In a finding that challenges conventional views of evolution, scientists have discovered that bacteria in a Wisconsin lake undergo predictable genetic changes with the seasons, only to reset and repeat the cycle year after year. The research, published in Nature Microbiology, reveals an unprecedented pattern of repetitive evolution in hundreds of bacterial species.
“I was surprised that such a large portion of the bacterial community was undergoing this type of change,” said Robin Rohwer, who led the research at The University of Texas at Austin. “I was hoping to observe just a couple of cool examples, but there were literally hundreds.”
The study draws from an extraordinary collection of 471 water samples gathered over two decades from Lake Mendota in Wisconsin. Using advanced computing technology, researchers analyzed genetic material from thousands of bacterial generations, creating the longest metagenome time series ever collected from a natural system.
Lake Mendota presents dramatically different environments across seasons – ice-covered in winter, algae-rich in summer. As conditions change, different strains within each bacterial species rise to dominance, only to be replaced when the seasons shift again. Despite experiencing thousands of generations of evolutionary pressure, most species return to nearly identical genetic states each year.
Brett Baker, a co-author of the study, describes the findings as “a total game changer in our understanding of how microbial communities change over time.” The research required massive computational power – analysis that would have taken 34 years on a laptop was completed in months using the Texas Advanced Computing Center.
The study also revealed how extreme weather can disrupt these cycles. In 2012, when the lake experienced an unusually hot and dry summer with early ice melt, one in five bacterial species showed major genetic shifts that persisted for years, particularly in genes related to nitrogen processing.
These findings gain significance as climate scientists predict more extreme weather events for the Midwestern United States. “Climate change is slowly shifting the seasons and average temperatures, but also causing more abrupt, extreme weather events,” Rohwer noted. “We don’t know exactly how microbes will respond to climate change, but our study suggests they will evolve in response to both these gradual and abrupt changes.”
The research, supported by multiple federal agencies and foundations, provides new insights into how microscopic life adapts to environmental change. A companion study examining viral evolution in the same lake samples was published simultaneously.