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Aouadhi C.,Pasteur Institute of Tunisia IPT | Aouadhi C.,University of Nantes | Aouadhi C.,French National Center for Scientific Research | Aouadhi C.,National Institute of Agronomy | And 8 more authors.
Food Microbiology | Year: 2012

Bacillus sporothermodurans produces highly resistant endospores that can survive ultra-high-temperature treatment in milk. The induction of endospore germination before a heat treatment could be an efficient method to inactivate these bacteria and ensure milk sterility. In this work, the rate of spore germination of B.sporothermodurans LTIS27 was measured in distilled water after high-pressure treatments with varying pressure (50-600MPa), treatment temperature (20-50°C), pressure-holding time (5-30min) and post-pressurization incubation time (30-120min) at 37°C or 4°C. The results showed that pressure-induced germination was maximal (62%) after a treatment at 200MPa and 20°C and increased with pressure-holding time and post-pressurization incubation time. Treatment temperature had no significant effect on germination. A central composite experimental design with three factors (pressure, pressure-holding time, and post-pressurization incubation time) using response surface methodology was used to optimize the germination rate in distilled water and in skim milk. No factor interaction was observed. Germination was induced at lower pressure and was faster in milk than in distilled water, but complete germination was not reached. The optimum germination obtained with experimental data was 5.0logcfu/mL in distilled water and 5.2logcfu/mL in milk from 5.7logcfu/mL of spores initially present in the suspension. This study shows the potential of using high hydrostatic pressure to induce the germination of B.sporothermodurans spores in milk before a heat treatment. © 2011 Elsevier Ltd.

Marrakchi R.,University of Carthage | Marrakchi R.,University of Montréal | Chouchani C.,University of Carthage | Cherif M.,National Institute of Agronomy | Ramotar D.,University of Montréal
Biochemistry and Cell Biology | Year: 2011

In Saccharomyces cerevisiae, rapamycin exposure inhibits the target of rapamycin (TOR) signaling pathway, causing a profound alteration in the transcription pattern of many genes, including those involved in ribosome biogenesis and nutritional changes. Deletion of the RRD1 gene encoding a peptidyl prolyl isomerase resulted in mutants that are resistant to rapamycin. These rrd1Δ mutants are unable to efficiently downregulate genes such as ribosomal protein genes, or to upregulate genes involved in diauxic shift. It is believed that the isomerase function of Rrd1 plays a role in changing the transcriptional profile upon rapamycin exposure. Herein, we set out to search for genes that when deleted in the rrd1Δ mutant would suppress the rapamycin-resistant phenotype. The analysis revealed that deletion of the SGS1 gene in the rrd1Δ mutant partially suppresses the rapamycin-resistant phenotype of the single rrd1Δ mutant. SGS1 encodes a helicase that functions in many biological processes, including transcriptional regulation. We further show, and for the first time, that Sgs1 is rapidly lost in the parent cells in response to rapamycin, but not by other agents. Interestingly, Sgs1 reduction was completely blocked in the rrd1Δ mutant, suggesting that Rrd1 is required to mediate this process. Genes such as PUT4 and HSP42, known to be upregulated in the parent in response to rapamycin, were not induced in the rrd1Δ mutant if the SGS1 gene was deleted. Since Sgs1 plays a role in transcriptional regulation, we propose that it acts as a repressor of a subset of rapamycin responsive genes. Thus, the observed Rrd1-dependent reduction in Sgs1 level may promote expression of specific classes of genes in response to rapamycin. © 2011 Published by NRC Research Press.

Acourene S.,Station of Algerian National Institute of Agricultural Research | Ammouche A.,National Institute of Agronomy
Journal of Industrial Microbiology and Biotechnology | Year: 2012

The present study deals with submerged ethanol, citric acid, and α-amylase fermentation by Saccharomyces cerevisiae SDB, Aspergillus niger ANSS-B5, and Candida guilliermondii CGL-A10, using date wastes as the basal fermentation medium. The physical and chemical parameters influencing the production of these metabolites were optimized. As for the ethanol production, the optimum yield obtained was 136.00 ± 0.66 g/l under optimum conditions of an incubation period of 72 h, inoculum content of 4% (w/v), sugars concentration of 180.0 g/l, and ammonium phosphate concentration of 1.0 g/l. Concerning citric acid production, the cumulative effect of temperature (30C°), sugars concentration of 150.0 g/l, methanol concentration of 3.0%, initial pH of 3.5, ammonium nitrate concentration of 2.5 g/l, and potassium phosphate concentration of 2.5 g/l during the fermentation process of date wastes syrup did increase the citric acid production to 98.42 ± 1.41 g/l. For the production of α-amylase, the obtained result shows that the presence of starch strongly induces the production of α-amylase with a maximum at 5.0 g/l. Among the various nitrogen sources tested, urea at 5.0 g/l gave the maximum biomass and α-amylase estimated at 5.76 ± 0.56 g/l and 2,304.19 ± 31.08 μmol/l/ min, respectively after 72 h incubation at 30C°, with an initial pH of 6.0 and potassium phosphate concentration of 6.0 g/l. © Society for Industrial Microbiology and Biotechnology 2011.

