Increase in Bacterial Community Diversity in Subsurface Aquifers Receiving Livestock Wastewater Input

Abstract

Despite intensive studies of microbial-community diversity, the questions of which kinds of microbial populations are associated with changes in community diversity have not yet been fully solved by molecular approaches. In this study, to investigate the impact of livestock wastewater on changes in the bacterial communities in groundwater, bacterial communities in subsurface aquifers were analyzed by characterizing their 16S rDNA sequences. The similarity coefficients of restriction fragment length polymorphism (RFLP) patterns of the cloned 16S ribosomal DNAs showed that the bacterial communities in livestock wastewater samples were more closely related to those in contaminated aquifer samples. In addition, calculations of community diversity clearly showed that bacterial communities in the livestock wastewater and the contaminated aquifer were much more diverse than those in the uncontaminated aquifer. Thus, the increase in bacterial-community diversity in the contaminated aquifer was assumed to be due to the infiltration of livestock wastewater, containing high concentrations of diverse microbial flora, into the aquifer. Phylogenetic analysis of the sequences from a subset of the RFLP patterns showed that the Cytophaga-Flexibacter-Bacteroides and low-G؉C gram-positive groups originating from livestock wastewater were responsible for the change in the bacterial community in groundwater. This was evidenced by the occurrence of rumen-related sequences not only in the livestock wastewater samples but also in the contaminated-groundwater samples. Rumen-related sequences, therefore, can be used as indicator sequences for fecal contamination of groundwater, particularly from livestock.Stock farming in Korea has increased considerably over the last decade due to changes in eating habits. Consequently, attention has been paid recently to pollution in the soil, surface water, and groundwater caused by intensive stock farming. The application of animal manure and livestock wastewater to surface soil results in a rapid increase in microbial biomass and nitrogenous nutrients (9, 21, 29). As animal manure and wastewater are important sources of nitrogen compounds, studies have been carried out mainly to analyze the community structure of microorganisms responsible for nitrogen transformations (25, 33). Also, a few papers (23, 62) have been dedicated to the study of the effect of livestock waste on groundwater quality in the context of various nutrients and some indicator bacteria. However, the effect of livestock manure and wastewater on bacterial-community structure in environments receiving livestock waste is currently poorly understood. In our recent study (12), subsurface aquifers in the Wonju stockfarming area (Fig. 1) were found to be heavily contaminated with nitrate and pollution indicator bacteria due to the infiltration of livestock wastewater. This study indicates that the composition and diversity of the bacterial community in groundwater may change dramatically through the introduction of livestock wastewater i...

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