A pan-European epidemiological study reveals honey bee colony survival depends on beekeeper education and disease control

Reports of honey bee population decline has spurred many national efforts to understand the extent of the problem and to identify causative or associated factors. However, our collective understanding of the factors has been hampered by a lack of joined up trans-national effort. Moreover, the impacts of beekeeper knowledge and beekeeping management practices have often been overlooked, despite honey bees being a managed pollinator. Here, we established a standardised active monitoring network for 5 798 apiaries over two consecutive years to quantify honey bee colony mortality across 17 European countries. Our data demonstrate that overwinter losses ranged between 2% and 32%, and that high summer losses were likely to follow high winter losses. Multivariate Poisson regression models revealed that hobbyist beekeepers with small apiaries and little experience in beekeeping had double the winter mortality rate when compared to professional beekeepers. Furthermore, honey bees kept by professional beekeepers never showed signs of disease, unlike apiaries from hobbyist beekeepers that had symptoms of bacterial infection and heavy Varroa infestation. Our data highlight beekeeper background and apicultural practices as major drivers of honey bee colony losses. The benefits of conducting trans-national monitoring schemes and improving beekeeper training are discussed

How Did Host Domestication Modify Life History Traits of Its Pathogens?

Understanding evolutionary dynamics of pathogens during domestication of their hosts and rise of agro-ecosystems is essential for durable disease management. Here, we investigated changes in life-history traits of the fungal pathogen Venturia inaequalis during domestication of the apple. Life traits linked to fungal dispersal were compared between 60 strains that were sampled in domestic and wild habitats in Kazakhstan, the center of origin of both host and pathogen. Our two main findings are that transition from wild to agro-ecosystems was associated with an increase of both spore size and sporulation capacity; and that distribution of quantitative traits of the domestic population mostly overlapped with those of the wild population. Our results suggest that apple domestication had a considerable impact on fungal characters linked to its dispersal through selection from standing phenotypic diversity. We showed that pestification of V. inaequalis in orchards led to an enhanced allocation in colonization ability from standing variation in the wild area. This study emphasizes the potential threat that pathogenic fungal populations living in wild environments represent for durability of resistance in agro-ecosystems

Central role and structure of the membrane pseudokinase YukC in the antibacterial <i>Bacillus subtilis</i> Type VIIb Secretion System

Posté dans BioRxiv le 9 mai 2020We previously linked TSHZ3 haploinsufficiency to autism spectrum disorder (ASD) and showed that embryonic or postnatal Tshz3 deletion in mice results in behavioral traits relevant to the two core domains of ASD, namely social interaction deficits and repetitive behaviors. Here, we provide evidence that cortical projection neurons (CPNs) and striatal cholinergic interneurons (SCINs) are two main and complementary players in the TSHZ3-linked ASD syndrome. We show that in the cerebral cortex, TSHZ3 is expressed in CPNs and in a proportion of GABA interneurons, while not in cholinergic interneurons or glial cells. TSHZ3-expressing cells, which are predominantly SCINs in the striatum, represent a low proportion of neurons in the ascending cholinergic projection system. We then characterized two new conditional knockout (cKO) models generated by crossing Tshz3 flox/flox with Emx1-Cre ( Emx1-cKO ) or Chat-Cre ( Chat-cKO ) mice to decipher the respective role of CPNs and SCINs. Emx1-cKO mice show altered excitatory synaptic transmission onto CPNs and plasticity at corticostriatal synapses, with neither cortical neuron loss nor impaired layer distribution. These animals present social interaction deficits but no repetitive patterns of behavior. Chat-cKO mice exhibit no loss of SCINs but changes in the electrophysiological properties of these interneurons, associated with repetitive patterns of behavior without social interaction deficits. Therefore, dysfunction in either CPNs or SCINs segregates with a distinct ASD behavioral trait. These findings provide novel insights onto the implication of the corticostriatal circuitry in ASD by revealing an unexpected neuronal dichotomy in the biological background of the two core behavioral domains of this disorder

The Antibacterial Type VII Secretion System of Bacillus subtilis: Structure and Interactions of the Pseudokinase YukC/EssB

