Lactobacilli are a diverse group of species that occupy diverse nutrient-rich niches associated with humans, animals, plants and food. They are used widely in biotechnology and food preservation, and are being explored as therapeutics. Exploiting lactobacilli has been complicated by metabolic diversity, unclear species identity and uncertain relationships between them and other commercially important lactic acid bacteria. The capacity for biotransformations catalysed by lactobacilli is an untapped biotechnology resource. Here we report the genome sequences of 213 Lactobacillus strains and associated genera, and their encoded genetic catalogue for modifying carbohydrates and proteins. In addition, we describe broad and diverse presence of novel CRISPR-Cas immune systems in lactobacilli that may be exploited for genome editing. We rationalize the phylogenomic distribution of host interaction factors and bacteriocins that affect their natural and industrial environments, and mechanisms to withstand stress during technological processes. We present a robust phylogenomic framework of existing species and for classifying new species.

a b s t r a c tLaboratory tests were conducted to investigate the effect of wetting-drying (W-D) cycles on the initiation and evolution of cracks in clay layer. Four identical slurry specimens were prepared and subjected to five subsequent W-D cycles. The water evaporation, surface cracks evolution and structure evolution during the W-D cycles were monitored. The effect of W-D cycles on the geometric characteristics of crack patterns was analyzed by image processing. The results show that the desiccation and cracking behaviour was significantly affected by the applied W-D cycles: the measured cracking water content θ c , surface crack ratio R sc and final thickness h f of the specimen increased significantly in the first three W-D cycles and then tended to reach equilibrium; the formed crack patterns after the second W-D cycle were more irregular than that after the first W-D cycle; the increase of surface cracks was accompanied by the decrease of pore volume shrinkage during drying. In addition, it was found that the applied W-D cycles resulted in significant rearrangement of specimen structure: the initially homogeneous and non-aggregated structure was converted to a clear aggregated-structure with obvious inter-aggregate pores after the second W-D cycle; the specimen volume generally increased with increasing cycles due to the aggregation and increased porosity. The image analysis results show that the geometric characteristics of crack pattern were significantly influenced by the W-D cycles, but this influence was reduced after the third cycle. This is consistent with the observations over the experiment, and indicates that the image processing can be used for quantitatively analyzing the W-D cycle dependence of clay desiccation cracking behaviour.

Problems related to unsaturated soils are frequently encountered in geotechnical or environmental engineering works. In most cases, for simplicity, one can study the problems by considering the suction effects on volume change or shear strength under isothermal conditions. Often, under these conditions, a temperature-independent water retention curve is considered in the analysis -obviously a simplification. When the temperature changes are too significant to be ignored, it is necessary to account for the thermal effects. This note presents a method for controlling suction with the vapour equilibrium technique at different temperatures. First, calibration of various saturated saline solutions was carried out at temperatures ranging from 20°C to 60°C. A mirror psychrometer was used to measure relative humidity generated by saturated saline solutions at different temperatures. The results obtained were in good agreement with the data from the literature. This information was then used to determine the water retention properties of MX80 clay, which showed that the retention curve shifts downward with increasing temperature. Résumé :On rencontre fréquemment des problèmes reliés aux sols non saturés dans des travaux de génie géotechnique ou environnemental. Dans la plupart des cas, dans un but de simplicité, les problèmes sont étudiés en considérant les effets de succion sur le changement de volume ou sur la résistance au cisaillement dans des conditions isothermes. Dans ces conditions, on considère très souvent dans l'analyse une courbe de rétention d'eau indépendante de la tempé-rature, ce qui est de toute évidence une simplification. Lorsque les changements de température sont trop importants pour être négligés, il est nécessaire de prendre en compte les effets thermiques. Dans cet article, on présente une mé-thode pour contrôler la succion au moyen d'une technique d'équilibre de vapeur à différentes températures. Première-ment, on a déterminé un étalonnage de diverses solutions salines saturées, à des température de 20°C à 60°C. Un miroir psychromètre a été utilisé pour mesurer l'humidité relative générée par des solutions salines saturées à différen-tes températures. Les résultats obtenus concordent bien avec les données de la littérature. Cette information a alors été utilisée pour déterminer les propriétés de rétention d'eau de l'argile MX80, ce qui a montré que la courbe de rétention se déplace vers le bas lorsque la température augmente.Mots clés : technique d'équilibre de vapeur, hygromètre, courbe de rétention d'eau, effets de température, bentonite compactée.[Traduit par la Rédaction] Tang and Cui 296

Bifidobacteria are well known for their human health-promoting effects and are therefore widely applied in the food industry. Members of the Bifidobacterium genus were first identified from the human gastrointestinal tract and were then found to be widely distributed across various ecological niches. Although the genetic diversity of Bifidobacterium has been determined based on several marker genes or a few genomes, the global diversity and evolution scenario for the entire genus remain unresolved. The present study comparatively analyzed the genomes of 45 type strains. We built a robust genealogy for Bifidobacterium based on 402 core genes and defined its root according to the phylogeny of the tree of bacteria. Our results support that all human isolates are of younger lineages, and although species isolated from bees dominate the more ancient lineages, the bee was not necessarily the original host for bifidobacteria. Moreover, the species isolated from different hosts are enriched with specific gene sets, suggesting host-specific adaptation. Notably, bee-specific genes are strongly associated with respiratory metabolism and are potential in helping those bacteria adapt to the oxygen-rich gut environment in bees. This study provides a snapshot of the genetic diversity and evolution of Bifidobacterium, paving the way for future studies on the taxonomy and functional genomics of the genus.

