Max Planck Institute for Marine Microbiology

A symbiosis between ciliates and bacteria plays a key role in removing nitrogen from lakes

Beneficial gut bacteria and their marine relatives use the same feeding strategies

Scientists identify new species of denitrifying endosymbionts in wastewater

New study reveals how ammonia-oxidizing archaea thrive in nutrient-poor waters 

Microorganisms play a crucial role in the production and conversion of greenhouse gases

Marine microorganisms play an instrumental role in Earth’s elemental cycles: among other things, they help to maintain the ocean’s role as a climate buffer. Katrin Knittel and her team at the Max Planck Institute for Marine Microbiology in Bremen study bacterial communities on the ocean floor in one of the planet’s most inhospitable regions: the Arctic.

Max Planck researchers collaborate with partners in more than 120 countries. In this article, they write about their personal experiences and impressions. Christina Bienhold from the Max Planck Institute for Marine Microbiology in Bremen spent two months on the research icebreaker Polarstern in the central Arctic. As co-leader of the ArcWatch-1 expedition she reached the North Pole in summer 2023.

At the Max Planck Institute for Marine Microbiology in Bremen, Marcel Kuypers’ and Nicole Dubilier’s departments are unraveling the mysteries of seagrass meadows. Their discoveries have been astonishing: microorganisms play a crucial role in the fitness, productivity, and element fluxes of plants, not just on land, but also in the sea.

No life is free of viruses. On Earth, at least, no organism seems to be spared from them. Susanne Erdmann and her team at the Max Planck Institute for Marine Microbiology in Bremen are studying viruses of the archaea, tiny single-celled organisms that lack a cell nucleus. Her research team investigates virus-like DNA elements, which may help us to explain how viruses actually originated.

It is truly a feat to create conditions like those in the deep ocean in a research laboratory. Gunter Wegener has mastered the art. Together with his team from the Max Planck Institute for Marine Microbiology in Bremen, he hopes to discover how microorganisms degrade methane and other hydrocarbons on the seabed.

Algae use armored, fucose-rich sugars as protective barriers, which can however be unlocked by bacteria – some of which are marine relatives of gut bacteria. They use a unique set of enzymes and shared molecular mechanisms with their gut cousins. By breaking the tough sugars of the algae into smaller units which are then available in the environment as “public goods”, these bacteria may act like probiotics for algae and simultaneously shape microbiomes and carbon flow in the ocean.

Hidden in the ocean, there are fascinating partnerships between microorganisms and animals: chemosynthetic symbioses. These partnerships play a key role in the marine sulfur cycle, which influences both life in the ocean and the climate. Particularly significant are dimethylsulfoniopropionate and dimethyl sulfide, substances which are produced and broken down by marine organisms. Chemosynthetic symbioses utilize and transform these sulfur compounds, potentially shaping the global sulfur cycle and climate regulation.

The most abundant group of bacteria in the sea are SAR11 bacteria. On average, they make up about a third of all bacteria and are known to be slow-growing. We observed that during a spring algal bloom off Helgoland, they divided very rapidly, but their overall numbers decreased. This was unusual because cell numbers and growth rates are often closely linked. Presumably, SAR11 was heavily preyed upon and was unable to compensate for the losses, despite strong growth. Our results show that accurate microscopic observations are and will remain important for ecological studies.

Seagrass beds are important coastal ecosystems that absorb large amounts of carbon through photosynthesis, even though they cover only a small area of the ocean. They release part of this carbon into the sediment through their roots as sugars. Astonishingly, large amounts of sugar are found in their rhizosphere. The seagrasses probably release sugar as a kind of excess-metabolism. At the same time, phenols derived from seagrass prevent microorganisms in the oxygen-poor sediment from breaking down the sugar directly.

Viruses are an integral and essential part of nature and perform important functions for their hosts and in our ecosystems. We have established a new prokaryotic virus-host model system in which the virus does not kill its host, but causes a long-term chronic infection. Chronic infections are well-known in eukaryotes, but only rarely discovered and poorly understood in prokaryotes. Our model system allows to study a chronic infection in a prokaryotic host in detail and to understand its implications for the host.