Mining zebrafish microbiota reveals key community-level resistance against fish pathogen infection

The long-known resistance to pathogens provided by host-associated microbiota fostered the notion that adding protective bacteria could prevent or attenuate infection. However, the identification of endogenous or exogenous bacteria conferring such protection is often hindered by the complexity of host microbial communities. Here, we used zebrafish and the fish pathogen Flavobacterium columnare as a model system to study the determinants of microbiota-associated colonization resistance. We compared infection susceptibility in germ-free, conventional and reconventionalized larvae and showed that a consortium of 10 culturable bacterial species are sufficient to protect zebrafish. Whereas survival to F. columnare infection does not rely on host innate immunity, we used antibiotic dysbiosis to alter zebrafish microbiota composition, leading to the identification of two different protection strategies. We first identified that the bacterium Chryseobacterium massiliae individually protects both larvae and adult zebrafish. We also showed that an assembly of 9 endogenous zebrafish species that do not otherwise protect individually confer a community-level resistance to infection. Our study therefore provides a rational approach to identify key endogenous protecting bacteria and promising candidates to engineer resilient microbial communities. It also shows how direct experimental analysis of colonization resistance in low-complexity in vivo models can reveal unsuspected ecological strategies at play in microbiota-based protection against pathogens.Subject terms: Microbiome, Microbial ecology     

Alterations in Cortical Morphology after Neonatal Stroke: Compensation in the Contralesional Hemisphere?

Although neonatal arterial ischemic stroke is now well‐studied, its complex consequences on long‐term cortical brain development has not yet been solved. In order to understand the brain development after focal early brain lesion, brain morphometry needs to be evaluated using structural parameters. In this work, our aim was to study and analyze the changes in morphometry of ipsi‐ and contralesional hemispheres in seven‐year‐old children following neonatal stroke. Therefore, we used surface‐based morphometry in order to examine the cortical thickness, surface area, cortical volume, and local gyrification index in two groups of children that suffered from neonatal stroke in the left (n = 19) and right hemispheres (n = 15) and a group of healthy controls (n = 30). Reduced cortical thickness, surface area, and cortical volumes were observed in the ipsilesional hemispheres for both groups in comparison with controls. For the group with left‐sided lesions, higher gyrification of the contralesional hemisphere was observed primarily in the occipital region along with higher surface area and cortical volume. As for the group with right‐sided lesions, higher gyrification was detected in two separate clusters also in the occipital lobe of the contralesional hemisphere, without a significant change in cortical thickness, surface area, or cortical volume. This is the first time that alterations of structural parameters are detected in the “healthy” hemisphere after unilateral neonatal stroke indicative of a compensatory phenomenon. Moreover, findings presented in this work suggest that lesion lateralization might have an influence on brain development and maturation.     

Biochemical Characterization,Molecular Cloning,and Structural Modeling of an Interesting β-1,4-Glucanase from Sclerotinia Sclerotiorum

The filamentous fungus Sclerotinia sclerotiorum produces a complete set of cellulolytic enzymes needed for efficient solubilization of native cellulose, the major component of plants. In this work, we reported the molecular characterization of an important glycosyl-hydrolase enzyme classified as endo-β-1,4-glucanase. The importance of this enzyme was revealed with the in-gel activity staining, showing a high degradation capacity of cellulose. When purified from native gel and ran in denaturing polyacrylamide gel, the polypeptide has an apparent molecular mass of about 34 kDa called Endo2. For further characterization of this protein, a mass spectrometry approach was carried out. The LC–MS/MS analysis revealed two peptides belonging to this enzyme. The genomic DNA and cDNA sequences were resolved by PCR amplification and sequencing, revealing a gene with two intron sequences. The open reading frame of 987 bp encoded a putative polypeptide of 328 amino acids having a calculated molecular mass of 33,297 Da. Yet, the molecular modeling and comparative investigation of different 3D cellulase structures showed that this endoglucanase isoform has probably two domains. A core domain having a high similarity with endoglucanases family 5 and a cellulose-binding domain having similarities with those of exo-type cellulases of family 1, linked together by a serine-threonine-rich region. These results are with great interests and show new characteristics of S. sclerotiorum glucanase.