Experimental Evolution of Bacillus subtilis Populations in Space: Mutation, Selection and Population Dynamics (MVP Cell-02)

The Experimental Evolution of Bacillus subtilis Populations in Space: Mutation, Selection and Population Dynamics (MVP Cell-02) investigation seeks to understand how organisms adapt to the space environment, an important component of future space exploration. Microbes may play fundamental roles in the development of biologically-based closed-loop regenerative life support, in-situ resource utilization, and will have extensive interactions with human and plant hosts. Further, microbes may pose challenges through virulence and contamination, and as nuisance factors such as biofilms in water supply and ventilation systems.

The goal of Experimental Evolution of Bacillus subtilis Populations in Space: Mutation, Selection and Population Dynamics (MVP Cell-02) is to understand the effects of the space environment on evolutionary processes in the bacterium Bacillus subtilis. Different mutant lines are grown along solid surfaces to allow continuous selection in the cultures, and to maximize the number of generations possible. Sequencing of winners identifies evolutionary rates, mechanisms, and targets of selection. The research team proposes printing wax barriers to make paths along a growth surface (polyethersulfone membranes), and spotting each starting position of each path with dormant spores of the experimental bacteria to ‘race’ different mutants.

Once on orbit, the material is wetted with growth medium, allowing the individual spots of B. subtilis to grow along their determined paths. This approach provides an opportunity for exponential growth only along the propagating edges, generating continuous selection, and amplifying selective pressures on the experimental populations. By monitoring the respective growth rate of different mutant lines maintained in each of these experimental conditions, the relative fitness of the lines can be estimated. Long-term changes in relative growth rate indicate adaptation.

Genomic sequencing of DNA from adapted cells (‘winners’ at the end of runs) identifies genetic changes within the respective populations. It is expected that rates of evolution will differ between microgravity, 1-g, and ground controls, and that the targets of mutations will differ as the different populations of bacteria adapt to their respective conditions. This research also utilizes the native ability of B. subtilis to uptake foreign DNA. Information-rich environmental DNA is added into the growth medium, and the populations are grown as above. By sampling the winners, and identifying if/what foreign genes are assimilated in each treatment, this experiment identifies potential genes of interest for future studies of genetic adaptation to the space environment.

This approach maximizes the number of generations possible, and maximizes the potential for evolutionary processes to occur. Multi-generational experimental evolution on bacteria aims to advance understanding of the evolutionary processes and challenges facing biological systems in long-term space exploration and habitation.

Given their large population sizes, short generation times, and central roles as both beneficial and detrimental factors relevant to long-term human spaceflight, it is essential to better understand the effects of the space environment on microbial evolutionary processes including mutation, selection, adaptation, and the identification of targets of selection unique to space and spaceflight. By performing multi-generational experimental evolution on bacteria on the International Space Station, this investigation aims to advance understanding of the evolutionary processes and challenges facing biological systems in long-term space exploration and habitation.

Results from this investigation could advance understanding of the evolutionary process and the dynamics of adaptive evolution in a model bacterium.

Space Station Research Explorer

ARC Space Biosciences

Redwire Space