Correlative Assessment of Fecal Indicators using Human Mitochondrial DNA as a Direct Marker

Abstract

Identifying the source of surface water fecal contamination is paramount to mitigating pollution and risk to human health. Fecal bacteria such as <i>E. coli</i> have been staple indicator organisms for over a century, however there remains uncertainty with <i>E. coli</i>-based metrics since these bacteria are abundant in the environment. The relationships between the presence of direct indicator of human waste (human mitochondrial DNA), human-specific <i>Bacteroidales</i>, and <i>E. coli</i> were studied for water samples taken from an urban creek system (Duck Creek Watershed, Cincinnati, OH) impacted by combined sewer overflows. Logistic regression analysis shows that human-specific <i>Bacteroidales</i> correlates much more closely to human mitochondrial DNA (<i>R</i> = 0.62) relative to <i>E. coli</i> (<i>R</i> = 0.33). We also examine the speciation of <i>Bacteroidales</i> within the Duck Creek Watershed using next-generation sequencing technology (Ion Torrent) and show the most numerous populations to be associated with sewage. Here we demonstrate that human-specific <i>Bacteroidales</i> closely follow the dynamics of human mitochondrial DNA concentration changes, indicating that these obligate anaerobes are more accurate than <i>E. coli</i> for fecal source tracking, lending further support to risk overestimation using coliforms, especially fecal coliforms and <i>E. coli</i>