His research interests are in the geomicrobiology and biogeochemistry of the ocean, with special emphasis on the deep subseafloor biosphere and marine ecosystem change. He has used scientific ocean drilling and cutting-edge transdisciplinary approaches to explore the nature and limits of deep microbial life, ecosystem functioning in biogeochemical carbon cycles, co-evolution of life and Earth, and planetary habitability on Earth and beyond. He was a shipboard microbiologist for the first deep biosphere-dedicated scientific ocean drilling on the US drilling research vessel JOIDES Resolution, Ocean Drilling Program (ODP) Leg 201 in the eastern equatorial Pacific and off Peru in 2002. In deep-sea research using Shinkai 6500 and ROVs, he first isolated two novel mesophilic chemolithoautotrophic epsilon-proteobacteria (Sulfrimonas autotrophica gen. nov., sp. nov. 2003, and Sulfurovum lithotrophicum gen. nov., sp. nov. 2004) from the Okinawa Trough hydrothermal fields, which isolates were appeared to be the most abundant, ecologically significant sulfur and/or hydrogen-metabolizing bacteria distributed in cold seeps and deep-sea hydrothermal environments worldwide. In 2005-2006, he was an Alexander von Humboldt Foundation Research Fellow at the Max Planck Institute for Marine Microbiology in Bremen, Germany, under the supervision of Prof. Bo Barker Jørgensen. Upon his return to Japan, he served as Deputy Director of Kochi Institute for Core Sample Research (KCC) and then as Deputy Director of the Research and Development Center for Ocean Drilling Science (ODS) at JAMSTEC.