Culture-independent methods for identifying microbial communities in cheese

International audienceThis review focuses on the culture-independent methods available for the description of both bacterial and fungal communities in cheese. Important steps of the culture-independent strategy, which relies on bulk DNA extraction from cheese and polymerase chain reaction (PCR) amplification of selected sequences, are discussed. We critically evaluate the identification techniques already used for monitoring microbial communities in cheese, including PCR-denaturing gradient gel electrophoresis (PCR-DGGE), PCR-temporal temperature gradient gel electrophoresis (PCR-TTGE) or single-strand conformation polymorphism-PCR (SSCP-PCR) as well as some other techniques that remain to be adapted to the study of cheese communities. Further, our analysis draws attention to the lack of data available on suitable DNA sequences for identifying fungal communities in cheese and proposes some potential DNA targets

Le champignon ectomycorhizien Cenococcum geophilum Fr. dans les hêtraies lorraines : structure génétique des populations et rôle dans la résistance à la sécheresse des racines superficielles du hêtre

The asexual ascomycete Cenococcum geophilum, known for its drought resistance, is a prominent fungus within the ectomycorrhizal comunities in the beech forests in northeastern France. A high level of genetic diversity between- and within- C. geophilum populations was observed. This result suggests the occurrence of a high rate of mitotic or meiotic recombinations and an effect of stand features on population structure. We compared respiration activities of C. geophilum and Lactarius-type ectomycorrhizas sampled from beech stands, during two growing seasons. When soil water potential is lower than -0.2 MPa, the respiration activity of C. geophilum ectomycorrhizas is significantly less altered than that of Lactarius-type ectomycorrhizas. Therefore, C. geophilum preserves the physiological integrity of beech root facing drought stress. In vitro tests did not reveal any metabolic effects which could explain the drought resistance of C. geophilum. In addition, no links between C. geophilum genotype and in vitro physiological behaviour were detected.Parmi les centaines d'espèces du cortège ectomycorhizien de la hêtraie Lorraine on trouve un ascomycète asexué, Cenococcum geophilum, qui présente des caractéristiques reconnues de résistance au stress hydrique. L'utilisation de techniques moléculaires a révélé une forte variabilité génétique au sein de cinq populations de C. geophilum. Cette variabilité, sous l'action de facteurs écogéographiques et de limitation des flux de gènes, conduit à une différenciation des populations. Des mesures d'activité respiratoire d'ectomycorhizes prélevées in situ, pendant deux saisons de végétation, montrent que, lorsque le potentiel hydrique du sol est inférieur à -0,2 MPa, les ectomycorhizes de C. geophilum ont une activité physiologique supérieure à celle des ectomycorrhizes du type Lactaire qui dominent numériquement. C. geophilum préserve donc mieux que le type Lactaire l'intégrité physiologique des racines en conditions hydriques limitantes. Des analyses in vitro n'ont pas mis en évidence de déterminisme métabolique à cette résistance. Elles n'ont pas non plus établi de lien entre résistance au stress hydrique et génotype de C. geophilum

Le champignon ectomycorhizien <em>Cenococcum geophilum</em> Fr. dans les hêtraies lorraines : structure génétique des populations et rôle dans la résistance à la sécheresse des racines superficielles du hêtre

The asexual ascomycete Cenococcum geophilum, known for its drought resistance, is a prominent fungus within the ecwmycorrhizal comunities in the beech forests in northeastern France. A high level of genetic diversity between-and within- C. geophilum populations was observed. This result suggests the occurrence of a high rate of mitotic or meiotic recombinations and an effect of stand features on population structure. We compared respiration activities of C. geophilum and Lacturius-type ectomycorrhias sampled from beech stands, during two growing seasons. When soil water potential is lower than -0.2 MPa, the respiration activity of C. geophilum ectomycorrhizas is signiticantly less altered than that of Laccarius-type ectornycorrhizas. Therefore, C. geophihim preserves the physiological integrity of beech root facing drought stress. ln vitro tests did not reveal any metabolic effects which could explain the drought resistance of C. geophilum. In addition, no links between C. geophilum genotype and in vitro physiological behaviour were detected.Parmi les centaines d'espèces du cortège ectomycorhizien de la hêtraie lorraine on trouve un ascomycète asexué, Cenococcum geophilum, qui présente des caractéristiques reconnues de résistance au stress hydrique. L'utilisation de techniques moléculaires a révélé une forte variabilité génétique au sein de cinq populations de C. geophilum. Cette variabilité, sous l'action de facteurs écogéographiques et de limitation des flux de gènes, conduit à une différenciation des .populations. Des mesures d'activité respiratoire d'ectomycorhizes prélevées in situ, pendant deux saisons de végétation, montrent que, lorsque le potentiel hydrique du sol est inférieur à -0,2 MPa, les ectomycorhizes de C. geophilum ont une activité physiologique supérieure à celle des ectomycorhizes du type Lactaire qui dominent numériquement. C. geophilum préserve donc mieux que le type Lactaire l'intégrité physiologique des racines en conditions hydriques limitantes. Des analyses in vitro n'ont pas mis en évidence de déterminisme métabolique à cette résistance. Elles n'ont pas non plus établi de lien entre résistance au stress hydrique et génotype de C. geophilum

