Citation:

Korajkic, A., B. McMinn, L. Parfrey, R. Knight, AND O. Shanks. Influence of solar radiation and biotic interactions on bacterial and eukaryotic communities associated with sewage decomposition in ambient water. Presented at ASM 2013 113th General Meeting, Denver, CO, May 18 - 21, 2013.

Impact/Purpose:

To inform the public.

Description:

Sewage and ambient water both consist of a highly complex array of bacteria and eukaryotic microbes. When these communities are mixed, the persistence of sewage-derived pathogens in environmental waters can represent a significant public health concern. Solar radiation and biotic interactions (predation and competition) influence pathogen decay, as demonstrated by experiments targeting indicator microorganisms. However, very little is known about the microbial community structure of each of these sources and how it shifts due to mixing and subsequent decomposition of the sewage contaminant. We compared the relative contribution of sunlight exposure and the presence of natural river microbiota on decay of sewage and ambient upper Mississippi River microbial communities using illumina sequencing of 16S and 18S hypervariable regions. Mixtures of primary treated sewage and river water were placed in dialysis bags and incubated in situ under ambient conditions for seven days using a submersible mesocosm. Treatments included: 1) exposure to sunlight and river microbiota, 2) exposure to sunlight in sterilized river water, 3) no sunlight exposure in the presence of river microbiota, and 4) no exposure to either variable. Bacterial alpha diversity estimates were greater in sewage compared to ambient river water, while the opposite was observed for eukaryotes. The microbial communities changed markedly as decomposition progressed (Permanova, p = 0.001) and this change is correlated between eukaryotic and bacterial communities (Mantel test, p = 0.001, R2 = 0.55). Permanova analysis indicated that both sunlight and biota sterilization treatments had a significant impact on community structure (p = 0.001) for bacteria, while only sunlight was significant for eukaryotes (p = 0.008). At late time points the eukaryotic community was dominated by the ciliate Tetrahymena, which was present at low levels in the sewage sample and subsequently bloomed. In addition, co-occurrence analyses identified a clear association between specific eukaryotes (Parabodo spp., Tetrahymena spp., and others) and several bacterial families. These findings suggest that biotic interactions can be a critical factor in the decomposition of fecal bacteria in freshwater habitats.

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