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Journal of Bacteriology, April 1999, p. 2593-2601, Vol. 181, No. 8
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Gliding Mutants of Myxococcus xanthus with High Reversal Frequencies and Small Displacements

Alfred M. Spormann1,2,* and Dale Kaiser3

Max-Planck-Institut für Terrestrische Mikrobiologie, 35043 Marburg, Germany,1 and Environmental Engineering and Science, Department of Civil and Environmental Engineering,2 and Departments of Biochemistry and Developmental Biology,3 Stanford University, Stanford, California 94305

Received 10 November 1998/Accepted 5 February 1998

Myxococcus xanthus cells move on a solid surface by gliding motility. Several genes required for gliding motility have been identified, including those of the A- and S-motility systems as well as the mgl and frz genes. However, the cellular defects in gliding movement in many of these mutants were unknown. We conducted quantitative, high-resolution single-cell motility assays and found that mutants defective in mglAB or in cglB, an A-motility gene, reversed the direction of gliding at frequencies which were more than 1 order of magnitude higher than that of wild type cells (2.9 min-1 for Delta mglAB mutants and 2.7 min-1 for cglB mutants, compared to 0.17 min-1 for wild-type cells). The average gliding speed of Delta mglAB mutant cells was 40% of that of wild-type cells (on average 1.9 µm/min for Delta mglAB mutants, compared to 4.4 µm/min for wild-type cells). The mglA-dependent reversals and gliding speeds were dependent on the level of intracellular MglA protein: mglB mutant cells, which contain only 15 to 20% of the wild-type level of MglA protein, glided with an average reversal frequency of about 1.8 min-1 and an average speed of 2.6 µm/min. These values range between those exhibited by wild-type cells and by Delta mglAB mutant cells. Epistasis analysis of frz mutants, which are defective in aggregation and in single-cell reversals, showed that a frzD mutation, but not a frzE mutation, partially suppressed the mglA phenotype. In contrast to mgl mutants, cglB mutant cells were able to move with wild-type speeds only when in close proximity to each other. However, under those conditions, these mutant cells were found to glide less often with those speeds. By analyzing double mutants, the high reversing movements and gliding speeds of cglB cells were found to be strictly dependent on type IV pili, encoded by S-motility genes, whereas the high-reversal pattern of mglAB cells was only partially reduced by a pilR mutation. These results suggest that the MglA protein is required for both control of reversal frequency and gliding speed and that in the absence of A motility, type IV pilus-dependent cell movement includes reversals at high frequency. Furthermore, mglAB mutants behave as if they were severely defective in A motility but only partially defective in S motility.

* Corresponding author. Mailing address: Environmental Engineering and Science, Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305-4020. Phone: (650) 723-3668. Fax: (650) 725-3164. E-mail: spormann{at}ce.stanford.edu.

Journal of Bacteriology, April 1999, p. 2593-2601, Vol. 181, No. 8
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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