Florence Mathieu

Ochratoxin A removal in synthetic and natural grape juices by selected oenological Saccharomyces strains

Aims:u2002 To assess, for the first time the efficiency in removing ochratoxin A (OTA) from laboratory medium [yeast peptone glucose (YPG)], synthetic grape juice medium (SGM) and natural grape juice by viable and dead (heat and acid‐treated) oenological Saccharomyces strains (five S. cerevisiae and one S. bayanus) compared with a commercial yeast walls additive.

Chemical Composition and Antimicrobial and Antioxidant Activities of Mentha (longifolia L. and viridis) Essential Oils

The study was aimed to investigate essential oil chemical composition (gas chromatography/flame ionization detection [GC-FID] and gas chromatography/mass spectrometry [GC-MS]) and antioxidant (1,1-diphenyl-2-picrylhydrazyl free radical (DPPH) and 2,2-azinobis-3-ethylbenzothiazoline-6-sulphonate [ABTS] assays) and antimicrobial (Gram-positive and Gram-negative bacteria, fungi, and yeast) activities of essential oils extracted from leaves of Mentha longifolia L. and Mentha viridis. GC-MS analysis revealed that M. longifolia was constituted by pulegone (54.41%) as a major component followed by isomenthone (12.02%), 1,8-cineole (7.41%), borneol (6.85%), and piperitenone oxide (3.19%). M. viridis was rich in carvone (50.47%), 1,8-cineole (9.14%), and limonene (4.87%). The antioxidant activity by ABTS assay showed IC(50) values of 476.3 +/- 11.7 and 195.1 +/- 4.2 mg/L for M. longifolia and M. viridis, respectively, the DPPH assays have resulted in a moderate IC(50) (>8000 mg/L and 3476.3 +/- 133 mg/L for M. longifolia and M. viridis, respectively). Antimicrobial activity showed that Listeria monocytogenes and Klebsiella pneumoniae bacteria were more inhibited by the 2 essential oils tested. Escherichia coli was least susceptible. A strong activity was also observed on fungi and yeasts. Carvone, thymol, and piperitone oxide have not been detected in Tunisian M. longifolia. Camphor is reported for the 1st time for M. viridis. Antioxidant and antibacterial activities were correlated to chemical composition.

Aspergillus westerdijkiae polyketide synthase gene “aoks1” is involved in the biosynthesis of ochratoxin A

Ochratoxin A (OTA) is a potential nephrotoxic, teratogenic, immunogenic, hepatotoxic and carcinogenic mycotoxin, produced by Aspergillus westerdijkiae NRRL 3174. Herein we describe the characterization of a putative OTA-polyketide synthase gene aoks1, cloned by using gene walking approach. The predicted amino acid sequence of the 2kb clone display 34-60% similarities to different polyketide synthase genes including lovastatine biosynthesis gene lovb in A. terreus, compactin biosynthesis gene mlcA in Penicillium citrinum and OTA biosynthesis gene otapksPN in P. nordicum. Based on the reverse transcription PCR and kinetic secondary metabolites production studies, aoks1 expression was found to be associated with OTA biosynthesis. Further a mutant, in which the aoks1 gene was inactivated by Escherichia coli hygromycin B phosphotransferase gene, lost the capacity to produce OTA, but still producing mellein. To our knowledge this report describes for the first time characterization of a gene involved in OTA biosynthesis, with the information about mellein which was proposed in the literature to be an intermediate OTA. This study also suggests that aoks1 may be the second polyketide synthase gene required for OTA biosynthesis in A. westerdijkiae NRRL 3174.

Characteristics and Genetic Determinants of Bacteriocin Activities Produced by Carnobacterium piscicola CP5 Isolated from Cheese

Abstract.Carnobacterium piscicola CP5, isolated from a French mold-ripened soft cheese, produced a bacteriocin activity named carnocin CP5, which inhibited Carnobacterium, Enterococcus and Listeria spp. strains, and among the Lactobacillus spp. only Lactobacillus delbrueckii spp. [24]. The activity was purified by ammonium sulfate precipitation, anion exchange, and hydrophobic interaction chromatography followed by reverse-phase high-performance liquid chromatography (RP-HPLC). This latter step separated two peaks with anti-listerial activity (CP51 and CP52). Carnocin CP51 was partially sequenced, and the N-terminal part revealed the presence of the “pediocin-like consensus” sequence-Tyr-Gly-Asn-Gly-Val-. Then, a degenerated 24-mer oligonucleotide probe was constructed from the N-terminal sequence and used to detect the structural gene. It was localized on a plasmid of about 40 kb. Cloning of restriction fragments of this one, followed by DNA sequencing, revealed the presence of the second anti-Listeria bacteriocin gene (CP52). By comparing sequences in data banks and confirming results with PCR reactions, carnocin CP51 shared homologies with carnobacteriocin BM1, and carnocin CP52 was similar to carnobacteriocin B2, both produced by C. piscicola LV17 [2]. However, carnobacteriocin A from C. piscicola LV17 gene was lacking in C. piscicola CP5, and the two microorganisms have been isolated from different ecological environments: C. piscicola CP5 and C. piscicola LV17 were isolated from soft cheese and vacuum-packed meat respectively. This fact could allow different application perspectives for C. piscicola CP5.

