Marine Molecular Microbiology

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.

Nitrogen fixation and ecology of heterotrophic bacteria in coastal temperate waters

Financed by: The Danish Council for Independent Research, 2017-2022

PI: Lasse Riemann

Total budget: 854,000 Euro

Brief Summary: The import of nitrogen (N) through biological N₂ fixation is essential for life in vast areas of the global ocean. The prevailing belief is that cyanobacteria using light are the only relevant N₂ fixing organisms and that N₂ fixation in coastal temperate waters is negligible. It has, however, now become evident that heterotrophic N₂ fixing bacteria with a fundamentally different ecology are widespread and active in marine waters, and that they can do high N₂ fixation in coastal waters. This cross-disciplinary project using cultivation, field and modeling approaches aims to establish knowledge on the ecology of heterotrophic N₂ fixing bacteria, quantify rates and factors controlling their N₂ fixation, and integrate these data into N budgets of coastal temperate waters. A significant N input from this novel group of N₂ fixers will establish a new paradigm in N₂ fixation research, and have broad implications for our understanding of the N and carbon cycling in coastal temperate waters.

Vitamin B1 limitation of bacterioplankton in coastal temperate waters

Financed by: Independent Research Fund Denmark, 2019 - 2022

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.

Previous PhD students (Riemann main supervisor)

• Søren Hallstrøm. “Nitrogen fixation in marine waters: Importance of environmental gradients”. PhD degree 01.2021. Email
• Elisabeth Münster Happel, "The effects of riverine DOM on microbial composition and function". PhD degree 24 August 2018. Email
• Daniel Jiro Ayala, "The early life of the European eel in the ichthyoplankton community of the Sargasso Sea". Main supervisor: Peter Munk. Co-supervisor: Lasse Riemann. PhD degree 27 October 2016.  Email
• Sachia Jo Traving, "Traits for bacterial carbon turnover in the marine environment: chemical complexity meets bacteria diversity". PhD degree 24 June 2016. Email
• Mikkel Bentzon-Tilia, "The Biology of heterotrophic nitrogen fixing bacteria in marine and estuarine waters". PhD degree 25. April 2014. Email
• Julie Dinasquet, "Top-down and bottom-up control of bacterial activity and community structure". PhD degree 13. March 2013, Linnaeus University, Sweden. Email
• Hanna Farnelid, "Distribution and activity of nitrogen fixing bacteria in marine and estuarine waters". PhD degree 25 January 2013, Linnaeus University, Sweden.
• Johanna Sjösted, "Effect of environmental factors on bacterioplankton community composition, diversity and functionality". PhD degree 1. February 2013, Linnaeus University, Sweden. Email
• Karin Holmfeldt "Regulation of bacterioplankton community composition - emphasis on viruses". Ph.D. degree 21 August 2009
• Kjärstin Hagman Boström "Nitrogen fixation by heterotrophic bacterioplankton in the Baltic Sea". Ph.D. degree 20 January 2006, University of Kalmar
• Cecilia Leitet "Plasmids and prophages in Baltic Sea Bacterioplankton". Filosofie Licentiat 27 January 2006, University of Kalmar

Previous PostDocs

• Dr. Subhendu Chakraborty, PostDoc. "Modelling particle-associated nitrogen fixation". 04-2019-12-2020. Email
• Dr. Mar Benavides, PostDoc. "Ecology of heterotrophic N₂ fixing bacteria in marine coastal waters". 01-2017 - 06-2018. Email
• Dr. Deniz Bombar, PostDoc. "Nitrogen fixing heterotrophic bacteria in coastal waters". 03-2014 - 06-2018. Email
• Dr. Sachia Jo Traving, PostDoc. "Interactions between dissolved organic matter and bacterioplankton in marine waters". 06-2016 - 2018. Email
• Dr. Ryan Paerl, PostDoc. "Ecophysiological adaptations of planktonic microbes". Started: 10-2014 - 12-2016. Email
• Dr. Sophie Charvet, PostDoc. "Development of an autonomous multisampler system for pelagic RNA sampling". 10-2014 - 08-2015. Associated with the AFISmon project. Email
• Dr. Ina Severin, "Ecology of heterotrophic nitrogen-fixing prokaryotes in marine waters". 06-2012 - 06-2014. Email
• Dr. Claudia Dziallas. "Evolution of symbiosis between ciliates and nitrogen-fixing prokaryotes " Marie Curie fellow. 01-2012 - 05-2014. Email
• Dr. Julie Dinasquet. "Bacterioplankton community composition and succession" 2013. Email
• Dr. Dusko Odic. Working on virus-host interactions and X-ray crystallography. The project was a collaboration with Prof. Janos Hajdu, University of Uppsala, Sweden. 2008-2009.

Previous Master students (Riemann main supervisor)

• Tobias Launbjerg, "Identity and activity of heterotrophic nitrogen fixing bacteria in resuspended sediments of the coastal Baltic Sea". Master degree 09-2020.
• Mads Obi Bergsten, "Composition and expression of ammonia oxygenase genes in two river outlets in the Baltic Sea". Master degree: 05-2017.
• Jeppe Nedergaard Pedersen, "Organic particles as hotspots for nitrogen fixation by marine heterotrophic bacteria". Master degree March 2017
• Regitze B C Lundgreen, "Marine snow particles in the oligotrophic Sargasso Sea as analysed by PCR amplicon sequencing: composition and linkage to the plankton". Master degree December 2016
• Liv Louise Victoria Backhaus, "Microbial decomposition of copepod carcasses in surface waters of the oligotrophic Sargasso Sea". Master degree January 2016
• Elisabeth Münster Happel, "Nitrogen fixation in the Baltic Sea - diurnal and vertical patterns". Mater degree June 2014. University of Copenhagen
• Daniel Jiro Ayala , "Diversity of fish larvae communities across the subtropical convergence zone of the Sargasso Sea". Master degree February 2012. Danish Technical Univ.
• Hanna Alfredsson "Prey Selection of European Eel ( Anguilla anguilla ) Larvae in the Sargasso Sea: a Molecular Approach". Master degree September 2009, University of Kalmar.