Inhibition of Growth of Microorganisms by Benzimidazoles.

Abstract

Growth of 2 algae which require vitamin B12, Euglena gracilis and Ochromonas malhamensis, and of 4 bacteria which synthesize B12, Rhizobium leguminosarum, R. meliloti, R. japonicum and R. trifolii, was completely inhibited by benzimidazole at 5 x 10-3 M concentration. The algae were inhibited by 5 x 10-3 M and the bacteria by 0.5- 1 x 10-3 M concentrations of 2-ethyl-5-methylbenzimidazole. O. malhamensis was inhibited by 0.45 x 10-3 M 5-methylbenzimidazole. Although the algae utilize B12 analogs which differ from B12 with respect to the benzimidazole moiety, neither could satisfy the B12 requirement with factor B plus benzimidazole or 5-methyl-benzimidazole. Although benzimidazole inhibition of E. gracilis was not competitive, the growth could be expressed graphically as a straight line when B12 concentration was 1 x 10-l2 to 1 x 10-11 M and benzimidazole was 108 times B12 concentration. Inhibitive levels of the benzimidazoles in diverse biological systems are discussed.