In the coldest, most isolated place on Earth, a group of scientists braves the icy winds in search of answers. Clad in thick, red gear that contrasts with the blue and white landscape, researchers retrieve worms from the frigid waters of the Southern Ocean circling Antarctica. They will bring these squirming creatures back to their labs to study how they manage to survive sub-zero temperatures without any protective gear.
“Antarctica has one of the most extreme environments on the planet,” said Cinzia Corinaldesi, a marine ecologist at Marche Polytechnic University. “And in marine ecosystems we have temperatures that can be very close to minus two degree [Celsius].”
Researchers collecting samples using specialized instruments in Antarctica.
Marco Lo Martire
While researchers had identified that some Antarctic marine animals make antifreeze proteins to adapt to the extreme cold, similar mechanisms in invertebrates remained poorly understood.1
In a study published in Science Advances, Corinaldesi and colleagues have shown that the microbiome of Antarctic worms produces cryoprotective proteins that help these creatures cope with freezing temperatures.2 The results provide insights into how the microbiome can help the host adapt to extreme environmental conditions.
The microbiome’s role in providing nutrition or immunity is well-established, said Harald Gruber-Vodicka, a marine symbiosis researcher at Max Planck Institute for Marine Microbiology, who was not involved with the study. “But cold protection as a symbiont service or a symbiont function was surprising and new.”
Corinaldesi and the team suspected that the microbiome might play a role in helping their host brave the cold, because microbes are frequently found in such conditions.3 To test this hypothesis, the team sequenced the bacterial DNA isolated from the guts, oral cavities, appendages, and outer protective covering of the worms they collected from Antarctic waters.
Researchers collected worms from Southern Ocean to study their cold adaptation strategies.
Marco Lo Martire
Analyzing the sequences revealed that bacteria belonging to the genera Meiothermus and Anoxybacillus made up most of the worms’ microbiome. Although scientists have found these species in frigid environments before, they are most commonly seen in high temperatures, such as hot springs.
The researchers found that these bacteria were not present in any other worm species whose metagenomes were available in gene banks. They also did not find these bacteria in the sediment where they collected the worms, indicating that the worms did not recently acquire these bacteria from their environment.
This led the team to investigate whether the worm-microbe connection started in the past and was passed down through the generations. They studied the relationship between the evolutionary history of the host—assessed by analyzing its mitochondrial genes—and that of the microbiome associated with the host. This revealed a high degree of phylosymbiosis, or similarity, suggesting that the microbes and the worms may have coevolved.
“The symbiosis started in ancient times, probably when the habitat was different, and now these bacteria are no longer present in the surrounding sediments of the animals,” said Corinaldesi.
To investigate how the worms benefit from their microbial inhabitants in these frigid climates, Corinaldesi and the team analyzed the genomes of Meiothermus and Anoxybacillus bacteria. They found genes encoding or related to cold-shock proteins, ice-binding proteins, and cryoprotective compounds like spermidine.
When they analyzed worm extracts using a proteomics approach, they found many of these proteins and several enzymes that are potentially useful for coping with extreme cold temperatures. Matching these proteins with established databases that describe protein sequences and their functions helped the team pinpoint that the bacteria, and not the worms, produced several of the cryoprotective proteins.
The fact that the microbiome produced specific proteins that can help the host cope with the cold was surprising, said Corinaldesi.
Gruber-Vodicka said that the genomic and proteomic approach taken by the team strengthens the study. “This first insight that the symbionts might play an important role is very intriguing,” he noted, but additional experiments are required to prove that the worms depend on the microbiome for cold adaptation.
“This is just a little piece of the [puzzle],” said Corinaldesi. “We need to continue with [the work] to expand information.”
