Nitrification is important in nitrogen (N) cycling of aquatic environments, but knowledge about its regulation and importance is sparse. Here we examined nitrification and ammonia oxidizers in the Baltic Sea. We investigated two sites with different catchment characteristics (agricultural and forest), the Bay of Gdánsk (south) and the Öre Estuary (north), and measured pelagic nitrification rates and abundance, composition and expression of ammonia monooxygenase (amoA) genes. Highest nitrification rates were found in the nutrient rich Bay of Gdańsk. Interestingly, abundances of ammonia-oxidizing archaea (AOA) and bacteria (AOB) were orders of magnitude lower than reported from other sites. Although AOA were most abundant at both sites, the highest expression levels were from AOB. Interestingly, few AOA and AOB taxa dominated amoA gene expression, with a Nitrosomarinus related phylotype showing widespread expression. AOA and AOB communities differed between sites and depths, respectively, with the composition in rivers being distinct. A storm event, causing an even depth distribution of nitrification and particles in the Bay of Gdańsk, indicated that the presence of particles stimulate nitrification. The study highlights coastal regions as dynamic sites of extensive pelagic nitrification, which may affect local food web dynamics and loss of N mediated by denitrification.

Bacteria are major drivers of biogeochemical nutrient cycles and energy fluxes in marine environments, yet how bacterial communities respond to environmental change is not well known. Metagenomes allow examination of genetic responses of the entire microbial community to environmental change. However, it is challenging to link metagenomes directly to biogeochemical process rates. Here, we investigate metagenomic responses in natural bacterioplankton communities to simulated environmental stressors in the Baltic Sea, including increased river water input, increased nutrient concentration, and reduced oxygen level. This allowed us to identify informative prokaryotic gene markers, responding to environmental perturbation. Our results demonstrate that metagenomic and metabolic changes in bacterial communities in response to environmental stressors are influenced both by the initial community composition and by the biogeochemical factors shaping the functional response. Furthermore, the different sources of dissolved organic matter (DOM) had the largest impact on metagenomic blueprint. Most prominently, changes in DOM loads influenced specific transporter types reflecting the substrate availability and DOC assimilation and consumption pathways. The results provide new knowledge for developing models of ecosystem structure and biogeochemical cycling in future climate change scenarios and advance our exploration of the potential use of marine microorganisms as markers for environmental conditions.

Freshwater woloszynskioid dinoflagellates were collected independently in Scotland and Portugal and found to belong to a previously unknown species of the genus Borghiella, here described as B. andersenii. The new species differs in morphology and nuclear-encoded LSU rDNA and ITS sequences from B. dodgei and B. tenuissima, the two species presently comprising the genus Borghiella. Unusual features of the new species were observed particularly during asexual reproduction, which took place in the motile stage -as in many other dinoflagellates -or in a so-called division cyst, recalling cell division in the family Tovelliaceae. Such diversity in cell division is rarely reported in dinoflagellates. Morphologically Borghiella andersenii differs from B. tenuissima in being only slightly compressed dorsoventrally whereas the latter species is flat. The slight compression is also visible in lateral view. Borghiella andersenii and B. dodgei are more challenging to discriminate but the apical structure complex is only half the length in B. andersenii compared with B. dodgei (3-4 vs 6 µm). This difference can only be accounted for in the scanning electron microscope. At the light microscopy level the epicone in B. andersenii is rounded whereas it is conical in B. dodgei. Sexual reproduction in Borghiella andersenii was homothallic by formation of planozygotes, followed by apparent resting cysts. Phylogenetic studies on woloszynskioids have recently shown that they comprise a polyphyletic assemblage, which has been divided into the three families Borghiellaceae, Tovelliaceae and Suessiaceae. New species of the three families are now being found rapidly in many parts of the world, proving that the techniques required to investigate these small, morphologically similar dinoflagellates are now in place and proving that such 'gymnodinioids' or 'woloszynskioids' comprise an often overlooked biological entity in both marine and freshwater biotopes. Based on LSU rDNA, B. andersenii is most closely related to B. tenuissima.

Heterotrophic bacteria are important drivers of nitrogen (N) cycling and the processing of dissolved organic matter (DOM). Projected increases in precipitation will potentially cause increased loads of riverine DOM to the Baltic Sea and likely affect the composition and function of bacterioplankton communities. To investigate this, the effects of riverine DOM from two different catchment areas (agricultural and forest) on natural bacterioplankton assemblages from two contrasting sites in the Baltic Sea were examined. Two microcosm experiments were carried out, where the community composition (16S rRNA gene sequencing), the composition of a suite of N-cycling genes (metagenomics) and the abundance and transcription of ammonia monooxygenase (amoA) genes involved in nitrification (quantitative PCR) were investigated. The river water treatments evoked a significant response in bacterial growth, but the effects on overall community composition and the representation of N-cycling genes were limited. Instead, treatment effects were reflected in the prevalence of specific taxonomic families, specific N-related functions and in the transcription of amoA genes. The study suggests that bacterioplankton responses to changes in the DOM pool are constrained to part of the bacterial community, whereas most taxa remain relatively unaffected.

Die Pandemie der vergangenen Monate brachte eine Verknappung an Möglichkeiten in allen Lebensbereichen. Im schulischen Kontext mussten neue Wege der Kommunikation und des Austausches beschritten werden. Wie sehr entstand dadurch Beziehungsverlust bei einzelnen Schulpartner*innen und wodurch war dieser Verlust gekennzeichnet? Dieser Beitrag ist die Reflexion einer Schulleiterin über Beziehungen, Beziehungsveränderungen und Beziehungsverlust zur Zeit der Corona-Pandemie.