Biological control of rice blast by the epiphytic bacterium Erwinia ananas transformed with a chitinolytic enzyme gene from an antagonistic bacterium, Serratia marcescens strain B2

Abstract

The gene chiA, encoding for the endochitinase ChiA, was cloned from Serratia marcescens strain B2, a tomato epiphytic bacterium, and introduced into the epiphytic bacterium Erwinia ananas NR-1, isolated from rice phylloplane. The gene chiA was introduced under the control of two types of promoter into a broad-host-range plasmid vector. The vector contained various fragments with promoter activity isolated from E. ananas chromosomal DNA. The constructed vectors were designated pchiA-V1pcf9 and pchiA-V1pcf53 for their respective promoters. E. ananas NR-1 transformed with either of these vectors produced and secreted ChiA. The antifungal activity of ChiA produced by transformed E. ananas NR-1 was demonstrated in vitro by the inhibition of Pyricularia oryzae germ tube elongation such as bursting of the hyphal tip. Transformed E. ananas NR-1 suppressed the incidence of rice blast caused by P. oryzae under greenhouse conditions; however, the magnitude of the suppressive effect depended on which promoter was used. Both transformants and the nontransformant E. ananas NR-1 survived on rice phylloplane. It is expected that the rice epiphytic bacterium E. ananas NR-1 carrying a chitinolytic enzyme gene is an efficient biological control agent against rice blast.