Studies on the nutritional physiology of Xanthomonas oryzae (Uyeda et Ishiyama) Dowson

Abstract

Nutritional physiology of Xanthomonas oryzae, the causal bacterium of the bacterial leaf blight of rice plants, has been studied with special reference to the carbon and nitrogen sources, in order to find out suitable synthetic medium for multiplication of this bacterium.The constitution of the basal medium used was as follows: l-glutamic acid 2g, KH2PO4 2g, sucrose 20g, FeSO4⋅7H2O 0.01g, MgCl2⋅6H2O 1g, MnSO4⋅4H2O 0.01g, and one liter of distilled water.The best carbon source was found to be sucrose, the most suitable concentration being 0.2∼1 per cent. Glucose (0.2∼1 per cent), mannose, galactose, maltose (1∼3 per cent), and succinic acid (1 per cent) were also found to be good carbon sources. It was observed that when sterilized by heating, the bacteria could not utilize fructose, but when sterilized by filtration without heating, fructose acts as a good carbon source.This bacterium needs organic nitrogens for its multiplication. The best nitrogen source was 0.1 per cent of l-glutamic acid. The next was l-cystine, multiplication of the bacteria being about a half of that in medium added with 0.1 per cent l-glutamic acid. As a nitrogen source, dl-valine, l-leucine, dl-isoleucine, dl-β-phenylalanine, tyrosine, dl-methionine, l-arginine-HCl, l-asparagine, and (NH4)2HPO4 seemed to be unfavorable compared with l-glutamic acid and l-cystine. Multiplication of the bacteria was considerably accelerated by a combination of l-glutamic acid (0.1 per cent), l-cystine (0.05 per cent), and (NH4)2HPO4 (0.3 per cent).From the above results, constitution of the most suitable synthetic medium for the bacteria was to be as follows: l-glutamic acid 1g, l-cystine 0.5g, (NH4)2HPO4 3g, KH2PO4 2g, sucrose 5g, FeSO4⋅7H2O 0.01g, MgCl2⋅6H2O 1g, MnSO4⋅4H2O 0.01g, and one liter of distilled water, pH 6.5∼7.0. However, the bacterial multiplication in this synthetic medium was still considerably inferior to that in the medium for the potato ring-rot bacteria. Further improvement of this medium is necessary in future.