Nedjimi B.,Ziane Achour University of Djelfa | Nedjimi B.,CSIC - Center of Edafology and Applied Biology of the Segura | Daoud Y.,National Institute of Agronomy | Carvajal M.,CSIC - Center of Edafology and Applied Biology of the Segura | Martinez-Ballesta M.C.,CSIC - Center of Edafology and Applied Biology of the Segura
Communications in Soil Science and Plant Analysis | Year: 2010

Lygeum spartum L. has been recently introduced in areas where salinity is high in soils. However, there are no studies about the physiological response of these plants to salt excess. The effect of sodium chloride (NaCl) on plant growth and water status was studied. Also, the effect of calcium (Ca) addition to salinity conditions was analyzed because of the coexistence of salinity and calcareous soils. Dry weight (DW), transpiration, and osmotic potential (ΨΠ) decreased with elevated NaCl and were restored with Ca2+, whereas moderate salinity had no effect. Fresh weight (FW), water potential (Ψω), and root hydraulic conductance (L0) decreased with salinity; Ca2+ supply had an ameliorative effect at moderate salinity. Sodium (Na+) increased in leaf sap at high levels of NaCl and was decreased by Ca2+. Lygeum spartum showed a resistance to moderate salinity, but the effect of Ca2+ depends on salinity intensity. Thus, the role of Ca2+ in the tolerance to salinity was emphasized. © Taylor & Francis Group, LLC.

Bendifallah L.,University of Boumerdès | Louadi K.,University of Mentouri Constantine | Doumandji S.,National Institute of Agronomy
Journal of Apicultural Science | Year: 2013

Coriander Coriandrum sativum L. (Apiaceae) is a year-round condiment and aromatic Mediterranean plant. It is cultivated in several countries in North Africa, in Europe, and Western Asia. In the El Harrach area of Algiers, the insect fauna visiting crop flowers includes Diptera (Syrphidae), Coleoptera, and Hymenoptera such as Chrysididae, Vespoidea, and Apoidea (Bees). The latter super-family comprises the majority of insect pollinators. Visiting bees belong to four families: Apidae, Andrenidae, Halictidae, and Colletidae. The main visitors are honeybees and six species of Andrenidae: Andrena flavipes, Andrena thoracica, Andrena lagopus, Andrena bimaculata, Andrena discors, and Andrena cinerea elliptica. The three species Andrena lagopus, Andrena bimaculata, and Andrena cinerea elliptica have 100% pollinating visits while Apis mellifera has only 63%. Andrena cinerea elliptica is the most frequent and the most abundant species.

Aouadhi C.,Pasteur Institute of Tunisia IPT | Aouadhi C.,National Institute of Agronomy | Rouissi Z.,Pasteur Institute of Tunisia IPT | Kmiha S.,Pasteur Institute of Tunisia IPT | And 2 more authors.
Food Microbiology | Year: 2016

Bacillus sporothermodurans cells were grown in various environmental conditions to study the effects of temperature, pH, and water activity of the sporulation medium on spore inactivation by nisin and heat treatment. The obtained results showed that the modification of the sporulation conditions affected the spore properties. In fact, the resistance of B. sporothermodurans spores to heat treatment combined with nisin (treatment at 95 °C for 12 min in the presence of 125 UI/ml) increases with increasing of pH level (7-9) and decreases as the acidity of the medium increases. While the sensitivity of B. sporothermodurans spores depends on the sporulation temperature. It increases with increasing the temperature from 4 to 37 °C, but starting with 42 °C, the sensitivity decreases. In the presence of NaCl as depressor, the resistance of B. sporothermodurans spores was higher compared with standard conditions (pH 7, 37 °C without NaCl or glycerol) with an inactivation rate does not exceed 2.79 log. This is the first study which contributed to understand the relationship between the sporulation conditions (pH, temperature and water activity) and the resistance of B. sporothermodurans spores to nisin and heat treatment. It shows that the sporulation conditions, particularly sporulation temperature, must be carefully taken into account during settling sterilization processes applied in the dairy industry. © 2015 Elsevier Ltd.

