Summary: The effect of different β-lactam antibiotics on the growth and morphology of Myxococcus xanthus has been examined. Exposure to penicillin and cephalexin resulted in spheroplast and filament formation, respectively. Mecillinam appeared to inhibit cell elongation and caused the formation of bent cells with central bulges. Myxospore formation was inhibited by cephalexin but not by mecillinam, although myxospores formed in the presence of mecillinam showed defects after germination. Germination of myxospores involves substantial cell-wall turnover as measured by uptake and loss of meso-diamino[14C]pimelic acid. Although turnover was observed when myxospores were germinated in the presence of mecillinam, the bacteria remained as spheres. Growth of these germinated myxospores following removal of mecillinam indicated that wall material laid down during the early stages of germination is stable and a rod shape could be re-established only by bipolar growth of new wall.
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