Effects of vanillin on rhizosphere microbial communities of cucumber (Cucumis sativus L.) seedlings

Cucumber seedlings grown in soil were treated with different concentrations of vanillin (0.02-0.2 mu mol/g soil). The rhizosphere soil bacterial and fungal community structures and their abundances were analyzed by PCR-denaturing gradient gel electrophoresis (DGGE) and quantitative PCR, respectively. The vanillin at 0.1 and 0.2 mu mol/g soil significantly reduced the cucumber seedling biomass. All concentrations of vanillin increased the abundances of soil bacteria and fungal communities but decreased the bacteria-to-fungi ratio. Vanillin changed the soil bacterial and fungal community structures, decreased the richness, evenness and diversity indices of soil bacterial community but increased that of fungal community. Principal component analysis showed that the fungal community structure was dependent on the vanillin concentration, however, 4-concentrations of vanillin (0.02-0.2 mu mol/g soil) had similar bacterial community structure. This study showed that vanillin changed the soil microbial communities and that bacterial and fungal communities responded differently to exogenous vanillin.