Microorganisms are the most abundant and diverse forms of life on Earth. Owing to their metabolic
versatility and capacity for rapid growth, they have played a central role in regulating
biogeochemical processes that ensure our planet’s habitability. Rarely, however, do species
experience conditions that are optimal for growth and reproduction. Many organisms contend with
these challenges by engaging in dormancy, a universal process whereby individuals enter a
reversible state of reduced metabolic activity. Dormancy generates a “seed bank” of long-lived
individuals that buffers a wide range of ecological processes, but dormancy is also a life-history
process that is shaped by the forces of evolution. In this proposal, we seek to understand the
maintenance of dormancy by studying spore-forming bacteria (i.e., Bacillus) when faced by
varying degrees of energy limitation. Sporulation is a complex and conserved trait that originated
billions of years ago. Nevertheless, sporulation can easily be lost under “good” conditions in just
hundreds of generations, which has consequences for the persistence and evolution of microbial
lineages. Advances in high-throughput sequencing technology provide unprecedented opportunity
for studying the evolution of dormancy, which will help us better understand the distribution,
abundance, and activity of life on Earth and perhaps elsewhere in the universe.
From test tubes to the globe, the overarching goal of our research is to identify the key ecological
and evolutionary processes that generate and maintain microbial biodiversity (Locey and Lennon
2016). In the current proposal we investigate how sporulation, a hallmark trait of a globally
dominant group of microorganisms, is maintained in the face of fluctuating and extreme
environmental conditions. Specifically, we address three major objectives pertaining to the
evolution of dormancy and energy limitation:
1) Accounting for genomic, transcriptional, and translational expenditures, we will estimate the
bioenergetic cost of making a spore and use this information to then model and predict scenarios
that favor the evolutionary retention versus loss of sporulation.
2) Using controlled and replicated experimental evolution trials, we will quantify the rate at which
sporulation is lost and then characterize how bacteria subsequently evolve when challenged by
contrasting energy regimes.
3) Leveraging large existing metagenomic databases, we will evaluate the loss of sporulation in a
range of ecosystems and use phylogenetic comparative methods to test theoretical predictions
about how trait decay should affect lineage diversification and rates of evolutionary change.
Our research team is uniquely qualified to accomplish the objectives of the proposed research.
Together, we have expertise in theoretical ecology and evolution, microbiology, genomics,
bioinformatics, and the biogeochemistry of energy-limited ecosystems. Novel evolutionary insight
into sporulation and alternate forms of dormancy will aid in understanding the long-term survival
and resilience of populations in the modern-day biosphere while shedding light on early Earth
evolution, including the persistence of life through mass extinction events. In addition to
generating basic knowledge regarding the robustness of complex traits, our findings will have
practical implications for planetary protection during future NASA missions.