Bacteria in the Arctic seabed are active all year round, researchers find

Despite marked seasonality in their habitat, bacterial communities in Arctic sediments are taxonomically and functionally very stable.

Researchers from Bremen, Germany studied the structure and function of bacteria in it. Sea floor Off Svalbard, during alternating periods of polar night and midnight sun. To do this, they developed a special sampling device, the elroot grab. Unlike bacterial communities in groundwater, sediment bacteria hardly change with the seasons. This is probably due to the fact that some hard-to-digest foods are available year-round on the seabed.

The Arctic is cold and hostile to life, yet it is home to many microorganisms whose activity significantly affects life on our planet. For example, bacteria in the ocean floor play a central role in processing the biomass of dead organisms, thereby converting the carbon it contains into hard-to-reduce substances that can be preserved for long periods of time. .

In addition to cold, irregular weather is a prominent feature of polar habitats—day and night do not change every twelve hours, but instead fluctuate between midnight sun and polar night throughout the year. This has a major impact on local primary production, which depends on sunlight. In summer, tiny algae thrive in seawater and life on land flourishes. In winter, primary production largely stops. Little research has been done on the extent to which the resulting fluctuations in organic matter input affect seafloor bacteria.

Addressing this knowledge gap, a team of researchers from the Max Planck Institute for Marine Microbiology in Bremen, Germany visited the Svalbard Peninsula at different times of the year to investigate the local bacterial sediment community. They offer now. Their results I ISME Journal.

Enzymes are more variable than bacteria.

The surprising thing is that Bacterial community The ocean floor does not behave as expected given the environmental conditions. “Although the input of organic material and its turnover rate fluctuate greatly during the year, the composition of the bacterial community hardly changes at first sight,” reports principal investigator Katrin Nuttall.

Bacteria on the ocean floor thus behave very differently from those in water, where many of them exhibit distinct weather patterns. “Benthic bacterial communities—that is, those in the seafloor—are very complex,” added Nuttall. “That’s what makes them so stable and strong, and it makes it so hard for us to study their dynamics.”

To better understand this unexpected behavior, Knittel and his team from the Max Planck Institute in Bremen have now investigated the so-called functional diversity of bacteria. How much does bacterial activity on the ocean floor change between midnight sun and polar night?

To find out, they analyzed which genes the bacteria have to break down algal sugars and to what extent they use them. “While bacterial community composition hardly varies between seasons, we found that gene expression of carbohydrate-degrading enzymes changes between winter and spring,” explains first author Sebastien Miksch, who led his Participated in this project as part of a doctoral thesis.

In winter, enzymes that break down a-glucans (eg, glycogen) predominate. A-glucans are intracellular storage compounds of heterotrophic bacteria, animals and fungi. They are also available the rest of the year, but are then less important. However, in the spring, there are more enzymes that break down B-glucan such as the algal component laminrin. Then there is so much B-glucan that some of it can be set aside as storage at the end of the year.

“These enzymes reflect which algal components – particularly algal sugars – are available to the bacteria in different seasons,” explains Knittel. “It’s not so different to go to the farmer’s market here: while there are many different fresh fruits and vegetables available in the sunny season, at some point during the winter the only thing left is the stored potatoes.”

Therefore, seafloor bacteria can use fresh material that sinks from the ocean. The water columnEspecially in spring and summer, like the aforementioned laminar. However, they can also use material that is already present on the seabed or is produced there. This includes tasty foods like mucin, but also tough bits like chitin. On them, bacteria hang around all year round. This source of food is especially important in winter, when other inputs are scarce. Their long-term availability Their long-term availability stabilizes the bacterial community in the seafloor.

“These findings are very small-scale, but they’re important in a larger context: When bacteria eat algal sugars, they release carbon dioxide. And carbon dioxide is a very important greenhouse gas,” Knittel notes. does. Thus, small ocean inhabitants can influence global processes.

Small, lightweight, practical: The Allroot Grab

Overall, the bacterial community in the Arctic seafloor is therefore remarkably similar across seasons. Despite the strong weather, the community is present and active in both seasons. However, it wasn’t just internal dynamics that made it difficult for Nuttall’s team to study the bacteria on the Spitsbergen seafloor. It is also methodologically challenging.

“It’s very difficult to get samples of the pore water between the seafloor and the sand grains without disturbing them,” explains doctoral student Cherin Moncada, who is also working on the project. “That’s why we developed our tool: Elroot Grab.” This sampling device, presented in An essay In the journal Limnology and Oceanography: Methods And named after its developer and co-author Andreas Elrot, it makes it possible to take sediment samples from sandy sediments without disturbing them.

The handle is so small and lightweight that it is perfect for use on small research vessels. “Andreas is a brilliant engineer and designed and built the Grab from scratch, manufacturing many of the components himself in a 3D printer,” says Moncada. “To date, we have collected more than 100 sediment samples from the Widden Sea and Svalbard’s fjords with the Elrot grab—and we plan to collect many more.”