Like Bill Murray in the movie Groundhog Day, bacteria in a Wisconsin lake are in some sort of endless cycle that they just can't seem to escape.. In a new study, scientists focused on studying why this happens, writes PHYS. org.

The team found that over the course of a year, most individual bacterial species in Lake Mendota evolve rapidly.. This probably occurs in response to dramatically changing seasons. The analysis showed that gene variants will rise and fall over generations, but hundreds of individual species will return to nearly the same copies as they were genetically before the thousand or so generations of evolutionary pressure. Note that the lifespan of individual microbes is approximately only a few days, and not entire seasons - scientists compared the genomes of bacteria to study changes in species over time.

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According to study co-author Robin Rover, a researcher at the University of Texas at Austin, he and his colleagues were surprised to find that most of the bacterial community was undergoing similar changes.. The team hoped to find only a few interesting examples, but there were literally hundreds of them..

Lake Mendota is known to change greatly from season to season, with ice in the winter and algae in the summer.. Within the same bacterial species, strains that are better adapted to one set of environmental conditions will outcompete other strains during a season, while other strains will have a chance to emerge during other seasons..

During the study, scientists used a unique archive of 471 water samples collected over two decades in Lake Mendota. For each water sample, scientists collected a metagenome, all the genetic sequences from DNA fragments left behind by bacteria and other organisms.. As a result, scientists were able to assemble the longest metagenome time series ever collected from a natural system.

According to Rover, the study's findings actually completely change our understanding of how microbial communities change over time.. Moreover, scientists believe that this study is just the beginning of what we can learn about microbial ecology and evolution in nature. The team notes that they were also able to identify longer-lasting genetic changes.

Observations indicate that in 212 the lake faced unusual conditions: the ice cover disappeared early, the summer was drier and hotter than usual, and the flow of water from the river flowing into the lake was significantly reduced. The scientists also noticed that algae, considered an important source of organic nitrogen for bacteria, was rarer than usual..

Scientists also discovered that bacteria in the lake experienced a significant gene shift that year..

The team believes that out of hundreds of bacteria they will only be able to detect one or two with a long-term shift. But instead, large sequence changes were found in one in five. Note that scientists were only able to study one species, but they believe that some other species have also undergone changes.

Previously, Focus wrote that a microorganism revealed a major evolutionary milestone.