The impact of nonheritable variation in division rates on population growth across environments

TL;DR

This study shows that nonheritable variation in cell division rates influences bacterial and algal population growth, especially under stress, and can explain observed differences between strains and mutants.

Contribution

It introduces models incorporating inter-individual variation in division rates to explain population responses to environmental stress, validated with algae growth data.

Findings

Variation reduces growth in favorable environments.

Variation mitigates population decline under stress.

Mutants exhibit higher variability, explaining slower growth.

Abstract

We analyse a series of bacterial growth models with in-built inter-individual variation in rates of cell division. We show that this variation leads to reduced population growth in favorable regimes and reduced population killing in detrimental environments. By treating environmental stress as a model parameter, we then show that the reduction in population growth aggravates with stress. We apply these models to data on growth rates for populations of green algae {\em Clamydomonas reinhardtii}. Specifically, we compare growth rates of two ancestral strains and respective mutation accumulation lines, measured along a stress gradient. The data had previously shown mutants growing consistently slower than ancestors, and this effect aggravating with stress. Here we show that this trend is expected if mutants are more variable than ancestors in individual rates of cell division, even if their means are higher. This can open new prospects for prediction of how populations respond to environmental changes.