Bacillus thermoleovorans S-II and B. thermoleovorans NR-9 produce bacteriocins, and these bacteriocins are designated thermoleovorin-S2 and thermoleovorin-N9, respectively. The bacteriocins are effective against all but the producing strain of B. thermoleovorans, as well as being effective against Salmonella typhimurium, Branhamella catarrhalis, Streptococcus faecalis, and Thermus aquaticus. Thermoleovorins are produced during log-phase growth and are inhibitory to actively growing cells. The bacteriocins are proteinaceous in nature, being sensitive to selected proteases (protease type XI and pepsin). They are stable at pHs of 3 to 10. Thermoleovorin-S2 was more thermostable than thermoleovorin-N9 at 70 and 80 degrees C. Thermoleovorins-S2 and -N9 apparently act by binding to the susceptible organisms, resulting in lysis of the cell. Thermoleovorins-S2 has an estimated M(r) of 42,000, while thermoleovorin-N9 has a M(r) of 36,000.