Motility mutants

More recently, Pilgram and Williams studied a slightly different case — competition between chemotactic Proteus mirabilis and a nonchemotactic but randomly motile mutant of the species ( 0) (see Figures 3 and 4 ). In both pure and mixed cultures of periodically agitated amino acid broth, the two strains grew to a 1 1 ratio after 14 hours. On the other hand, in both pure and mixed cultures of semisolid agar the ratio of chemotactic to randomly motile strains was greater than 5 1 after 14 hours. 

The final experimental reports were by Freter al. (21, 22, 23), who studied growth of Vibrio cholerae in mouse and rabbit large intestine (see Figure 5 and Table 3. Here three strains were compared the chemotactic wild type, an immotile mutant strain, and a nonchemotactic but randomly motile mutant strain. In well-stirred continuous flow culture, all three strains grew in proportion. In the intestinal loops, the nonchemotactic strain was rapidly displaced by the chemotactic wild type. Most interestingly, in another experiment the randomly motile strain was also rapidly displaced by the immotile strain. Apparently, in this situation at least, motility without chemo-taxis was a liability for the cells. 

Figure 5. Time course of growth of chemotactic parent and randomly motile mutant strains of Vibrio cholerae in mouse large intestine. Reproduced, with permission, from Ref. 21. Copyright 1979, American Society for Clinical Nutrition.

Table 3. Displacement of Randomly Motile Mutant Strain of Vibrio cholerae by Immotile Mutant Strain in Mouse Large Intestine...

Non-motile mutants of E. coli, designated cheM and cheD, have been shown to possess a defect lying between the chemoreceptor and the general chemotaxis pathway. The gene products have been shown to be integral membrane proteins, cheM giving a series of polypeptides (M, 60,000 to 63,000) as does cheD (M 63,000 - 66,000), and shown to correspond with the MCPs. 

Bray, D. Hollenbeck, P.J. (1988). Growth cone motility and guidance. Ann. Rev. Cell Biol. 4,43-61. Bray, D. Vasiliev, J. (1989). Networks from mutants. Nature 338,203-204. 

Andre, E., Brink, M., Gerisch, G., Isenberg, G., Noegel, A., Schleicher, M., Segall, J.E., Wallraff, E. (1989). A Dictyostelium mutant deficient in severin, an F-actin fragmenting protein, shows normal motility and chemotaxis. J. Cell Biol. 108, 985-995. 

Wessels. D., Soil, D.R.. Knecht, D.. Loomis. W.F., De Lozanne. A., Spudich, J. (1989). Myosin IB null mutants of Dictyostelium exhibit abnormalities in motility. Cell Mot. Cytoskel. 20,301-315. 

While confirming the general normality of the mutant mice and problems with lymphocyte homeostasis, these studies focused on identifying defects in peripheral leukocytes. The Lsc- - mice had a twofold increase in circulating neutrophils and lymphocytes but normal platelet counts and red blood cells. In functional studies, the Lsc-/ neutrophils showed a reduced ability to stimulate formation of Rho-GTP and abnormal pseudopod development in response to fMLP. An increased motility and lower adherence of the neutrophils when stimulated with fMLP (Francis et ah, 2006) are similar to the behavior of B cells from Lsc / mice when stimulated with serum (Girkontaite et ah, 2001). While these studies imply a role for a G12/i3 Lsc-RhoA pathway in the phenotypes of these cells, the molecular details are not yet known. 

In addition to a role in symbiosis, the presence of the VLCFA may also be important for the life of the symbiont in the soil. Recently, it was shown that a mutant in genes encoding for the fatty acyl transferases that are in the five gene VLCFA cassette of R. leguminosarum biovar viciae 3841 also fail to incorporate VLCFA into their LA and they are also less resistance to desiccation, impaired in biofilm formation, and in motility (Vanderlinde et al., 2009). Thus, in addition to promoting rhizobial life inside the plant host, the presence of VLCFA in LPS may also be important for life of the symbiont in the soil. 

The ppk mutant of P. aeruginosa was also deficient in type-IV pili-mediated twitching and in swarming motility (Rashid and Kornberg, 2000). Some suggestions on the molecular mechanisms of PolyP- PPK action in motility were made (Rashid and Kornberg, 2000). These included the possible role of PolyP in the phosphorylation of Che-Y-like proteins or modulation of the Ca2+ level (Rashid and Kornberg, 2000). 

After ppkl inactivation, the knockout mutants show no growth defects when compared with the parent strain. One of the remarkable defects in these mutants was the loss of motility (Rashid and Kornberg, 2000 Rashid et al, 2000a,b). A low-residual polyphosphate kinase activity was detected in these mutants (Zago et al., 1999) and attributed to the activity of the ppkl gene (Zhang et al., 2002). However, one cannot exclude the existence of other pathways of PolyP synthesis in this bacterium. 

The involvement of coronin in various actin-driven processes has been also supported by genetic studies. In coronin-nuU mutants cell motility is reduced to less than half the rate in respect to wild type, cytokinesis is impaired and the rate of pino- and phagocytosis is reduced. A more detailed... 

Fig. 1.9. Kinesin mutant design and single-molecule motility results based on an optical trapping assay, (a) WT full CS. (b) 2G CS with mutated residues (light area in CS). (c) DEL CS is absent. The structure is based on PDB 2K1N, modified to incorporate the Drosophila CS (SwissProt ID P17210). (d) Stall force histogram. Sohd hnes Gaussian fits for WT and 2G a DEL histogram was not fitted because of the unknown number of stalls below the minimum detection force threshold. See [27] for details...

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