Files in this Data Supplement:

• Supplemental file 1 - Rarefaction curves of NifH, 16S rRNA gene, and McrA OTUs of the clone libraries constructed for the deep-sea methane seep sediments of Okhotsk Sea. (Fig. S1); NifH and NifH-like sequences from putative clusters III-x, V, and VI obtained from the deep-sea methane seep sediments of Okhotsk Sea aligned using the Clustal_X program. (Fig. S2); homodimer ribbon model of the putative nitrogenase Fe protein (NifH) of clone 25H-0N-17, constructed via molecular modeling using the online Swiss Model facility (Fig. S3); UniFrac dendrogram of environment clustering analysis of nifH-encoding microbial assemblages from various marine environments where nifH clone libraries were constructed with the PCR primers of Mehta et al. (Fig. S4).
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