Fluid flow stimulates chemosynthesis in a Greek salad of hydrothermal microbes
Most visitors to Paliochori Beach on the Greek island of Milos may not be aware of the bay’s shallow hydrothermal community, a veritable Greek salad of microbes, which lies within snorkeling distance. apnea from the shore.
Hydrothermalism in the coastal sediments of Paliochori Bay strongly affects biogeochemical processes there and supports chemosynthesis, which allows certain microorganisms such as sulfur-oxidizing bacteria to use chemical energy rather than light, such as photosynthetic plants or algae do this, to convert carbon dioxide into cellular material. .
However, the impact of fluid flow on microbial community composition and chemosynthetic production rates are unknown because it is difficult to measure microbial processes under natural conditions, especially in hydrothermal systems.
A new study uses an innovative approach to examine the bay’s shallow water hydrothermal system and the production of microbes there on the spot and near-natural conditions as a model to assess the importance of hydrothermal fluid circulation on chemosynthesis.
By examining microbial communities directly in hydrothermally impacted sandy bay sediments, the study demonstrates “the importance of fluid flow in shaping the composition and activity of microbial communities in hydrothermal vents. in shallow water, identifying them as hotspots of microbial activity”. according to the article, “Fluid flow stimulates chemoautotrophy in hydrothermally influenced coastal sediments”, published in Earth & Environment Communications, a Nature Portfolio magazine.
Additionally, “the study shows how productive shallow-water hydrothermal vents really are and how quickly microbes adapt to changing conditions,” says co-lead author Stefan Sievert, associate scientist in the Department of Biology. from the Woods Hole Oceanographic Institution (WHOI).
During the study, the researchers performed two sets of stable isotope probing experiments using carbon dioxide labeled with the stable isotope carbon 13C as a tracer to determine the ability of microbes to fix carbon, i.e. the conversion of carbon dioxide into biomass. The study deployed incubation devices along a transect at a vent in the bay and injected the tracer at different depths in the sediments, in open or closed fluid flow mode, and left the devices in place for 6 hours or 24 hours before picking them up. again.
The amount of carbon fixation was determined by measuring the incorporation of labeled carbon dioxide into fatty acids, a key component that makes up the cell membrane, in combination with assessing the composition of the microbial community using DNA and RNA-based approaches.
The study “extends current knowledge of black carbon fixation in coastal sandy sediments to areas affected by hydrothermal activity,” according to the paper. The researchers’ data reveal that active fluid flow at this shallow-water hydrothermal vent site of sandy sediments maintains carbon sequestration rates that are among the highest determined for coastal margin sediments, highlighting the influence of hydrothermalism in supporting chemoautotrophic production by providing the necessary chemicals in the form of electron donors such as hydrogen sulfide, and acceptors such as oxygen.
Extrapolating the production from the studied vent site to the overall bay vent area of approximately 4 acres, 7 metric tons of carbon are produced there per year. “That’s about the same annual production per area as a 4-acre cornfield,” says Sievert.
The study also revealed a highly active microbial community capable of responding rapidly to environmental changes. The production of chemosynthetic products in Milos is mainly driven by Campylobacteriaceae, which dominated communities in open incubations, but declined in closed incubations. Other bacteria, especially Gammaproteobacteriaalso increased in open-flow incubations, while others, like Deltaproteobacteria and Thermodesulfobacteria increased in closed incubations. In general, the community changed from a community dominated by chemosynthetic microbes to a community with a higher proportion of heterotrophic microbes, i.e. microbes that use organic carbon for food, just like humans . The study found that the microbial community changed in response to different conditions within hours, which is very fast and took the investigators by surprise.
Performing the microbial level measurements and identifying the different microbes at the hydrothermal vent site was a collaborative effort. This collaboration included Sievert’s expertise in using the incubation device and identifying microbes based on DNA and RNA-based techniques. Additionally, the lab of co-lead author Solveig Bühring, a researcher at the University of Bremen, provided data on the incorporation of labeled carbon dioxide into the fatty acids of microbes.
“What drives me to do this research is my curiosity to understand how things work. I’m interested in knowing what microbes do and how they help the ecosystem function,” says Sievert.
“Each individual microbe is so small, but their combined impact is so immense,” he adds. “Microbes are kind of the engines of our planet, essentially driving all of the biogeochemical cycles, such as the nitrogen and sulfur cycles.”
This work was funded by the National Science Foundation (NSF, USA) through grant OCE-1124272 and by the Deutsche Forschungsgemeinschaft through the Emmy Noether program. Additionally, Sievert received support from the WHOI Investment in Science Fund. The authors are also grateful to the General Directorate of Antiquities and Cultural Heritage of Athens for granting them permission to acquire and process samples.