Bacteriophage Adherence to Mucus Mediates Preventive Protection against Pathogenic Bacteria

Peer reviewe

Effect of resource availability on evolution of virulence and competition in an environmentally transmitted pathogen

Understanding ecological and epidemiological factors driving pathogen evolution in contemporary time scales is a major challenge in modern health management. Pathogens that replicate outside the hosts are subject to selection imposed by ambient environmental conditions. Increased nutrient levels could increase pathogen virulence by pre-adapting for efficient use of resources upon contact to a nutrient rich host or by favouring transmission of fast-growing virulent strains. We measured changes in virulence and competition in Flavobacterium columnare, a bacterial pathogen of freshwater fish, under high and low nutrient levels. To test competition between strains in genotype mixtures, we developed a quantitative real-time PCR assay. We found that a virulent strain maintained its virulence and outcompeted less virulent strains independent of the nutrient level and resource renewal rate while a less virulent strain further lost virulence in chemostats under low nutrient level and over long-term serial culture under high nutrient level. Our results suggest that increased outside-host nutrient levels might maintain virulence in less virulent strains and increase their contribution to epidemics in aquaculture. The results highlight a need to further explore the role of resource in the outside-host environment in maintaining strain diversity and driving evolution of virulence among environmentally growing pathogens.Peer reviewe

Population genetic structure of aposematic alpine wood tiger moths (Parasemia plantaginis)

Alpine landscape with natural fragmentation restricts gene flow among populations and causes spatio-genetic structuring (high genetic differentiation) in species living there. Consequently, alpine habitat fragmentation and dispersal barriers should make isolated populations such as wood tiger moth (Parasemia plantaginis) populations prone to lose genetic diversity by local adaptation and fixation of fittest phenotype in each local population. This species is also known to be aposematic. Yellow colour on the males’ hind wings in wood tiger moth is presumed to work more efficiently against visual hunting predators due to increased conspicuousness. In addition, in field experiments with wood tiger moth, females with red hind wings were avoided more than those with orange hind wings. Therefore, yellow and red phenotypes are expected to reach fixation by directional selection in each given local population. Alternatively, uniform stabilizing selection imposed by predators can lead to constant allele frequencies throughout their distribution range. However, this species are very variable across its entire distribution both locally and regionally. Despite this dramatic variation for P. plantaginis throughout its range, it is not clear if observed phenotypic variation matches genetic divergence among populations. The main objective of the thesis was to investigate the spatio-temporal population genetic structure and differentiation of P. plantaginis population over two consecutive years in different Alpine regions in Italy, Austria, and Switzerland. The investigation was conducted using the pattern of variation at 10 microsatellite loci and in a 664 bp portion of the COI gene in the mtDNA. Expected heterozygosity was high and similar within all regions. Bayesian analyses revealed just one P. plantaginis population as a whole. This was supported by pairwise FST value, AMOVA and COI results, which indicated no differentiation among populations during two successive sampling years 2009-2010. Hence, high genetic diversity and weak population differentiation suggest high gene flow and/ or high population density in P. plantaginis. We speculate that in spite of extensive gene flow, this species remain morphologically polymorphic because the homogenizing effect of high gene flow has been compensated by differential environmental and ecological selective forces along the altitudinal gradient. However, given high gene flow (both current and past), and lack of strong post-settlement selection pressure, selective forces due to altitude are not strong enough to significantly differentiate the studied population in terms of microsatellites and mtDNA

Roles of adenine methylation and genetic mutations in adaptation to different temperatures in Serratia marcescens

Epigenetic modifications can contribute to adaptation, but the relative contributions of genetic and epigenetic variation are unknown. Previous studies on the role of epigenetic changes in adaptation in eukaryotes have nearly exclusively focused on cytosine methylation (m5C), while prokaryotes exhibit a richer system of methyltransferases targetting adenines (m6A) or cytosines (m4C, m5C). DNA methylation in prokaryotes has many roles, but its potential role in adaptation still needs further investigation. We collected phenotypic, genetic, and epigenetic data using single molecule real-time sequencing of clones of the bacterium Serratia marcescens that had undergone experimental evolution in contrasting temperatures to investigate the relationship between environment and genetic, epigenetic, and phenotypic changes. The genomic distribution of GATC motifs, which were the main target for m6A methylation, and of variable m6A epiloci pointed to a potential link between m6A methylation and regulation of gene expression in S. marcescens. Evolved strains, while genetically homogeneous, exhibited many polymorphic m6A epiloci. There was no strong support for a genetic control of methylation changes in our experiment, and no clear evidence of parallel environmentally induced or environmentally selected methylation changes at specific epiloci was found. Both genetic and epigenetic variants were associated with some phenotypic traits. Overall, our results suggest that both genetic and adenine methylation changes have the potential to contribute to phenotypic adaptation in S. marcescens, but that any environmentally induced epigenetic change occurring in our experiment would probably have been quite labile

