Optical properties of dissolved organic matter relate to different depth-specific patterns of archaeal and bacterial community structure in the North Atlantic Ocean

Abstract

Prokaryotic abundance, activity and community composition were studied in the euphotic, intermediate and deep waters off the Galician coast (NW Iberian margin) in relation to the optical characterization of dissolved organic matter (DOM). Microbial (archaeal and bacterial) community structure was vertically stratified. Among the Archaea, Euryarchaeota, especially Thermoplasmata, was dominant in the intermediate waters and decreased with depth, whereas marine Thaumarchaeota, especially Marine Group I, was the most abundant archaeal phylum in the deeper layers. The bacterial community was dominated by Proteobacteria through the whole water column. However, Cyanobacteria and Bacteroidetes occurrence was considerable in the upper layer and SAR202 was dominant in deep waters. Microbial composition and abundance were not shaped by the quantity of dissolved organic carbon, but instead they revealed a strong connection with the DOM quality. Archaeal communities were mainly related to the fluorescence of DOM (which indicates respiration of labile DOM and generation of refractory subproducts), while bacterial communities were mainly linked to the aromaticity/age of the DOM produced along the water column. Taken together, our results indicate that the microbial community composition is associated with the DOM composition of the water masses, suggesting that distinct microbial taxa have the potential to use and/or produce specific DOM compounds.

High dark inorganic carbon fixation rates by specific microbial groups in the Atlantic off the Galician coast (NW Iberian margin)

“…Recent metagenomic analyses have found genes encoding different subunits of the carbon monoxide dehytrogenase associated with Alteromonas (Smedile et al ., ). The high DIC uptake (particularly in the SSLs) by these taxa could be related to transporters of amino acids and TonB involved in the transport of carbohydrates (Baker et al ., ) and the availability of organic matter compounds easily degradable in the subsurface and upper mesopelagic waters off the Galician waters (Dobal‐Amador et al ., ; Guerrero‐Feijóo et al ., ), which might favour anaplerotic metabolism (Erb, ; Sauer and Eikmanns, ). In contrast to SAR406 and Alteromonas , most members of the SAR202 clade did not fix DIC or their activity was below the detection limit (see Fig.…”

“…The key stations where the biological measurements were performed are also indicated and labelled in red (8, 11, 16, 108 and 111). Modified version of Guerrero‐Feijóo and colleagues (). [Colour figure can be viewed at http://wileyonlinelibrary.com]…”

“…The main water masses in the Atlantic sampled along a section off the Galician coast (Fig. ) are described in Guerrero‐Feijóo and colleagues (). Briefly, the basic physico‐chemical features of the main water masses encountered in the two expeditions (BIO‐PROF‐1 and BIO‐PROF‐2) are shown in Fig.…”

“…The abundance and vertical distribution of the major microbial groups (Bacteria and Archaea) were previously studied in this area (Guerrero‐Feijóo et al ., ). The contribution of Bacteria to the total microbial community decreased from the euphotic zone to bathypelagic waters while the relative abundance of Thaumarchaeota increases with depth (Guerrero‐Feijóo et al ., ).…”

“…The abundance and vertical distribution of the major microbial groups (Bacteria and Archaea) were previously studied in this area (Guerrero‐Feijóo et al ., ). The contribution of Bacteria to the total microbial community decreased from the euphotic zone to bathypelagic waters while the relative abundance of Thaumarchaeota increases with depth (Guerrero‐Feijóo et al ., ). The contribution of the most abundant bacterial taxa to the total bacterial abundance was depth‐specific, showing that the relative abundance of SAR11 and Alteromonas decreased with depth and the contribution of SAR202 and SAR324 was increasing towards deeper waters (Dobal‐Amador et al ., ).…”