Deep, dark ocean waters represent the largest marine environment on Earth. Studying how microbes survive in these cold, high-pressure habitats is difficult, due to the cost of accessing the deep sea and the challenges associated with collecting and maintaining organisms under their native conditions. Without more affordable and advanced equipment for studying pressure-loving “namely piezophilic” microbes, major parts of the ocean will remain underexplored.
In a new paper in Frontiers in Microbiology, DCO Deep Life researchers Marc Garel and Christian Tamburini (Aix-Marseille University, CNRS, MIO, France), with colleagues, discuss the advantages of sampling and maintaining deep-sea microbes under high-pressure conditions . By continuously mimicking deep-sea pressure levels, the researchers avoid giving the microbes “the bends” and obtain a more accurate picture of their identities and activity levels compared to procedures performed after the samples decompress. These results confirm previous findings and show that scientists who used sampling methodologies which allow decompression likely have underestimated the activities of deep-sea microbes and their ability to cycle carbon .
During the collection of microbes from their habitats, the sampling container—a titanium bottle—collects and maintains the water at its native pressure. At the surface, the researchers can transfer different volumes of the sample under the same pressure to new bottles using a pressure generator—a critical step when studying piezophiles. The sampler used in this study also extends the water depth at which scientists can successfully sample. “Our old system was up to 40 MPa and the new system is up to 60 MPa,” said Tamburini, “so now we can cover the majority of the ocean.”
The researchers mounted the MIO-HPLab container system on a conductivity, temperature, and depth (CTD) carousel to collect water samples from a 3000-meter water depth in the Mediterranean Ocean, during a PEACETIME oceanographic cruise. They maintained one set of samples under the pressure level of the deep ocean and let the other decompress to surface pressure. Then they transferred smaller amounts into new, sterile seawater and incubated these cultures for up to 43 days.
In the samples maintained under deep pressure, the microbes consumed oxygen to eat organic carbon compounds in the seawater much more rapidly than samples that had decompressed, indicating that the pressurized microbes were more active. Scientists have made similar estimates of microbial activity previously, but often at surface pressures, which could lead to an underestimation of the microbes’ ability to cycle carbon.
The researchers also used DNA/RNA sequencing to identify microbes present in the samples. After incubation, the community that had decompressed was distinctly different from the community maintained under pressure and also lacked known piezophilic bacteria that grew in the pressurized cultures.
Together, these results confirm that studying deep-sea microbes under their native conditions yields a better picture of how they survive in a challenging environment.
Deep-sea microbes receive very little organic carbon from the ocean’s surface, and by the time food has filtered down to the deep, the best parts are already eaten. In future work, the researchers are interested in investigating the role of microbes in recycling these less-appetizing forms of carbon. The researchers also hope to grow and maintain deep-sea microbial species in culture for more “in-depth” study.