Overlooked Diversity of Ultramicrobacterial Minorities at the Air-Sea Interface

Members of the Candidate phylum Patescibacteria, also called Candidate Phyla Radiation (CPR), are described as ultramicrobacteria with limited metabolic capacities. Wide diversity and relative abundances up to 80% in anaerobic habitats, e.g., in groundwater or sediments are characteristic for Candidatus Patescibacteria. However, only few studies exist for marine surface water. Here, we report the presence of 40 patescibacterial candidate clades at air-sea interfaces, including the upper water layer, floating foams and the sea-surface microlayer (SML), a < 1 mm layer at the boundary between ocean and atmosphere. Particle-associated (>3 μm) and free-living (3–0.2 μm) samples were obtained from the Jade Bay, North Sea, and 16S rRNA (gene) amplicons were analyzed. Although the abundance of Cand. Patescibacteria representatives were relatively low (<1.3%), members of Cand. Kaiserbacteria and Cand. Gracilibacteria were found in all samples. This suggests profound aerotolerant capacities of these phylogenetic lineages at the air-sea interface. The presence of ultramicrobacteria in the >3 μm fraction implies adhesion to bigger aggregates, potentially in anoxic niches, and a symbiotic lifestyle. Due to their small sizes, Cand. Patescibacteria likely become aerosolized to the atmosphere and dispersed to land with possible implications for affecting microbial communities and associated processes in these ecosystems.J.R.: C.S., O.W. and this study were funded by the European Research Council project PASSME, grant number GA336408. The picture of seafoam was taken during a campaign funded by the Assemble Plus project MIDSEAS (European Union’s Horizon 2020 research and innovation program, Grant Agreement No. 730984). D.P.R.H. was supported by the European Regional Development Fund/Estonian Research Council funded by “Mobilitas Plus Top Researcher grant MOBTT24”. A.J.P. received funding by the Ministerium für Kultur und Wissenschaft des Landes Nordrhein-Westfalen (“Nachwuchsgruppe Alexander Probst”). The APC was funded by the Open Access Publication Fund of the University of Duisburg-Essen.J.R.: C.S., O.W. and this study were funded by the European Research Council project PASSME, grant number GA336408. The picture of seafoam was taken during a campaign funded by the Assemble Plus project MIDSEAS (European Union’s Horizon 2020 research and innovation program, Grant Agreement No. 730984). D.P.R.H. was supported by the European Regional Development Fund/Estonian Research Council funded by “Mobilitas Plus Top Researcher grant MOBTT24”. A.J.P. received funding by the Ministerium für Kultur und Wissenschaft des Landes Nordrhein-Westfalen (“Nachwuchsgruppe Alexander Probst”). The APC was funded by the Open Access Publication Fund of the University of Duisburg-Essen

Effect of large magnetotactic bacteria with polyphosphate inclusions on the phosphate profile of the suboxic zone in the Black Sea

