The impact of chlorothalonil application on soil bacterial and fungal populations as assessed by denaturing gradient gel electrophoresis

Abstract

The impact of the fungicide chlorothalonil on dominant bacterial and fungal populations following application to turfgrass, forest, and agricultural soils was investigated. Chlorothalonil was applied to each soil at three rates, representing 0.2, 1 and 5 times the recommended label rate for turfgrass, and incubated for a 2-week period. Changes to the microbial community caused by the chlorothalonil application were assessed following DNA extraction, PCR-amplification using both bacteria domain- and fungal-specific primers, then separation with denaturing gradient gel electrophoresis (DGGE). Digitized DGGE images were used to determine two parameters: the number of bands per lane and the Shannon–Wiener index of diversity ( H′), both of which were used only for comparison of the different treatments, and not as true diversity measurements. Bands appearing to be either enhanced or inhibited as a result of the chlorothalonil treatment were excised and sequenced. Increased rates of chlorothalonil impacted eight bacterial populations (two inhibitions, four enhancements, and two non-specific responses) and four fungal populations (all inhibitions). Band number and H′ indicated an altered but not significantly different ( P<0.05) bacterial and fungal community structure following chlorothalonil application. Sequencing of excised DGGE bands indicated an impact on several groups of bacteria ( Cytophaga–Flavobacterium–Bacteroides, α-, β-, γ-, and δ-proteobacteria) and two fungal taxa (zygomycota and ascomycota). Although changes to the overall community structure of dominant species were non-significant, we conclude that following a single chlorothalonil application and a short incubation period, community changes including both enhancement and inhibition of a variety of dominant organisms can occur.