Summary: The structural components in cell walls of three mutants of a facultative alkaliphile, C-125, defective in certain cell-wall components were characterized in detail. The cell walls of the wild-type C-125 were thick and increased in thickness when grown at high pH. Electron microscopy showed that triple layers developed when the bacteria were grown in an alkaline environment. In contrast, cell walls of teichuronopeptide (TUP)-defective mutants consisted of a single layer. For both the wild-type and mutants, the cell-wall concentrations of the acidic structural polymers teichuronic acid and TUP increased with respect to peptidoglycan as culture pH increased. For all four strains, the anion content of their cell walls was the greatest at high pH. The cell-wall density of the negatively charged compounds (uronic acids plus L-glutamic acid) was calculated as about 3 and 9 equivalents (I cell wall region) for C-125 cells grown at pH 7 and 10, respectively. At high pH, the specific growth rates of the two TUP-defective mutants were much lower than those of the wild-type. It is concluded that increased levels of acidic polymers in the cell walls of alkaliphilic bacteria may be a necessary adaptation for growth at elevated pH.


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