15:50 〜 16:10
[BBG01-06] Anammox bacteria contribute to fixed nitrogen loss in the deep-sea sediments.
★Invited Papers
キーワード：アナモックス、窒素循環、安定同位体測定、深海表層堆積物、モデリング
Anaerobic ammonium oxidation (anammox) and denitrification are the two major sinks of fixed nitrogen in marine ecosystems. Anammox bacteria oxidize ammonium to dinitrogen gas with nitrite as an electron acceptor. The significant contribution of anammox bacteria to nitrogen removal has been reported in oxygen deficient water columns and coastal marine sediments. Recently, functional genes related to anammox bacteria have been detected even in deep-sea sediments. However, anammox distributions and activities in deep-sea benthic nitrogen cycle remain uncertain. In this study, we conducted biogeochemical and molecular analyses of sediment columns collected from diverse Northwest Pacific sites, including bathyal trough (Sagami Bay), abyssal plain and hadal trenches (Japan Trench, Izu-Ogasawara Trench). Microbial community composition was characterized using SSU rRNA gene tag sequencing. Concentrations and isotope composition of porewater ammonium, nitrite, and nitrate were determined. TOC, TN concentrations and isotope composition of sediment were measured. Relative abundance of anammox bacteria was high in bathyal trough and hadal trench bottom stations which presented relatively high ammonium concentrations (~ 20μM) and nitrite concentrations (~ 4μM). The cooccurrence of anammox and nitrifiers was observed in the surface of sediments, where enrichment of 15N in ammonium was observed. It might be attributed to isotope effect associated with aerobic and anaerobic ammonium oxidation. Furthermore, we developed a one-dimensional diffusion-reaction model to determine nitrogen flux of each microbial pathway. In our previous work, we determined nitrogen and oxygen isotope effect of a marine anammox species. To investigate nitrogen removal rate of anammox, nitrogen and oxygen isotope effect of a marine anammox species were newly included in the model. In this talk, I will present our recent challenges to determine both of distributions and activities of anammox and nitrogen-related microorganisms in the deep-sea sediments by combined molecular and stable isotopic analyses.