What Lurks at the Bottom of the Sea?

When Friederike Gründger and her team cracked open the long, heavy cylinders of black sediment drawn from the ocean floor, they were surprised to find pockets of yellowish-green slime buried within two of the samples. The average person may not consider the appearance of such unseemly goo as a cause for celebration, but the biologists knew that this slime, otherwise known as biofilm, was a highly unusual find in this particular location, and could even play a role in terms of climate change.

This group from the Centre for Arctic Gas Hydrates, Environment, and Climate (CAGE) at UiT The Arctic University of Norway set out to investigate the microscopic and macroscopic organisms living in or around cold seep sites such as Gas Hydrate Pingos (GHP) in the Svalbard area. These dome-like, geological structures leak methane gas into the ocean water with the potential to travel to the surface and enter our atmosphere, possibly advancing climate change.

Underwater organisms thrive on deadly greenhouse gas

Some of the organisms living at these sites are relevant to this process, as they have adapted to live off the methane and convert it into harmless compounds such as carbonate and water. This activity is called anaerobic oxidation of methane (AOM) and has a global impact on the diffusion of underwater methane. The most relevant entities contributing to this process are methanotrophic archaea (ANME -1, -2, and -3) and sulphate-reducing bacterial (SRB), two microorganisms usually found living co-dependently in colonies. It is still unclear, however, where they can be reliably found and how involved they are in such methane control.

Slimy biofilm coats microbial communities; provides protection

Biofilms are glue-like substances that encase clusters of microbes to provide extra protection against the elements. They can be found all throughout nature, even on the human body; biofilms can lead to complications in wound care and adhere to your teeth as plaque. But they are also found on the ocean floor, protecting the microbial communities that set up shop near areas of methane accumulation. Where they are not usually found, however, is within the cracks and crevices of seabed sediment – at least, not as far as we know. But Gründger et al.’s research may be showing us once again how the ocean is constantly capable of surprising us.

Research findings surprise scientists

Here are the highlights from the recently published article from Gründger et. al. in Scientific Reports:

- This is the first case of biofilms, visible to the naked eye, found in the cracks of methane-rich sediment in Arctic waters. It could prove to be a common occurrence of which we were previously unaware.

- Both biofilm samples found were shown to have a very unique microbial composition with ANME-1 as the dominating group. This has only been seen once before, as reef-forming microbial mats in the Black Sea.

- Although ANME-1 and SRB microbes usually help one another to absorb methane, there was no direct cell-to-cell contact between the two in these particular biofilms. This leads our scientists to wonder if ANME-1 could filter the methane without the presence of the SRB, something previously thought impossible.

Reference
Methane-fuelled biofilms predominantly composed of methanotrophic ANME-1 in Arctic gas hydrate-related sediments. Friederike Gründger, Vincent Carrier, Mette M. Svenning, Giuliana Panieri, Tobias R. Vonnahme, Scott Klasek & Helge Niemann. Scientific Reports,volume 9, Article number: 9725 (2019), DOI:https://doi.org/10.1038/s41598-019-46209-5.

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