Subinhibitory Arsenite Concentrations Lead to Population Dispersal in Thiomonas sp.

Biofilms represent the most common microbial lifestyle, allowing the survival of microbial populations exposed to harsh environmental conditions. Here, we show that the biofilm development of a bacterial species belonging to the Thiomonas genus, frequently found in arsenic polluted sites and playing a key role in arsenic natural remediation, is markedly modified when exposed to subinhibitory doses of this toxic element. Indeed, arsenite [As(III)] exposure led to a considerable impact on biofilm maturation by strongly increasing the extracellular matrix synthesis and by promoting significant cell death and lysis within microcolonies. These events were followed by the development of complex 3D-biofilm structures and subsequently by the dispersal of remobilized cells observed inside the previously formed hollow voids. Our results demonstrate that this biofilm community responds to arsenite stress in a multimodal way, enhancing both survival and dispersal. Addressing this complex bacterial response to As(III) stress, which might be used by other microorganisms under various adverse conditions, may be essential to understand how Thiomonas strains persist in extreme environments

The identification of QTL controlling ergot sclerotia size in hexaploid wheat implicates a role for the Rht dwarfing alleles

The fungal pathogen Claviceps purpurea infects ovaries of a broad range of temperate grasses and cereals, including hexaploid wheat, causing a disease commonly known as ergot. Sclerotia produced in place of seed carry a cocktail of harmful alkaloid compounds that result in a range of symptoms in humans and animals, causing ergotism. Following a field assessment of C. purpurea infection in winter wheat, two varieties ‘Robigus’ and ‘Solstice’ were selected which consistently produced the largest differential effect on ergot sclerotia weights. They were crossed to produce a doubled haploid mapping population, and a marker map, consisting of 714 genetic loci and a total length of 2895 cM was produced. Four ergot reducing QTL were identified using both sclerotia weight and size as phenotypic parameters; QCp.niab.2A and QCp.niab.4B being detected in the wheat variety ‘Robigus’, and QCp.niab.6A and QCp.niab.4D in the variety ‘Solstice’. The ergot resistance QTL QCp.niab.4B and QCp.niab.4D peaks mapped to the same markers as the known reduced height (Rht) loci on chromosomes 4B and 4D, Rht-B1 and Rht-D1, respectively. In both cases, the reduction in sclerotia weight and size was associated with the semi-dwarfing alleles, Rht-B1b from ‘Robigus’ and Rht-D1b from ‘Solstice’. Two-dimensional, two-QTL scans identified significant additive interactions between QTL QCp.niab.4B and QCp.niab.4D, and between QCp.niab.2A and QCp.niab.4B when looking at sclerotia size, but not between QCp.niab.2A and QCp.niab.4D. The two plant height QTL, QPh.niab.4B and QPh.niab.4D, which mapped to the same locations as QCp.niab.4B and QCp.niab.4D, also displayed significant genetic interactions

Field pathogenomics reveals the emergence of a diverse wheat yellow rust population

BACKGROUND: Emerging and re-emerging pathogens imperil public health and global food security. Responding to these threats requires improved surveillance and diagnostic systems. Despite their potential, genomic tools have not been readily applied to emerging or re-emerging plant pathogens such as the wheat yellow (stripe) rust pathogen Puccinia striiformis f. sp. tritici (PST). This is due largely to the obligate parasitic nature of PST, as culturing PST isolates for DNA extraction remains slow and tedious. RESULTS: To counteract the limitations associated with culturing PST, we developed and applied a field pathogenomics approach by transcriptome sequencing infected wheat leaves collected from the field in 2013. This enabled us to rapidly gain insights into this emerging pathogen population. We found that the PST population across the United Kingdom (UK) underwent a major shift in recent years. Population genetic structure analyses revealed four distinct lineages that correlated to the phenotypic groups determined through traditional pathology-based virulence assays. Furthermore, the genetic diversity between members of a single population cluster for all 2013 PST field samples was much higher than that displayed by historical UK isolates, revealing a more diverse population of PST. CONCLUSIONS: Our field pathogenomics approach uncovered a dramatic shift in the PST population in the UK, likely due to a recent introduction of a diverse set of exotic PST lineages. The methodology described herein accelerates genetic analysis of pathogen populations and circumvents the difficulties associated with obligate plant pathogens. In principle, this strategy can be widely applied to a variety of plant pathogens

Breakdown of the Yr17 resistance to yellow rust of wheat in northern Europe

The gene Yr17, conferring resistance to Puccinia striiformis f.sp.tritici, was introduced into northern European wheat cultivars in the mid 1970s. Virulence for Yr17 was not detected until 1994, when it was identified in the UK and Denmark. In both countries, susceptible Yr17 cultivars were grown on an increasingly large area over the next four years and this was followed by a rise in the frequency of corresponding virulence to 100% . Elsewhere in northern Europe Yr17 cultivars were grown on a relatively small scale during this period. However, virulence for Yr17 was detected in France and Germany in 1997 and reached a frequency in excess of 70% by 1999, suggesting an influx of pathogen spores from UK or Denmark. Migration of pathogen spores around northern Europe clearly plays an important role in determining the virulence composition of local populations of Puccinia striiformis f. sp. tritici. It is vital that this should be reflected in cooperation between national virulence monitoring projects.Contournement du gène de résistance Yr17 à la rouille jaune du blé en Europe du Nord. Le gène de résistance Yr17 vis-à-vis de Puccinia striiformis f. sp. tritici, agent de la rouille jaune du blé, a été introduit dans les cultivars Nord-Européens à partir de 1975. La virulence correspondante n'a été détectée qu'en 1994 en Angleterre et au Danemark. Dans ces deux pays, la superficie des terres emblavées par des cultivars portant Yr17 et sensibles à la rouille jaune a augmenté de 1994 à 1997 et est restée très importante jusqu'en 1998. La virulence vis-à-vis de Yr17 a atteint 100 % . Dans les autres pays du Nord de l'Europe, les cultivars Yr17 sensibles à la rouille jaune ont été cultivés sur de petites surfaces. Toutefois la virulence vis-à-vis de Yr17 a été détectée en France et en Allemagne en 1997 avec une fréquence de plus de 70 % en 1999, suggérant une migration des spores du parasite à partir de l'Angleterre ou du Danemark. La migration des spores joue un rôle déterminant dans la composition des populations locales de P. striiformis f. sp. tritici. Il est impératif que des projets de coopération de suivi des virulences soient coordonnés à l'échelle européenne