Hydrolytic enzyme activity of Paenibacillus sp. strain B2 and effects of the antagonistic bacterium on cell integrity of two soil-borne pathogenic fungi

Abstract

Paenibacillus sp. strain B2, isolated from the mycorrhizosphere of Sorghum bicolor and having an antagonistic activity towards soil-borne fungal pathogens, possessed extracellular cellulolytic, proteolytic, chitinolytic and pectinolytic enzyme activities. The eventual role of these lytic enzymes in cellular interactions between Paenibacillus sp. strain B2 and Phytophthora parasitica and Fusarium oxysporum was investigated by electron microscopy and molecular cytology. Electron microscopic observations showed that the presence of Paenibacillus sp. strain B2 resulted in disorganisation of cell walls and/or cell contents of P. parasitica and F. oxysporum. However, when P. parasitica was treated with commercial purified cellulase, protease, chitinase and pectinase, only protease had an inhibitory effect on mycelial growth. It is proposed that the inhibitory effect of Paenibacillus sp. strain B2 on the growth of soil-borne fungal pathogens is probably derived from more than one mechanism. Author Keywords: Hydrolytic enzymes; Paenibacillus sp. strain B2; Cell integrity; Wall metabolism; Phytophthora parasitica; Fusarium oxysporum