Abstract
Methane is one of the major end products from photosynthetic organic matter. Based on stable carbon and hydrogen isotopic compositions of methane, biological pathways mainly consisting of carbon dioxide reduction coupled to molecular hydrogen oxidation and acetate fermentation and abiological pathways such as thermal degradation of organic matter have been systematically classified. However, recent advances in subseafloor biosphere research have unveiled the complexity of processes involved in the transformation, migration and fate of methane. Particularly, it has been recognized that marine sediments with high flux of methane harbor novel lineages of microorganisms, the physiological traits of which are largely unknown due to their resistance to cultivation. In this review article, microbiological investigations that shed light on DNA-based microbial community structures and metabolic diversity and activity related to methane production and consumption in organic-rich marine sediments are briefly summarized.
