Sinking biogenic particles mediate the large-scale export of photosynthetically fixed C from the surface to the deep ocean, in what is known as the marine biological carbon pump. These particles constitute resource-rich microenvironments that get heavily colonized by microbes, which play a key role in particle degradation, ultimately affecting the efficiency of carbon sequestration. Moreover, particles have been found to be hotspots for other biogeochemical processes, e.g., related to the sulfur and nitrogen cycles. Thus, the colonizing microbiome not only modifies the architecture and fate of marine particles but may also play a major role in ocean biogeochemistry. A broad-scale picture of the particle microbiome has emerged in recent years, showing that particle-associated communities are taxonomically and functionally divergent from the free-living ones, but many unknowns still remain. This session welcomes presentations on all aspects concerning the particle microbiome, including their role in the formation and fate of ocean particles, their taxonomic and functional diversity, the cellular and molecular microbial mechanisms involved in particle colonization (e.g. chemotaxis, biofilm formation, cell-to-cell signaling), patterns of particle community assembly and microbial interactions within particles, among others. The session will also provide a platform to share new insights into the biogeography, ecology, and biogeochemistry of particle-associated communities, and their potential interactions with the free-living realm.
Lead Organizer: Marta Sebastian, Institut de Ciencies del Mar (msebastian@icm.csic.es)
Co-organizers:
Laura Alonso-Sáez, AZTI (laura@azti.es)
Otto X. Cordero, Massachusetts Institute of Technology (ottox@mit.edu)
Viena Puigcorbe, Institut de Ciencies del Mar (vienap@icm.csic.es)
Presentations
06:30 PM
Mesoscale eddies impact the structure and distribution of particle-attached non-cyanobacterial diazotrophs in the subtropical Northeast Atlantic (4831)
Primary Presenter: Elena Cerdán, Aix-Marseille Université / Mediterranean Institute of Oceanography (elena.cerdan@mio.osupytheas.fr)
The biological dinitrogen (N<sub>2</sub>) fixation process converts atmospheric N2 into biologically available ammonia. In the ocean, it is carried out by a group of microorganisms termed diazotrophs, mainly attributed to cyanobacteria such as <em>Trichodesmium</em>. However, recent studies revealed the wide distribution of non-cyanobacterial diazotrophs (NCDs), which contrary to cyanobacteria, cannot photosynthesise and depend on organic matter to meet their nutritional requirements. While their taxonomy and ecology are yet to be explored, it is thought these groups live associated with organic sinking particles, populated particulate marine-aggregates playing a crucial role in sinking organic matter in deep waters and carbon sequestration. In the context of the relevance that ocean mesoscale structures play in regulating N<sub>2</sub> fixation and sinking particle fluxes, the diversity and relative abundance of the particle-attached NCD community was investigated across an anticyclonic eddy in the Canary Eddy Corridor. Community differences were observed between the core and periphery of the eddy. Such groups were impacted by water mass flows and its unique physicochemical properties, highlighting the importance of an anticyclonic eddy, as an example of a recurrent mechanism of matter transport between surface and deep ocean. The results highlight the key role of NCDs in mesoscale dynamics when determining particle transport, providing new understanding on the functioning of both carbon and nitrogen cycles, as well as on interactions between particle-associated organisms and ocean mesoscale structures.
06:30 PM
Heterotrophic Cultured Bacteria Represent a Substantial Diversity of the Deep Ocean and Particle Microbiome (5353)
Primary Presenter: Silvia Acinas, ICM-CSIC (sacinas@icm.csic.es)
It is well known that only a small fraction of the marine microbial diversity, which mainly belong to the so-called rare biosphere, can be retrieved by isolation. However, this paradigm has not been fully tested at a broad scale, especially in the deep ocean and in the ocean particle microbiome. Here, we compared 16S rRNA gene sequences from a large collection (>2000) of cultured heterotrophic marine bacteria with global 16S rRNA metabarcoding (16S Tags) datasets covering surface, mesopelagic and bathypelagic ocean samples that included 16 of the 22 samples used for isolation. These global datasets represent 60.322 unique 16S amplicon sequence variants (ASVs). Our results reveal a significantly higher proportion of isolates identical to ASVs in deeper ocean layers, which included the isolation of 3 of the top 10 most abundant 16S ASVs in the global bathypelagic ocean, related to the genera Sulfitobacter, Halomonas and Erythrobacter. These isolates contributed differently to the prokaryotic communities across different plankton size fractions, recruiting between 38% in the free-living fraction (0.2 -0.8 μm) and up to 45% in the largest particles (20-200 μm) in the bathypelagic ocean. Our findings support the hypothesis that sinking particles in the bathypelagic act as resource-rich habitats, suitable for the growth of heterotrophic bacteria with a copiotroph lifestyle that can be cultured, and that these cultivable bacteria can also thrive as free-living bacteria.
