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Pasulka, AL, Levin LA, Steele JA, Case DH, Landry MR, Orphan VJ.  2016.  Microbial eukaryotic distributions and diversity patterns in a deep-sea methane seep ecosystem. Environmental Microbiology. 18:3022-3043.   10.1111/1462-2920.13185   AbstractWebsite

Although chemosynthetic ecosystems are known to support diverse assemblages of microorganisms, the ecological and environmental factors that structure microbial eukaryotes (heterotrophic protists and fungi) are poorly characterized. In this study, we examined the geographic, geochemical and ecological factors that influence microbial eukaryotic composition and distribution patterns within Hydrate Ridge, a methane seep ecosystem off the coast of Oregon using a combination of high-throughput 18S rRNA tag sequencing, terminal restriction fragment length polymorphism fingerprinting, and cloning and sequencing of full-length 18S rRNA genes. Microbial eukaryotic composition and diversity varied as a function of substrate (carbonate versus sediment), activity (low activity versus active seep sites), sulfide concentration, and region (North versus South Hydrate Ridge). Sulfide concentration was correlated with changes in microbial eukaryotic composition and richness. This work also revealed the influence of oxygen content in the overlying water column and water depth on microbial eukaryotic composition and diversity, and identified distinct patterns from those previously observed for bacteria, archaea and macrofauna in methane seep ecosystems. Characterizing the structure of microbial eukaryotic communities in response to environmental variability is a key step towards understanding if and how microbial eukaryotes influence seep ecosystem structure and function.

Pasulka, AL, Goffredi SK, Tavormina PL, Dawson KS, Levin LA, Rouse GW, Orphan VJ.  2017.  Colonial tube-dwelling ciliates influence methane cycling and microbial diversity within methane seep ecosystems. Frontiers in Marine Science. 3   10.3389/fmars.2016.00276   Abstract

In a variety of marine ecosystems, microbial eukaryotes play important ecological roles; however, our knowledge of their importance in deep-sea methane seep ecosystems is limited. Microbial eukaryotes have the potential to influence microbial community composition and diversity by creating habitat heterogeneity, and may contribute to carbon cycling through grazing or symbiotic associations with microorganisms. In this study, we characterized the distribution, substrate variability and ecology of a particular group of microbial eukaryotes, known as folliculinid ciliates, at methane seeps along the eastern Pacific margin. Folliculinid ciliates were recently recognized as an abundant and ecologically important component of hydrothermal vent ecosystems, but their ecology in methane seeps has not been examined. Folliculinid ciliates inhabited methane seeps from Costa Rica to Oregon, suggesting a broad distribution in the eastern Pacific. Using phylogenetic analyses of the 18S rRNA gene, two different species of folliculinid were identified. Folliculinids occupied a range of physical substrates, including authigenic carbonate rocks, shells of dead vesicomyid clams, polychaete tubes and gastropod shells. Molecular analysis of folliculinid associated microorganisms (16S rRNA and particulate methane monooxygenase) revealed that these ciliates not only influence overall microbial diversity, but also and have a specific relationship with bacteria in the ‘Deep sea-2’ methanotroph clade. Natural δ13C isotope signatures of folliculinids (-35‰) and their 13C-enrichment patterns in shipboard 13CH4 stable isotope-probing experiments indicated these ciliates and their associated microbes are involved in cycling methane-derived carbon. Folliculinids were significantly enriched in 13C after the addition of 13CH4 over short-term (3-8 day) incubations. Together, these results suggest that folliculinid ciliates represent a previously overlooked contributor to the ecology and biogeochemical cycling of deep-sea methane seep ecosystems.

Parker, EA, Rippy MA, Mehring AS, Winfrey BK, Ambrose RF, Levin LA, Grant SB.  2017.  Predictive power of clean bed filtration theory for fecal indicator bacteria removal in stormwater biofilters. Environmental Science & Technology. 51:5703-5712.   10.1021/acs.est.7b00752   AbstractWebsite

Green infrastructure (also referred to as low impact development, or LID) has the potential to transform urban stormwater runoff from an environmental threat to a valuable water resource. In this paper we focus on the removal of fecal indicator bacteria (FIB, a pollutant responsible for runoff associated inland and coastal beach closures) in stormwater biofilters (a common type of green infrastructure). Drawing on a combination of previously published and new laboratory studies of FIB removal in biofilters, we find that 66% of the variance in FIB removal rates can be explained by clean bed filtration theory (CBFT, 31%), antecedent dry period (14%), study effect (8%), biofilter age (7%), and the presence or absence of shrubs (6%). Our analysis suggests that, with the exception of shrubs, plants affect FIB removal indirectly by changing the infiltration rate, not directly by changing the FIB removal mechanisms or altering filtration rates in ways not already accounted for by CBFT. The analysis presented here represents a significant step forward in our understanding of how physicochemical theories (such as CBFT) can be melded with hydrology, engineering design, and ecology to improve the water quality benefits of green infrastructure.

Parker, ED, Forbes VE, Nielsen SL, Ritter C, Barata C, Baird DJ, Admiraal W, Levin L, Loeschke V, Lyytikainen-Saarenmaa P, Hogh-Jensen H, Calow P, Ripley BJ.  1999.  Stress in ecological systems. Oikos. 86:179-184.   10.2307/3546584   AbstractWebsite
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