International audienceType VIIb secretion systems (T7SSb) were recently proposed to mediate different aspects of Firmicutes physiology, including bacterial pathogenicity and competition. However, their architecture and mechanism of action remain largely obscure. Here, we present a detailed analysis of the T7SSb-mediated bacterial competition in Bacillus subtilis, using the effector YxiD as a model for the LXG secreted toxins. By systematically investigating protein-protein interactions, we reveal that the membrane subunit YukC contacts all T7SSb components, including the WXG100 substrate YukE and the LXG effector YxiD. YukC's crystal structure shows unique features, suggesting an intrinsic flexibility that is required for T7SSb antibacterial activity. Overall, our results shed light on the role and molecular organization of the T7SSb and demonstrate the potential of B. subtilis as a model system for extensive structure-function studies of these secretion machineries. IMPORTANCE Type VII secretion systems mediate protein extrusion from Gram-positive bacteria and are classified as T7SSa and T7SSb in Actinobacteria and in Firmicutes, respectively. Despite the genetic divergence of T7SSa and T7SSb, the high degree of structural similarity of their WXG100 substrates suggests similar secretion mechanisms. Recent advances revealed the structures of several T7SSa cytoplasmic membrane complexes, but the molecular mechanism of secretion and the T7SSb architecture remain obscure. Here, we provide hints on the organization of T7SSb in B. subtilis and a highresolution structure of its central pseudokinase subunit, opening new perspectives for the understanding of the T7SSb secretion mechanism by using B. subtilis as an amenable bacterial model

Pairwise correlations between phenotypic traits.

<p>Scatter plots indicating the degree of correlation between traits (below diagonal) and pairwise Pearson's correlation R values (above diagonal). Pearson’s correlation coefficients were calculated from averaged data from each strain for sporulation capacity, spore size and hyphal growth. Statistical significant correlation coefficients are indicated as following: ** P-value < 0.01 and *** P-value < 0.001. Calculations were performed for domestic (A panel) and wild (B panel) populations, respectively.</p

Quantitative distribution of life history trait variables.

<p>Distribution of quantitative variables: hyphal growth 24 days after deposits on agar (cm), germination rate (in logit units), sporulation capacity (in Log₁₀ units), and spore size (μm). Blue histograms correspond to the wild population and green ones correspond to the domestic population.</p

Quantitative distribution of life history trait variables between wild (blue) and domestic population (green).

<p>The horizontal line in boxplots represents the median. A significant difference between populations is observed for the sporulation capacity and spore size. Sporulation average in wild population: 122,400 spores mL^-1; and in domestic population: 199,955 spores mL^-1. Spore size average is 9.2 μm in the wild population and is 9.5 μm in the domestic population.</p

Pseudomonas fluorescens MFE01 delivers a putative type VI secretion amidase that confers biocontrol against the soft‐rot pathogen Pectobacterium atrosepticum

International audienceThe type VI secretion system (T6SS) is a contractile nanomachine widespread in Gram‐negative bacteria. The T6SS injects effectors into target cells including eukaryotic hosts and competitor microbial cells and thus participates in pathogenesis and intermicrobial competition. Pseudomonas fluorescens MFE01 possesses a single T6SS gene cluster that confers biocontrol properties by protecting potato tubers against the phytopathogen Pectobacterium atrosepticum (Pca). Here, we demonstrate that a functional T6SS is essential to protect potato tuber by reducing the pectobacteria population. Fluorescence microscopy experiments showed that MFE01 displays an aggressive behaviour with an offensive T6SS characterized by continuous and intense T6SS firing activity. Interestingly, we observed that T6SS firing is correlated with rounding of Pectobacterium cells, suggesting delivery of a potent cell wall targeting effector. Mutagenesis coupled with functional assays then revealed that a putative T6SS secreted amidase, Tae3 Pf , is mainly responsible for MFE01 toxicity towards Pca. Further studies finally demonstrated that Tae3 Pf is toxic when produced in the periplasm, and that its toxicity is counteracted by the Tai3 Pf inner membrane immunity protein

Priming and polymerization of a bacterial contractile tail structure. 1" 2" 17"

Zoued, Abdelrahim Durand, Eric Brunet, Yannick R Spinelli, Silvia Douzi, Badreddine Guzzo, Mathilde Flaugnatti, Nicolas Legrand, Pierre Journet, Laure Fronzes, Remi Mignot, Tam Cambillau, Christian Cascales, Eric eng Research Support, Non-U.S. Gov't England Nature. 2016 Mar 3;531(7592):59-63. doi: 10.1038/nature17182. Epub 2016 Feb 24.International audienceContractile tails are composed of an inner tube wrapped by an outer sheath assembled in an extended, metastable conformation that stores mechanical energy necessary for its contraction. Contraction is used to propel the rigid inner tube towards target cells for DNA or toxin delivery. Although recent studies have revealed the structure of the Type VI secretion system contractile sheath, the mechanisms by which its polymerization is controlled and coordinated with inner tube assembly remain unsolved. In this study, we report that the starfish-like TssA dodecameric complex interacts with tube and sheath components. Fluorescence microscopy experiments revealed that TssA binds first to the T6SS membrane core complex and then initiates tail polymerization. TssA remains at the tip of the growing structure and incorporates new tube and sheath blocks. Based on these results, we propose that TssA primes and coordinates tail tube and sheath biogenesis