Soil bacteria evolve with climate change – sciencedaily

While evolution is normally thought to take place over millions of years, researchers at the University of California at Irvine have found that bacteria can evolve in response to climate change in 18 months. In a study published in the Proceedings of the National Academy of Sciences, UCI biologists have found that evolution is a way for soil microbes to cope with global warming.

Soil microbiomes – the collection of bacteria and other microbes in the soil – are a key driver of the global carbon cycle; microbes break down dead plant material to recycle nutrients back into the ecosystem and release carbon into the atmosphere. Multiple environmental factors influence the composition and function of soil microbiomes, but these responses are typically studied from an ecological perspective, asking which microbial species increase or decrease in abundance as environmental conditions change. In the present study, the UCI team investigated whether bacterial species present in the soil also evolve when their environment changes.

“We know that evolution can happen very quickly in bacteria, such as in response to antibiotics, but we don’t know how important evolution could be for bacteria in the environment with climate change going on.” said Dr Alex Chase, senior author of and former UCI graduate student.

Several inherent characteristics should allow soil microbes to adapt quickly to new climatic conditions. Microbes are abundant and can reproduce in just a few hours, so a rare genetic mutation that allows adaptation to new climatic conditions could happen by chance over a short period of time. However, most of what is known about bacterial evolution comes from controlled laboratory experiments, where bacteria are grown in vials with artificial food. It was not clear whether evolution is happening fast enough in soils to be relevant to the effects of current rates of climate change.

“Current predictions of how climate change will affect microbiomes hypothesize that microbial species are static. So we wanted to test whether bacteria can evolve quickly in natural environments such as soil, ”explained Dr Chase.

To measure evolution in a natural environment, the researchers deployed a first-ever bacterial evolution experiment in the field, using a soil bacterium called Curtobacterium. The researchers used 125 “microbial cages” filled with microbial food made up of dead plant material. (The cages allow the transport of water, but not other microbes.) The cages then exposed the bacteria to a range of climatic conditions across an elevation gradient in southern California. The team conducted two parallel experiments over 18 months measuring both ecological and evolutionary responses of bacteria.

“The microbial cages have allowed us to control the types of bacteria present, while exposing them to different environmental conditions at different sites. We were then able to test, for example, how the hot, arid conditions of the desert site affected the genetic diversity of a single species of Curtobacterium, ”said Dr Chase.

After 18 months, the scientists sequenced the bacterial DNA from the microbial cages of the experiments. In the first experiment containing a diverse soil microbiome, different Curtobacterium species changed in abundance, an expected ecological response. In the second experiment over the same period, the genetic diversity of a single Curtobacterium bacterium changed, revealing an evolutionary response to the same environmental conditions. The authors conclude that ecological and evolutionary processes have the potential to contribute to how a soil microbiome responds to changing climatic conditions.

“The study shows that we can observe rapid evolution of soil microbes, and this is an exciting achievement. Our next goal is to understand the importance of evolutionary adaptation for soil ecosystems under future climate change.” said co-author Jennifer Martiny, professor of ecology and evolutionary biology who co-leads the UCI Microbiome Initiative.

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