Organic matter degradation in marine environments is essential for the recycling of nutrients, especially under conditions of anoxia where organic matter tends to accumulate. However, little is known about the diversity of the microbial communities responsible for the mineralization of organic matter in the absence of oxygen, as well as the factors controlling their activities. Here, we determined the active heterotrophic prokaryotic community in the sulphidic water column of the Black Sea, an ideal model system, where a tight coupling between carbon, nitrogen and sulphur cycles is expected. Active microorganisms degrading both dissolved organic matter (DOM) and protein extracts were determined using quantitative DNA stable isotope probing incubation experiments. These results were compared with the metabolic potential of metagenome-assembled genomes obtained from the water column. Organic matter incubations showed that groups like Cloacimonetes and Marinimicrobia are generalists degrading DOM. Based on metagenomic profiles the degradation proceeds in a potential interaction with members of the Deltaproteobacteria and Chloroflexi Dehalococcoidia. On the other hand, microbes with small genomes like the bacterial phyla Parcubacteria, Omnitrophica and of the archaeal phylum Woesearchaeota, were the most active, especially in protein-amended incubations, revealing the potential advantage of streamlined microorganisms in highly reduced conditions.

Microorganisms attached to particles have been shown to be different from free-living microbes and to display diverse metabolic activities. However, little is known about the ecotypes associated with particles and their substrate preference in anoxic marine waters. Here, we investigate the microbial community colonizing particles in the anoxic and sulfide-rich waters of the Black Sea. We incubated beads coated with different substrates in situ at 1000 and 2000 m depth. After 6 h, the particleattached microbes were dominated by Gamma-and Alpha-proteobacteria, and groups related to the phyla Latescibacteria, Bacteroidetes, Planctomycetes and Firmicutes, with substantial variation across the bead types, indicating that the attaching communities were selected by the substrate. Further laboratory incubations for 7 days suggested the presence of a community of highly specialized taxa. After incubation for 35 days, the microbial composition across all beads and depths was similar and primarily composed of putative sulfur cycling microbes. In addition to the major shared microbial groups, subdominant taxa on chitin and proteincoated beads were detected pointing to specialized microbial degraders. These results highlight the role of particles as sites for attachment and biofilm formation, while the composition of organic matter defined a secondary part of the microbial community.

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Large quantities of carbon are stored in marine dissolved organic matter (DOM), and its recycling has a major effect on the carbon cycle. Microbes are responsible for turnover of DOM. Little is known about how the complex pool of DOM shapes microbial communities and vice versa, especially in anoxic systems. In this study, we characterized the DOM pool with high-resolution Fourier transform ion cyclotron resonance mass spectrometry and analyzed the microbial community composition with 16S rRNA gene amplicon sequencing across a redox gradient in the Black Sea. The chemical stratification of the water column was clearly reflected in the microbial community, with different putative autotrophic taxa abundant across redox zones. The nitrate maximum was characterized by a high abundance of Thaumarchaeota, the suboxic zone by Gammaproteobacteria Chromatiales, while Epsilonbacteraeota Campylobacterales were abundant at the onset of the sulfidic zone. Compared to the variance in the microbial community, the molecular composition of DOM was relatively uniform across the sampled depths. However, underlying differences in the oxidation state of the DOM molecular formulas showed distinct changes that were linked to the redox zones, possibly connecting autotrophic metabolisms to changes in the DOM composition. In addition, known heterotrophs like Planctomycetes Phycisphaerae and Chloroflexi Anaerolineales were linked to more oxidized molecular forms of DOM, and not to the identified redox zones, suggesting that these fermentative organisms are reliant on newly formed carbon molecules. Our study suggests that the metabolism of autotrophic microbes influences the composition of DOM across the Black Sea water column.

Carbon cycling in anoxic marine sediments is dependent on uncultured microbial communities. Niches of heterotrophic microorganisms are defined by organic matter (OM) type and the different phases in OM degradation. We investigated how OM type defines microbial communities originating from organic-rich, anoxic sediments from the Baltic Sea. We compared changes in the sediment microbial community, after incubation with different stable isotope labeled OM types [i.e., particulate algal organic matter (PAOM), protein, and acetate], by using DNA stable isotope probing (DNA-SIP). Incorporation of 13C and/or 15N label was predominantly detected in members of the phyla Planctomycetes and Chloroflexi, which also formed the majority (>50%) of the original sediment community. While these phylum-level lineages incorporated label from all OM types, phylogenetic analyses revealed a niche separation at the order level. Members of the MSBL9 (Planctomycetes), the Anaerolineales (Chloroflexi), and the class Bathyarchaeota, were identified as initial degraders of carbohydrate-rich OM, while other uncultured orders, like the CCM11a and Phycisphaerales (Planctomycetes), Dehalococcoidia, and JG30-KF-CM66 (Chloroflexi), incorporated label also from protein and acetate. Our study highlights the importance of initial fermentation of complex carbon pools in shaping anoxic sediment microbial communities and reveals niche specialization at the order level for the most important initial degraders in anoxic sediments.

DNA sequencing efforts of environmental and other biological samples disclose unprecedented and largely untapped opportunities for advances in the taxonomy, ecology, and geographical distributions of our living world. To realise this potential, DNA-derived occurrence data (notably sequences with dates and coordinates) – much like traditional specimens and observations – need to be discoverable and interpretable through biodiversity data platforms. The Global Biodiversity Information Facility (GBIF) recently headed a community effort to assemble a set of guidelines for publishing DNA-derived data. These guidelines target the principles and approaches of exposing DNA-derived occurrence data in the context of broader biodiversity data. They cover a choice of terms using a controlled vocabulary, common pitfalls, and good practices, without going into platform-specific details. Our hope is that they will benefit anyone interested in better exposure of DNA-derived occurrence data through general biodiversity data platforms, including national biodiversity portals. This paper provides a brief rationale and an overview of the guidelines, an up-to-date version of which is maintained at https://doi.org/10.35035/doc-vf1a-nr22. User feedback and interaction are encouraged as new techniques and best practices emerge.

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Calls for science to innovate by including stakeholders' in the creation of marine knowledge have been rising, to create impact beyond laboratories and to contribute to the empowerment of local communities when interacting with marine and coastal ecosystems. As a transdisciplinary group of scientists working on co-designing research projects, this paper draws upon our experiences to further define the concept and seek to improve the process of co-design. We highlight the key barriers for co-design processes to contribute to increasing stakeholders' capacity to produce intended effects on marine policy. We suggest that stakeholder engagement requires overcoming the resistance to non-scientific knowledge sources and considering power asymmetries in the governance and management of the ocean. We argue that power and politics must be placed at the very heart of the production of a co-designed marine science and must be an aspect of the facilitation itself. In this paper, we aim to provide insights to navigate throughout the journey of stakeholder engagement, with the critical perspective necessary to make this process socially and environmentally effective.