Welcome to the Core Topic Marine Microbiology! Here, we focus on and study the smallest life forms within our oceans to understand their vast, often invisible, impact on global ecosystems and environmental health. These microorganisms, which include microscopic algae, bacteria, archaea, fungi, and viruses, form the foundation of the ocean’s ecological networks. Though tiny, microorganisms are the engines that drive essential biogeochemical cycles, which are the natural processes that move elements like carbon, nitrogen, and oxygen throughout Earth’s air, water, and soil.
Marine microorganisms play a central role in the health and balance of marine ecosystems. These microorganisms are not only the primary producers in the ocean, converting sunlight into chemical energy, but they are also the engines of decomposition and nutrient recycling. In surface waters, microscopic algae like phytoplankton absorb carbon dioxide during photosynthesis, generating oxygen and providing an essential food source for higher organisms in the food web, including fish and marine mammals. In the deeper ocean, bacteria and archaea break down organic material, releasing nutrients and sustaining life even in the absence of sunlight (Fig. 1).
Our department stands at the intersection of microbiology and biogeochemistry, studying microbial processes that drive biogeochemical cycles in marine environments—from open oceans to coastal zones. We leverage advanced technologies like genomic sequencing, mass spectrometry, and modeling to study microbial genetics, metabolic processes, and ecological interactions. We seek to understand how microorganisms impact the composition of organic matter, modulate greenhouse gas fluxes, and transform essential nutrients. For instance, our research investigates microbial responses to environmental factors like temperature, nutrient quantity, and quality, examining how these interactions influence ocean health and biogeochemical cycles. Our work also emphasizes the interdependence of marine microorganisms and organic matter, exploring how microbial community structures and metabolic functions both affect and are affected by Earth’s shifting climate and ecosystems. Through field studies and controlled laboratory experiments, we provide insights into the ecological roles, genetic diversity, and adaptability of the ocean microbiome under stressors such as warming, acidification, expanding oxygen minimum zones, and pollution. Below, we present key projects that exemplify our commitment to advancing knowledge of the ocean microbiome’s influence on global biogeochemical processes, ecosystem dynamics, and climate resilience.
In the EU HORIZON project ICEBERG (Innovative Community Engagement for Building Effective Resilience and Arctic Ocean Pollution-control Governance), we focus on a different aspect of global change: the impact of anthropogenic pollution in the form of microplastics on the microbial community and biogeochemistry. By analyzing the biodiversity and function of plastic-associated bacteria using 16S rRNA gene amplicon sequencing, metagenomics, and metatranscriptomics, we try to identify potential pathogens and their resistance mechanisms to antibiotics and thus assess the potential risks of microplastics for human and ecosystem health with a focus on the Arctic Ocean.
In the projects HOMER (Humboldt Organic MattEr Remineralization) and INDICOM (Composition, production, and recycling of recalcitrant organic matter in the bathypelagic Indian Ocean), we investigate biological and biogeochemical processes that affect the turnover of organic matter in the deep ocean, using exploratory field studies and enrichment experiments. While the field observations aimed at determining the effects of environmental variables such as temperature, pressure, and oxygen on the composition of organic matter in the deep sea, enrichment experiments with high molecular weight dissolved organic matter (HMW-DOM) from the surface and the deep sea, under elevated temperature, tested various hypotheses on the influence of organic matter concentration and composition on the activity of heterotrophic microbes.
The project BIOCAT (Biogeochemistry-Atmosphere Processes in the Bay of Bengal), aims to identify the physical and biogeochemical/microbial processes in the Bay of Bengal (BoB) that are crucial for the development and maintenance of the oxygen minimum zone (OMZ) and to assess the efficiency of the biological pump using drifting sediment traps. Freshly produced organic matter is largely remineralized by heterotrophic microorganisms on short timescales of days to months, and only a smaller fraction is exported to the dark ocean and turned over at substantially slower rates. To understand the particle dynamics and their effect on the oxygen regime in the Bay of Bengal (BoB), we will investigate the transfer efficiency of the carbon export and decipher the composition and function of microorganisms using state-of-the-art approaches such as metagenomic and metatranscriptomics which will be applied to seawater and sediment trap samples to characterize the phylogeny and functionality of these microbes. Thereby, relationships between organic matter qualitative composition and the biological pump efficiency, including assessment of microbial metabolism (e.g., organic matter degradation and uptake), will help to improve future ocean-climate predictions.
