Is there a common water-activity limit for the three domains of life?

Archaea and Bacteria constitute a majority of life systems on Earth but have long been considered inferior to Eukarya in terms of solute tolerance. Whereas the most halophilic prokaryotes are known for an ability to multiply at saturated NaCl (water activity (a w) 0.755) some xerophilic fungi can germinate, usually at high-sugar concentrations, at values as low as 0.650-0.605 a w. Here, we present evidence that halophilic prokayotes can grow down to water activities of <0.755 for Halanaerobium lacusrosei (0.748), Halobacterium strain 004.1 (0.728), Halobacterium sp. NRC-1 and Halococcus morrhuae (0.717), Haloquadratum walsbyi (0.709), Halococcus salifodinae (0.693), Halobacterium noricense (0.687), Natrinema pallidum (0.681) and haloarchaeal strains GN-2 and GN-5 (0.635 a w). Furthermore, extrapolation of growth curves (prone to giving conservative estimates) indicated theoretical minima down to 0.611 a w for extreme, obligately halophilic Archaea and Bacteria. These were compared with minima for the most solute-tolerant Bacteria in high-sugar (or other non-saline) media (Mycobacterium spp., Tetragenococcus halophilus, Saccharibacter floricola, Staphylococcus aureus and so on) and eukaryotic microbes in saline (Wallemia spp., Basipetospora halophila, Dunaliella spp. and so on) and high-sugar substrates (for example, Xeromyces bisporus, Zygosaccharomyces rouxii, Aspergillus and Eurotium spp.). We also manipulated the balance of chaotropic and kosmotropic stressors for the extreme, xerophilic fungi Aspergillus penicilloides and X. bisporus and, via this approach, their established water-activity limits for mycelial growth (∼0.65) were reduced to 0.640. Furthermore, extrapolations indicated theoretical limits of 0.632 and 0.636 a w for A. penicilloides and X. bisporus, respectively. Collectively, these findings suggest that there is a common water-activity limit that is determined by physicochemical constraints for the three domains of life

Hypogravity increases cyclopiazonic acid sensitivity of rat soleus muscle

International audienceThe functional capacity of skeletal muscle sarcoplasmic reticulum was explored in slow rat soleus muscle after 21 days of hindlimb suspension. The sarcoplasmic reticulum function was assessed in intact and saponin-skinned fibers by using cyclopiazonic acid, a specific Ca(2+)-adenosinetriphosphatase inhibitor. After hindlimb unweighting, the sensitivity to cyclopiazonic acid of intact and skinned soleus fibers becomes similar to that found in fast-twitch muscles. This change could be related to the expression of fast Ca2(+)-adenosinetriphosphatase-pump protein in unloaded soleus muscles and agrees with a transformation of soleus muscle from slow- to fast-twitch type. These results also indicate that specific pharmacological tools, like cyclopiazonic acid, could be used to analyze subcellular functional changes due to hindlimb unweighting

Sym'Previus. La microbiologie prévisionnelle, du laboratoire à l'industrie agroalimentaire = Predictive microbiology, from laboratory to food industry

International audienceL'industrie agroalimentaire et les pouvoirs publics sont contraints à une vigilance accrue sur la sécurité microbiologique des aliments proposés au consommateur en raison des graves conséquences (coût humain, pertes commerciales et pertes d'image) que peut entraîner une non-conformité sur une marque ou un type de produits. Les acteurs des filières agro-industrielles doivent répondre aux attentes du marché et être capables d'assumer pleinement leur responsabilité quant à la sécurité de leur fabrication. La sécurité microbiologique des produits alimentaires exige des connaissances solides et complexes sur la contamination naturelle des matières premières et des produits transformés, sur la capacité de survie des micro-organismes au cours des traitements de transformation, et leur développement aux différents stades de conservation. C'est dans ce contexte que s'inscrit le projet Sym'Previus ; il s'agit d'un outil d'aide à la prévision de l'évolution des populations microbiennes dans les aliments, à l'usage des professionnels de l'alimentation. Disponible sur Internet, cet outil rassemble d'une part, une base de données issues de la bibliographie, de l'industrie et de programmes de recherche, et d'autre part, un module de simulation du comportement microbien s'appuyant sur les outils actuels de la microbiologie prévisionnelle. Hormis la possibilité de prévoir le niveau de contamination d'un microorganisme à un instant de la vie d'un produit (de la fabrication à la consommation), Sym'Previus permet d'optimiser un procédé, une chaîne du froid, mais aussi d'accompagner la formulation et le développement d'un nouveau produit. = Predictive microbiology can be divided into two groups of models, named primary and secondary models. Primary models describe the evolution of the bacterial population with time. These models use parameters which may vary as the environmental factors change. Secondary models describe how those parameters vary with the environmental factors. Sym'Previus meets the French expertise in Predictive Microbiology of major food companies, technical centres and public research institutes. This project aims at proposing an assistance in the managing of the food safety. It is composed from two main softwares. Firstly, a database where information on the behaviour of microorganisms in/on foods and natural contamination of foods are structured. A query system, called MIEL, specifically developed for the database, allows to formulate specific interrogation with a specific selection of food and microorganisms. Secondly, a user-friendly software simulates the growth of microorganisms in food matrix

