Factors Influencing the Persistence of Fecal Bacteroidesin Stream Water (original) (raw)

Laboratory microcosm experiments were used to assess the eff ects of environmental parameters on the persistence of the Bacteroides 16S rRNA genes derived from equine fecal samples in stream water to investigate the utility of Bacteroides spp. as fecal indicator organisms. Quantitative real-time polymerase chain reaction (qPCR) was used to measure gene concentrations over time with treatments designed to compare fi ltered vs. unfi ltered stream water, fecal aggregate size, initial fecal concentrations, and water temperatures. Comparison of Bacteroides16S rRNA genes/mL in microcosms constructed with unfi ltered stream water and fi ltered stream water indicated that stream water fi ltration to remove indigenous microorganisms followed by temperature had the largest eff ects on gene persistence. Firstorder exponential decay functions were fi tted to the data from each microcosm constructed using unfi ltered stream water, and the decay constants (k) ranged from 0.0071 h -1 in the microcosms incubated at 5°C to 0.0336 h -1 in a set of microcosms incubated at 25°C. Analysis of k calculated from the 10 experimental treatments indicated that k is more highly correlated to temperature than initial Bacteroides 16S rRNA gene starting concentrations. Th e equation resulting from graphing k (as the dependent variable) vs. temperature (as the independent variable) best fi t a peak, Gaussian, 3 parameter function with a maximum decay at 30°C, a r 2 of 0.83 and all parameters were signifi cant (P < 0.0015). Th us this data suggest that factors that reduce biological activity, such as physical removal of stream microorganisms by fi ltration and low temperature, result in slower Bacteroides 16S rRNA gene decay.