The Black Sea is the world’s largest anoxic basin and a model system for studying processes across redox gradients. In between the oxic surface and the deeper sulfidic waters there is an unusually broad layer of 10–40 m, where neither oxygen nor sulfide are detectable. In this suboxic zone, dissolved phosphate profiles display a pronounced minimum at the upper and a maximum at the lower boundary, with a peak of particulate phosphorus in between, which was suggested to be caused by the sorption of phosphate on sinking particles of metal oxides. Here we show that bacterial polyphosphate inclusions within large magnetotactic bacteria related to the genus Magnetococcus contribute substantially to the observed phosphorus peak, as they contain 26–34% phosphorus compared to only 1–5% in metal-rich particles. Furthermore, we found increased gene expression for polyphosphate kinases by several groups of bacteria including Magnetococcaceae at the phosphate maximum, indicating active bacterial polyphosphate degradation. We propose that large magnetotactic bacteria shuttle up and down within the suboxic zone, scavenging phosphate at the upper and releasing it at the lower boundary. In contrast to a passive transport via metal oxides, this bacterial transport can quantitatively explain the observed phosphate profiles.We are grateful for the competent technical assistance of Ronny Baaske, Christian Burmeister, Christin Laudan and Christian Meeske. We are greatly indebted to Cindy Lee and Bo Barker Jørgensen for providing extremely helpful comments on an earlier version of the manuscript. Horst D. Schulz and René Friedland are acknowledged for stimulating discussions on the modeling approach. We thank the captain and the crew of the R/V “Maria S. Merian” for the excellent support on board and the DFG (MSM33) and BMBF (01DK12043) for financing the cruise. The particle analysis was funded by the BMBF (03F0663A). S.B. was funded by a BONUS BLUEPRINT project (03F0679A awarded to KJ; http://blueprint- project.org), supported by BONUS (Art 185), funded jointly by the EU and the German Federal Ministry of Education and Research (BMBF). T. S. was funded by the German research foundation (DFG) (awarded to K.J., JU 367/16-1). Metagenome sequencing was done at the Swedish National Genomics Infrastructure (NGI) at SciLifeLab (Sweden).We are grateful for the competent technical assistance of Ronny Baaske, Christian Burmeister, Christin Laudan and Christian Meeske. We are greatly indebted to Cindy Lee and Bo Barker Jørgensen for providing extremely helpful comments on an earlier version of the manuscript. Horst D. Schulz and René Friedland are acknowledged for stimulating discussions on the modeling approach. We thank the captain and the crew of the R/V “Maria S. Merian” for the excellent support on board and the DFG (MSM33) and BMBF (01DK12043) for financing the cruise. The particle analysis was funded by the BMBF (03F0663A). S.B. was funded by a BONUS BLUEPRINT project (03F0679A awarded to KJ; http://blueprint- project.org), supported by BONUS (Art 185), funded jointly by the EU and the German Federal Ministry of Education and Research (BMBF). T. S. was funded by the German research foundation (DFG) (awarded to K.J., JU 367/16-1). Metagenome sequencing was done at the Swedish National Genomics Infrastructure (NGI) at SciLifeLab (Sweden)

Sea foams are ephemeral hotspots for distinctive bacterial communities contrasting sea-surface microlayer and underlying surface water

The occurrence of foams at oceans’ surfaces is patchy and generally short-lived, but a detailed understanding of bacterial communities inhabiting sea foams is lacking. Here, we investigated how marine foams differ from the sea-surface microlayer (SML), a <1-mm-thick layer at the air–sea interface, and underlying water from 1 m depth. Samples of sea foams, SML and underlying water collected from the North Sea and Timor Sea indicated that foams were often characterized by a high abundance of small eukaryotic phototrophic and prokaryotic cells as well as a high concentration of surface-active substances (SAS). Amplicon sequencing of 16S rRNA (gene) revealed distinctive foam bacterial communities compared with SML and underlying water, with high abundance of Gammaproteobacteria. Typical SML dwellers such as Pseudoalteromonas and Vibrio were highly abundant, active foam inhabitants and thus might enhance foam formation and stability by producing SAS. Despite a clear difference in the overall bacterial community composition between foam and SML, the presence of SML bacteria in foams supports the previous assumption that foam is strongly influenced by the SML. We conclude that active and abundant bacteria from interfacial habitats potentially contribute to foam formation and stability, carbon cycling and air–sea exchange processes in the ocean.This work was supported by the European Research Council (ERC) project ”Parameterization of the Sea-Surface Microlayer Effect” (PASSME, grant number GA336408), and the Leibniz Association project ”Marine biogenic production, organic aerosols and maritime clouds: a process chain” (MarParCloud, grant number SAW-2016-TROPOS-2). DPRH was supported by the European Regional Development Fund/Estonian Research Council-funded Mobilitas Pluss Top Researcher (grant numbers MOBTT24 and P200028PKKH).This work was supported by the European Research Council (ERC) project ”Parameterization of the Sea-Surface Microlayer Effect” (PASSME, grant number GA336408), and the Leibniz Association project ”Marine biogenic production, organic aerosols and maritime clouds: a process chain” (MarParCloud, grant number SAW-2016-TROPOS-2). DPRH was supported by the European Regional Development Fund/Estonian Research Council-funded Mobilitas Pluss Top Researcher (grant numbers MOBTT24 and P200028PKKH)