Dormant microbes can 'switch on' to cope with climate change

The results have important implications for predicting the impact of global warming on ecosystems.

Microbes are integral to ecosystem function, because of their key roles as pathogens, food sources and in nutrient recycling. To understand the profound impact of climate change on the function of different ecosystems, it is therefore necessary to study the microbial communities within them.

"Microbial communities can respond to warming in the short term by acclimation -- developing unique traits to suit the environment -- or through the longer term by adaptation, where they make evolutionary changes over many generations," explains lead author Thomas Smith, Research Associate at the Georgina Mace Centre for the Living Planet, Imperial College London, UK. "But there is also a third mechanism, called species sorting, whereby the composition of the overall community -- that is, which species are present -- alters with changes in temperature. The importance of species sorting relative to acclimation and adaptation has not previously been explored in the context of microbial community responses to changing temperature. "

To address this, the team carried out a species sorting experiment, where they grew replicate soil bacteria communities collected from a single site at different temperatures ranging from 4°C to 50°C. They then measured the growth and metabolism of each isolated strain of bacteria across these different temperatures to determine their thermal performance, and studied the genetic sequences of isolated bacteria to see how temperature-response traits evolved over time.

They found that evolutionarily and functionally distinct communities emerged at each of the temperature conditions, driven by the resuscitation of microbial strains that had been inactive under previous environmental conditions. This suggests that -- rather than new bacteria moving into a community to suit the new conditions -- the parent community harbours multiple bacterial strains that are pre-adapted to survive at different temperatures and can switch on when their preferred temperature is reached. As a result, microbial communities in nature are likely to be able to respond rapidly to temperature fluctuations.

"Understanding the relative importance of acclimation, adaptation and species sorting in the assembly and turnover of microbial communities is key to determining how quickly they can respond to temperature changes. Until now, a mechanistic basis of these community-level responses had not been discerned ," concludes senior author Thomas Bell, Professor of Microbial Ecology at the Georgina Mace Centre for the Living Planet, Imperial College London. "We have found that the resuscitation of functional diversity within a microbial community can allow the whole community to survive in response to temperature changes. Further studies on other microbial communities -- such as those residing in water -- will support more accurate predictions of the effects of climate change on different ecosystems."