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Journal of Bacteriology, October 1998, p. 5357-5368, Vol. 180, No. 20
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
A Chaperone in the HSP70 Family Controls Production
of Extracellular Fibrils in Myxococcus xanthus
Robby M.
Weimer,
Chad
Creighton,
Angela
Stassinopoulos,
Philip
Youderian, and
Patricia L.
Hartzell*
Department of Microbiology, Molecular Biology
and Biochemistry, University of Idaho, Moscow, Idaho 83844-3052
Received 20 April 1998/Accepted 5 August 1998
Three independent Tn5-lac insertions in the S1 locus of
Myxococcus xanthus inactivate the sglK gene,
which is nonessential for growth but required for social motility and
multicellular development. The sequence of sglK reveals
that it encodes a homologue of the chaperone HSP70 (DnaK). The
sglK gene is cotranscribed with the upstream
grpS gene, which encodes a GrpE homologue. Unlike sglK, grpS is not required for social motility
or development. Wild-type M. xanthus is encased in
extracellular polysaccharide filaments associated with the multimeric
fibrillin protein. Mutations in sglK inhibit cell cohesion,
the binding of Congo red, and the synthesis or secretion of fibrillin,
indicating that sglK mutants do not make fibrils. The
fibR gene, located immediately upstream of the
grpS-sglK operon, encodes a product which is predicted to
have a sequence similar to those of the repressors of alginate biosynthesis in Pseudomonas aeruginosa and
Pseudomonas putida. Inactivation of fibR leads
to the overproduction of fibrillin, suggesting that M. xanthus fibril production and Pseudomonas alginate production are regulated in analogous ways. M. xanthus and
Pseudomonas exopolysaccharides may play similar roles in a
mechanism of social motility conserved in these gram-negative bacteria.
*
Corresponding author. Mailing address: Department of
Microbiology, Molecular Biology and Biochemistry, University of Idaho, Moscow, ID 83844-3052. Phone: (208) 885-0572. Fax: (208) 885-6518. E-mail: hartzell{at}uidaho.edu.

Present address: Department of Biology, University of Utah, Salt
Lake City, UT 84112.
Journal of Bacteriology, October 1998, p. 5357-5368, Vol. 180, No. 20
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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