Starvation induces physiological changes that act on the cryotolerance of Lactobacillus acidophilus RD758

International audienceThe relationship between lactose starvation and cryotolerance was investigated in Lacto-bacillus acidophilus RD758. Cryotolerance was measured from the acidification activity of cells recovered after 18-h lactose starvation. It was compared to that of nonstarved cells, both of them in a stationary phase and in the same medium. This measurement allowed quantifying the initial acidification activity before freezing, as well as the loss of acidifica-tion activity during freezing and the rate of loss during frozen storage. Even if initial acidifi-cation activity was similar for nonstarved and starved bacteria, the latter displayed a significantly better resistance to freezing and frozen storage at À20 C. To investigate the mechanisms that triggered these cryotolerance phenomena, the membrane fatty acid composition was determined by gas chromatography, and the proteome was established by 2-D electrophoresis, for starved and nonstarved cells. The main outcome was that the improved cryotolerance of starved cells was ascribed to two types of physiological responses as a result of starvation. The first one corresponded to an increased synthesis of unsaturated, cyclic, and branched fatty acids, to the detriment of saturated fatty acids, thus corresponding to enhanced membrane fluidity. The second response concerned the upregulation of proteins involved in carbohydrate and energy metabolisms and in pH homeostasis, allowing the cells to be better prepared for counteracting the stress they encountered during subsequent cold stress. These two phenomena led to a cross-protection phenomenon, which allowed better cryotolerance of Lb. acidophilus RD758, following cellular adaptation by starvation

Segmentation multi-résolution basée sur la texture ; Application à la segmentation de très grandes images de microscopie cellulaire

International audienceCe papier présente une stratégie de segmentation multi-échelle, mettant en oeuvre un modèle d'arbre de Markov caché appliqué sur les valeurs des coefficients en ondelettes, pour la segmentation de différents types de stroma sur de très grands volumes de données images

Arthrobacter bergerei sp. nov. and Arthrobacter arilaitensis sp. nov., novel coryneform species isolated from the surfaces of cheeses

International audienceFourteen isolates of two different bacterial species isolated from the surface of smear-ripened cheeses were found to exhibit many characteristics of the genus Arthrobacter. The isolates were aerobic, Gram-positive, catalase-positive, non-spore-forming and non-motile. The cell-wall peptidoglycan contained lysine, alanine and glutamic acid. rrs sequence analysis indicated that the new isolates Re117T and Ca106T are closely related to the Arthrobacter nicotianae group and showed highest sequence similarity (>98 %) to Arthrobacter nicotianae and Arthrobacter protophormiae. However, DNA–DNA hybridization studies indicated that the strains represented two novel genomic species within the genus Arthrobacter and did not belong to A. nicotianae or A. protophormiae (<43 % DNA–DNA relatedness). On the basis of the phylogenetic and phenotypic distinctiveness of the new isolates, these bacteria should be classified as two novel Arthrobacter species, for which the names Arthrobacter bergerei sp. nov. and Arthrobacter arilaitensis sp. nov. are proposed. Type strains have been deposited in culture collections as Arthrobacter bergerei Ca106T (=CIP 108036T=DSM 16367T) and Arthrobacter arilaitensis Re117T (=CIP 108037T=DSM 16368T)

Culture conditions affect Lactobacillus reuteri DSM 17938 ability to perform glycerol bioconversion into 3-hydroxypropionic acid

