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The glass vials, containing bacteria for the 500-year study, are displayed here. The spores are dehydrated using silicon bead desiccators before being sealed. Ulrich et al., PLOS One, 2018.Certain bacteria are renowned for their ability to endure extreme conditions, from scorching temperatures to chemical assaults and dehydration. But how long can they truly survive? In 2014, a team of researchers dried a collection of bacteria, sealed them in small glass vials, and in 500 years, someone will have the privilege of completing this enduring study.
The five-century-long experiment was designed by scientists from the University of Edinburgh in Scotland, collaborating with colleagues from Germany and the U.S., with the goal of deepening humanity's understanding of bacterial longevity. The catch? None of them (or their descendants) will be alive to witness the results.
In an email interview, Charles Cockell, one of the scientists behind the experiment, explained the motivation was simple. 'Most scientific studies are constrained by grant timelines or human lifespans, but nature operates over much longer spans. We wanted to design an experiment that better aligns with the timeframes relevant to microbial research.'
For the study, the team filled 800 vials with two types of bacteria: Chroococcidiopsis and Bacillus subtilis. Chroococcidiopsis is a resilient, primitive bacterium that thrives in extreme environments like hot springs and deserts, while Bacillus subtilis is one of the most extensively studied bacteria, capable of entering a dormant state (as spores) when facing environmental stress. The vials were completely sealed off from air, with half of them encased in lead to protect against radiation and other potential DNA-damaging influences.
Every two years, for a quarter of a century, the team will check if the bacteria remain viable. After that, the testing interval will extend to once every 25 years until the 500-year study concludes.
The tests themselves are simple, involving rehydration and colony counting. But how does one communicate the details of the experiment to researchers 400 years from now? Instructions were printed on paper and saved on a flash drive, with a clear request for future scientists to update both the language and technology used during their 25-year checkups.
The first round of analysis took place in 2016, with findings published in December 2018 in PLOS. The results? After two years of isolation, the bacterial spores showed almost no reduction in viability. Some of the surviving spores were then intentionally exposed to harsher conditions, such as high salt concentrations or a space-like vacuum — these samples, unsurprisingly, displayed a higher loss of viability.
So what’s the ideal outcome of such a long-term experiment? 'There isn’t a perfect result,' Cockell explains. 'Our goal is to understand how fast microbes die and what mathematical model best represents their demise over centuries.'
Certain bacteria are so tough that they can survive for millions of years, as long as they're preserved in some way. For instance, in 1995, scientists revived bacteria found in 25-million-year-old tree sap, and others from beetles trapped in amber 135 million years ago. In 2000, researchers found bacteria in New Mexico salt deposits that had remained viable for 250 million years.