Secondary and adjunct cultures

Chapter 11International audienceTwo types of cultures are used in cheesemaking: primary and secondary. The primary cultures include all the starter lactic acid bacteria that are involved in acid production during cheese manufacturing. The secondary and adjunct cultures are involved in cheese ripening. They are called secondary cultures to distinguish them from the primary acid–producing starters, and are as important as the primary ones in those cheeses in which they are found. They include yeasts, for example, Geotrichum candidum; molds, for example, Penicillium camemberti and Penicillium roqueforti; and bacteria, for example, Brevibacterium, Corynebacterium, Staphylococcus, Propionibacterium sp., and heterofermentative lactobacilli. They are added to provide well-defined functions, such as, gas production, aspect, coloration, and development of the typical flavor. In the present chapter, the most important groups of secondary microbiota, the species found in cheeses, the properties used in their selection, and the form and use of these cultures as adjuncts will be described

Structural transformation of the (233)[011] Σ=11 tilt grain boundary in silicon

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Climb of dissociated dislocations in silicon

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Mucor: A Janus-faced fungal genus with human health impact and industrial applications

International audienceThe Mucor genus, a polyphyletic group pertaining to early diverging lineages of fungi, includes a high number of ubiquitous species. Some species have positive or negative impacts on human activities. Indeed, certain pathogenic Mucor species are a threat for animal and human health and identified more frequently as mycosis causative agents, especially in immunocompromised patients. On the contrary, a small number of Mucor species have been used for centuries in food manufacturing for cheese ripening or Asian fermented food production. Some species are also used as biotechnologically important microorganisms due to their high growth rates, dimorphism (for certain species) and their previously unsuspected potential for secondary metabolite production. Despite all these important roles played by Mucor spp., they have been less investigated than ascomycetous or basidiomycetous species and their taxonomy, metabolism and ecology are less documented when compared to their counterparts in the so-called higher fungi. Nevertheless, research focusing most often on the emblematic Mucor circinelloides species has led to increased knowledge on the biology of this genus, and overall on fungal biology. This is particularly documented for fungal dimorphism or light-induced gene regulation. The aim of this review is to give an overview of the current knowledge on Mucor morphology, taxonomy, ecology and genetics and of its importance regarding human health and industrial applications

Molecular systematics in the genus Mucor with special regards to species encountered in cheese.

International audienceThe genus Mucor, a member of the order Mucorales, comprises different species encountered in cheeses. Although fungi play a fundamental role in cheese manufacturing and ripening, the taxonomy of many fungal species found in cheese is poorly defined; indeed, this is the case for Mucor spp. In the present study, we assessed the phylogenetic relationships among 70 Mucor strains, including 36 cheese isolates, by using a five gene phylogenetic approach combined with morphological analyses. Overall, at least six species of Mucor were identified among the cheese isolates including a possible new taxon. The present study also suggests that the genus Mucor comprises undescribed taxa and needs to be properly defined

Plasticity of a silicon bicrystal: a HREM study

A perfect silicon bicrystal containing only one pure tilt grain boundary (GB) Σ=9 (122) [011] is used as a model in order to study the very early stages of the mechanisms occurring at atomic scale close to the GB. The high resolution electron microscopy observations showed that most dislocations induced by the deformation integrated the GB by glide and climb. The evolution of the structure of the original GB has been studied for different strains and at different temperatures. The accumulation of the DSC dislocations into the GB leads to a variation in the misorientation angle between the two grains. In compression it increases, whereas it decreases in tension. Consequently, various E GBs have been detected. The key points are that, firstly, the structural evolution of the GB can be described with a limited number of structural units and secondly, depending on the deformation temperature, one Σ GB can exhibit two different structures.Le bicristal de silicium contenant le joint de flexion Σ=9 (122) [011] est utilisé comme matériau modèle pour étudier, à l'aide de la microscopie électronique à haute résolution, les mécanismes de déformation à l'échelle atomique. Les mystères des tout premiers stades de déformation du joint ont été élucidés. On a montré que les dislocations créées dans les grains par la contrainte extérieure s'incorporaient au joint par glissement et par montée. L'étude de l'évolution de la structure du joint de grains a été menée pour différentes conditions de déformation et de température. L'accumulation de dislocations DSC le long du joint entraîne une variation de l'angle de desorientation entre les grains; en compression l'angle augmente et différents Σ sont balayés lors de la déformation. Les points importants sont que l'évolution du joint peut se décrire à l'aide d'un nombre limité d'unités structurales et que, pour un même Σ, différentes structures sont obtenues en fonction de la température de déformation

Effect of temperature, pH, and water activity on Mucor spp. growth on synthetic medium, cheese analog and cheese

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