Metagenomic Analysis of hadopelagicmicrobial assemblages thriving in the deepest part of the Mediterranean Sea. The Matapan-Vavilov Deep (MVD).

The hadopelagic zone is classified as the bottomest part of the oceanic zone laying below the abyssopelagic zone at depths of greater than 6000m. Above these extreme depths sits the marine pelagic zone which is situated anywhere deeper than 200m below sea level, this area comprises of the largest marine subsystem and makes up more than 2/3rds of the oceanic volume today. This area and below is currently one of the least explored ecosystems on earth.

The MVD canyon has a max depth of 5267m below sea level and its exact position geographically is at the seabed of the Ionian sea approximately 56km south west of Pylos City in Greece. The fact that it is so unexplored is one of the reasons the study was done, to see and get the first published results as to what is happening way down there, what species thrive and how.

The paper doesnt have a specific methods section, it is joined onto the introduction and what they state is that from a depth of 4908m, in june 2010- 150 litres of hadopelagic seawater was collected for metagenomic analyses. The temperature of the water ranged slightly but there wasnt a massive fluctation and the same was stated for salinity, this was done to ensure there  werent any other causes for dominance if any was found. From this collected water, environmental DNA was extracted and then tested in the following ways, the DNA was put under metagenomic analysis to see what exact species were down there, and then the general prokaryotic community was examined by comparing the communities 16S rRNA composition and comparing it to a well established library of already shown compositions. For the community they also measured the levels of dark primary production (DPP) and the prokaryotic heterotrophic productions (PHP's) at 6 depth horizons to observe if there was a depth related trend

The results showed that this was the case for the PHP as this decreased rapidly the deeper they went, with the lowest value being at the lowest depth. The DPP showed a different trend oddly as it was quite constant the deeper they went up to a depth of 3500m which matches the previous results obtained for this profile within this Sea. Below 3500m at the hadopelagic water depths there was a 3x fold recession of these values, and this also corroborates what was seen in previous studies around these depths. They finally found that in these waters at this depth there was a clear 96.2% dominance by the Eubacteria.

From the community measurements they found that overall the prokaryotic diversity is very poor, which coincides with the dominance of the Eubacteria as they are present and so dominant at the expense of other bacteria. Then they found that of all the sequences located they were classified within the same clade and that is the deep ecotype clade, and this dominance also explains the decrease in DPD, the same as before, but obviously the conclusions are a bit more conclusive having a clade to relate them too.

So from this study the conclusions were quite easy to come to, that there are a low number of viral genomes down there and that the whole area is dominated by low trophic level bacteria clearly as they are the only ones who can survive under the lack of light and high pressure conditions.

This study is very new and very interesting as it is one of a kind, as no real studies have gone this deep and indetailed so as with other papers i've reviewed it will hopefully spark a sudden interest and increase the number of studies done.

Reference:

Smedile,F., Messina,E., La Cono,V., Tsoy,O., Monticelli,L., Borghini,M., Giuliano,L., Golyshin,P., Mushegian,A & Yakimov,M.  Metagenomic Analysis of hadopelagic microbial assemblages thriving at the deepest part of Mediterranean Sea, Matapan-Vavilov Deep. Environmental Microbiology (2013) 15(1), 167-182.