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Physiology and Biochemistry

Selective Toxicity of Isoflavonoid Phytoalexins to Gram-Positive Bacteria. Samuel S. Gnanamanickam, Visiting scientist, Department of Plant Biology, The University of Hull, Hull, HU6 7RX, United Kingdom, Present address of senior author: Center for Advanced Study in Botany, University of Madras, Madras 600005, India; David A. Smith, lecturer, Department of Plant Biology, The University of Hull, Hull, HU6 7RX, United Kingdom, Present address: Department of Plant Pathology, The University of Kentucky, Lexington 40546, USA. Phytopathology 70:894-896. Accepted for publication 6 March 1980. Copyright The American Phytopathological Society. DOI: 10.1094/Phyto-70-894.

The isoflavonoid phytoalexins, kievitone and phaseollin, were found to be selectively toxic to Gram-positive bacteria. In a standard paper-disk bioassay, 1050 μg kievitone or phaseollin inhibited the growth of all seven Gram-positive, but none of the eight Gram-negative, bacteria tested. Phaseollidin and phaseollinisoflavan also possessed such selective toxicity to Gram-positive bacteria. Further assays showed that even 2 μg kievitone (0.56 108 mole), which proved to be the most toxic of the compounds examined, inhibited the growth of Corynebacterium fascians, Bacillus subtilis, and Micrococcus luteus.

Additional keywords: antibiotic.