Variation in the virulence of Xanthomonas oryzae. II. Difference in protease activity of X. oryzae isolates.

Abstract

Protease activity of various X. oryzae isolates including N7301 mutant clones and several wild types was investigated in relation with their virulence. Activity was assayed by halo-colony (H-C) ratio method on casein media, and also by ordinary Casein-Lowry method on crude enzyme solution obtained from culture filtrate.It was found that X. oryzae showed marked protease activity. The protease activity in crude enzyme solution was enhanced along with bacterial multiplication, and decreased after stationary stage of bacterial growth. The activity was stable at pH ranging from 6 to 9, optimum at pH 9.3, and seemed an alkaline protease. Several other properties of the enzyme were also investigated.Among wild-type isolates of X. oryzae, H-C ratio was considerably correlated with the virulence. Virulent isolates showed higher H-C ratio than less virulent ones, and also halos of virulent isolates were much clearer. Among N7301 mutant clones, however, the correlationship was not distinct. According to Casein-Lowry method, no close relationship was found between protease activity and bacterial virulence.