Experimental Tests for an Evolutionary Trade‐Off between Growth Rate and Yield inE. coli

Abstract

Theoretical studies have predicted a trade-off between growth rate and yield in heterotrophic organisms. Here we test for the existence of this trade-off by analyzing the growth characteristics of 12 E. coli B populations that evolved for 20,000 generations under a constant selection regime. We performed three different tests. First, we analyzed changes in growth rate and yield over evolutionary time for each population. Second, we tested for a negative correlation between rate and yield across the 12 populations. Finally, we isolated clones from four selected populations and tested for a negative correlation between rate and yield within these populations. We did not find evidence for a trade-off based on the first two tests. However, we did observe a trade-off based on the within-population correlation of yield and rate. Our results indicate that, at least for the populations studied here, an analysis of the within-population diversity might be the most sensitive test for the existence of a trade-off. The observation of a trade-off within, but not between, populations suggests that the populations evolved different genetic solutions for growth in the selective environment, which in turn led to different physiological constraints.

Population consequences of mutational events: effects of antibiotic resistance on the r/K trade-off

“…Any trade-off between r max and K could then be observed, and would in fact be expected. Long-term evolution experiments using E. coli support this prediction (Novak et al 2006). After evolutionary time periods most populations were found to consist of strains that displayed a negative association between r max and K (Novak et al 2006), consistent with the hypothesis that selection removed the variation in overall fitness contributed by mutation over time, revealing a functional trade-off between r max and K. The main conclusion we can draw is that mutation is not bound by any inherent functional or physiological constraint that generates a trade-off between r max and K. Rather, such trade-offs are the product of the combination of mutation and selection.…”

Bacterial Quorum Sensing Stabilizes Cooperation by Optimizing Growth Strategies

“…In contrast, the ⌬luxOU mutant maximizes growth yield at the expense of a lower overall growth rate, particularly at low cell densities, which allows it to perform well in monoculture but renders it susceptible to defector invasion. This contrast in growth strategies has relevance to previous investigations into the trade-offs between growth rate and growth yield, and the plasticity conferred by QS may allow cells to evade this trade-off by matching growth strategies appropriately to the prevailing environmental conditions (60)(61)(62).…”

The yield of experimental yeast populations declines during selection

“…Other experiments have failed to find evidence for a trade-off between growth rate and yield. Novak et al [20] analysed populations of Escherichia coli over 20 000 generations of selection in a glucoselimited environment and observed a trade-off among genotypes isolated from single samples (one replicate population at a single time-point), but not among 12 replicate populations after 20 000 generations of selection, nor across samples isolated at different time-points for each selection line (which was our strategy). These results are difficult to interpret because yield was estimated on microwell plates (200 ml) whereas selection was performed in 10 ml of media in Erlenmeyer flasks.…”

“…These results are difficult to interpret because yield was estimated on microwell plates (200 ml) whereas selection was performed in 10 ml of media in Erlenmeyer flasks. Furthermore, Novak et al [20] assayed whole-population samples to test for a decline in yield during selection, and the genetic variation along the rate/yield trade-off within the samples may have masked that trade-off.…”