Abundance and composition of particles and their attached microbiomes along an Atlantic Meridional Transect

Abstract

Particulate organic matter plays a significant role in the marine carbon cycle. Its sinking exports organic carbon from the surface to deep oceans. Using fractionated filtration, we analysed particles of 3 – 10 µm and >10 µm and their microbiomes in thirty-five stations along a latitudinal transect of the Atlantic Ocean and provide new insights into the composition, community dynamics, and catabolic potential of particle-attached bacteria. Samples were taken during an Atlantic Meridional Transect (AMT22), which traversed six distinctive ocean provinces. Using 16S rRNA amplicon sequencing and fluorescence in situ hybridisation, we could show a strong variation between particle-attached and free-living bacterial communities at each station and across the biogeographical provinces – a dynamic likely driven by chlorophyll a concentrations, temperature, and the oxygen content of the respective biogeographical provinces. Whereas the <3 µm fraction was primarily composed of SAR11, SAR86, Prochlorococcus and Bacteroidetes of the NS9 and NS5 clades, particle-attached communities were dominated by other Bacteroidetes (Polaribacter spp.), diverse Gammaproteobacteria including members of the genera Alteromonas and Vibrio, Alphaproteobacteria, Planctomycetes, OM27 and Verrucomicrobia. In three provinces, we quantified particle abundance and analysed their glycan composition using four lectins targeting fucose, galactose, N-acetylgalactosamine and mannose. Particles were mainly composed of fucose glycans with only a minor abundance of the other glycans, and particle abundance was directly correlated with the chlorophyll a concentrations. Functional analysis of 54 metagenome-assembled genomes retrieved from bacterial communities attached to small particles showed that particle-attached Bacteroidetes, Planctomycetes and Verrucomicrobia displayed key roles in the degradation of sulfated fucose-containing polysaccharides. We also identified gene clusters potentially encoding the utilisation of mannan and laminarin, suggesting an adaptation to the glycan composition of the particles, potentially resulting in niche diversification. Together, our results provide insights into particle-attached bacteria and their ecological strategies in the Atlantic.

Marine particle microbiomes during a spring diatom bloom contain active sulfate-reducing bacteria

“…However, bacterial proteins were present in all of the three selected time points, with a notable peak at day 144, and their taxonomic composition was very similar to that observed via 16S rRNA gene amplicon sequencing. Overall, the composition of particle bacterial microbiomes agreed with other reports from similar environments (Reintjes et al 2023, Schultz et al 2020, Heins et al 2021, Crump et al 1999).…”

“…In the photic zone, anaerobic micro-niches have been less widely investigated and the prevalence of sulfate-reducing bacteria is uncertain in the proximity of oxygen-producing living algal cells. Aggregates composed of living algae are rather known for a diverse microbiome of aerobic, heterotrophic bacteria that degrade complex algal organic matter, such as polysacchariderich exudates (Enke et al 2019, Reintjes et al 2023, although anaerobic metabolism such as diazotrophy is also known to occur (Riemann et al 2022). Within this microbiome, bacteria are selected by factors such as host physiology and genotype (Ahern et al 2021), the surrounding environment (Barreto Filho et al 2021) and via stochastic processes (Stock et al 2022).…”

“…Despite their importance in carbon sequestration (e.g., Bligh et al 2022), vertical connectivity (Mestre et al 2018), and their documented complexity (e.g. Reintjes et al 2023), particle-associated (PA) bacterial communities are less well understood than their free-living counterparts. In fact, they are often overlooked due to the sometimes fragile nature of particles, in combination with the practice of pre-filtration to exclude larger organisms prior to molecular analyses (e.g.…”

Microbial remineralization processes during post-spring-bloom excess phosphate in the northern Baltic Sea

“…Of these, Sporichthyaceae (Actinobacteria) has been associated with a free-living lifestyle (Bashenkhaeva et al 2020). By contrast, Cryomorphaceae (Bacteroidia) and Mycobacterium (Actinobacteria) have been associated with a particle-attached lifestyle (Delmont et al 2014, Reintjes et al 2023, Allgaier et al 2007), and from these, contribution of Mycobacterium to the community-wide predicted LAPase activity was observed only at the end of the experiment.…”

Marine particle microbiomes during a spring diatom bloom contain active sulfate-reducing bacteria

“…Bligh et al 2022 ), vertical connectivity (Mestre et al 2018 ), and their documented complexity (e.g. Reintjes et al 2023 ), particle-associated (PA) bacterial communities are less well understood than their free-living counterparts. In fact, they are often overlooked due to the sometimes fragile nature of particles, in combination with the practice of pre-filtration to exclude larger organisms prior to molecular analyses (e.g.…”