Assessment of the bacterial community structure in a Brazilian clay soil treated with atrazine

In the present paper, the bacterial communities in two soils, one from an agricultural sugarcane cropped field and the other from an unperturbed soil with similar geopedological characteristics, were characterized using the Fluorescence In Situ Hybridization (FISH) method. FISH consists of in situ identification of bacteria using fluorescent labeled 16S rRNA targeted oligonucleotide probes visualizable under epifluorescence microscope. In the cultivated soil, in line with agricultural practice, the pre-emergence herbicide atrazine had been regularly applied each year at a concentration of 5 L/ha. The Shannon Diversity and Evenness Indices were also calculated using the phylogenetic data obtained from the FISH analysis. Although, at the sampling time (6 months after soil atrazine treatment), no residual herbicide concentration was found, the overall bacterial community results show a lower diversity and evenness in the agricultural soil than in the unperturbed one, demonstrating how microbiological indicators are sensitive to anthropogenic disturbance. In the natural soil, the dominant groups were alpha-Proteobacteria, beta-Proteobacteria, and gamma-Proteobacteria (representing more than 50 % of the bacteria), but in the agricultural soil, their abundance decreased significantly and represented just 31 % of the bacteria domain.