Biological control for rice blast disease by employing detachment action with gelatinolytic bacteria

We screened collagenolytic/gelatinolytic bacteria from rice leaves and soil which degraded the fungal extracellular matrix to establish a novel biological control measure inhibiting germling adhesion on the host plant surface against airborne fungal diseases such as rice blast disease Magnaporthe oryzae B. Coch. Two different screening methods, i.e., screening from the leaf-associated bacterial library and direct screening from leaf and soil with or without collagen incubation, were conducted. Screening from the collagen treated material resulted in a higher number of gelatinolytic isolates than without collagen treatment. The selected bacteria were identified as Acidovorax, Sphingomonas, Chryseobacterium, and Pseudomonas genera by 16S rDNA sequence. Based on treatment with EDTA and addition of divalent cations, four of the five screened isolates tested produced a metalloproteinase. Furthermore, the enzymes produced by Acidovorax and Sphingomonas sp. were categorized as calcium-dependent metalloproteinases, and the enzymes produced by Chryseobacterium sp. were categorized as calcium/zinc-dependent metalloproteinases. The screened bacterial culture showed inhibitory effects on spore adhesion on the plastic cover glass, and disease protective effects on rice. This study suggests that bacteria inhibiting germling adhesion by phytopathogenic fungi may have promise as a biological agent.