What happens when organisms are exposed to higher temperatures?
Evolutionary biologist Macarena Toll-Riera takes us through her latest findings where she studies evolutionary changes in an Antarctic bacterium when exposed to a steady increase in temperatures.
We all have been alarmed about climate change. Anxiety aside, ever wondered how our bodies might adapt to these changes? According to the US National Oceanic and Atmospheric Administration (NOAA), global temperatures have risen by 0.08 ºC every decade since the 1890s, with the year 2021 being the hottest. Repercussions of this warming are already seen in the wild: on the coasts of Florida, sand temperatures have been above 31 ºC during summers for the last four seasons. As a result of this, every newborn sea turtle has been female and this has heavily skewed the sex ratios in sea turtle populations. In the deeper waters, many fish species are changing their spawning habitats and escaping to the cooler parts.
To study the effect of rising temperatures on cellular functions, scientists are exposing organisms to higher temperatures and monitoring the changes. These studies are often challenging, especially in large organisms due to their relatively small population numbers and bigger genomes. Small populations have fewer chances of survival when exposed to unfavorable conditions and might cause the entire population to decay, and eventually extinct. Microbes, on other hand, exist as large populations, have shorter generation times, and therefore, are excellent models to study these effects across many generations in a reasonable span of time.
Dr. Macarena Toll-Riera at the Institute for Integrative Biology, ETH-Zurich
Macarena chose an Antarctic bacterium, Pseudoalteromonas haloplanktis for her study because she was fascinated by the protein structures in cold-adapted microbes. “Since they must be stable at very low temperatures, their proteins are flexible and structurally different from mesophiles (organisms that grow between 20 ºC and 45 ºC)”, explains Macarena. Moreover, there are many features that are unique in cold-adapted organisms that would help understand the effects of temperature better. For instance, they have a larger thermal safety margin, that is, they live at temperatures that are several degrees below their upper thermal limit. At slightly higher temperatures, these cold-adapted bacteria tend to grow faster and this is baffling.
In this study, Macarena exposed the bacterial populations to periodically increasing temperatures ranging from 15 ºC to 30 ºC. “In my grant, I proposed to grow them until 37 ºC, but I found they didn’t grow beyond 30 ºC”, she adds stating that 30 ºC was the upper thermal tolerance for her bugs beyond which they could no longer survive.
Image credit: Gleb Ebert, doctoral researcher at ETH Zurich.
On sequencing the populations that survive at 30 ºC, she found prominent mutations in Lon protease, a protein that degrades abnormal proteins. In most organisms, Lon proteases degrade misfolded proteins and serve as a quality control mechanism. This mechanism breaks down beyond organisms’ upper thermal tolerance and causes cells to die. An ongoing study in the group aims to understand the role of the mutated Lon protease in bacterial death in depth.
Dr. Macarena Toll Riera is a PRIMA group leader at ETH, Zurich. The journey of this study was challenging for her as she had to juggle between her two pregnancies and the experiments. Moreover, the journal Science Advances took more than a year after submission to decide on the acceptance, which was a long and difficult wait “Indeed most of the time was waiting time, for example, we had to wait almost 4 months to get the first round of revisions! Luckily the revisions itself were quite straightforward” she explains.
This is a Behind-the-discovery article featuring the researchers’ vision behind the experiments and future directions. We also aim to highlight the challenges involved and other academic conversions. Write to us for a feature.