Genetic control of rhizosheath formation in pearl millet.

The rhizosheath, the layer of soil that adheres strongly to roots, influences water and nutrients acquisition. Pearl millet is a cereal crop that plays a major role for food security in arid regions of sub-Saharan Africa and India. We previously showed that root-adhering soil mass is a heritable trait in pearl millet and that it correlates with changes in rhizosphere microbiota structure and functions. Here, we studied the correlation between root-adhering soil mass and root hair development, root architecture, and symbiosis with arbuscular mycorrhizal fungi and we analysed the genetic control of this trait using genome wide association (GWAS) combined with bulk segregant analysis and gene expression studies. Root-adhering soil mass was weakly correlated only to root hairs traits in pearl millet. Twelve QTLs for rhizosheath formation were identified by GWAS. Bulk segregant analysis on a biparental population validated five of these QTLs. Combining genetics with a comparison of global gene expression in the root tip of contrasted inbred lines revealed candidate genes that might control rhizosheath formation in pearl millet. Our study indicates that rhizosheath formation is under complex genetic control in pearl millet and suggests that it is mainly regulated by root exudation.

Ligilactobacillus salivarius functionalities, applications, and manufacturing challenges.

Ligilactobacillus salivarius is a lactic acid bacteria that has been gaining attention as a promising probiotic. Numerous strains exhibit functional properties with health benefits such as antimicrobial activity, immunological effects, and the ability to modulate the intestinal microbiota. However, just a small number of them are manufactured at an industrial scale and included in commercial products. The under exploitation of L. salivarius strains that remain in the freezer of companies is due to their incapacity to overcome the environmental stresses induced by production and stabilization processes.The present study summarizes the functionalities and applications of L. salivarius reported to date. It aims also at providing a critical evaluation of the literature available on the manufacturing steps of L. salivarius concentrates, the bacterial quality after each step of the process, and the putative degradation and preservation mechanisms. Here, we highlight the principal issues and future research challenges for improving the production and long-term preservation at the industrial scale of this microorganism, and probably of other probiotics.Key points• L. salivarius beneficial properties and commercialized products.• Production conditions and viability of L. salivarius after stabilization processes.• Prospects for identifying preservation mechanisms to improve L. salivarius stability.

Understanding the responses of Saccharomyces cerevisiae yeast strain during dehydration processes using synchrotron infrared spectroscopy.

For the first time, synchrotron infrared spectroscopy was performed on yeast during dehydration processes in real time with simultaneously controlled relative humidity and temperature. This led us to investigate the biochemical modification in relation to the dehydration of Saccharomyces cerevisiae. The correlation between the hydration level and yeast survival was observed. Following the test conditions, the modification of the protein structure was observed. However, no evident modification of the lipid composition resulting from dehydration was observed. Furthermore, the results showed that the medium rich in nutrients and glutathione precursors can improve yeast survival during dehydration at 45 °C. This could be related to the high relative amounts of CH3 groups in the lipid composition assigned to the low lipid oxidation level in this case. Our work demonstrated the feasibility of using S-FTIR for investigating yeast responses to dehydration processes in real time. This method can be used for understanding the effect of dehydration/rehydration on the biochemical modification of yeast.

Cyclopropanation of unsaturated fatty acids and membrane rigidification improve the freeze-drying resistance of Lactococcus lactis subsp. lactis TOMSC161.

This work aimed at characterizing the biochemical and biophysical properties of the membrane of Lactococcus lactis TOMSC161 cells during fermentation at different temperatures, in relation to their freeze-drying and storage resistance. Cells were cultivated at two different temperatures (22 and 30 °C) and were harvested at different growth phases (from the middle exponential phase to the late stationary phase). Bacterial membranes were characterized by determining the fatty acid composition, the lipid phase transition, and the membrane fluidity. Cultivability and acidification activity losses of L. lactis were quantified after freezing, drying, and 3 months of storage. The direct measurement of membrane fluidity by fluorescence anisotropy was linked to lipid composition, and it was established that the cyclopropanation of unsaturated fatty acids with concomitant membrane rigidification during growth led to an increase in the freeze-drying and storage resistance of L. lactis. As expected, cultivating cells at a lower fermentation temperature than the optimum growth temperature induced a homeoviscous adaptation that was demonstrated by a lowered lipid phase transition temperature but that was not related to any improvement in freeze-drying resistance. L. lactis TOMSC161 was therefore able to develop a combined biochemical and biophysical response at the membrane level during fermentation. The ratio of cyclic fatty acids to unsaturated fatty acids (CFA/UFA) appeared to be the most relevant parameter associated with membrane rigidification and cell resistance to freeze-drying and storage. This study increased our knowledge about the physiological mechanisms that explain the resistance of lactic acid bacteria (LAB) to freeze-drying and storage stresses and demonstrated the relevance of complementary methods of membrane characterization.

Cell growth and resistance of Lactococcus lactis subsp. lactis TOMSC161 following freezing, drying and freeze-dried storage are differentially affected by fermentation conditions.

