Indications for algae-degrading benthic microbial communities in deep-sea sediments along the Antarctic Polar Front

Abstract

a b s t r a c tPhytoplankton blooms in surface waters of the oceans are known to influence the food web and impact microbial as well as zooplankton communities. Numerous studies have investigated the fate of phytoplankton-derived organic matter in surface waters and shelf sediments, however, little is known about the effect of sinking algal biomass on microbial communities in deep-sea sediments. Here, we analyzed sediments of four regions in the Southern Atlantic Ocean along the Antarctic Polar Front that had different exposures to phytoplankton bloom derived organic matter. We investigated the microbial communities in these sediments using high-throughput sequencing of 16S rRNA molecules to determine microorganisms that were active and catalyzed reporter deposition fluorescence in situ hybridization to infer their abundance and distribution. The sediments along the Antarctic Polar Front harbored microbial communities that were highly diverse and contained microbial clades that seem to preferably occur in regions of high primary productivity. We showed that organisms affiliated with the gammaproteobacterial clade NOR5/OM60, which is known from surface waters and coastal sediments, thrive in the deepsea. Benthic deep-sea NOR5 were abundant, diverse, distinct from pelagic NOR5 and likely specialized on the degradation of phytoplankton-derived organic matter, occupying a similar niche as their pelagic relatives. Algal detritus seemed to not only fuel the benthic microbial communities of large areas in the deep-sea, but also to influence communities locally, as we found a peak in Flavobacteriaceae-related clades that also include degraders of algal biomass. The results strongly suggest that phytoplanktonderived organic matter was rapidly exported to the deep-sea, nourished distinct benthic microbial communities and seemed to be the main energy source for microbial life in the seafloor of vast abyssal regions along the Antarctic Polar Front.

Bacterioplankton reveal years-long retention of Atlantic deep-ocean water by the Tropic Seamount

“…4b, Supplementary Table S6) independent of sampling depth and location. Specifically, there was no indication that obligate benthic species [36][37][38] (e.g. JTB255) were present among the sheath-water bacteria, whilst the dominant identified taxa (e.g.…”

A Unique Benthic Microbial Community Underlying the Phaeocystis antarctica-Dominated Amundsen Sea Polynya, Antarctica: A Proxy for Assessing the Impact of Global Changes

“…The Anaerolineae were a major member of Chloroflexi at Stn 10, whereas sequences clustered in class SAR202 and TK17 were more abundant at Stns 17, 19, and 83. Members of Bacteroidetes that have been reported as major organic matter decomposers in SO sediment (Carr et al, 2013;Ruff et al, 2014;Learman et al, 2016) were substantially low with relative abundance less than 5% of total 16S rRNA gene sequences in the polynya (Figure 2).…”

“…In fine-grained marine sediment receiving high organic material input, Delta-and Gamma-proteobacteria have been reported as the predominant bacterial groups (Rooney-Varga et al, 1997;Bowman and McCuaig, 2003;Bissett et al, 2006;Liu et al, 2015). Similarly, in most benthic systems of the SO, where organic materials primarily originate from diatom blooms in the water column, proteobacterial groups such as Deltaand Gamma-proteobacteria occupy ecological niches as primary mineralizers of organic materials in the sediments (Bowman and McCuaig, 2003;Baldi et al, 2010;Ruff et al, 2014;Learman et al, 2016). Therefore, our observation of high Planctomycetes abundance, an average of 40% of total sequences (Figure 2) in ASP sediments, is intriguing.…”

“…Because microbial community composition, diversity, and metabolic activity are significantly influenced by environmental change (Bertics and Ziebis, 2009;Nguyen and Landfald, 2015;Sebastián et al, 2018;Kim et al, 2019;Richert et al, 2019), characterization of microbial distribution provides relevant information on spatial and temporal variations in environmental conditions (Fuhrman, 2009;Schauer et al, 2010;Robador et al, 2016). However, little is known about benthic microbial communities in the Southern Ocean (SO), where environmental changes due to global warming are occurring rapidly (Baldi et al, 2010;Ruff et al, 2014;Learman et al, 2016).…”

“…Consequently, as global warming continues, the heat flux intensity of the CDW may stimulate ice melting, which results in changes in phytoplankton productivity and community composition (Deppeler and Davidson, 2017), thereby regulating the function of the ASP in carbon sequestration (Thoma et al, 2008;Lee et al, 2017). The composition and metabolic activities of benthic microbial communities are ultimately determined by the quality and quantity of the organic matter supplied from the overlying water column (Franco et al, 2007;Bienhold et al, 2012;Ruff et al, 2014;Hoffmann et al, 2017). Therefore, given that microbial communities respond quickly to environmental change (Danovaro et al, 2000;Luria et al, 2016), quantitative and qualitative information on benthic microbial communities and their metabolic activities is essential for assessing the response of these ecosystems to climate change-induced variations in primary productivity in the water column of the SO.…”