Submitted to: Peptides
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 4, 1999
Publication Date: N/A
Interpretive Summary: Amino acids are the building blocks of proteins and are found in all living things. An amino acid containing a structural modification called a "carborane" was found to be non-toxic to plants and is used in some types of cancer treatment. In our studies, we showed that this modified amino acid kills bacteria and in some situations is almost as effective as the antibacterial agent streptomycin. The relatively selective bactericidal effects of this unusual amino acid suggests that research on this and related carboranyl-based amino acid analogs may provide interesting leads in the search for antibacterial agents and/or in the development of new strategies to ensure the delivery of safe food products to the consumer.
Racemic o-carboranylalanine (o-Cba) was found non-phytotoxic to the tobacco and sunflower plants and not toxic against various filamentous fungi (Zygo- and Ascomycetes). While the growth of Pythium and Phytophthora colonies as well as the biotrophic hyphae of the sunflower downy mildew fungus Plasmopara halstedii (Oomycetes) were not affected by o-Cba, the asexual spores of P. halstedii were extremely sensitive. The antibacteria effect of o-Cba in some species was comparable to that of streptomycin. Gram positive bacteria (Bacillus, Corynebacterium, Curtobacterium, Micrococcus, Rhodococcus, and Staphylococcus) exhibited higher sensitivity than Gram negative ones (Agrobacterium, Erwinia, Escherichia, Pseudomonas, Rhizobium, and Xanthomonas)to this carborane-containing amino acid analogue. The sensitivity of individual species within the same genus varied to a greater extent than the average sensitivity of various genera. Moreover, the composition of the nutrient medium markedly influenced the toxicity of o-Cba: for all taxonomic groups, the antimicrobial effect of this unnatural amino acid could be diminished with histidine, but not with phenylalanine.