Growth inhibition of Prevotella ruminicola by protamine

Growth of Prevotella ruminicola strains B(1)4 (subsp. brevis) and D31d (subsp. ruminicola), was inhibited by protamine, a polycationic, low molecular mass protein. Results showed that protamine has a bacteriocidal effect when present in concentrations exceeding 30 micrograms ml-1. Protamine exerted its toxic effects by disrupting the outer membrane, which was demonstrated by: (i) an increased sensitivity to hydrophobic antibiotics (novobiocin and monensin) and (ii) release of the periplasmic enzyme alkaline phosphatase following short-term exposure to protamine. Although the concentrations of protamine inhibitory to P. ruminicola are relatively low, the effects of such a compound are probably too broad to permit its successful use in terms of manipulating ruminal proteolysis.