Relationship commitment and monitoring alternatives using Facebook in unmarried romantic relationships

textRecent technological innovations affecting romantic relationships include the rise in prominence of social networking sites (SNSs), including Facebook. SNSs have become an increasingly fundamental part of developing and maintaining relationships. A majority of research focuses on the ways in which individuals access SNSs. Less studied is how individuals' use of SNSs affects their romantic relationships. An important aspect of the stability of romantic relationships is the construct of commitment. Relationship commitment is conceptualized as the intent to continue a relationship into the future and is composed of many constructs that can either keep individuals in or pull them away from the relationship. One aspect that may pull individuals away from their relationship is the quality and availability of potential alternatives, or relationship forms other than the current one. There is evidence that using tools like Facebook may prompt individuals to pay attention to alternative relationship options. This study examined how SNSs use may affect current relationships with a sample of 645 unmarried individuals in dating relationships and with current Facebook accounts. All participants completed measures of their Facebook use, relationship commitment, and attention to relationship alternatives. A sub-sample of 432 participants were randomly assigned to one of two study conditions. One condition prompted participants to view the Facebook profiles of friends that they might consider as possible relationship partners and the other condition prompted participants to view organizations they follow on Facebook. Analyses indicated that Facebook monitoring condition did not predict differences in individuals' reported commitment. However, hierarchical regression analyses using the full sample revealed that high levels of online monitoring of alternatives were associated with low levels of commitment for both males and females, but more so for males. Analyses also revealed that low levels of satisfaction predicted high levels of monitoring of alternatives and high levels of Facebook use predicted high levels of online monitoring of alternatives. These results suggest that tools such as Facebook can be used to monitor alternatives, yet doing so may negatively affect current romantic relationships. Future studies should explore these relationships by using a repeated measures design to assess change over time.Human Development and Family Science

Rearing background and exposure environment together explain higher survival of aquaculture fish during a bacterial outbreak

1. Parasitic diseases represent one of the greatest challenges for aquaculture worldwide and there is an increasing emphasis on ecological solutions to prevent infections. One proposed solution is enriched rearing, where traditional stimulus‐poor rearing tanks are equipped with different types of structures to increase habitat complexity. Such spatial enrichment is known to increase survival of fish during parasite epidemics, but the underlying mechanisms are still unclear. 2. We studied whether enriched rearing affected infection of an important fish pathogen Flavobacterium columnare in young Atlantic salmon (Salmo salar) and sea‐migrating brown trout (Salmo trutta). First, we used natural bacterial exposures and multiple fish populations in a common garden experiment to address the role of host genetic background in effects of enriched rearing. Second, fish from standard and enriched rearing were experimentally exposed to controlled bacterial doses in standard and enriched environments in a full factorial design to explore the relative roles of rearing background and environment of exposure on survival of fish. 3. Enriched rearing significantly increased survival of fish during the natural bacterial outbreak. This effect was also fairly consistent and observed in eight of the ten fish populations. In the controlled exposure, fish exposed in enriched environment had higher survival regardless of their rearing background, suggesting a stronger impact of the environment on the disease progression. Additionally, the survival in the enriched environment was the highest among the fish of enriched rearing background, supporting the idea of their higher resistance. 4. Synthesis and applications. Our study suggests that the enhanced survival of fish in enriched rearing is a result of a combined effect of the environment and improved fish condition and, to a lesser degree, from host genetic background. This has important implications for when and how environmental enrichment should be applied. Overall, these results indicate that environmental enrichment has the potential to improve survival of fish during parasitic epidemics and thus reduce use of antibiotics in aquaculture.peerReviewe

A multilocus sequence analysis scheme for characterization of Flavobacterium columnare isolates

Background: Columnaris disease caused by Flavobacterium columnare is a serious problem in aquaculture, annually causing large economic losses around the world. Despite considerable research, the molecular epidemiology of F. columnare remains poorly understood. Methods: We investigated the population structure and spatiotemporal changes in the genetic diversity of F. columnare population in Finland by using a multilocus sequence typing (MLST) and analysis (MLSA) based on DNA sequence variation within six housekeeping genes. A total of 83 strains of F. columnare were collected from eight different areas located across the country between 2003 and 2012. Results: Partial sequencing of six housekeeping genes (trpB, tuf, atpA, rpoD, gyrB and dnaK) revealed eight sequence types and a moderate level of genetic diversity (H = 0.460). Phylogenetic analysis of the concatenated protein-encoding gene sequence data (ca. 3,509 nucleotides) formed two lineages, which could be further divided into five clusters. All analysed F. columnare strains appeared to have a genetic origin distinct from that of another important fish pathogen form the genus Flavobacterium, F. psychrophilum. Although the value of the index of association between alleles, 0.292 (P < 0.001), supports some degree of clonality for this species in Finland, recombination has introduced molecular diversity to the population almost three times more than mutation. Conclusion: The results suggest that Finnish F. columnare strains have an epidemic population structure followed by clonal expansion of successful genotypes. Our study with reproducible methodology and comparable results establishes a robust framework for the discrimination and phylogenetic analysis of F. columnare isolates, which will help to improve our understanding about geographic distribution and epidemiology of columnaris disease.peerReviewe

Application of high resolution melting assay (HRM) to study temperature-dependent intraspecific competition in a pathogenic bacterium

Studies on species’ responses to climate change have focused largely on the direct effect of abiotic factors and in particular temperature, neglecting the effects of biotic interactions in determining the outcome of climate change projections. Many microbes rely on strong interference competition; hence the fitness of many pathogenic bacteria could be a function of both their growth properties and intraspecific competition. However, due to technical challenges in distinguishing and tracking individual strains, experimental evidence on intraspecific competition has been limited so far. Here, we developed a robust application of the high-resolution melting (HRM) assay to study head-to-head competition between mixed genotype co-cultures of a waterborne bacterial pathogen of fish, Flavobacterium columnare, at two different temperatures. We found that competition outcome in liquid cultures seemed to be well predicted by growth yield of isolated strains, but was mostly inconsistent with interference competition results measured in inhibition tests on solid agar, especially as no growth inhibition between strain pairs was detected at the higher temperature. These results suggest that, for a given temperature, the factors driving competition outcome differ between liquid and solid environments.peerReviewe