Study of the antifungal activity of Bacillus vallismortis ZZ185 in vitro and identification of its antifungal components.

An endophytic Bacillus vallismortis ZZ185 was isolated from healthy stems of the plant Broadleaf Holly (Ilex latifolia Thunb) collected in Nanjing, China. Both the culture filtrate and the n-butanol extract of strain ZZ185 showed strong growth inhibition activity in vitro against the phytopathogens Fusarium graminearum, Alternaria alternata, Rhizoctonia solani, Cryphonectria parasitica and Phytophthora capsici. The results showed that the filtrate and extract reduced the symptoms of wheat seedlings infected with A. alternata and F. graminearum by about 90% and 50%, respectively, based on the comparison of the lengths of zones on the seminal roots showing cortical browning with those of the roots of uninfected controls. The antifungal activity of the culture filtrate was significantly correlated with cell growth of strain ZZ185. The active metabolite in the filtrate was relatively thermally stable with more than 50% of the antifungal activity of the culture filtrate being retained even after being held at 121 degrees C for 30 min. Meanwhile, the antifungal activity of the filtrate against the growth of A. alternata and F. graminearum remained almost unchanged (>75%) when the culture was exposed to a pH ranging from 1 to 8, but significantly reduced after the filtrate had been exposed to basic conditions. From the n-butanol extract of the filtrate, the antifungal compounds were isolated as a mixture of Bacillomycin D (n-C14) and Bacillomycin D (iso-C15). The strong antifungal activity implied that the endophytic B. vallismortis ZZ185 and its bioactive components might provide an alternative resource for the biocontrol of plant diseases.