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Biomedical subjects

Paul B Rainey

Publications and source records attributed to Paul B Rainey.

8 recordsLinked to original sources
PubMed2003

Evolution of cooperation and conflict in experimental bacterial populations.

A fundamental problem in biology is the evolutionary transition from single cells to multicellular life forms. During this transition the unit of selection shifts from individual cells to groups of cooperating cells. Although there is much theory, there are few empirical studies. Here we describe an evolutionary transition that occurs in experimental populations of Pseudomonas fluorescens propagated in a spatially heterogeneous environment. Cooperating groups are formed by over-production of an adhesive polymer, which causes the interests of individuals to align with those of the group. The costs and benefits of cooperation, plus evolutionary susceptibility to defecting genotypes, were analysed to determine conformation to theory. Cooperation was costly to individuals, but beneficial to the group. Defecting genotypes evolved in populations founded by the cooperating type and were fitter in the presence of this type than in its absence. In the short term, defectors sabotaged the viability of the group; but these findings nevertheless show that transitions to higher orders of complexity are readily achievable, provide insights into the selective conditions, and facilitate experimental analysis of the evolution of individuality.

Bacterial Adhesion↗
PubMed2002

The role of parasites in sympatric and allopatric host diversification.

Exploiters (parasites and predators) are thought to play a significant role in diversification, and ultimately speciation, of their hosts or prey. Exploiters may drive sympatric (within-population) diversification if there are a variety of exploiter-resistance strategies or fitness costs associated with exploiter resistance. Exploiters may also drive allopatric (between-population) diversification by creating different selection pressures and increasing the rate of random divergence. We examined the effect of a virulent viral parasite (phage) on the diversification of the bacterium Pseudomonas fluorescens in spatially structured microcosms. Here we show that in the absence of phages, bacteria rapidly diversified into spatial niche specialists with similar patterns of diversity across replicate populations. In the presence of phages, sympatric diversity was greatly reduced, as a result of phage-imposed reductions in host density decreasing competition for resources. In contrast, allopatric diversity was greatly increased as a result of phage-imposed selection for resistance, which caused populations to follow divergent evolutionary trajectories. These results show that exploiters can drive diversification between populations, but may inhibit diversification within populations by opposing diversifying selection that arises from resource competition.

Animals↗
PubMed2002

Mechanisms linking diversity, productivity and invasibility in experimental bacterial communities.

Decreasing species diversity is thought to both reduce community productivity and increase invasibility to other species. However, it remains unclear whether identical mechanisms drive both diversity-productivity and diversity-invasibility relationships. We found a positive diversity-productivity relationship and negative diversity-invasibility and productivity-invasibility relationships using microcosm communities constructed from spatial niche specialist genotypes of the bacterium Pseudomonas fluorescens. The primary mechanism driving these relationships was a dominance (or selection) effect: more diverse communities were more likely to contain the most productive and least invasible type. Statistical elimination of the dominance effect greatly weakened the diversity-invasibility relationship and eliminated the diversity-productivity relationship, but also revealed the operation of additional mechanisms (niche complementarity, positive and negative interactions) for particular combinations of niche specialists. However, these mechanisms differed for invasibility and productivity responses, resulting in the invasibility-productivity relationship changing from strongly negative to weakly positive. In the absence of the dominance effect, which may be an experimental artefact, decreasing diversity can have unexpected or no effects on ecosystem properties.

Colony Count, Microbial↗
PubMed2002

Antagonistic coevolution between a bacterium and a bacteriophage.

Antagonistic coevolution between hosts and parasites is believed to play a pivotal role in host and parasite population dynamics, the evolutionary maintenance of sex and the evolution of parasite virulence. Furthermore, antagonistic coevolution is believed to be responsible for rapid differentiation of both hosts and parasites between geographically structured populations. Yet empirical evidence for host-parasite antagonistic coevolution, and its impact on between-population genetic divergence, is limited. Here we demonstrate a long-term arms race between the infectivity of a viral parasite (bacteriophage; phage) and the resistance of its bacterial host. Coevolution was largely driven by directional selection, with hosts becoming resistant to a wider range of parasite genotypes and parasites infective to a wider range of host genotypes. Coevolution followed divergent trajectories between replicate communities despite establishment with isogenic bacteria and phage, and resulted in bacteria adapted to their own, compared with other, phage populations.

Biological Evolution↗
PubMed2002

Adaptive divergence in experimental populations of Pseudomonas fluorescens. I. Genetic and phenotypic bases of wrinkly spreader fitness.

A central feature of all adaptive radiations is morphological divergence, but the phenotypic innovations that are responsible are rarely known. When selected in a spatially structured environment, populations of the bacterium Pseudomonas fluorescens rapidly diverge. Among the divergent morphs is a mutant type termed "wrinkly spreader" (WS) that colonizes a new niche through the formation of self-supporting biofilms. Loci contributing to the primary phenotypic innovation were sought by screening a WS transposon library for niche-defective (WS(-)) mutants. Detailed analysis of one group of mutants revealed an operon of 10 genes encoding enzymes necessary to produce a cellulose-like polymer (CLP). WS genotypes overproduce CLP and overproduction of the polymer is necessary for the distinctive morphology of WS colonies; it is also required for biofilm formation and to maximize fitness in spatially structured microcosms, but overproduction of CLP alone is not sufficient to cause WS. A working model predicts that modification of cell cycle control of CLP production is an important determinant of the phenotypic innovation. Analysis of >30 kb of DNA encoding traits required for expression of the WS phenotype, including a regulatory locus, has not revealed the mutational causes, indicating a complex genotype-phenotype map.

Adaptation, Physiological↗
PubMed2002

Autolysis and autoaggregation in Pseudomonas aeruginosa colony morphology mutants.

Two distinctive colony morphologies were noted in a collection of Pseudomonas aeruginosa transposon insertion mutants. One set of mutants formed wrinkled colonies of autoaggregating cells. Suppressor analysis of a subset of these mutants showed that this was due to the action of the regulator WspR and linked this regulator (and the chemosensory pathway to which it belongs) to genes that encode a putative fimbrial adhesin required for biofilm formation. WspR homologs, related in part by a shared GGDEF domain, regulate cell surface factors, including aggregative fimbriae and exopolysaccharides, in diverse bacteria. The second set of distinctive insertion mutants formed colonies that lysed at their center. Strains with the most pronounced lysis overproduced the Pseudomonas quinolone signal (PQS), an extracellular signal that interacts with quorum sensing. Autolysis was suppressed by mutation of genes required for PQS biosynthesis, and in one suppressed mutant, autolysis was restored by addition of synthetic PQS. The mechanism of autolysis may involve activation of the endogenous prophage and phage-related pyocins in the genome of strain PAO1. The fact that PQS levels correlated with autolysis suggests a fine balance in natural populations of P. aeruginosa between survival of the many and persistence of the few.

Bacterial Adhesion↗