IIn the coldest, most remote place on Earth, a team of scientists braved the icy winds to find answers. Wearing thick red gear that contrasts with the blue-and-white landscape, researchers recover worms from the frigid waters of the Southern Ocean that surround Antarctica. They will take the squirming creatures back to the lab to study how they survive in sub-zero temperatures without any protective gear.
“Antarctica has one of the most extreme environments on Earth,” says Cinzia Corinaldesi, a marine ecologist at the Polytechnic University of Marche. “In marine ecosystems, we can have temperatures very close to minus two degrees [Celsius]”.
Researchers use specialized instruments to collect samples in Antarctica.
Marco Lo Martial
While researchers have found that some Antarctic marine animals produce antifreeze proteins to adapt to extreme cold, similar mechanisms in invertebrates remain poorly understood.1
In a study published in scientific progressCorinaldesi and colleagues demonstrated that the microbiome of Antarctic worms produces cryoprotective proteins that help these organisms cope with freezing temperatures.2 These results provide insights into how the microbiome helps the host adapt to extreme environmental conditions.
The role of the microbiome in providing nutrition or immunity is well known, said Harald Gruber-Vodicka, a marine symbiosis researcher at the Max Planck Institute for Marine Microbiology, who was not involved in the study. “But cold protection as a symbiotic service or symbiotic function is surprising and novel.”
Corinaldesi and team suspected that the microbiome might play a role in helping the host withstand the cold, since microorganisms are often found in such conditions.3 To test this hypothesis, the team sequenced bacterial DNA isolated from the guts, mouths, appendages and outer protective coating of worms collected in Antarctic waters.
Researchers collected worms from the Southern Ocean to study their cold adaptation strategies.
Marco Lo Martial
Analyzing the sequences showed that bacteria belonging to the genus Thermobacteria and Anaerobic bacteria Make up the majority of the worm’s microbiota. Although scientists have found these species in cold environments before, they are most commonly found in high-temperature environments, such as hot springs.
The researchers found that these bacteria were not present in any other worm species with metagenomes in the gene pool. They also did not find these bacteria in the sediment where the worms were collected, suggesting that the worms had not recently acquired these bacteria from their environment.
This prompted the research team to investigate whether the association between worms and microbes began in the past and was passed down from generation to generation. They studied the relationship between the evolutionary history of the host (assessed by analyzing its mitochondrial genes) and the evolutionary history of the host-associated microbiome. This reveals a high degree of phylosymbiosis or similarity, showing that microorganisms and worms may have co-evolved.
“This symbiosis began in ancient times, probably when the habitats were different, and now these bacteria are no longer present in the sediments around the animals,” Conardesi said.
To study how the worms benefit from these cold-climate microbial inhabitants, Corinaldesi and team analyzed the worms’ genomes. Thermobacteria and Anaerobic bacteria bacteria. They found genes that encode or are related to cryoprotective compounds such as cold shock proteins, ice-binding proteins and spermidine.
When they analyzed the worm extract using proteomics methods, they found that many of these proteins and several enzymes may help cope with extreme cold temperatures. Matching these proteins to existing libraries describing protein sequences and their functions helped the team determine that bacteria, not worms, produced several of the cryoprotective proteins.
The fact that the microbiome produces specific proteins that help the host cope with cold was surprising, Corinaldesi said.
Gruber-Vodicka said the research was enhanced by the genomic and proteomic approaches the team took. “The initial insight that symbionts may play an important role is very interesting,” he noted, but more experiments are needed to prove that the worms rely on the microbiome to adapt to the cold.
“This is just a small part of it [puzzle],” Conardesi said. “We need to continue [the work] to expand the scope of information.
