Applying bacterial growth theory to understand the evolution of thermal performance

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Temperature affects biology at all levels, from single molecules to whole organisms. However, the effects of temperature on important cellular processes including protein synthesis and nutrient uptake remain poorly understood. Resolution of this longstanding and hotly debated puzzle is essential for developing a better understanding of how organisms respond to long-term changes in environmental temperature. Here, the investigators will address this issue for two groups of bacteria from extreme environments that have independently adapted to high temperatures. The approach will combine the extension of recently developed theory with the novel application of new technologies for monitoring protein synthesis. This research will provide a general predictive framework with the potential to transform our understanding of the evolution of thermal physiology. The investigators will also integrate research and education through mentoring and outreach at both K-12 and university levels. Graduate students will be trained to communicate their research to the general public, increasing the outreach efforts to the community. Modules on effect of temperature on biological systems will be developed and presented at different venues to reach a broad spectrum of K-12 students. Finally, underrepresented students will be involved in all aspects of this research.Understanding the links between temperature, metabolism and fitness remains a fundamental challenge in evolutionary physiology. The longstanding debate over the relative importance of thermodynamic effects on physiological rates versus biochemical adaptation for the temperature dependence of organism performance has been particularly contentious. To better distinguish among alternative mechanisms that may contribute to the evolution of thermal performance, the PI proposes to extend recently developed theory on the interdependence of microbial growth rate and gene expression to investigate how temperature effects on fitness arise from both thermodynamic effects on metabolic rates and cell allocation trade-offs between protein synthesis and nutrient metabolism. Growth theory models will determine the relationship between growth rate and resource allocation at different temperatures for ecologically divergent members of two clades of thermophilic cyanobacteria that have convergently radiated along geothermal gradients. Further, characterization of ribosome activity with a next-generation sequencing approach will connect the organism-level phenomena described by the models with their underlying molecular mechanisms of gene expression. The experimental design will enable the determination of the relative contributions of temperature effects on physiological rates versus temperature-compensating, adaptive mechanisms for the evolution of thermal performance. It will improve on existing theory by simultaneously accounting for both the temperature effects on metabolic rates and the constraints imposed on growth by finite cellular resources, thereby enabling improved predictions for how gene expression, metabolism and fitness change along an organism's thermal niche. Together, the research will provide a fresh perspective on the mechanisms that drive niche differentiation and thermal specialization. The educational impacts of these research will also involve training and mentoring of students from the postdoctoral level to K-12 and include students from underrepresented populations.This project is co-funded by the Integrative Ecological Physiology Program in the Division of Integrative Organismal Systems and by the Experimental Program to Stimulate Competitive Research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.