, 2008). Our results suggest that Archaea occupy a significant portion of the prokaryotic communities in aged Mn crusts and sandy sediments. The microbial communities on/within basaltic glass and rocks on the seafloor have been well studied (Fisk et al., 2003; Lysnes

et al., 2004; Mason et al., 2007; Einen et al., 2008; Santelli et al., 2008); however, little is known about those on well-developed Mn crusts on the aged seafloor. For the first time, we analyzed the composition and diversity of Archaea and Bacteria on an Lapatinib aged Mn crust (Fig. 3 and Table 1). The archaeal clones recovered from the Mn crust were affiliated with MGI Crenarchaeota (Delong, 1992; Fuhrman et al., 1992) and with the pSL12-related group (Barns et al., 1996) (Fig. S2a). MGI includes the chemolithoautotrophic ammonia-oxidizing archaeon Nitrosopumilus maritimus (Könneke et al., 2005). The pSL12-related group may also include ammonia oxidizers as inferred by the analysis of 16S rRNA and archaeal amoA genes (Mincer et al., 2007; Kato et al., 2009b). Several microdiverse phylogenetic clusters within MGI have been defined in previous reports (Massana et al., 2000; GSK269962 Takai et al., 2004;

Durbin & Teske, 2010). Our MGI clones recovered from the overlying seawater were affiliated with the MGI-γ (Fig. S2a). Those from the Mn crust and sediment samples were affiliated with other MGI clusters such as the α, η–κ–υ, ι and ɛ–ζ–θ clusters (Fig. S2a). In the case study of the South Pacific Gyre (Durbin & Teske, 2010), the relative abundance of the MGI-α in the archaeal clone libraries has been high in the overlying seawater and those of the MGI-η and –υ have been high in the libraries from the sediments. Although it

is unclear what kinds of factors are responsible for the relative abundance of each MGI Acetophenone cluster among deep-sea environments, these differences may reflect differences in geography, environmental characteristics and/or experimental procedures (such as the DNA extraction methods and the PCR primers used). In contrast to Archaea, diverse bacterial phylotypes were detected in the Mn crust, sediment and seawater samples. All analyses, i.e., Chao1 species estimates and the Shannon index (Table 1) and rarefaction curves (Fig. S3), indicated that the community diversity of Bacteria in the crust sample was comparable to or higher than that in sediment and overlying seawater. In addition, the diversity of Bacteria was higher in all samples than those of Archaea (Table 1). The bacterial diversity of the Mn crust was comparable to or higher than those of seafloor basaltic rocks reported previously (Lysnes et al., 2004; Mason et al., 2007; Santelli et al., 2008), suggesting that aged Mn crusts provide a habitat for diverse Bacteria as in basaltic rocks. Bacterial phylotypes dominated in all libraries (75.3–94.3% of the total clone numbers; Fig. 3).