Microbial nitrous oxide production associated with aquatic invertebrates

动物肠道为微生物氮转化提供了独特而丰富的微环境，这需要从概念上和定量上整合到整个水生微生物氮循环中。我们最近发现，大量水生无脊椎动物排放大量的温室气体一氧化二氮（N2O） （Stief et al. 2009）。我们的初步研究结果表明，缺氧动物肠道中摄入的微生物不完全反硝化导致了N2O而不是N2的优先排放。然而，新的发现表明，N2O的产生也可能发生在生长在某些物种外骨骼上的微生物生物膜中。因此，本研究将探讨水生动物产生N2O的不同机制。1)肠道内容物的分子微生物分析将验证细菌在被食用时所经历的氧-缺氧转变导致不完全诱导反硝化的假设。2)摄食实验将揭示水生无脊椎动物肠道中是否摄入了储存NO3的硅藻来促进N2O的产生。3)示踪实验将确定和量化外骨骼生物膜中N2O生成的途径。总的来说，这些实验将提高我们对水生生态系统中迄今为止被忽视的一氧化二氮来源的理解。

Animal guts provide distinct and abundant microenvironments for microbial nitrogen conversions, which calls for a conceptual and quantitative integration into the overall aquatic microbial nitrogen cycle. We recently discovered that a large variety of aquatic invertebrates emits substantial amounts of the greenhouse gas nitrous oxide (N2O) (Stief et al. 2009). Our initial findings suggested that the preferential emission of N2O instead of N2 was due to incomplete denitrification of ingested microbes in the anoxic animal gut. New findings, however, suggest that N2O production may also take place in microbial biofilms that grow on the exoskeleton of some species. Therefore, the proposed research will investigate the different mechanisms of N2O production associated with aquatic animals. 1) Molecular microbial analysis of the gut contents will test the hypothesis that the oxic-anoxic transition experienced by bacteria when they are eaten leads to the incomplete induction of denitrification. 2) Feeding experiments will reveal whether ingested NO3 --storing diatoms fuel the N2O production in the gut of aquatic invertebrates. 3) Tracer experiments will identify and quantify pathways of N2O production in exoskeletal biofilms. Taken together, these experiments will improve our understanding of a so far overlooked source of N2O from aquatic ecosystems.