Scientists have discovered Cyclobacter cryohalorentis seeds in the 5,000-year-old ice of the Scalisoara Ice Cave in Romania. The strain, designated SC65A.3, exhibits remarkable resistance to 10 widely used antibiotics, including treatments for severe infections like tuberculosis and urinary tract infections.
Isolated colony of Cyclobacter SC65A.3 on R2A medium at 4°C (A) and on TSA medium at 15°C (B). Image credit: Ioana Paun et al., doi: 10.3389/fmicb.2025.1713017.
Cyclobacter is a genus that comprises approximately 50 bacterial species adapted to cold and saline environments.
First identified in 1986, Cyclobacter immobilis is recognized as the type species and has a broad distribution.
This species forms cream to orange colonies and is capable of growing at low temperatures, withstanding a range of 35-37°C and various salinities. Some species are known to be pathogenic to humans and animals.
Characteristically, they are strictly aerobic, catalase, and oxidase-positive, utilizing amino acids and organic acids as carbon sources, albeit demonstrating limited biochemical diversity.
“Despite its ancient origin, the SC65A.3 strain isolated from the Scalisoara Ice Cave is resistant to modern antibiotics and possesses over 100 resistance-related genes,” stated Dr. Cristina Purcarea, a researcher at the Biological Institute of the Romanian Academy in Bucharest.
“Moreover, it has demonstrated the ability to inhibit the growth of several prominent antibiotic-resistant ‘superbugs’, showcasing significant enzymatic activity with considerable biotechnological potential.”
Cyclobacter SC65A.3 was isolated from a 5,000-year-old ice layer within a 25.33-meter ice core in the Scalisoara Ice Cave.
“Our research on Cyclobacter SC65A.3, retrieved from ancient cave ice deposits, sheds light on how antibiotic resistance evolved naturally in the environment long before modern antibiotics were introduced,” Dr. Purcarea added.
Researchers sequenced the Cyclobacter SC65A.3 genome to pinpoint genes that allow bacteria to endure extreme cold and those that support antimicrobial resistance and activity.
They tested the strain against 28 antibiotics, including 10 commonly prescribed for bacterial infections, many of which are known to encounter resistance due to specific genes or mutations that diminish their effectiveness.
“The 10 antibiotics to which we found resistance are widely utilized in oral and injectable therapies for various serious bacterial infections in clinical settings,” Dr. Purcarea explained.
The resistance profile of this strain indicates that cold-adapted bacteria may act as reservoirs for resistance genes.
“As the ice melts and releases these microorganisms, the resistance genes could spread to contemporary bacteria, exacerbating the global challenge of antibiotic resistance,” Dr. Purcarea remarked.
“Conversely, they produce unique enzymes and antimicrobial compounds that could lead to the development of new antibiotics, industrial enzymes, and other biotechnological advancements.”
These findings were published in the journal Frontiers in Microbiology.
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Victoria Ioana Paun et al. 2026. First genome sequence and functional profiling of Cyclobacter SC65A.3 preserved in 5,000-year-old cave ice: Insights into ancient resistomes, antimicrobial power, and enzyme activity. Frontiers in Microbiology 16; doi: 10.3389/fmicb.2025.1713017
Source: www.sci.news
