Microbial nitrous oxide production associated with aquatic invertebrates

动物肠道为微生物氮素转化提供了独特和丰富的微环境，这就要求将概念和数量整合到整个水生微生物氮素循环中。我们最近发现，各种各样的水生无脊椎动物排放大量的温室气体一氧化二氮(N2O)(Stief等人)。2009年)。我们的初步发现表明，N2O而不是N2的优先排放是由于摄入的微生物在缺氧的动物肠道中没有完全反硝化。然而，新的发现表明，一些物种外骨骼上生长的微生物生物膜也可能产生N2O。因此，这项拟议的研究将探讨与水生动物相关的不同N2O产生机制。1)肠道内容物的分子微生物分析将检验这样的假设，即细菌在被食用时经历的缺氧-缺氧转变导致反硝化作用的不完全诱导。2)喂养实验将揭示摄入的储存N3的硅藻是否为水生无脊椎动物肠道中N2O的产生提供燃料。3)示踪器实验将识别和量化外骨骼生物膜中产生N2O的途径。综上所述，这些实验将提高我们对水生生态系统中迄今被忽视的N2O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.