Aouadhi C.,Pasteur Institute of Tunisia IPT | Aouadhi C.,National Institute of Agronomy | Rouissi Z.,Pasteur Institute of Tunisia IPT | Mejri S.,National Institute of Agronomy | Maaroufi A.,Pasteur Institute of Tunisia IPT
Food Microbiology | Year: 2014

Spores of Bacillus sporothermodurans are known to be a contaminant of dairy products and to be extremely heat-resistant. A central composite experimental design with three factors using response surface methodology was used to evaluate the effect of nisin (50-150UI/mL), temperature (80-100°C), and temperature-holding time (10-20min) on the inactivation of B.sporothermodurans LTIS27 spores in distilled water, in skim milk and in chocolate milk. The experimental values were shown to be significantly in good agreement with the values predicted by the quadratic equation since the adjusted determination coefficients (Radj 2) were around 0.97. By analyzing the response surfaces plots, the inactivation was shown to be higher in distilled water than in skim milk under all the conditions tested. Five-log cycle reductions of B.sporothermodurans spores were obtained after a treatment at 95°C for 12min in presence of 125UI of nisin/mL in distilled water or at 100°C for 13min in presence of 134UI of nisin/mL in skim milk or at 100°C for 15min in presence of 135UI of nisin/mL in chocolate milk. This study showed the efficiency of nisin (15-184UI/mL) in combination with temperature (73-106°C) to inactivate spores of B.sporothermodurans in milk. © 2013 Elsevier Ltd.

Irie M.,University of Tsukuba | Tarhouni J.,National Institute of Agronomy
Journal of Physics: Conference Series | Year: 2015

The industries related to the ceramics such as construction bricks, pottery and tile are the important sectors that cover the large part of the working population in Tunisia. The raw materials, clay or silt are excavated from opencast site of limestone clay stratum. The opencast site give the negative impact on landscape and environment, risks of landslide, soil erosion etc. On the other hand, a most serious problem in water resource management, especially in arid land such as Tunisia, is sedimentation in reservoirs. Sediment accumulation in the reservoirs reduces the water storage capacity. The authors proposed the exploitation of the sediment as raw material for the ceramics industries in the previous studies because the sediment in Tunisia is fine silt. In this study, the potential of the water reservoirs in Tunisia as the resource of the raw material for the ceramics industries is estimated from the sedimentation ratio in the water reservoirs.

Benabderrahim M.A.,Institute of Arid Lands IRA | Hamza H.,Institute of Arid Lands IRA | Haddad M.,Institute of Arid Lands IRA | Ferchichi A.,National Institute of Agronomy
Plant Biosystems | Year: 2015

This work investigated the variability in drought tolerance under arid conditions of Mediterranean alfalfa genotypes with the overall aim to assess the main criteria that are associated with the relative tolerance and to discover the most tolerant ecotypes. For this, 16 alfalfa genotypes originating from seven countries of the Mediterranean basin were tested in an experimental station in south of Tunisia. The trial was conducted under two irrigation treatments. The first was normally irrigated by providing an amount of water corresponding to the potential evapotranspiration of the crop, and in the second with water deficit which was applied by stopping the irrigation during 8 weeks in summer. A significant decrease was observed under water deficit for biomass production, leaf stem ratio and water use efficiency. The sensitive index, in stress treatment, varies between 13.8% and 46.2% for dry yield. Results showed that some genotypes exhibited high-forage yield potential even in the presence of stress, mainly Amerist, Sardi10 and Siriver. Proline accumulation in leaves was greater in water-stressed plants, while the K+ osmo-regulatory role was not definite. High biomass production, accumulation of proline and constancy of K+ in leaves are the most important criteria for tolerant alfalfa. © 2013,Società Botanica Italiana.

PubMed | National Institute of Agronomy
Type: | Journal: Journal of applied microbiology | Year: 2017

To understand the mode of action of thyme essential oil as an alternative biofungicide.The chemical composition of thyme essential oil isolated by hydrodistillation from the aerial parts of Thymus vulgaris was analyzed. The main constituents of thyme essential oil were thymol (76.96%), -cymene (9.89%), -terpinene (1.92%) and caryophyllene oxide (1.69%). The antifungal activity of the oil and its pure major component (thymol) was assessed by the in vitro assay against Mycosphaerella graminicola. Thyme oil exhibited higher antifungal activity than thymol. The expression pattern of genes involved in fungal development and detoxification acting in M.graminicola under thyme oil and thymol treatment was analyzed. Thyme oil overexpressed more than thymol the genes the genes encoding for the efflux pump (MgMfs1, MgAtr4), the regulatory subunit of PKA (MgBcy1) and the MAPK MgHog1. Thyme oil repressed the expression of the genes encoding for the efflux pump MgAtr4, the MAPK (MgSlt2) and the regulatory subunit of PKA (MgBcy1). However, thymol repressed only MgAtr4 and MgSlt2 expression.These data highlight the ability of thyme oil to target genes involved in fungal development and virulence of the yeast-like fungi M. graminicola, which explain its higher antifungal activity.These findings will probably be useful to design an alternative biofungicide which will not lead to pathogen multi-drug resistance. This article is protected by copyright. All rights reserved.

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