The finding is based on research conducted on bacteria living on opposite sides of 'Evolution Canyons' I and II in Israel, which has a hot and cold facing slope.
The scientists came to their conclusion by looking at the appearance of the bacteria as well as their genes, and are now hoping that their study will start a new trend in research.
'Evolution Canyons' I and II are similar, each with a hot south-facing slope and a cooler north-facing slope. The sun-exposed 'African' south-facing slopes get eight times more solar radiation than the shady, green, lush 'European' north-facing slopes.
In the study, the researchers analysed 131 strains of Bacillus simplex and found that bacteria on different slopes have evolved differently, forming different 'ecotypes' of the same species.
"We expected that 'ecotype' formation was linked to temperature but we had no initial clue of which specific cell attributes could have led to the adaptation. To find out, we definitely had to study the appearance of the bacteria, not only their genes," said Dr Johannes Sikorski from DSMZ in Germany.
The cell membrane is one of the most important and complex parts of a cell, containing different fatty acid molecules, of which the branching type can change depending on temperature to keep the cell alive.
The researchers discovered significant differences in the fatty acids of several ecotypes that live on different slopes in Evolution Canyon.
"Bacteria respond to temperature by altering their fatty acid composition in a constitutive, long-term fashion. We found that 'African' ecotypes from the hot slopes had more heat-tolerant fatty acids and 'European' ecotypes from the cool slopes had more cold-tolerant fatty acids in their membranes," said Sikorski.
While most of the modern evolutionary studies rely on genetic data alone, this study focussed on the result of the genetic changes, i.e. what the bacteria look like.
"It is not a 'sexy' technique like genomics or proteomics but it gives a more comprehensive insight into the result of adaptation of the cell membrane. Right now it is not possible to deduce the composition of a cell membrane using genomics or proteomics alone. To understand evolution we need to explain the consequences of genetic differences for the organism in its natural environment," said Sikorski.
The study is published in the August issue of Microbiology.