- Zeng, Quan

Bacterial etiolation and decline (BED), caused by Acidovorax avenae, is an emerging disease of creeping bentgrass on golf courses in the United States. We performed the first comprehensive analysis of A. avenae on a nationwide collection of turfgrass- and maize-pathogenic A. avenae. Surprisingly, our results reveal that the turfgrass-pathogenic A. avenae in North America are not only highly divergent but also belong to two distinct phylogroups. Both phylogroups specifically infect turfgrass but [Read more]

- Bertels, Frederic

Mobile genetic elements can be found in almost all genomes. Possibly the most common nonautonomous mobile genetic elements in bacteria are repetitive extragenic palindromic doublets forming hairpins (REPINs) that can occur hundreds of times within a genome. The sum of all REPINs in a genome can be viewed as an evolving population because REPINs replicate and mutate. In contrast to most other biological populations, we know the exact composition of the REPIN population and the sequence of each me [Read more]

- Doulcier, Guilhem

Interactions among microbial cells can generate new chemistries and functions, but exploitation requires establishment of communities that reliably recapitulate community-level phenotypes. Using mechanistic mathematical models, we show how simple manipulations to population structure can exogenously impose Darwinian-like properties on communities. Such imposition causes communities to participate directly in the process of evolution by natural selection and drives the evolution of cell-level int [Read more]

- Rose, Caroline J.

The evolutionary transition to multicellularity has occurred on numerous occasions, but transitions to complex life forms are rare. While the reasons are unclear, relevant factors include the intensity of within versus between group selection that are likely to shape the course of life cycle evolution. A highly structured environment eliminates the possibility of mixing between evolving lineages thus ensuring strong competition between groups. Less structure intensifies competition within groups [Read more]

- Black, Andrew J.

Evolutionary transitions in individuality are central to the emergence of biological complexity. Recent experiments provide glimpses of processes underpinning the transition from single cells to multicellular life and draw attention to the critical role of ecology. Here we emphasise this ecological dimension and argue that its current absence from theoretical frameworks hampers development of general explanatory solutions. Using mechanistic mathematical models, we show how a minimal ecological s [Read more]

- Yıldırım, Yeşerin

Pleurobranchaea maculata is a rarely studied species of the Heterobranchia found throughout the south and western Pacific–and recently recorded in Argentina–whose population genetic structure is unknown. Interest in the species was sparked in New Zealand following a series of dog deaths caused by ingestions of slugs containing high levels of the neurotoxin tetrodotoxin. Here we describe the genetic structure and demographic history of P. maculata populations from five principle locations in New [Read more]

- Bertels, Frederic

Convergent evolution describes the process of different populations acquiring similar phenotypes or genotypes. Complex organisms with large genomes only rarely and only under very strong selection converge to the same genotype. In contrast, independent virus populations with very small genomes often acquire identical mutations. Here we test the hypothesis of whether convergence in early HIV-1 infection is common enough to serve as an indicator for selection. To this end, we measure the number of [Read more]

- Pichugin, Yuriy

Author summary Mode of reproduction is a defining trait of all organisms, including colonial bacteria and multicellular organisms. To produce offspring, aggregates must fragment by splitting into two or more groups. The particular way that a given group fragments defines the life cycle of the organism. For instance, insect colonies can reproduce by splitting or by producing individuals that found new colonies. Similarly, some colonial bacteria propagate by fission or by releasing single cells, w [Read more]

- Czuppon, Peter

Sexually reproducing populations with self-incompatibility bear the cost of limiting potential mates to individuals of a different type. Rare mating types escape this cost since they are unlikely to encounter incompatible partners, leading to the deterministic prediction of continuous invasion by new mutants and an ever increasing number of types. However, rare types are also at an increased risk of being lost by random drift. Calculating the number of mating types that a population can maintain [Read more]

- Gerth, M.L.