International audienceThe platform molecule 3-hydroxypropionic acid (3-HP) can be produced using Lactobacillus reuteri through a twostep bioprocess that involves a growth phase followed by a bioconversion phase. The bioproduction is performed by resting cells that convert glycerol into 3-HP and 1,3-propanediol in fed-batch mode. This work aimed at studying the effect of the growth conditions of L. reuteri DSM 17938 during the first step, on the glycerol bioconversion into 3-HP during the second step. A Plackett and Burman design was carried out to test, in controlled bioreactors, the effect of 11 growth conditions simultaneously, at fixed bioconversion conditions. The supplementation of the growth medium with vitamin B12 and cysteine displayed a negative effect on the 3-HP bioproduction. The addition of glucose, phytone peptone, Tween 80, 1,2-propanediol and betaine in the growth medium, together with a low temperature and an optimal pH of 6.0 during the growth phase increased the bioconversion duration from 56 h to 89 h at a glycerol feeding rate of 0.5 g$h L1. A validating experiment displayed that the 3-HP titer, 3-HP production yield and 3-HP specific production rate were significantly improved by 25 %, 150 % and 61 %, respectively

Influence of depth and time on diversity of free-living microbial community in the variably saturated zone of a granitic aquifer

Contacts: [email protected], [email protected] audienceWe investigated the temporal and vertical changes in the microbial communities related to hydrological variations an aquifer (Brittany, France). Five water samplings were carried out, spanning three hydrological cycles in the variably and the permanently saturated zones. Seasonal variations in the major anion concentrations (NO -3 , SO24 and Cl-) indicated that different physical processes occurred during the recharge process in the two zones. The variably saturated zone is mainly dominated by diffusion and advection processes from the soil, whereas the permanently saturated zone is controlled by moderate advective transfer from the variably saturated zone. Bacterial diversity was investigated by flow cytometry, 16S rRNA and narG genes analyses. Part of this diversity was new in that 6 of the 27 16S rRNA gene sequence phylotypes were unknown even at the class or phylum level. The narG gene analysis did not reveal any clear variation in time or depth within the nitrate reducers' community. In contrast, 16S rRNA gene analyses showed modifications of community composition that could be related to the hydrologic and chemical contrast between the two zones. It was concluded that the physical processes of water transfer could influence bacterial diversity at the soil-aquifer interface

The impact of fluid-dynamic stress in stirred tank bioreactors on the synthesis of cellulases by Trichoderma reesei at the intracellular and extracellular levels

International audienceCellulases for bioethanol production are mainly made by fed-batch fermentation using a filamentous fungus, Trichoderma reesei. Agitation at different scales impacts on morphology, rheology and growth rate and can be correlated by EDCFεmax. Typically, EDCFεmax is much smaller at commercial scale and fungal size, viscosity and growth rate are greater. Here, to increase understanding, continuous culture in 3 L bioreactors using two EDCFεmax values were undertaken. The higher EDCFεmax decreased the cellulase production (concentration, 21%; specific production rate, 24%; protein yield, 20%) whilst proteomic analysis showed, at an intracellular level, a decrease of cellulase and hemicellulase synthesis. An increase of stress proteins also occurred, which may help cells to limit the impact of fluid dynamic stress. Also, cellulase production during continuous culture at the bench varied with EDCFεmax similarly to that between bench and commercial scale during fed-batch culture

Fructose oligosaccharides as a novel cryoprotectant for mammalian cells

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Effect of dairy matrices on the survival of Streptococcus thermophilus, Brevibacterium aurantiacum and Hafnia alvei during digestion

This study evaluated the ability of dairy matrices, different in composition (with and without fat) and structure (liquid and gel), to enhance microorganisms survival through digestion. The viability of three dairy microorganisms Streptococcus thermophilus, Brevibacterium aurantiacum and Hafnia alvei was measured during in vitro and in vivo digestion. S. thermophilus was highly sensitive to gastric stress, and was not found in the duodenal compartment. B. auranticum was moderately sensitive to gastric stress but resistant to duodenal stress. H. alvei was highly resistant to both stresses. LIVE/DEAD confocal microscopy´s images, probed the effect of low pH on microorganisms survival. However, in vivo analyses (16S rRNA gene metabarcoding) failed to confirm in vitro observations since tested microorganisms were not detected. Despite of the different evolutions during digestion on buffer capacity, lipolysis, and rheological characteristics, we did not observe any protective effect of the dairy matrices on microorganisms survival