Vertical stratificaction of bacterial communities driven by multiple environmental factors in the dark waters off the Galician coast (NW Spain)

scientific articleThe processesmediatedbymicrobialplanktoniccommunitiesoccuralongtheentirewatercolumn,yet the microbialactivityandcompositionhavebeenstudiedmainlyinsurfacewaters.Thisresearchex- amined theverticalvariationinbacterialabundance,activityandcommunitycompositionandstructure from surfacedownto5000mdepthfollowingalongitudinaltransectofftheGaliciancoast(NWIberian margin, from43°N, 9°W to43°N, 15°W). Communityactivityandcompositionchangedwithdepth.The leucine incorporationratesdecreasedfromtheeuphoticlayertothebathypelagicwatersbythreeorders of magnitude,whereasprokaryoticabundancedecreasedonlybyoneorderofmagnitude.Therelative abundance ofSAR11and Alteromonas, determined bycatalyzedreporteddeposition fluorescenceinsitu hybridization(CARD-FISH),decreasedwithdepth.Meanwhile,thecontributionofSAR202andSAR324 wassignificantly higherinthedeeperlayers(i.e.NEADW,NorthEastAtlanticDeepWaterandLDW, LowerDeepWater)thanintheeuphoticzone.Bacterialcommunitystructure,assessedbyAutomated Ribosomal IntergenicSpacerAnalysis(ARISA),wasdepth-specific. Adistancebasedlinearmodel (DistLM) revealedthatthevariabilityfoundinbacterialcommunitystructurewasmainlyexplainedby temperaturenitrate,phosphate,dissolvedorganicmatter(DOM) fluorescence, prokaryoticabundance, leucine incorporationandtoalesserextentsalinity,oxygen,CDOMabsorbanceanddissolvedorganic carbon concentration.Ourresultsdisplayedabacterialcommunitystructureshapednotonlybydepth- relatedphysicochemicalfeaturesbutalsobyDOMquality,indicatingthatdifferentprokaryotictaxahave the potentialtometabolizeparticularDOMsources.Postprint2,421