Organic matter availability drives the spatial variation in the community composition and activity of Antarctic marine bacterioplankton

Abstract

Carbon cycling by Antarctic microbial plankton is poorly understood but it plays a major role in CO 2 sequestration in the Southern Ocean. We investigated the summer bacterioplankton community in the largely understudied Weddell Sea, applying Illumina amplicon sequencing, measurements of bacterial production and chemical analyses of organic matter. The results revealed that the patchy distribution of productive coastal polynyas and less productive, mostly ice-covered sites was the major driver of the spatial changes in the taxonomic composition and activity of bacterioplankton. Gradients in organic matter availability induced by phytoplankton blooms were reflected in the concentrations and composition of dissolved carbohydrates and proteins. Bacterial production at bloom stations was, on average, 2.7 times higher than at less productive sites. Abundant bloom-responsive lineages were predominately affiliated with ubiquitous marine taxa, including Polaribacter, Yoonia-Loktanella, Sulfitobacter, the SAR92 clade, and Ulvibacter, suggesting a widespread genetic potential for adaptation to sub-zero seawater temperatures. A co-occurrence network analysis showed that dominant taxa at stations with low phytoplankton productivity were highly connected, indicating beneficial interactions. Overall, our study demonstrates that heterotrophic bacterial communities along Weddell Sea ice shelves were primarily constrained by the availability of labile organic matter rather than low seawater temperature.

Seasonal dynamics and diversity of Antarctic marine viruses reveal a novel viral seascape

“…The increasing abundances of Flavobacteria bacteriophages coincided with the bacterial bloom, whereas Gammaproteobacteria bacteriophages were most dominant after the bloom (cluster C). Such successional pattern can be explained by the association of Antarctic Flavobacteria with Chl-a uorescence, and their degradation of diverse complex organic compounds 69,70 . They make labile compounds available to other bacteria such as the Gammaproteobacteria and Alphaproteobacteria 69 .…”

Nutritional Status Regulates Bacteria‐Virus Interactions in the Northern South China Sea

“…Moreover, SAR11 is typically dominant in oligotrophic environments (Zhao et al., 2013), as the small size characteristic of Alphaproteobacteria has advantage of acquiring regenerated nutrients for their growth and survival (Liu et al., 2017). However, many members within Bacteroidetes, including Flavobacteriaceae and Saprospiraceae, are often reported to be associated with phytoplankton blooms in other regions (Piontek et al., 2022; Teeling et al., 2012), and have the ability to breakdown high‐molecular‐weight DOC at the low energy cost (Guillemette et al., 2018; Teira et al., 2011). These results corroborated that environmental conditions at S1 differed from other two stations (S2 and S3), with being substrate‐rich at S1 and relatively substrate‐low at S2 and S3.…”

Sea Ice Melting Drives Substantial Change in Dissolved Organic Matter in Surface Water off Prydz Bay, East Antarctic

“…Piontek et al. (2022) investigated bacterioplankton community, bacterial production and dissolved organic matter in Weddell Sea, an Antarctic marginal sea, and found a tight coupling between phytoplankton and bacteria during the phase of rapid ice loss, such that bacterial carbon re‐mineralization increased in response to the increased availability of fresh organic matter in the expanding ice‐free regions. Therefore, the melting of sea‐ice in the Southern Ocean is likely to create a condition with high plankton production, high concentrations of DOM and enrichments of biolabile, protein‐like compounds in surface water.…”

“…Changes in marine DOM would have a significant impact on the global carbon cycle (Romera‐Castillo et al., 2016). In addition, DOM serves many functional roles in marine ecosystems, such as fueling bacterial respiration, protecting plankton from UV damage, and mobilizing pollutants (Hansell, 2002; Nelson & Siegel, 2013; Piontek et al., 2022). Thus, determining the concentration, composition, and reactivity of DOM in seawater is necessary for a holistic understanding of marine biogeochemical cycles and the response of marine ecosystems to rapid climate warming.…”