BioProject

To decipher the response of mesopelagic prokaryotic communities to input of nutrients, we tracked changes in prokaryoticabundance, extracellular enzymatic activities, heterotrophic production, dark dissolved inorganic carbon (DIC) fixation, communitycomposition (16S rRNA sequencing) and community gene expression (metatranscriptomics) in 3 microcosm experiments withwater from the mesopelagic North Atlantic. More...

To decipher the response of mesopelagic prokaryotic communities to input of nutrients, we tracked changes in prokaryoticabundance, extracellular enzymatic activities, heterotrophic production, dark dissolved inorganic carbon (DIC) fixation, communitycomposition (16S rRNA sequencing) and community gene expression (metatranscriptomics) in 3 microcosm experiments withwater from the mesopelagic North Atlantic. Responses in 3 different treatments amended with thiosulfate, ammonium or organicmatter (i.e. pyruvate plus acetate) were compared to unamended controls. The strongest stimulation was found in the organicmatter enrichments, where all measured rates increased >10-fold. Strikingly, in the organic matter treatment, the dark DICfixation rates —assumed to be related to autotrophic metabolisms— were equally stimulated as all the other heterotrophic-relatedparameters. This increase in DIC fixation rates was paralleled by an up-regulation of genes involved in DIC assimilation viaanaplerotic pathways. Alkaline phosphatase was the metabolic rate most strongly stimulated and its activity seemed to be relatedto cross-activation by nonpartner histidine kinases, and/or the activation of genes involved in the regulation of elemental balanceduring catabolic processes. These findings suggest that episodic events such as strong sedimentation of organic matter into themesopelagic might trigger rapid increases of originally rare members of the prokaryotic community, enhancing heterotrophic andautotrophic carbon uptake rates, ultimately affecting carbon cycling. Our experiments highlight a number of fairly unstudiedmicrobial processes of potential importance in mesopelagic waters that require future attention. Less...