Fig 1.
Overview of the Saccharomyces cerevisiae multi-mutualist system, strain types, and experimental environments.
(a) Schematic representation of the engineered strains used in this study and how they were combined to assemble different community types. Two metabolic overproduction backgrounds were used: an adenine-overproducing strain unable to synthesize lysine (AdeOP) and a lysine-overproducing strain unable to synthesize adenine (LysOP). Communities were constructed by pairing four AdeOP strains with four LysOP strains, generating multiple unique cross-feeding consortia (b) Experimental media conditions. Communities of Saccharomyces cerevisiae overproduction strains growing in media with and without external resources present. The communities were grown in two types of media: no external resources added (light yellow background) and with some external resources added (darker yellow background). Replicate communities growing in these media types were maintained for four weeks.
Fig 2.
Plot of proportion of evolving multi-mutualist communities that retained strains of adenine overproducers (AdeOP) and lysine overproducers (LysOP) of Saccharomyces cerevisiae.
Communities with no external mutualistic resources in the media lost more strains over time. AdeOP strains were lost more frequently than LysOP strains under obligate and when external nutrients were present in the media. Adding nutrients to the media increased individual strain persistence for both mutualist types.
Fig 3.
Individual strain persistence over time of adenine overproducers (AdeOP, left panel) and lysine overproducers (LysOP, right panel) of Saccharomyces cerevisiae.
Each colored line represents a distinct genotype within the AdeOP or LysOP guild (strain IDs shown in the legend; full genotypes listed in S1 Table). Error bars indicate the standard error of the proportion of replicate communities in which the strain persisted (calculated as √(p(1 − p)/n), where p is the persistence proportion and n is the number of replicate communities). Communities with no external resources in the media lost strains more quickly and more strains over time. This effect was more pronounced for adenine overproducers.
Fig 4.
Starvation resistance of ancestral and evolved Saccharomyces cerevisiae mutualist types over time.
a) Adenine overproducing (AdeOP) strains perish at a faster rate than b) Lysine overproducing strains (LysOP). The dotted lines at 48 and 72 h for LysOP strains are estimates since mortality was first measured at 96 h.
Fig 5.
Measurement of trait evolution.
Changes in A) overproduction B) resource use efficiency C) growth rate in a) adenine overproducers (AdeOP) and b) lysine overproducers (LysOP) of Saccharomyces cerevisiae after 4 weeks of evolution in media with and without external resources present. Statistical analyses were performed using linear mixed-effects models, with significance of fixed effects assessed using F tests (lmerTest package in R). Letters denote statistically significant differences at P < 0.05. Overproduction and resource use efficiency in both overproducer types changed depending upon the media type in which communities were maintained. Growth rate did not change significantly for either overproduction type.