, 2001) These results suggest that putative ammonia- (or in some

, 2001). These results suggest that putative ammonia- (or in some cases, sulfur- and/or arsenite-) oxidizing chemolithoautotrophs are present on the Mn crust surface. The detection of the phylotypes related to ammonia-oxidizing Archaea and Bacteria in the Mn crust suggests that these putative ammonia oxidizers may play a role as primary producers in the microbial ecosystem on Mn oxides that coats old seamounts in western Pacific. Although the ammonium concentration in the open ocean is generally extremely low (<5 μM) (Rees et al., 2006; Herfort et al., 2007; Agogue et al., 2008), ammonia-oxidizing Archaea belonging to MGI Crenarchaeota can grow under these conditions using ammonium as the energy source (Martens-Habbena

et al., 2009). Ammonia-oxidizing bacteria can also grow at learn more low concentrations

of ammonium (Bollmann & Laanbroek, 2001; Bollmann et al., 2002). In fact, we detected both bacterial and archaeal amoA genes, which encode the alpha subunit of the ammonia monooxygenase, from DNA extracted from the Mn crust (the data will be published elsewhere). Ammonia is the most likely chemical species to be utilized as an electron donor for microbial growth on the Mn crust. Dissolved organic carbon compounds in deep-sea water may resist microbial growth (Barber, PI3K Inhibitor Library mw 1968). Buried organic compounds from surface seawater may be limited on the Mn crust because little sandy sediment is formed (Fig. 1a). Accordingly, H2, CH4, H2S, Fe2+ and Mn2+ from the degradation of organic compounds by anaerobes and fermenters would be limited on the Mn crust. Fe2+ and reduced sulfides contained in basaltic rocks are thought to be energy sources for the microorganisms on the rocks (Bach & Edwards, 2003; Santelli et al., 2008), but the argument is still controversial (Templeton et al., 2009). Our data suggest 6-phosphogluconolactonase that ammonia in surrounding seawater is likely to be an important energy source for sustaining the microbial ecosystem on the Mn crust. Furthermore, the presence of ammonia-oxidizing bacteria on oceanic basaltic rocks has

been supported by the detection of 16S rRNA genes related to these members such as Nitrosospira (Mason et al., 2008; Santelli et al., 2008). These facts lead to the hypothesis that the ammonia oxidizers play a role in the microbial ecosystem on outcrops of the global seafloor including bare young basalts and aged Mn crusts. One of the subjects in the study of oceanic Mn nodules and crusts is the mechanism of their creation and growth. Microorganisms may play a role in the accumulation of Mn oxides by biofilm formation on rocks on the seafloor (Wang & Müller, 2009). This notion is consistent with the detection of abundant microorganisms, both Bacteria and Archaea, within/on the Mn crust (Fig. 2). Mn-oxidizing bacteria, which are thought to play a role in Mn precipitation in the first step of the biomineralization model for Mn crusts as a bioseed (Wang & Müller, 2009), have been isolated from marine environments (Tebo et al., 2005).

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