Genome content and phylogenomics reveal both ancestral and lateral evolutionary pathways in plant-pathogenic Streptomyces species

© 2016, American Society for Microbiology. All Rights Reserved. Streptomyces spp. are highly differentiated actinomycetes with large, linear chromosomes that encode an arsenal of biologically active molecules and catabolic enzymes. Members of this genus are well equipped for life in nutrient-limited environments and are common soil saprophytes. Out of the hundreds of species in the genus Streptomyces, a small group has evolved the ability to infect plants. The recent availability of Streptomyces genome sequences, including four genomes of pathogenic species, provided an opportunity to characterize the gene content specific to these pathogens and to study phylogenetic relationships among them. Genome sequencing, comparative genomics, and phylogenetic analysis enabled us to discriminate pathogenic from saprophytic Streptomyces strains; moreover, we calculated that the pathogen-specific genome contains 4,662 orthologs. Phylogenetic reconstruction suggested that Streptomyces scabies and S. ipomoeae share an ancestor but that their biosynthetic clusters encoding the required virulence factor thaxtomin have diverged. In contrast, S. turgidiscabies and S. acidiscabies, two relatively unrelated pathogens, possess highly similar thaxtomin biosynthesis clusters, which suggests that the acquisition of these genes was through lateral gene transfer

Origine, évolution et mesure de la biodiversité des eaux souterraines (analyse moléculaire du genre Niphargus (Crustacea))

Malgré des conditions de vie contraignantes, les eaux souterraines abritent une faune très diversifiée. Au sein du genre Niphargus et à partir d'outils moléculaires, ce travail teste tout d'abord l'impact des phénomènes de convergence sur l'estimation de la biodiversité. Parallèlement, l'influence de la stabilité et de la forte fragmentation du milieu sur l'origine de cette biodiversité sont analysées. Les résultats démontrent une forte sous-estimation de la biodiversité par la taxonomie morpho-anatomique et soulignent l'importance de la diversité cachée. Ce travail soutient également le rôle central des isolements géographiques dans l'évolution des organismes et l'émergence d'un fort endémisme, mais suggèrent néanmoins la possibilité d'importantes phases de dispersionLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Towards a simple way to collect eDNA using a 3D-printed passive sampler

Environmental DNA has emerged as a revolutionary approach to monitor aquatic biodiversity. The study of the DNA released by macro-organisms in their habitat offers a fast, non-invasive and sensitive approach to monitor their presence. Despite its many advantages, methodological challenges limit the widespread use of eDNA. Among them, eDNA sampling represents one of the most challenging step. Often based on the filtration of a large volume of water, this process can be long and tedious, requiring human intervention and special care, and which is not applicable to a wide range of habitats. As an alternative to filtration, passive eDNA sampling using natural substrates appears to be a promising solution. This approach uses the natural properties of some minerals (eg. silica), organisms (eg. sponges) or even communities (e.g. biofilms) to collect and preserved eDNA. Yet, such approaches are difficult to standardize and may not be applicable in many habitats. To circumvent that problem, we have designed 3D-printed samplers made of hydroxyapatite (HAp samplers), a mineral known for its high binding affinity with DNA. The shape of the samplers has been designed to facilitate their handling in laboratory and field experiments. Here we describe and test the ability of HAp samplers to recover freshwater eDNA. We show that HAp samplers recover DNA with high efficiency and are effective even on small amounts of waterlouse eDNA. However, the eDNA recovery is also highly variable across experiments. We show that by understanding the physico-chemical interactions between DNA and the HAp sampler surface, we could improve the replicability of the process and provide a robust alternative to filtration

Transcriptome-wide deregulation of gene expression by artificial light at night in tadpoles of common toads