Cupins form one of the most functionally diverse superfamilies of proteins, with members performing a wide range of catalytic, non-catalytic, and regulatory functions. HutD is a predicted bicupin protein that is involved in histidine utilization (Hut) in Pseudomonas species. Previous genetic analyses have suggested that it limits the upper level of Hut pathway expression, but its mechanism of action is unknown. Here, we have determined the structure of PfluHutD at 1.74 Å resolution in several cr [Read more]

- Shewaramani, Sonal

Author Summary When organisms are exposed to different environments, the rates and types of mutations that spontaneously arise in each environment can vary due to differing mutagenic pressures imposed by each environment, and these can potentially influence the evolution of the organism. Little is known about the types of mutations that arise when facultative anaerobes are grown in the absence of oxygen. To investigate the effect of oxygen availability on spontaneous mutation at the genome level [Read more]

- Colombi, Elena

Horizontal gene transfer can precipitate rapid evolutionary change. In 2010 the global pandemic of kiwifruit canker disease caused by Pseudomonas syringae pv. actinidiae (Psa) reached New Zealand. At the time of introduction, the single clone responsible for the outbreak was sensitive to copper, however, analysis of a sample of isolates taken in 2015 and 2016 showed that a quarter were copper resistant. Genome sequences of seven strains showed that copper resistance – comprising czc/cusABC and c [Read more]

- Lind, Peter A.

Model microbial systems provide opportunity to understand the genetic bases of ecological traits, their evolution, regulation and fitness contributions. Experimental populations of Pseudomonas fluorescens rapidly diverge in spatially structured microcosms producing a range of surface-colonising forms. Despite divergent molecular routes, wrinkly spreader (WS) niche specialist types overproduce a cellulosic polymer allowing mat formation at the air–liquid interface and access to oxygen. Given the [Read more]

- McCann, Honour C.

Recurring epidemics of kiwifruit (Actinidia spp.) bleeding canker disease are caused by Pseudomonas syringae pv. actinidiae (Psa). In order to strengthen understanding of population structure, phylogeography, and evolutionary dynamics, we isolated Pseudomonas from cultivated and wild kiwifruit across six provinces in China. Based on the analysis of 80 sequenced Psa genomes, we show that China is the origin of the pandemic lineage but that strain diversity in China is confined to just a single cl [Read more]

- Liu, Yunhao

The two-component system CbrAB is the principal regulator for cellular metabolic balance in Pseudomonas fluorescens SBW25 and is necessary for growth on many substrates including xylose. To understand the regulatory linkage between CbrAB and genes for xylose utilization (xut), we performed transposon mutagenesis of ΔcbrB to select for Xut+ suppressors. This led to identification of crc and hfq. Subsequent genetic and biochemical analysis showed that Crc and Hfq are key mediators of succinate-pro [Read more]

- Bertels, Frederic

Selfish genetic elements, suchas insertion sequences and transposons are found inmost genomes. Transposons are usually identifiable by their high copy number within genomes. In contrast, REP-associated tyrosine transposases (RAYTs), a recently described class of bacterial transposase, are typically present at just one copy per genome. This suggests that RAYTs no longer copy themselves and thus they no longer function as a typical transposase. Motivated by this possibility we interrogated thousan [Read more]

- Farr, Andrew D.

Knowledge of adaptive processes encompasses understanding the emergence of new genes. Computational analyses of genomes suggest that new genes can arise by domain swapping; however, empirical evidence has been lacking. Here we describe a set of nine independent deletion mutations that arose during selection experiments with the bacterium Pseudomonas fluorescens in which the membrane-spanning domain of a fatty acid desaturase became translationally fused to a cytosolic di-guanylate cyclase, gener [Read more]

- Straub, Christina

Interactions between commensal microbes and invading pathogens are understudied, despite their likely effects on pathogen population structure and infection processes. We describe the population structure and genetic diversity of a broad range of co-occurring Pseudomonas syringae isolated from infected and uninfected kiwifruit during an outbreak of bleeding canker disease caused by P. syringae pv. actinidiae (Psa) in New Zealand. Overall population structure was clonal and affected by ecological [Read more]

- Lind, Peter A.

Predicting evolutionary change poses numerous challenges. Here we take advantage of the model bacterium Pseudomonas fluorescens in which the genotype-to-phenotype map determining evolution of the adaptive ‘wrinkly spreader’ (WS) type is known. We present mathematical descriptions of three necessary regulatory pathways and use these to predict both the rate at which each mutational route is used and the expected mutational targets. To test predictions, mutation rates and targets were determined f [Read more]

- Remigi, Philippe

Observations of bacteria at the single-cell level have revealed many instances of phenotypic heterogeneity within otherwise clonal populations, but the selective causes, molecular bases, and broader ecological relevance remain poorly understood. In an earlier experiment in which the bacterium Pseudomonas fluorescens SBW25 was propagated under a selective regime that mimicked the host immune response, a genotype evolved that stochastically switched between capsulation states. The genetic cause wa [Read more]

- Quistad, Steven D.

