Marine Molecular Microbiology

Nitrogen fixation in a changing Arctic ocean: an overlooked source of nitrogen?

Financed by: Independent Research Fund Denmark, 2023-2025

PI: Lasse Riemann; Collaborators: Colin Stedmon (DTUaqua) and Takuhei Shiozaki (Univ. Tokyo, Japan)

Budget: 386,600 Euro

Brief Summary: Since primary production in the Arctic Ocean (AO) is limited by nitrogen (N) availability, knowledge about sources and sinks of N is of critical importance. Surprisingly, a few recent studies have presented sporadic data suggesting N2 fixation in the AO. This import of bioavailable N could be of fundamental importance for N and carbon biogeochemistry in the AO, but data are scarce. This cross-disciplinary and international project aims to quantify pelagic N2 fixation in the AO – a biological process hitherto unaccounted for. In situ measurements, experiments, and use of cutting-edge methodology will provide unprecedented data on fixation rates, identity of the active organisms, and insights into controlling factors in a cross-Arctic Ocean survey. This information is essential for prediction of primary production in the future AO, particularly in the face of climate change.

Future stimulated nitrogen fixation: threatening the health of coastal ecosystems?

Financed by: Independent Research Fund Denmark, 2021-2024

PI: Lasse Riemann; Co-PI: Caroline Löscher (SDU) and Stiig Markager (AU)

Budget: 829,419 Euro

Brief Summary: Nitrogen (N) is often the limiting factor for plankton productivity in coastal waters. N₂ fixation is a globally important process in marine waters, and sporadic data document such fixation from Danish waters. Nevertheless, despite eutrophication may be critically impacted by N supply via N₂ fixation, data on the extent, regulation, and importance of this process does not exist for Danish waters. This is a prerequisite for an efficient and sustainable environmental management – in particular, because climate change is predicted to increase the future magnitude and relative importance of N₂ fixation in our waters. In the proposed project, field and experimental work will systematically quantify N₂ fixation in Danish waters and sediments, identify the organisms responsible, and determine the factors regulating the process. These data will feed a model on pools, sources, sinks and fluxes of N providing vital information for future Danish environmental management of coastal marine waters.

Pathogenic Vibrio bacteria in the current and future Baltic Sea waters: mitigating the problem (BaltVib)

Financed by: The Danish Council for Independent Research under the EU COFUND call "Biodiversity and Climate change", 2021-2023

Co-PI: Lasse Riemann (Coordinator: Prof. Matthias Labrenz, IOW, Germany)

UCPH budget: 301,277 Euro

Brief Summary: Vibrio – microbes that are part of the natural bacterioplankton in temperate marine waters – have in recent years flourished in the Baltic Sea, probably stimulated by elevated surface water temperatures. Several Vibrio species are human pathogens. It is hence of great concern that Vibrio-related wound infections and fatalities have increased dramatically along the Baltic coasts. Future climate change is predicted to escalate this problem, posing a significant threat to human health and the Baltic tourism industry. However, the projections do not yet take into account the influence of ‘ecosystem engineers’ such as mussels and macrophytes on Vibrio diversity and abundance. Recent data indicate that in some of the ‘ecosystem engineers’ habitats the abundance of pathogenic Vibrio spp. is reduced. This opens up the option for nature-based solution (NbS) strategies to control pathogenic vibrios in the nearshore habitat where humans interact with the sea. However, climate change will also affect the structure and functioning of the ecosystem engineers, with as yet unknown consequences for the Vibrio populations in the Baltic Sea. BaltVib aims to delineate the current and future Vibrio status, determine biotic and abiotic key factors regulating Vibrio prevalence, and identify NbSs to mitigate the problem. This will be accomplished through interdisciplinary integration of marine, microbiological, molecular and socioecological expertise carried by partners from seven Baltic nations.

Vitamin B1 limitation of bacterioplankton in coastal temperate waters

Financed by: Independent Research Fund Denmark, 2019 - 2023

PI: Lasse Riemann; Co-PIs: Ryan Paerl, Anders Andersson

Total budget: 385,000 EURO 

Brief summary: Vitamin B1 is a required nutrient for virtually all cells, yet is produced by only a small subset. In recent breakthrough work, we showed that B1/precursor bioavailability periodically limits bulk growth of bacterioplankton in the Baltic Sea. Moreover, via metagenomics analyses, we show that B1-auxotrophy is widespread amongst wild bacterioplankton around the globe. In the proposed project, field and experimental work in estuaries on both sides of the Atlantic Ocean, and cultivation work, will be integrated to test the hypothesis that: “Vitamin B1 is a hitherto overlooked factor that significantly influences bacterioplankton growth and community dynamics in coastal temperate waters”. This would constitute a paradigm shift with implications for our perception of microbial nutrient cycling, but also with ramifications for productivity of higher trophic levels, and ultimately for our understanding and management of temperate estuaries as resources and recipients.