Inhibition of growth and cell wall morphogenesis of Bacillus subtilis by extracellular slime produced by Physarum flavicomum.

Slime secreted by microplasmodia of the myxomycete Physarum flavicomum inhibited the uptake of glucose and amino acids, as well as growth and cell division of the bacterium Bacillus subtilis. Morphological changes such as production of chains, swollen cells, and/or cell lysis, occurred coincident with these physiological inhibitory events. These phenomena were all dependent on the concentration of slime present in the growth medium. Electron microscopy revealed that the cell walls of slime-inhibited cells were undergoing degradation and the process was most pronounced in the swollen cells. Isolated cell walls of B. subtilis were also found to undergo degradation upon incubation with slime. Boiled slime did not exhibit lytic activity on native cell walls, but boiled cell walls were degraded by native slime. The inhibitory effect of slime seemed to be, at least in part, due to an inherent peptidase (protease) activity. B. subtilis eventually overcomes the inhibition exhibited by slime due to the production of an antagonist of slime.