5,000-year-old bacteria thawed in Romanian ice cave

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Whether it’s the ocean’s deepest hydrothermal vents or tall mountain peaks, bacteria is likely surviving and thriving. Ice caves can host a wide variety of microorganisms and offer biologists a bevy of genetic diversity that still has to be studied. And it could help save lives.

A team of scientists in Romania tested antibiotic resistance profiles with a bacterial strain that was hidden in a 5,000-year-old layer of ice inside an underground ice cave. This bacteria may be key to finding new strategies to prevent the continued rise of antibiotic resistance. The new bacterial strain called Psychrobacter SC65A.3 is detailed in a study published today in the journal Frontiers in Microbiology.

“The Psychrobacter SC65A.3 bacterial strain isolated from Scărişoara Ice Cave, despite its ancient origin, shows resistance to multiple modern antibiotics and carries over 100 resistance-related genes,” Dr. Cristina Purcarea, a study co-author and microbiologist at the Institute of Biology Bucharest of the Romanian Academy, said in a statement. “But it can also inhibit the growth of several major antibiotic-resistant ‘superbugs’ and showed important enzymatic activities with important biotechnological potential.”

Drilling for bacterial gold

Antibiotic resistance occurs when bacteria evolve to resist the antibiotics that doctors use to treat infections. This can make certain bacterial infections difficult to treat and is a growing problem. The World Health Organization estimates that it was responsible for 1.27 million deaths worldwide in 2019. Finding new sources of antibiotics is crucial to the future of public health. 

The new strain found in the ice cave is a strain of the genus Psychrobacter. These bacteria are adapted to cold environments and can infect humans or animals. While Psychrobacter bacteria have biotechnological potential, scientists do not quite understand the antibiotic resistance profiles of these bacteria.

“Studying microbes such as Psychrobacter SC65A.3 retrieved from millennia-old cave ice deposits reveals how antibiotic resistance evolved naturally in the environment, long before modern antibiotics were ever used,” said Purcarea.

The team drilled an 82-foot ice core from an area of the cave known as the Great Hall. This enormous ice core represents a 13,000-year timeline, giving scientists an idea of what sorts of organisms were alive and when. The ice fragments taken from the core were placed in sterile bags and kept frozen on their way back to the lab to avoid contamination. Back in the lab, they  isolated various bacterial strains and sequenced their genomes. The sequencing can tell which genes allow the strain to survive in low temperatures and which indicate antimicrobial resistance and activity.

Next, they tested for resistance of the SC65A strain against 28 antibiotics from 10 classes. Many of these are commonly used to treat bacterial infections, including antibiotics that have resistance genes or mutations that help them resist antibiotics. This way, they could see whether the predicted mechanisms translated into measurable resistance. 

“The 10 antibiotics we found resistance to are widely used in oral and injectable therapies used to treat a range of serious bacterial infections in clinical practice,” Purcarea explained. 

Diseases such as tuberculosis, colitis, and urinary tract infections (UTIs) can be treated with some of the antibiotics that SC65A.3 is resistant to, including rifampicin, vancomycin, and ciprofloxacin.

SC65A.3 is the first Psychrobacter strain that is resistant to certain antibiotics, including trimethoprim, clindamycin, and metronidazole. Those antibiotics often treat UTIs, infections of lungs, skin, or blood, and the reproductive system. SC65A.3’s resistance profile suggests that the bacterial strains that can survive extremely cold environments may be reservoirs of resistance genes. These resistance genes contain specific DNA sequences that help them survive exposure to drugs.

A mixed bag

While long frozen viruses and bacteria sound like a sci-fi nightmare, there is some very real risk involved from unknown and understudied bacterial strains. But there is also some good news. 

“If melting ice releases these microbes, these genes could spread to modern bacteria, adding to the global challenge of antibiotic resistance,” Purcarea said. “On the other hand, they produce unique enzymes and antimicrobial compounds that could inspire new antibiotics, industrial enzymes, and other biotechnological innovations.”

The Psychrobacter SC65A.3 genome has almost 600 genes with unknown functions, which could hold clues to treating other diseases. It also has 11 genes that may be able to kill or stop the growth of other bacteria, fungi, and viruses.

As antibiotic resistance grows, learning more about these ancient genomes and uncovering their potential shows the major role that the natural environment played in the spread and evolution of antibiotic resistance. 

“These ancient bacteria are essential for science and medicine,” Purcarea concluded, “but careful handling and safety measures in the lab are essential to mitigate the risk of uncontrolled spread.”

 

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