Testing the mathematical model’s predictions. A: Members of the Mesodinium genus occupy different regions in model trait space. Within a single lineage, trait values can also be manipulated by altering prey type (e.g., M. chamaeleon’s plastid retention and photosynthetic capacity differ depending upon prey identity, Moeller & Johnson (2018)). B: Competition experiments will combine Mesodinium lineages under fixed environmental (prey and light) conditions. C: The outcome of competition will be measured via population dynamics. D: By measuring competitive outcomes as a function of environmental conditions (here, 16 measurements are represented by x’s, with outcomes colour coded), we can infer the shape of the fitness landscape (gray lines). We will repeat experiments with multiple Mesodinium lineage pairs.
A central challenge to the design of microbial systems is coupling desirable metabolic functions (e.g., biosynthesis of special molecules, degradation of waste products) with the energy sources required to support them. In microbial consortia, this challenge has been addressed by pairing different organisms with syntrophic life histories. However, this introduces a new challenge of managing potentially conflicting selection pressures that may destabilize the consortium. Here, we propose to lay the foundation for an alternate approach: directly coupling photosynthetic energy generation with other metabolic processes within a single organism. In this project, which spans two years of effort, we propose to combine mathematical and empirical approaches to elucidate the design potential of this system. We seek to specifically identify (1) the environmental conditions that favor plastid retention, (2) how these conditions selected for acquisition in natural systems, and (3) the evolved traits that underpin variable plastid reliance in the Mesodinium genus. This information will allow us to identify environments and organisms for which kleptoplasty—and other forms of acquired metabolism—may be a viable engineering goal.