06:30 PM
Network analysis of particle-associated microbiome revealed potential key taxa driving carbon export during a subarctic spring phytoplankton bloom (5568)
Primary Presenter: Akiko EBIHARA, Atmosphere and Ocean Research Institute, The University of Tokyo (ebihara-a@aori.u-tokyo.ac.jp)
To help identify key microbial taxa driving carbon export during a spring phytoplankton bloom in the subarctic ocean, we examined prokaryotic and eukaryotic microbiome of sinking and suspended particles collected at initial (March) and later (May) bloom stages. The weighted gene correlation network analysis (WGCNA) detected four microbial subnetworks preferentially associated with the sinking particles. Distinct distribution patterns of these subnetworks across water layers (chlorophyll maximum, pycnocline, mesopelagic, and bottom boundary) and months suggest that they occupied different niches. The partial least square (PLS) regression result indicated that one subnetwork (MiB) was a significant predictor of the sinking particulate organic carbon flux in the upper layers (r2 = 0.41, p = 0.0041). Among the MiB members, the prokaryotic key taxa responsible for the PLS regression model, assessed using the variable importance in projection score, consisted of polymer degraders such as Bacteroidota (Saprospiraceae, Flavobacteriaceae) and Gammaproteobacteria (Halieaceae). The corresponding eukaryotic taxa consisted of not only a bloom forming taxon (Bacillariophyta) but also pseudofungi (Oomycetes) and fungi (Chytridiomycetes). Our results revealed the key microbial taxa potentially involved in the regulation of biological carbon pump during phytoplankton bloom.
06:30 PM
Impact of particle flux on the vertical distribution and diversity of size-fractionated prokaryotic communities in two East Antarctic polynyas (6671)
Primary Presenter: Viena Puigcorbé, Institut de Ciències del Mar (viena.puigcorbe@outlook.com)
Antarctic polynyas are highly productive open water areas surrounded by ice where extensive phytoplankton blooms occur, but little is known about how these surface blooms influence carbon fluxes and prokaryotic communities from deeper waters. By sequencing the 16S rRNA gene, we explored the vertical connectivity of the prokaryotic assemblages associated with particles of three different sizes in two polynyas with different surface productivity, and we linked it to the magnitude of the particle export fluxes measured using 234Th as particle tracer. Between the sunlit and the mesopelagic layers (700 m depth), we observed compositional changes in the prokaryotic communities associated with the three size-fractions, which were mostly dominated by Flavobacteriia, Alphaproteobacteria, and Gammaproteobacteria. Interestingly, the vertical differences between bacterial communities attached to the largest particles decreased with increasing 234Th export fluxes, indicating a more intense downward transport of surface prokaryotes in the most productive polynya. This was accompanied by a higher proportion of surface prokaryotic taxa detected in deep particle-attached microbial communities in the station with the highest 234Th export flux. Our results support recent studies evidencing links between surface productivity and deep prokaryotic communities and provide the first evidence of sinking particles acting as vectors of microbial diversity to depth in Antarctic polynyas, highlighting the direct influence of particle export in shaping the prokaryotic communities of mesopelagic waters.
06:30 PM
Eddy Events Trigger Diatom Export in the Sargasso Sea (7280)
Primary Presenter: Marc Fontánez Ortiz, Arizona State University (mafonta1@asu.edu)
Sinking particles are important conduits of organic carbon from the euphotic zone to the deep ocean and microhabitats for diverse microbial communities, but little is known about what determines their origin and community composition. To assess the connections of the microbial communities between the euphotic zone and sinking particles, we carried out indicator and differential abundance analyses of prokaryotes and photoautotrophs using 16S rDNA. Samples were collected in the Sargasso Sea during the spring and summer of 2012 within mesoscale eddies (10–100 km), features that can affect the vertical and temporal composition of pelagic and particle-attached microbes. We found that γ-proteobacteria such as Pseudoalteromonas sp. and Vibrio sp., common particle-associated bacteria often linked with zooplankton, dominated the sequence libraries of the sinking particles. The analysis also revealed that members of Flavobacteria, particularly the fish pathogen Tenacibaculum sp., were indicators taxa of sinking particles. Interestingly, we also found that the large centric diatom, Rhizosolenia sp., generally rare in the oligotrophic Sargasso Sea, dominated photoautotrophic communities of sinking particles collected in the center of an anticyclonic eddy with unusual upwelling due to eddy-wind interactions. We hypothesize that the steady contribution by picophytoplankton to particle flux is punctuated by pulses of production and flux of larger-sized phytoplankton in response to episodic eddy upwelling events and can lead to higher export of particulate organic matter during the summer.
SS096P Exploring the Ocean Particle Microbiome
Description
Time: 6:30 PM
Date: 8/6/2023
Room: Mezzanine