Effect of the bacteriocin carnocin CP5 and of the producing strain Carnobacterium piscicola CP5 on the viability of Listeria monocytogenes ATCC 15313 in salt solution, broth and skimmed milk, at various incubation temperatures

Carnobacterium piscicola CP5, isolated from French mould-ripened soft-cheese, produced a bacteriocin named carnocin CP5 in a wide range of incubation temperatures, from 4 degrees C to 30 degrees C. The ability of a crude bacteriocin, of a partially-purified form, and of the producer strain to inhibit growth of Listeria monocytogenes ATCC 15313 was examined in salt solution, broth and skimmed milk between 4 degrees C and 30 degrees C. When carnocin CP5 was added to a L. monocytogenes ATCC 15313 culture, an adsorption on cells and a bactericidal effect with a cell lysis occurred. At 30 degrees C, with carnocin CP5 or with C. piscicola CP5, a transitory bactericidal effect was observed. Subsequent experiments at 4 degrees C, 7 degrees C or 15 degrees C, showed a more prolonged bactericidal effect. Thus at 7 degrees C, partially-purified carnocin CP5 reduced an initial population level of L. monocytogenes of 10(3) cfu/ml to non-detectable level within 7 days. However, in some cases, with extended incubation, the carnocin CP5 effect was no longer visible, the L. monocytogenes population grew again. This phenomenon was probably due to the presence of a sub-population of bacteriocin-resistant variants.

Effect of amino acids containing sulfur on dithiolopyrrolone antibiotic productions by Saccharothrix algeriensis NRRL B‐24137

Aims:u2002 To study the effect of sulfur‐containing amino acids (L‐cysteine, L‐cystine, L‐methionine and DL‐ethionine) on the production of dithiolopyrrolone antibiotics by Saccharothrix algeriensis NRRL B‐24137.

Season's Variation Impact on Citrus aurantium Leaves Essential Oil: Chemical Composition and Biological Activities

Citrus aurantium leaves essential oils (EOs) were evaluated for chemical composition and antioxidant and antibacterial activities. The vegetable material, taken 5 times during the year, has undergone the hydrodistillation to prepare EO. Chemical characterization by gas chromatography/mass spectrometry and GC/flame ionization detection allowed the identification of 46 compounds, and a notable quantitative and qualitative differences between the different Petitgrain samples according to the harvest time. Linalool (43.2% to 65.97%), linalyl acetate (0.77% to 24.77%), and α-terpineol (9.29% to 12.12%) were the main components. The most important number of components was registered for summer EOs (July and September). The 5 EOs submitted biological activities screening, namely, antioxidant and antimicrobial activities. Weak antioxidant activities (IC(50) values >10000 mg/L) were registered by both 1,1-diphenyl-2-picrylhydrazyl and 2,2-azinobis-3-ethylbenzothiazoline-6-sulphonate assays, mostly because the weak amount of phenols in EOs. Antibacterial activities (12 microorganisms) were registered against Gram-positive bacteria [Bacillus subtilis (MIC = 2.7 mg/mL), Staphylococcus aureus (4.8 mg/mL)], and moderated ones against yeasts [Saccharomyces cerevisiae (9.2 mg/mL)] and fungi [Mucor ramannianus (5 mg/mL)]. Positive correlations between the identified compounds and the antimicrobial activities were noted. Many compounds were correlated to antimicrobial activity mainly caryophyllene oxide against Escherichia coli (R(2) = 0.99), S. cerevisiae (R(2) = 0.99), and Fusarium culmorum (R(2) = 0.99).

Partitioning of ochratoxin A in mycelium and conidia of Aspergillus carbonarius and the impact on toxin contamination of grapes and wine

Aims:u2002 Aspergillus carbonarius is an important ochratoxin A (OTA)‐producing fungus which is responsible for toxin contamination of grapes and wine. The objectives of this study were to examine the partitioning of OTA in mycelium and conidia of a range of A. carbonarius strains on artificial grape juice and defined media, to determine the excretion patterns of OTA from these spores, and the effect of organic acids used in wine production on OTA excretion from conidia.

Isolation and partial characterization of antimicrobial compounds from a new strain Nonomuraea sp. NM94

An actinomycete strain NM94 was isolated from a Saharan soil sample by a dilution agar plating method using chitin-vitamins B medium supplemented with penicillin. The strain presented the morphological and chemical characteristics of the genus Nonomuraea. On the basis of 16S rDNA analysis and physiological tests, this isolate was found to be quite different from the known species of Nonomuraea and might be new. The strain NM94 secreted several antibiotics on yeast extract malt extract glucose medium that were active against some Gram-positive bacteria, yeast, and fungi. The antibiotics were extracted with dichloromethane and detected by bioautography on silica gel plates using Mucorramannianus and Bacillussubtilis as the test organisms. Among these antibiotics, a complex called 94A showed interesting antifungal activity. It was selected and purified by reverse-phase HPLC. This complex was composed of five compounds. Spectroscopic studies by infrared, mass, and 1H NMR of the compounds were carried out. Initial results showed that these molecules differed from the known antibiotics produced by other Nonomuraea species.

Isolation and partial characterization of pigment‐like antibiotics produced by a new strain of Streptosporangium isolated from an Algerian soil

Aims:u2002 Identification of a new actinomycete strain Sg3, belonging to the genus Streptosporangium and partial characterization of the produced antibacterial activities.