Bacteria are known to thrive in an incredibly wide variety of habitats and conditions ranging from the human gut to hot springs. Scientists are trying to understand how bacteria manage to learn to survive in various conditions and thus to learn about the process of evolution itself. For this, researchers often perturb environmental variables such as temperature or pH, usually one at a time, even though in nature such variables typically act together. In an effort to study what is likely the situation in nature, the research group of Dr. Sutirth Dey at IISER Pune has chosen to expose bacteria to unpredictable fluctuations in multiple environmental parameters.
The group exposed bacteria to different combinations of conditions (pH, salt, hydrogen peroxide), where the successive environments were picked randomly. After 30 days the group monitored the growth rate of the bacteria.
Describing their observations, Dey said, “We had expected that the bacteria would do better in the environment in which they have been selected. This did not happen. Instead, we found that the growth rate of the bacteria was higher under conditions like antibiotics and heavy metals, environments that they had never experienced before”
On further investigation, the group found that this ability to withstand new environments/stresses is not related to an increased mutation rate and could instead be related to their increased ability to throw out toxins from the cell (efflux activity).
“We found that exposure to unpredictable fluctuations in the environment could itself help bacteria evolve an increased ability to throw out toxins, including antibiotics, from the cell at a faster rate. This surprising observation gives us new clues to understanding evolvability in bacteria”, said Dey summarizing their findings.
It is commonly thought that injudicious use of antibiotics cause antibiotic-resistance in bacteria. This study opens the possibility that environmental variability can potentially lead to similar outcomes. Given that the climatic variability has increased greatly over the last few years, it is likely that bacteria could display resistance against drugs they haven’t been exposed to before. This could potentially have serious public health consequences.
This work has recently been published in the Journal of Evolutionary Biology (28:1131-1143) and was authored by Shraddha Karve, Sachit Daniel, Yashraj Chavhan, Abhishek Anand, Somendra Singh Kharola and Sutirth Dey.
This research received financial support from the Department of Biotechnology, Government of India and internal funding from Indian Institute of Science Education and Research, Pune.
–Reported by Shanti Kalipatnapu