Typically, the number of individuals in a population is a good estimate of whether or not bacteria can evolve under certain conditions. Larger populations carry more biological variation and adapt faster to new environments. This primarily happens as at least some of the population may cope with the sudden changes in the environment. However, this makes them more vulnerable to the new environment. Dr. Sutirth Dey’s lab at IISER Pune recently investigated this question in depth.

The lab performed experiments with E coli populations of various sizes and introduced them into a mixture of three antibiotics. They were made to evolve for four hundred generations. They studied if adapting in larger numbers under constant environment makes the E coli populations more capable of facing future changes in environmental conditions.

They measured the efflux activity of E coli. Efflux activity is defined as the bacteria’s ability to pump out unwanted material of the cell. The group observed that efflux activity is higher for smaller populations while it decreased for larger populations. While larger population adapts faster in alternative environments, its fitness level is worse compared to smaller population.

This study is the first of its kind which shows that larger populations of bacteria become more vulnerable to stresses created by novel environments. Evolution of drug resistance is an important topic today. This study demonstrates a novel link between population size and immediate response to environmental changes and contributes to the field of evolution. It also provides insights on such populations when they experience environmental changes in spurts.

Reference article: Chavhan, Y. D.,  Karve, S. M., and Dey, S. 2019. Adapting in larger numbers can increase the vulnerability of Escherichia coli populations to environmental changes. Evolution 73:836-846. DOI: 10.1111/evo.13700.

This work received funding from the Department of Biotechnology, Council for Scientific and Industrial Research (CSIR), and IISER Pune.

Compiled with inputs from Prof. Sutirth Dey, IISER Pune

- Reported by Dr. Madhura Joglekar, Graphic by Rafeeque Mavoor