The Seabed as Natural Laboratory: Lessons From Uncultivated Methanotrophs

Abstract

The anaerobic oxidation of methane (AOM) by archaeal methanotrophs(ANME) functions as a major sink in oceanic methane geochemistry, and is a key biogeochemial process in the anoxic seabed. Unfortunately, demonstration of the biochemical pathway of AOM has not been possible because of the lack of pure cultures of ANME and their partner sulfate-reducing bacteria. The main reason for failing to isolate these microorganisms by cultivation is their slow growth, which is most likely a consequence of the low energy yield of the AOM reaction. This chapter discusses how in situ biogeochemical and microbiological observations of natural seabed communities and in vitro enrichments contribute to understanding of the ecology and physiology of these “uncultivables”. Successful in vitro enrichment strategies include selecting seabed inoculates with abundant ANME populations, increasing the availability of dissolved methane and sulfate by flow through reactors and hydrostatic pressure, and maintaining the apparent temperature, pH, and salinity optima of AOM, the energy delivering process.