International audienceArtificial light at night (ALAN) affects numerous physiological and behavioural mechanisms in various species by po- tentially disturbing circadian timekeeping systems and modifying melatonin levels. However, given the multiple direct and indirect effects of ALAN on organisms, large-scale transcriptomic approaches are essential to assess the global ef- fect of ALAN on biological processes. Moreover, although studies have focused mainly on variations in gene expression during the night in the presence of ALAN, it is necessary to investigate the effect of ALAN on gene expression during the day. In this study, we combined de novo transcriptome sequencing and assembly, and a controlled laboratory experi- ment to evaluate the transcriptome-wide gene expression response using high-throughput (RNA-seq) in Bufo bufo tad- poles exposed to ecologically relevant light levels. Here, we demonstrated for the first time that ALAN affected gene expression at night (3.5% and 11% of differentially expressed genes when exposed to 0.1 and 5 lx compared to con- trols, respectively), but also during the day (11.2% of differentially expressed genes when exposed to 5 lx compared to controls) with a dose-dependent effect. ALAN globally induced a downregulation of genes (during the night, 58% and 62% of the genes were downregulated when exposed to 0.1 and 5 lx compared to controls, respectively, and dur- ing the day, 61.2% of the genes were downregulated when exposed to 5 lx compared to controls). ALAN effects were detected at very low levels of illuminance (0.1 lx) and affected mainly genes related to the innate immune system and, to a lesser extend to lipid metabolism. These results provide new insights into understanding the effects of ALAN on organism. ALAN impacted the expression of genes linked to a broad range of physiological pathways at very low levels of ALAN during night-time and during daytime, potentially resulting in reduced immune capacity under environmen- tal immune challenges

Integrating multiple species criteria and species hypotheses in subterranean biology

Decades of debates around the species problem have resulted in the emergence of a unified species concept with multiple criteria to delimit species taxa. Many biologists now agree to consider species as separately evolving segments of metapopulation lineages (i.e. the species concept), and to consider species taxa (i.e. the elementary units used in biodiversity science) as scientific hypotheses of separately evolving entities. In this framework, sets of species hypotheses are generated using different criteria (i.e. morphological distinguishability, genetic isolation) that mirror the properties expressed by species at different times and sequential orders during the extended and heterogeneous process of speciation. This conceptual and methodological advance in taxonomy has several implications for biodiversity science. First, species taxa represent a heterogeneous set of hypotheses whose properties are contingent on the heterogeneous, continuous and extended nature of speciation. Second, species databases need to integrate information on the diverse properties of species by attributing specimens to multiple species hypotheses generated using different delimitation criteria. Third, biodiversity science at large can provide novel insights into biodiversity processes by incorporating multiple species hypotheses into the analysis of biodiversity patterns. Here, we show how these implications have been taken into account by subterranean biologists. First, we briefly review the criteria and methods used to delimit species in subterranean biology and the diverse sets of species hypotheses they generated. Second, we present a new generation of species occurrence databases that integrate different species criteria and hypotheses while fully respecting the scientific rigor of taxonomy. Last, we show how incorporating multiple species hypotheses into macroecological analyses of European groundwater fauna bolsters our under­standing of the factors shaping large-scale patterns of species richness and geographic range size

Phenotypic Heterogeneity of Genomically-Diverse Isolates of <i>Streptococcus mutans</i>

<div><p>High coverage, whole genome shotgun (WGS) sequencing of 57 geographically- and genetically-diverse isolates of <i>Streptococcus mutans</i> from individuals of known dental caries status was recently completed. Of the 57 sequenced strains, fifteen isolates, were selected based primarily on differences in gene content and phenotypic characteristics known to affect virulence and compared with the reference strain UA159. A high degree of variability in these properties was observed between strains, with a broad spectrum of sensitivities to low pH, oxidative stress (air and paraquat) and exposure to competence stimulating peptide (CSP). Significant differences in autolytic behavior and in biofilm development in glucose or sucrose were also observed. Natural genetic competence varied among isolates, and this was correlated to the presence or absence of competence genes, <i>comCDE</i> and <i>comX</i>, and to bacteriocins. In general strains that lacked the ability to become competent possessed fewer genes for bacteriocins and immunity proteins or contained polymorphic variants of these genes. WGS sequence analysis of the pan-genome revealed, for the first time, components of a Type VII secretion system in several <i>S. mutans</i> strains, as well as two putative ORFs that encode possible collagen binding proteins located upstream of the <i>cnm</i> gene, which is associated with host cell invasiveness. The virulence of these particular strains was assessed in a wax-worm model. This is the first study to combine a comprehensive analysis of key virulence-related phenotypes with extensive genomic analysis of a pathogen that evolved closely with humans. Our analysis highlights the phenotypic diversity of <i>S. mutans</i> isolates and indicates that the species has evolved a variety of adaptive strategies to persist in the human oral cavity and, when conditions are favorable, to initiate disease.</p></div

Clinical isolates used in this study.

*<p>V403- human blood isolate from R. Facklam, Centers for Disease Control, Atlanta, Ga <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061358#pone.0061358-Macrina2" target="_blank">[112]</a>.</p><p>HK- Hong Kong, ZA- South Africa, Switz.- Switzerland. SGP- Supra-gingival plaque, ISOC- initial stages of oral colonization, CF-caries free, CA-caries active.</p