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Most DNA-based microbial source tracking (MST) approaches target host-associated organisms within the order Bacteroidales, but the gut microbiota of humans and other animals contain organisms from an array of other taxonomic groups that might provide indicators of fecal pollution sources. To discern between human and nonhuman fecal sources, we compared the V6 regions of the 16S rRNA genes detected in fecal samples from six animal hosts to those found in sewage (as a proxy for humans). We focused on 10 abundant genera and used oligotyping, which can detect subtle differences between rRNA gene sequences from ecologically distinct organisms. Our analysis showed clear patterns of differential oligotype distributions between sewage and animal samples. Over 100 oligotypes of human origin occurred preferentially in sewage samples, and 99 human oligotypes were sewage specific. Sequences represented by the sewage-specific oligotypes can be used individually for development of PCR-based assays or together with the oligotypes preferentially associated with sewage to implement a signature-based approach. Analysis of sewage from Spain and Brazil showed that the sewage-specific oligotypes identified in U.S. sewage have the potential to be used as global alternative indicators of human fecal pollution. Environmental samples with evidence of prior human fecal contamination had consistent ratios of sewage signature oligotypes that corresponded to the trends observed for sewage. Our methodology represents a promising approach to identifying new bacterial taxa for MST applications and further highlights the potential of the family Lachnospiraceae to provide human-specific markers. In addition to source tracking applications, the patterns of the fine-scale population structure within fecal taxa suggest a fundamental relationship between bacteria and their hosts., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

Untreated sewage discharges and limited agricultural manure management practices contribute to fecal pollution in rural Brazilian waterways. Most microbial source tracking studies have focused on Bacteroidales, and few have tested host-specific indicators in underdeveloped regions. Sequencing of sewage and human and animal feces with Illumina HiSeq revealed Prevotellaceae as the most abundant family in humans, with Lachnospiraceae and Ruminococcaceae also comprising a large proportion of the microbiome. These same families were also dominant in animals. Bacteroides, the genus containing the most commonly utilized human-specific marker in the United States was present in very low abundance. We used oligotyping to identify Prevotella and Blautia sequences that can distinguish human fecal contamination. Thirty-five of 61 Blautia oligotypes and 13 of 108 Prevotella oligotypes in humans were host-specific or highly abundant (i.e. host-preferred) compared to pig, dog, horse and cow sources. Certain human Prevotella and Blautia oligotypes increased more than an order of magnitude along a polluted river transect in rural Brazil, but traditional fecal indicator levels followed a steady or even decreasing trend. While both Prevotella and Blautia oligotypes distinguished human and animal fecal pollution in Brazil surface waters, Blautia appears to contain more discriminatory and globally applicable markers for tracking sources of fecal pollution., (© 2014 Society for Applied Microbiology and John Wiley & Sons Ltd.)