Antibiotics as protectant bactericide against bacterial leaf blight of rice plant

Abstract

1. Since the antibacterial effect of cellocidin on X. oryzae was antagonized by cysteine and glutathione, cellocidin was considered to interact with -SH groups.2. The oxidation of various intermediates of the Krebs' cycle by the cell-free extracts of X. oryzae, prepared by sonic oscillator, and also the effect of cellocidin on the oxidation, were studied by measuring the reduction of triphenyl tetrazolium chloride. It was found that cellocidin at the minimum growth-inhibitory concentration (10ppm) inhibited selectively NAD requiring dehydrogenases, such as α-ketoglutarate dehydrogenase, glutamic dehydrogenase, and malic dehydrogenase, but did not inhibit NAD non-requiring dehydrogenases, such as succinic dehydrogenase and urease.3. Effect of cellocidin on oxygen uptake by cell-free extracts of X. oryzae prepared by sonic oscillator, was studied in the presence of related metabolic intermediate of the Krebs' cycle as substrates. It was found that the oxygen uptake was inhibited by cellocidin at a concentration of 100mcg/ml when substrates such as α-ketoglutarate, iso-citrate etc. which require NAD as co-enzyme for oxidation, were used, but was not inhibited when succinate was used as substrate.4. Effect of cellocidin on the system α-ketoglutarate→succinate, of X. oryzae, was studied. When the oxidation of succinate was inhibited by the addition of malonate, the oxidation of α-ketoglutarate, in the presence of NAD, by cell-free extracts of X. oryzae, was inhibited by cellocidin at a concentration of 1mcg/ml, which is smaller than the minimum growth-inhibitory concentration. Therefore cellocidin was considered to be an inhibitor on the system α-ketoglutarate→succinate.5. Cellocidin, at a concentration of 100ppm, did not inhibit electron transport system, such as NADH2 oxidase and NAD reductase, of cell-free preparations of X. oryzae.6. The incorporation of 14C-amino acids into the protein fraction of X. oryzae was not inhibited by cellocidin at a concentration of 10ppm.