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Isolation and characterization of a suppressor mutation that restores Myxococcus xanthus exopolysaccharide production

Qian Xu^1,

¹ Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
² Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA
³ Molecular Biology Institute and School of Dentistry, University of California-Los Angeles, Los Angeles, CA 90095, USA

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 that 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.

Correspondence
Zhaomin Yang
zmyang{at}vt.edu
Wesley P. Black
weblack{at}vt.edu

Present address: Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, NC 27599-7290, USA.

Two supplementary tables, listing additional Myxococcus xanthus strains used in this study and phenotypes of selected M. xanthus strains and progenies from selected crosses, are available with the online version of this paper.