Emerging concepts on microbial processes in the bathypelagic ocean – ecology, biogeochemistry and genomics.

This papersynthesizesrecentfindingsregardingmicrobialdistributionsandprocessesinthe bathypelagicocean(depth 41000 m).Abundance,productionandrespirationofprokaryotesreflect suppliesofparticulateanddissolvedorganicmattertothebathypelagiczone.Betterresolutionof carbonfluxesmediatedbydeepmicrobesrequiresfurthertestingonthevalidityofconversionfactors. Archaea, especiallymarine Crenarchaeota GroupI,areabundantindeepwaterswheretheycanfix dissolvedinorganiccarbon.Virusesappeartobeimportantinthemicrobialloopindeepwaters, displayingremarkablyhighvirustoprokaryoteabundanceratiosinsomeoceanicregions.Sequencing of 18SrRNAgenesrevealedatremendousdiversityofsmall-sizedprotistsinbathypelagicwaters. Abundancesofheterotrophicnanoflagellates(HNF)andciliatesdecreasewithdepthmoresteeplythan prokaryotes;nonetheless,dataindicatedthatHNFconsumedhalfofprokaryoteproductioninthe bathypelagiczone.Aggregatesareimportanthabitatsfordeep-watermicrobes,whichproducemore extracellularenzymes(onaper-cellbasis)thansurfacecommunities.Thetheoryofmarinegel formationprovidesaframeworktounravelcomplexinteractionsbetweenmicrobesandorganic polymers.Recentdataontheeffectsofhydrostaticpressureonmicrobialactivitiesindicatethat bathypelagicmicrobialactivityisgenerallyhigherunder in situ pressureconditionsthanatatmospheric pressures.High-throughputsequencingof16SrRNAgenesrevealedaremarkablediversityof Bacteria in the bathypelagicocean.Metagenomicsandcomparativegenomicsofpiezophilesrevealnotonlythe high diversityofdeepseamicrobesbutalsospecificfunctionalattributesofthesepiezophilicmicrobes, interpretedasanadaptationtothedeepwaterenvironment.Takentogether,thedatacompiledon bathypelagicmicrobesindicatethat,despitehigh-pressureandlow-temperatureconditions,microbes in thebathypelagicoceandynamicallyinteractwithcomplexmixturesoforganicmatter,respondingto changesintheocean’sbiogeochemicalstate