MICROCOSMS · Exploring microbial community stability across mutational spectra

Interactions in which all partners benefit, known as mutualisms, underpin many vital ecosystem functions all across nature. Recent work by myself and others has shown that mutualisms can readily break down via a few independence-enabling mutations, especially under environmental stress. Understanding the mechanisms that ensure mutualism stability is of increased importance for environmental, health, and societal problems. An unexplored question is the impact that large variations in mutational rates and spectra can have on in this process. Indeed, mutator strains, variants with highly elevated and biased mutation rates, readily take over microbial populations when there is ample adaptive opportunity, such as under environmental stress. These dramatic changes in spontaneous mutagenesis can have opposing effects on mutualism stability. On the one hand, they can lead to adaptive mutations appearing more rapidly, promoting partners survival and hence stabilising mutualisms. On the other hand, they may accelerate the acquisition of independence-enabling mutations, hence destabilising mutualism. With MICROCOSMS, I will address this open question by combining computer simulation with experimental evolution and genomics. I will experimentally evolve pairwise auxotrophic E. coli communities, genetically engineered to contain mutator variants that alter the mutational spectrum available. Pairwise communities will be assessed for mutualism stability when subject to both adaptive evolution, under strong antibiotic pressure, and non-adaptive evolution, where populations are subject to severe bottlenecking. These will be matched to simulations predicting the outcome of adaptive and non-adaptive evolution. By producing key insights into the stability of mutualisms under environmental stress, MICROCOSMS will form a knowledge base that will aide in protecting environmental and human-based ecosystems against disruptions.