FIG. 4.

Effect of the cyaB mutation on M. xanthus growth and spore germination under osmotic stress. Growth of M. xanthus wild-type (closed symbols) and cyaB mutant (open symbols) cells in CYE medium with 0.15 M NaCl (A) or 0.15 M sucrose (B) or without either (dashed lines). NaCl or sucrose was added at the point indicated by the arrow. The cells were cultured at 30°C with shaking, and the cell densities were determined with a hemacytometer. The data are expressed as the means for triplicate experiments. (C) Spore germination of M. xanthus wild-type (closed bars), cyaB mutant (open bars), and cyaA mutant (shaded bars) spores in CYE medium containing various concentrations of sucrose. Spores were harvested from 6- to 8-day-old fruiting bodies on CF plates, sonicated for 2 min, and treated with heat (60°C for 15 min). The spores were inoculated to 10⁷ cells/ml in CYE medium containing up to 0.2 M sucrose and incubated at 30°C with continuous shaking until almost all spores in the medium without addition or sucrose were germinated, and then the number of ungerminated spores in each culture was counted with a hemacytometer. The percent germination (germinated spores per inoculated spores) is the mean of duplicate experiments. The standard deviations are shown by error bars.