Scientists in the US have uncovered fresh insights into how some of the earliest life forms on Earth adapted to a world with increasing oxygen levels.
The research, led by Montana State University (MSU) and published in Nature Communications, sheds light on how ancient microbes evolved in extreme environments, offering clues about the origins of life on our planet.
For more than 20 years, professor Bill Inskeep, from MSU's Department of Land Resources and Environmental Sciences, has studied microorganisms living in the hot springs of Yellowstone National Park.
In this latest study, Inskeep and colleague Mensur Dlakic, an associate professor in the Department of Microbiology and Cell Biology, wanted to add to their understanding of how life evolved before and during the Great Oxidation Event – when Earth’s atmosphere changed dramatically around 2.4 billion years ago, shifting from almost non-existent levels of oxygen to the 20% oxygen we breathe today.
To do this, they examined microbes living in two thermal springs – Conch Spring and Octopus Spring – both located in Yellowstone National Park's Lower Geyser Basin. These sites were chosen because they are similar in many ways, except that Conch Spring has higher levels of oxygen than Octopus Spring. This meant they were able to study two contrasting thermal environments with both low and high levels of oxygen.
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The team focused on three types of thermophiles (heat-loving microbes) that live in both springs, where water temperatures reach a blistering 88°C (190°F). When oxygen levels started to rise in the Great Oxidation Event, these microbes were likely some of the first to adapt, says Inskeep.
These microbes live in ‘streamers’ – thin, thread-like structures that sway in the flowing hot water, much like tiny underwater plants. Although streamers in both springs look similar, the scientists found that they host very different communities of microbes.
They discovered that the streamers in Octopus Spring, which has more oxygen, also has a greater diversity of microbial life. "Octopus Spring contained ~10 populations not seen in Conch Spring and these included additional early-evolved bacteria as well as additional archaea," says Inskeep.
By analysing their genes, the researchers found that microbes in the low-oxygen Conch Spring had highly active genes adapted for survival in an oxygen-poor environment. Meanwhile, the microbes in Octopus Spring expressed genes better suited for higher oxygen levels, suggesting they had evolved to thrive as the atmosphere became richer in oxygen.
Inskeep and Dlakic's work is helping scientists piece together how life adapted to Earth’s changing conditions over billions of years – and Yellowstone seems to be the perfect place to conduct this type of research. "It would be very difficult to reproduce this kind of an experiment in the laboratory," explains Inskeep. "Imagine trying to recreate hot-water streams with just the right amounts of oxygen and sulphide.
"And that's what's so nice about studying these environments. We can make these observations in the exact geochemical conditions that these organisms need to thrive."
While these ancient microbes may seem far removed from human life, they offer a fascinating glimpse into how all living things – including us – have evolved to survive, adds Dlakic. "It may seem counterintuitive to understand complex life by studying something that's simple, but that's really how it has to start.”
Find out more about the study: Respiratory processes of early-evolved hyperthermophiles in sulfidic and low-oxygen geothermal microbial communities
Main image: Lower Geyser Basin, Yellowstone National Park/Getty
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