When drying a clayey soil, shrinkage and then cracking on soil surface occur due to water loss by evaporation, this phenomenon seems to be temperature dependent. In the present work, experimental tests were conducted on saturated slurry to investigate the desiccation cracking behavior at three temperatures (22, 60 and 105 °C). The initiation and propagation of desiccation cracks during drying was monitored using a digital camera. By applying computer image processing technique, the surface crack ratio (R SC ) which is the ratio of the surface area of cracks to the total surface area of specimen, was defined to quantify crack networks at different water contents. The experimental results show that the initial critical water content (w IC ), which corresponds to the initiation of desiccation crack, increases with temperature rise. After the initiation of a crack, the ratio R SC increases with decreasing water content and then keeps almost constant when the water content becomes lower than the critical water content (w FC ). By comparing the cracking curve with shrinkage curve, it has been found that the cracking curve, to some extent, reflects the shrinkage properties of soil since the w FC is related to the shrinkage limit and slightly influenced by temperature.

International audienceThe tensile strength of soil is an important mechanical parameter that controls the development of tension cracks. In this study, randomly distributed polypropylene fibers were employed to improve soil tensile behavior. Direct tensile tests were conducted on fiber-reinforced soil specimens with different fiber contents compacted at different water contents dry densities. Desiccation tests were also performed to evaluate the effectiveness of fiber reinforcement in improving soil tensile cracking resistance. The tensile test results showed that fiber inclusion significantly increased the soil peak strength, reduced the postpeak strength, changed the brittle tensile failure behavior to a more ductile one. Soil tensile strength increased with the increase in fiber content. The tensile strength of both reinforced unreinforced specimens decreased with increasing water content increased with increasing dry density. Moreover, a higher soil dry density showed a more positive effect in mobilizing the reinforcement benefit of fibers. Based on the fiber/soil interfacial interaction mechanisms, the fiber reinforcement benefits on soil tensile behavior were analyzed. A linear relationship was obtained between the fiber reinforcement benefit the fiber/soil interfacial shear strength. The desiccation test results showed that fiber inclusion significantly decreased soil cracking. The surface crack reduction ratio increased while the average crack width length decreased with increasing fiber content, suggesting that fiber reinforcement was efficient in impeding soil tensile failure

Extensive investigations have been and are being carried out on a stiff clay from an underground research laboratory located at Mol (Belgium) called Boom clay, in the context of research into deep nuclear waste disposal. Suction effects in deep Boom clay block samples were investigated through the characterisation of the water retention and of the swelling properties of the clay. The data obtained allowed an estimation of the sample initial suction that was reasonably compatible with the in-situ state of stress at a depth of 223 m. The relationship between suction and stress changes during loading and unloading sequences were also examined by running oedometer tests with suction measurements. A rather wide range of the ratio s/σ' v (being s the suction and σ' v the effective vertical stress) was obtained (0.61 -1), different from that proposed by Bishop et al;(1974). Finally, the effect of suction release under an isotropic stress close to the estimated sample suction was investigated. A slight swelling (1.7%) was observed and further compression provided a satisfactory value of the overconsolidation ratio confirming the suggestions of taking some precautions before putting a swelling sample in contact with water as suggested by Graham et al. (1987). The various experimental data gathered in this study finally evidenced a relatively good state of conservation of the block sample used.

Oedometer tests were carried out with loading/unloading/reloading on natural saturated Ypresian clay taken from several depths. Common unloading/reloading loops were identified. Further examination of the unloading or reloading curves shows that each path can be satisfactorily considered as bi-linear with a small and a larger slopes separated by a threshold vertical stress. This threshold stress can be considered as the swelling pressure corresponding to the void ratio just before the unloading or reloading. Indeed, upon unloading, when the applied stress is higher than the threshold stress or swelling pressure, the mechanical effect is dominant and only small mechanical rebound is observed, corresponding to a small microstructure change; by contrast, when the applied stress is lower than the swelling pressure, physico-chemical effect becomes prevailing, and soil swelling occurs with a larger microstructure change. Upon reloading, when the applied stress is lower than the swelling pressure, the microstructure is not significantly affected thanks to the contribution of the physico-chemical repulsive force, leading to a small volume change; on the contrary, beyond the swelling pressure, the mechanical effect becomes dominant giving rise to larger volume change corresponding to the microstructure collapse. Like unsaturated expansive soils, it is found that there is a good relationship between the swelling pressure (threshold stress) and the void ratio just before the unloading or reloading. This is confirmed by the results from the data reported in the literature on Boom and London clays. It can be then deduced that the unloading/reloading loop is rather due to the competition between the mechanical and physico-chemical effects on the microstructure changes than the viscosity effect as commonly admitted.