Microbial communities underpin earth’s biological and biogeochemical processes, but their complexity hampers understanding. Here we draw upon predictions from the theory of selfish genetic elements (SGEs), combined with approaches from experimental evolution, comparative metagenomics and biochemistry, and show how naturally occurring SGEs can be used to manipulate genes that underpin community function. Communities comprising hundreds of bacterial genera established from garden compost were prop [Read more]

- Yulo, P.R.J.

Cell shape is a fundamental property in bacterial kingdom. MreB is a protein that determines rod-like shape, and its deletion is generally lethal. Here, we deleted the mreB homolog from rod-shaped bacterium Pseudomonas fluorescens SBW25 and found that ΔmreB cells are viable, spherical cells with a 20% reduction in competitive fitness and high variability in cell size. We show that cell death, correlated with increased levels of elongation asymmetry between sister cells, accounts for the large fi [Read more]

- Hugoson, Eric

Metagenomics and single-cell genomics have revolutionized the study of microorganisms, increasing our knowledge of microbial genomic diversity by orders of magnitude. A major issue pertaining to metagenome-assembled genomes (MAGs) and single-cell amplified genomes (SAGs) is to estimate their completeness and redundancy. Most approaches rely on counting conserved gene markers. In miComplete, we introduce a weighting strategy, where we normalize the presence/absence of markers by their median dist [Read more]

- Rogers, David W.

Genome-wide sequence divergence between populations can cause hybrid sterility through the action of the anti-recombination system, which rejects crossover repair of double strand breaks between nonidentical sequences. Because crossovers are necessary to ensure proper segregation of homologous chromosomes during meiosis, the reduced recombination rate in hybrids can result in high levels of nondisjunction and therefore low gamete viability. Hybrid sterility in interspecific crosses of Saccharomy [Read more]

- Theodosiou, Loukas

Abstract We review and synthesize evidence from the fields of ecology, evolutionary biology and population genetics to investigate how the presence of abiotic stress can affect the feedback between ecological and evolutionary dynamics. To obtain a better insight of how, and under what conditions, an abiotic stressor can influence eco-evolutionary dynamics, we use a conceptual predator–prey model where the prey can rapidly evolve antipredator defences and stress resistance. We show how abiotic st [Read more]

- Bertels, Frederic

One of the most intriguing puzzles in biology is the degree to which evolution is repeatable. The repeatability of evolution, or parallel evolution, has been studied in a variety of model systems, but has rarely been investigated with clinically relevant viruses. To investigate parallel evolution of HIV-1, we passaged two replicate HIV-1 populations for almost one year in each of two human T-cell lines. For each of the four evolution lines, we determined the genetic composition of the viral popu [Read more]

- Gallie, Jenna

Repeated evolution of functionally similar phenotypes is observed throughout the tree of life. The extent to which the underlying genetics are conserved remains an area of considerable interest. Previously, we reported the evolution of colony switching in two independent lineages of Pseudomonas fluorescens SBW25. The phenotypic and genotypic bases of colony switching in the first lineage (Line 1) have been described elsewhere. Here, we deconstruct the evolution of colony switching in the second [Read more]

- Rainey, Paul B.

Over the last two decades interest in direct realisation of evolutionary process and the possibilities presented by real time evolution experiments with microbes have escalated. Long-term selection experiments with bacteria have made increasingly transparent the process of evolution by natural selection. In this short article we consider what next for the field and do so by highlighting two areas of interest: the genotype-to-phenotype map and the constraints it imposes on evolution, and studies [Read more]

- Ardré, Maxime

Cellulose over-producing wrinkly spreader mutants of Pseudomonas fluorescens SBW25 have been the focus of much investigation, but conditions promoting the production of cellulose in ancestral SBW25, its effects and consequences have escaped in-depth investigation through lack of in vitro phenotype. Here, using a custom built device, we reveal that in static broth microcosms ancestral SBW25 encounters environmental signals at the air-liquid interface that activate, via three diguanylate cyclase-e [Read more]

- Bons, Eva

The evolution of HIV during acute infection is often considered a neutral process. Recent analysis of sequencing data from this stage of infection, however, showed high levels of shared mutations between independent viral populations. This suggests that selection might play a role in the early stages of HIV infection. We adapted an existing model for random evolution during acute HIV-infection to include selection. Simulations of this model were used to fit a global mutational fitness effects di [Read more]

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