Enlargement of Deinococcus grandis spheroplasts requires Mg

While the cell wall strictly controls cell size and morphology in bacteria, spheroplasts lack cell walls and can become enlarged in growth medium under optimal conditions. Optimal conditions depend on the bacterial species. We frequently observed extreme enlargement of spheroplasts of the radiation-resistant bacterium Deinococcus grandis in Difco Marine Broth 2216, but not in TGY broth (a commonly used growth medium for Deinococcus). Thorough investigation of media components showed that the presence of Mg2+ or Ca2+ promoted extreme spheroplast enlargement, synthesizing the outer membrane. Our findings strongly suggest that Mg2+ or Ca2+ enlarges spheroplasts, which could change the lipid composition of the spheroplast membrane.