The depths of the Oceans on this world are unexplored territory by humans. Until recently. Scientists have created equipment that can withstand the pressure of the depth of the sea to begin exploring the world unseen by many land-bound eyes. Little did we know there was an underwater land teeming with life, especially microbial life. This article discusses the microbial communities that may be contributors to the methane levels found in our ocean sediments.
The Prokaryotic biomass found in the deep sea sediments are greater than 10<sup>5</sup> microbial cells/cm<sup>3</sup>; this holds true for roughly 1000 meters below the seafloor. These microbes just might represent one-tenth to one-third of the living biomass on Earth. But the relationship between the microbial community and the conditions of the sub-seafloor environments are largely unknown to us. The scientists in this article explain that their interest lies in the Archaeal and Bacterial communities of the sub-seafloor sediments and how they can distinguish the community based on the presence or absence of methane hydrate (essentially methane trapped within a crystal water structure forming something like ice).
Archaeal microbes were found to grow at the seafloor level, and decreased in number as they drew closer to the zone of stability for methane hydrate deeper in the sub-seafloor. Bacterial microbes were much more at home in the sub-seafloor levels closer to the methane hydrate. Bacteria from the phylum Chloroflexi and Planctomycetes were found to be the predominant microbes in this unknown environment; small numbers of Actinobacteria, Bacteriodetes and Firmicutes were also found in this habitat.
A few interesting facts to take note of is that in sites of high sedimentation rates, there appeared to be a higher availability of buried nutrients to allow for inhabitation at greater depths. In their testing the scientists also found that the structure of microbial communities found at methane hydrate sites were very similar across the locations they tested in the Pacific Ocean. In sites lacking hydrates, they found that Chloroflexi was the dominant phylum; this factor was so consistent that it helped them to distinguish hydrate sites from non-hydrate sites. Archaeal microbes were also affected by the presence of methane hydrate. The communities found in sediments above hydrate sites consisted primarily of DSAG members (Deep-Sea Archaeal Group), where predominant Archaea in non-hydrate sites were MCG members (Miscellaneous Crenarchaeotic Group).