Bacteria capable of rapidly evolving cannot withstand an increase in heat that exceeds their maximum tolerable temperature by one degree: they will not resist global warming, which has already recorded the hottest temperature in the last 10,000 years. .
Cold-tolerant bacteria living in Antarctica cannot genetically adapt to extreme heat spikes caused by global warming, a study that examined the limits of evolutionary adaptation of an iconic bacterium has found.
the biologist Macarena Toll Rierafrom ETH Zurich and his team, investigated a bacterium called Pseudoalteormonas haloplanktiswhich lives in Antarctic coastal waters and is one of the best-studied cold-adapted organisms.
This bacterium can live at temperatures ranging from 2.5 ºC below zero to 29 ºC, but shows the first signs of heat stress from 20 ºC.
In their study, published in the journal “Science Advances”, the researchers explain that they have cultivated the Antarctic bacterium for hundreds of generations at increasingly hot temperatures, to observe how it adapts evolutionarily to these environmental changes.
They observed that populations could only shift their survival limit an additional degree Celsius. At higher temperatures, everything stops for these bacteria: even after the researchers continued to grow the bacteria for 300 generations at 30 degrees, no populations survived the 31 degree mark.
The study authors attribute the limit of evolutionary salvation primarily to misfolded proteins that accumulate and no longer break down when heat increases.
They identified up to 940 mutations in the sequenced genomes. The most common genetic mutation was located in the so-called lon proteasewhich plays an important role in the removal of protein debris – fails at temperatures above 30 degrees.
They also detected two other significant mutations, present between 87.5% and 85% of the bacteria subjected to heat: they affect, respectively, the reduction in the number of one of the two chromosomes possessed by the bacterium studied and the biosynthesis of its wall (which surrounds and protects the bacterial cell).
The problem is that why these mutations occur and how they help manage heat isn’t known, so the experiments the new research provides don’t bode well for the future ability of bacterial organisms to adapt to ongoing climate change.
While the researchers did their best to promote a gradual evolutionary thermal adaptation of P. haloplanctisand although bacteria are by nature rapidly evolving organisms, they could not gain more than 1°C of maximum tolerance.
They point out in their article that, although global climate change is a gradual process, it also brings abrupt and extreme weather events, such as heat waves, hurricanes and droughts, whose impacts on bacterial populations seem worrying. .
They point out that these episodes are already significantly affecting wild populations and have even led to the extinction of some local populations of bumblebees, corals, bats and algae.
There is a genetic mechanism scalable rescue, by which a population, which would have disappeared in the face of increased temperature, pollution or any other environmental stressor, is able to survive thanks to the appearance of new mutations which confer resistance. But evolutionary rescue also has its limits.
Because evolutionary rescue is more difficult in large macroscopic organisms with smaller populations, rescue limits will be more common for microbial organisms, especially if they live at temperatures close to their thermal tolerance and are affected by events extreme weather: they can cause temperatures above their thermal. tolerance.
Models predict that if global warming reaches 3.5°C by the end of the 21st century, marine heat waves will increase in length, intensity and frequency, reaching an average duration of 112 days and 2.5° C above the maximum sea surface temperature, the researchers point out in their paper.
Currently, the average global temperature increase is 1.2ºC above pre-industrial levels: the current temperature is the hottest in the last 10,000 years and three times higher than the average temperature of the last 2,000 years.
Bacteria also struggle to survive in these environments that we record and experience on a human scale, in an endless ascent into the unknown.
A limit to the evolutionary rescue of an Antarctic bacterium in the face of rising temperatures. Macarena Toll-Riera et al. Science Advances, July 15, 2022, Vol 8, Issue 28. DOI:10.1126/sciadv.abk3511