Two new effective semiselective crystal violet pectate media for isolation of Pectobacterium and Dickeya

Pectolytic bacteria, including Pectobacterium spp. and Dickeya spp., are best isolated on crystal violet pectate (CVP), a semiselective medium containing pectin. The source of pectin is essential, because pectolytic bacteria are not able to degrade all of them. The aims of this study were to identify a new pectin source and to perfect formulations of semiselective CVP media to isolate the pectolytic bacteria Pectobacterium spp. and Dickeya spp. from different environmental compartments (plants, soil and water). The AG366 pectin, selected after screening six different formulations, was incorporated into single-layer (SL-CVPAG366) and double-layer (DL-CVPAG366) CVP media. Both media were compared with those based on Bulmer, Sigma-Aldrich and Slendid-Burger pectins, using 39 Pectobacterium and Dickeya strains. All strains formed deep cavities on AG366-CVPs, whereas nine did not produce cavities on Bulmer or Sigma-Aldrich media. Recovery rates were similar on DL-CVPAG366, Sigma-Aldrich and Bulmer CVPs for a given taxon, and did not differ significantly between SL- and DL-CVPAG366. Pectolytic bacteria were successfully isolated on both media from field samples of diseased potatoes, carrots, tobacco, onions, radishes and ornamentals. AG366 is thus a high-performance pectin source for the elaboration of CVP media suitable to isolate Dickeya and Pectobacterium. It is also efficient for enrichment purposes in liquid medium. The validation of AG366 as an improved source of pectin to recover the polyphagous Pectobacterium and Dickeya in different environmental compartments is essential given the current worldwide emergence and recrudescence of these bacteria

Two new effective semiselective crystal violet pectate media for isolation of Pectobacterium and Dickeya

Pectolytic bacteria, including Pectobacterium spp. and Dickeya spp., are best isolated on crystal violet pectate (CVP), a semiselective medium containing pectin. The source of pectin is essential, because pectolytic bacteria are not able to degrade all of them. The aims of this study were to identify a new pectin source and to perfect formulations of semiselective CVP media to isolate the pectolytic bacteria Pectobacterium spp. and Dickeya spp. from different environmental compartments (plants, soil and water). The AG366 pectin, selected after screening six different formulations, was incorporated into single-layer (SL-CVPAG366) and double-layer (DL-CVPAG366) CVP media. Both media were compared with those based on Bulmer, Sigma-Aldrich and Slendid-Burger pectins, using 39 Pectobacterium and Dickeya strains. All strains formed deep cavities on AG366-CVPs, whereas nine did not produce cavities on Bulmer or Sigma-Aldrich media. Recovery rates were similar on DL-CVPAG366, Sigma-Aldrich and Bulmer CVPs for a given taxon, and did not differ significantly between SL- and DL-CVPAG366. Pectolytic bacteria were successfully isolated on both media from field samples of diseased potatoes, carrots, tobacco, onions, radishes and ornamentals. AG366 is thus a high-performance pectin source for the elaboration of CVP media suitable to isolate Dickeya and Pectobacterium. It is also efficient for enrichment purposes in liquid medium. The validation of AG366 as an improved source of pectin to recover the polyphagous Pectobacterium and Dickeya in different environmental compartments is essential given the current worldwide emergence and recrudescence of these bacteria

Tissue distribution and polymorphism of minor histocompatibility antigens involved in GVHR

A graft-vs-host reaction (GVHR) develops after major histocompatibility complex (MHC)-compatible bone marrow-transplantation. In the genetic combination studied, B10.D2 donor cells differed from those of (DBA/2 x B10.D2)F1 mice for multiple DBA/2 minor histocompatibility antigens (mHAg) and minor lymphocyte stimulating (Mls) antigens. We investigated the distribution and the cell type expression of mHAg in tissues that were potential GVHR targets, by means of specific T-cell clones derived from mice undergoing reaction. The T-cell clones studied had a CD4+ phenotype and recognized 12 distinct mHAg that were not be product of the Mls-1a gene and that were presented predominantly in association with MHC class II A molecules. Our results indicate that DBA/2 alleles coding for mHAg are frequent in both laboratory and geographically unrelated wild mice. Each mHAg displays an individual pattern of expression on cells present in thymus, skin, gut, and liver. In addition, chimeric mice and established cell lines allowed the identification of cell types expressing mHAg. We found that most mHAg are present on lymphoid and monocyte-macrophage cells, whereas one, distinguished by its absence from lymphoid cells and damaged tissues, is expressed by monocyte-macrophage cells