AIMS: To investigate the effects of fermentation parameters on the cell growth and on the resistance to each step of the freeze-drying process of Lactococcus lactis subsp. lactis TOMSC161, a natural cheese isolate, using a response surface methodology. METHODS AND RESULTS: Cells were cultivated at different temperatures (22, 30 and 38°C) and pH (5·6, 6·2 and 6·8) and were harvested at different growth phases (0, 3 and 6 h of stationary phase). Cultivability and acidification activity losses of Lc. lactis were quantified after freezing, drying, 1 and 3 months of storage at 4 and 25°C. Lactococcus lactis was not damaged by freezing but was sensitive to drying and to ambient temperature storage. Moreover, the fermentation temperature and the harvesting time influenced the drying resistance of Lc. lactis. CONCLUSIONS: Lactococcus lactis cells grown in a whey-based medium at 32°C, pH 6·2 and harvested at late stationary phase exhibited both an optimal growth and the highest resistance to freeze-drying and storage. SIGNIFICANCE AND IMPACT OF THE STUDY: A better insight on the individual and interaction effects of fermentation parameters made it possible the freeze-drying and storage preservation of a sensitive strain of technological interest. Evidence on the particularly damaging effect of the drying step and the high-temperature storage is presented.

A low membrane lipid phase transition temperature is associated with a high cryotolerance of Lactobacillus delbrueckii subspecies bulgaricus CFL1.

The mechanisms of cellular damage that lactic acid bacteria incur during freeze-thaw processes have not been elucidated to date. Fourier transform infrared spectroscopy was used to investigate in situ the lipid phase transition behavior of the membrane of Lactobacillus delbrueckii ssp. bulgaricus CFL1 cells during the freeze-thaw process. Our objective was to relate the lipid membrane behavior to membrane integrity losses during freezing and to cell-freezing resistance. Cells were produced by using 2 different culture media: de Man, Rogosa, and Sharpe (MRS) broth (complex medium) or mild whey-based medium (minimal medium commonly used in the dairy industry), to obtain different membrane lipid compositions corresponding to different recovery rates of cell viability and functionality after freezing. The lipid membrane behavior studied by Fourier transform infrared spectroscopy was found to be different according to the cell lipid composition and cryotolerance. Freeze-resistant cells, exhibiting a higher content of unsaturated and cyclic fatty acids, presented a lower lipid phase transition temperature (Ts) during freezing (Ts=-8°C), occurring within the same temperature range as the ice nucleation, than freeze-sensitive cells (Ts=+22°C). A subzero value of lipid phase transition allowed the maintenance of the cell membrane in a relatively fluid state during freezing, thus facilitating water flux from the cell and the concomitant volume reduction following ice formation in the extracellular medium. In addition, the lipid phase transition of freeze-resistant cells occurred within a short temperature range, which could be ascribed to a reduced number of fatty acids, representing more than 80% of the total. This short lipid phase transition could be associated with a limited phenomenon of lateral phase separation and membrane permeabilization. This work highlights that membrane phase transitions occurring during freeze-thawing play a fundamental role in the cryotolerance of Lb. delbrueckii ssp. bulgaricus CFL1 cells.

[Optimization of anesthesia for emergency abdominal surgery in the elderly]. / Optimisation de la prise en charge anesthésique en chirurgie abdominale urgente chez le sujet âgé

OBJECTIVES: Peroperative haemodynamic profile comparison of two anaesthetic protocols for emergency abdominal surgery of old patients. PATIENTS AND METHODS: Non-randomized monocentric study. Patients in the Optimization group were prospectively studied. Anaesthesia was induced by etomidate-succinylcholine and maintained with effect site and end-tidal target controlled administration of remifentanil and desflurane respectively to keep the BIS values between 45 and 55. These patients were matched with retrospectively studied patients constituting the Control group. The latter's were anaesthetized with etomidate-succinylcholine and anaesthesia was maintained by manually controlled administration of sufentanil and desflurane to keep systolic arterial pressure (SAP) within a range of more or less 30% of preoperative baseline SAP. RESULTS: Twelve patients (86+/-5 yrs) were included in the Optimization group, 11 (86+/-4 yrs) in the Control group. The time spent at a SAP within more or less 30% of baseline values was 92+/-7% and 71+/-29% of total anesthesia time in the Optimization and Control groups respectively (p<0.05). That spent at a SAP less than 15 and 30% of baseline values was 23+/-11% et 3+/-5% of total anaesthesia time in the Optimization group, whereas in the MAN group it was 65+/-21% and 27+/-30% respectively (p<0.05). Desflurane and ephedrine consumption was less in the Optimization group as well as crystalloid or colloid volume loading. CONCLUSION: Anaesthetic agents target controlled administration and/or neurophysiologic depth of anaesthesia monitoring improve the time course of the haemodynamic effects in elderly patients undergoing abdominal surgery in emergency.

[Which doses of anaesthetic agents in centenarian patients? Interest of BIS monitoring]. / Posologies des agents anesthésiques chez le centenaire ? Intérêt du monitorage par le BIS.

A 106-year-old female underwent emergency colectomy for peritonitis secondary to ischemic colitis. Following induction of anaesthesia with 18 mg etomidate (0,4 mg/kg), BIS monitoring allowed to perform surgery with an averaged desflurane end-tidal concentration and remifentanil infusion as low as 0.9% and 0.057 microg/kg/minute respectively. The mean BIS value was of 45+/-4 (min = 38, max = 50), systolic arterial pressure was maintained within+/-10% of control values during 72% of anaesthesia duration (160 min) and the maximal drop did not exceed 27%. No adrenergic agent was used. This observation underlined the interest of BIS when anaesthetic requirement are difficult to estimate rapidly.