin nlmC and comC, it was demonstrated that both genes are likely to be regulated by a bifunctional ComE. In a comE null mutant, comC gene expression was increased similarly to a fully induced wild-type. In contrast, nlmC gene expression was nearly abolished. Deletion of ComD exerted a similar effect on both genes to that observed with the comE null mutation. Electrophoretic mobility shift assays (EMSAs) with purified ComE revealed specific shift patterns dependent on the presence of one or both direct repeats in the nlmC–comC promoter region. The two direct repeats were also required for the promoter activity of both nlmC and comC. These results suggest that gene regulation of comC in S. mutans is fundamentally different from that reported for S. pneumoniae, which implicates a unique regulatory mechanism that allows the coordination of bacteriocin production with competence development.
doi:10.1099/mic.0.2007/005975-0
PMCID: PMC2062498  PMID: 17526837

Results 1-3 (3)