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Journal of Bacteriology, March 1999, p. 1496-1507, Vol. 181, No. 5
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Regulated Exopolysaccharide Production in Myxococcus xanthus

Sang-Hoon Kim,dagger Srinivas Ramaswamy,Dagger and John Downard*

Department of Botany and Microbiology, University of Oklahoma, Norman, Oklahoma 73019-0245

Received 22 June 1998/Accepted 16 December 1998

Myxococcus xanthus fibrils are cell surface-associated structures composed of roughly equal amounts of polysaccharide and protein. The level of M. xanthus polysaccharide production under different conditions in the wild type and in several mutants known to have alterations in fibril production was investigated. Wild-type exopolysaccharide increased significantly as cells entered the stationary phase of growth or upon addition of Ca2+ to growing cells, and the polysaccharide-induced cells exhibited an enhanced capacity for cell-cell agglutination. The activity of the key gluconeogenic pathway enzyme phosphoenolpyruvate carboxykinase (Pck) also increased under these conditions. Most fibril-deficient mutants failed to produce polysaccharide in a stationary-phase- or Ca2+-dependent fashion. However, regulation of Pck activity was generally unimpaired in these mutant strains. In an stk mutant, which overproduces fibrils, polysaccharide production and Pck activity were constitutively high under the conditions tested. Polysaccharide production increased in most fibril-deficient strains when an stk mutant allele was present, indicating that these fibril-deficient mutants retained the basic cellular components required for fibril polysaccharide production. In contrast to other divalent cations tested, Sr2+ effectively replaced Ca2+ in stimulating polysaccharide production, and either Ca2+ or Sr2+ was required for fruiting-body formation by wild-type cells. By using transmission electron microscopy of freeze-substituted log-phase wild-type cells, fibril material was observed as a cell surface-associated layer of uniform thickness composed of filaments with an ordered structure.

* Corresponding author. Mailing address: Department of Botany and Microbiology, University of Oklahoma, 770 Van Vleet Oval, Norman, OK 73019-0245. Phone: (405) 325-6302. Fax: (405) 325-7619. E-mail: jdownard{at}ou.edu.

dagger Present address: Department of Microbiology, Michigan State University, East Lansing, MI 48824.

Dagger Present address: Institute for the Study of Human Bacterial Pathogenesis, Department of Pathology, Baylor College of Medicine, Houston, TX 77030.

Journal of Bacteriology, March 1999, p. 1496-1507, Vol. 181, No. 5
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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