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Surfing on the seascape: Adaptation in a changing environment.

ABSTRACT: The environment changes constantly at various time scales and, in order to survive, species need to keep adapting. Whether these species succeed in avoiding extinction is a major evolutionary question. Using a multilocus evolutionary model of a mutation-limited population adapting under strong selection, we investigate the effects of the frequency of environmental fluctuations on adaptation. Our results rely on an "adaptive-walk" approximation and use mathematical methods from evolutionary computation theory to investigate the interplay between fluctuation frequency, the similarity of environments, and the number of loci contributing to adaptation. First, we assume a linear additive fitness function, but later generalize our results to include several types of epistasis. We show that frequent environmental changes prevent populations from reaching a fitness peak, but they may also prevent the large fitness loss that occurs after a single environmental change. Thus, the population can survive, although not thrive, in a wide range of conditions. Furthermore, we show that in a frequently changing environment, the similarity of threats that a population faces affects the level of adaptation that it is able to achieve. We check and supplement our analytical results with simulations.

SUBMITTER: Trubenova B

PROVIDER: S-EPMC6771940 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Bacterial rapid surfing motility is a novel surface adaptation of Pseudomonas aeruginosa in the presence of the glycoprotein mucin. Here, we show that other Gram-negative motile bacterial species, including Escherichia coli, Salmonella enterica, Vibrio harveyi, Enterobacter cloacae, and Proteus mirabilis, also exhibit the physical characteristics of surfing on the surface of agar plates containing 0.4% mucin, where surfing motility was generally more rapid and less dependent on medium viscosity than was swimming motility. As previously observed in Pseudomonas aeruginosa, all surfing species exhibited some level of broad-spectrum adaptive resistance, although the antibiotics to which they demonstrated surfing-mediated resistance differed. Surfing motility in P. aeruginosa was found to be dependent on the quorum-sensing systems of this organism; however, this aspect was not conserved in other tested bacterial species, including V. harveyi and S. enterica, as demonstrated by assaying specific quorum-sensing mutants. Thus, rapid surfing motility is a complex surface growth adaptation that is conserved in several motile bacteria, involves flagella, and leads to diverse broad-spectrum antibiotic resistance, but it is distinct in terms of dependence on quorum sensing.IMPORTANCE This study showed for the first time that surfing motility, a novel form of surface motility first discovered in Pseudomonas aeruginosa under artificial cystic fibrosis conditions, including the presence of high mucin content, is conserved in other motile bacterial species known to be mucosa-associated, including Escherichia coli, Salmonella enterica, and Proteus mirabilis Here, we demonstrated that key characteristics of surfing, including the ability to adapt to various viscous environments and multidrug adaptive resistance, are also conserved. Using mutagenesis assays, we also identified the importance of all three known quorum-sensing systems, Las, Rhl, and Pqs, in P. aeruginosa in regulating surfing motility, and we also observed a conserved dependence of surfing on flagella in certain species.

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Surfing on the seascape: Adaptation in a changing environment.

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