Cold-seep microbial communities are more abundant at deeper depths in the Japan Trench land slope.

We have analyzed the microbial communities in the cold-seep sediment samples obtained from different depths (5800∼7500 m) of the Japan Trench land slope. The results indicated that the typical cold-seep microbial communities of bacteria and archaea were basically similar in different depth environments and consisted of the delta-Proteobacteria (including sulfate reducing bacterial group) as well as methanogenic archaea, which played an important role in sulfur circulation in the seep environment. More abundant microbes were also identified in deeper cold-seep environments. These observations suggested that the cold-seep activity at the deepest depths of the Japan Trench might be more dynamic than in the shallower land slope. This is the first suggestion describing the relationship between microbial mass and cold-seep activity.