Frequency and Occurrence of 16S rRNA Bacteroides Molecular Markers in the Gila River, Arizona

Bacteria belonging to the genus Bacteroides have been suggested as alternative fecal indicators to Escherichia coli or fecal coliforms because they make up a significant portion of the fecal bacterial population, have little potential for re-growth in the environment, and have a high degree of host specificity that likely reflects differences in host animal digestive systems. The Gila River is listed on the 303d list and it is comprised of the Upper Gila River Watershed from Coolidge Dam to the Arizona-New Mexico border and covers about 6,000 square miles. In this study our team used microbial source tracking (MST) techniques designed to target specific diagnostic sequences within the Bacteroides genome present in feces from different animals; coupled with conventional microbial methods to determine the dominant sources of fecal contamination in the Gila River. The objective was to differentiate between human, ruminant and bovine fecal contamination by targeting 16S rRNA Bacteroides molecular markers found in the literature. In this study we assessed 3 Bacteroides based assays evaluating human, bovine, and ruminant sources. Results indicate that 29% of total samples assayed (n=74) show high levels of total coliforms and E. coli, 39% show contributions of human molecular markers, and 14% show bovine molecular markers. Additionally, we found that seasonal changes contribute to the microbial load present in water within the region due to storm events in which increased overland flow is bringing additional pollution into the watershed.