Effect of virginiamycin on the growth cycle of Bdellovibrio.

The two components of virginiamycin, virginiamycin M (VM) and virginiamycin S (VS), were used to explore the life cycle of symbiosis-dependent and -independent strains of Bdellovibrio bacteriovorus during multiplication in a two-membered system with either living or heat-inactivated Escherichia coli or in axenic cultures. Relatively high concentrations of these inhibitors separately were required to stop growth under all the conditions, but the minimum inhibitory concentration of the single components was reduced 1,000-fold by the association of VM and VS. No dissociation between mass growth and cell division was observed with VM; VS specifically halted cell division without affecting the kinetics of macromolecules formation and overall growth. This effect on cell division was only obtained when the antibiotic was added during the first half of the multiplication cycle and was reversible at any time.