Slim Smaoui

Bioactive Secondary Metabolites from a New Terrestrial Streptomyces sp. TN262

During our search for Streptomyces spp. as new producers of bioactive secondary metabolites, the ethyl acetate extract of the new terrestrial Streptomyces isolate TN262 delivered eight antimicrobially active compounds. They were identified as 1-acetyl-β-carboline (1), tryptophol (2), cineromycin B (3), 2,3-dihydrocineromycin B (4), cyclo-(tyrosylprolyl) (5), 3-(hydroxyacetyl)-indole (6), brevianamide F (7), and cis-cyclo-(l-prolyl-l-leucyl) (8). Three further metabolites were detected in the unpolar fractions using GC–MS and tentatively assigned as benzophenone (9), N-butyl-benzenesulfonamide (10), and hexanedioic acid-bis-(2-ethylhexyl) ester (11). This last compound is known as plasticizer derivatives, but it has never been described from natural sources. In this article, we describe the identification of the new Streptomyces sp. isolate TN262 using its cultural characteristics, the nucleotide sequence of the corresponding 16S rRNA gene and the phylogenetic analysis, followed by optimization, large-scale fermentation, isolation of the bioactive constituents, and determination of their structures. The biological activity of compounds (2), (3), (4), and those of the unpolar fractions was addressed as well.

Taxonomy, purification and chemical characterization of four bioactive compounds from new Streptomyces sp. TN256 strain

A new actinomycete strain designated TN256, producing antimicrobial activity against pathogenic bacteria and fungi, was isolated from a Tunisian Saharan soil. Morphological and chemical studies indicated that strain TN256 belonged to the genus Streptomyces. Analysis of the 16S rDNA sequence of strain TN256 showed a similarity level ranging between 99.79 and 97.8% within Streptomyces microflavus DSM 40331T and Streptomyces griseorubiginosus DSM 40469T respectively. The comparison of its physiological characteristics showed significant differences with the nearest species. Combined analysis of the 16 S rRNA gene sequences (FN687758), fatty acids profile, and results of physiological and biochemical tests indicated that there were genotypic and phenotypic differentiations of that isolate from other Streptomyces species neighbours. These date strongly suggest that strain TN256 represents a novel species with the type strain Streptomyces TN256 (=CTM50228T). Experimental validation by DNA–DNA hybridization would be required for conclusive confirmation. Four active products (1–4) were isolated from the culture broth of Streptomyces TN256 using various separation and purification steps and procedures. 1: N-[2-(1H-indol-3-yl)-2 oxo-ethyl] acetamide ‘alkaloid’ derivative; 2: di-(2-ethylhexyl) phthalate, a phthalate derivative; 3: 1-Nonadecene and 4: Cyclo (l-Pro-l-Tyr) a diketopiperazine ‘DKP’ derivative. The chemical structure of these four active compounds was established on the basis of spectroscopic studies NMR and by comparing with data from the literature. According to our biological studies, we showed in this work that the pure compounds (1–4) possess antibacterial and antifungal activities.

Chemical composition, techno-functional and sensory properties and effects of three dietary fibers on the quality characteristics of Tunisian beef sausage.

This study determined the effects of three dietary fibers namely, VITACEL LC200 powdered cellulose (LC200), barley beta-glucan concentrate (BBC), and VITACEL KF500 potato fiber (KF500), on the techno-functional and sensory properties and quality characteristics of Tunisian beef sausage. The findings revealed interesting functional properties for LC200 fiber. This fiber displayed high water binding capacity (WBC) and oil binding capacity (OBC), values of 16.2 g/g and 10.2 g/g, respectively, which are higher than reported for most fruit and vegetable fiber concentrates. The application of LC200 improved the masticability and elasticity of beef sausage formulations and minimized their hardness and production costs without negatively affecting their sensory properties. Overall, the findings demonstrate the potential functional and economic utility of LC200 fiber as a promising source of dietary fiber.

Bio-preservative effect of the essential oil of the endemic Mentha piperita used alone and in combination with BacTN635 in stored minced beef meat

The major compounds in Mentha piperita essential oil (EOMP) were menthol (33.59%) and iso-menthone (33%). The biopreservative effect of EOMP used alone at 0.25 or 0.5% and in combination with the semi-purified bacteriocin BacTN635 at 500 or 1000AU/g, on minced beef meat was evaluated by microbiological, physicochemical and sensory analyses during storage at 4°C for 21days. EOMP used alone limited the microbial deterioration of minced meat (P<0.05). Furthermore, the combination between EOMP and BacTN635 led to a decrease in TBARS values and slowed down the accumulation of MetMb. This combination was more efficient (P<0.05) against microflora proliferation and enhanced the sensory acceptability extending thus the shelf life of meat beef by approximately 7days. On the basis of these results, physicochemical and sensorial parameters could be used for constructing regression models to predict overall acceptability. Overall, the strongest preservative effect was achieved by using the combination of EOMP at 0.5% with BacTN535 at 1000AU/g.

Antimicrobial activity and bioguided fractionation of Rumex tingitanus extracts for meat preservation.

This study was undertaken to investigate the antibacterial and antifungal activities of Rumex tingitanus leaves extracts as well as the identification of bioactive components and their performance in meat preservation. Total phenolics and flavonoids showed the highest content of phenolics and flavonoids in the ethyl acetate fraction (Rt EtOAcF). For antimicrobial efficacy, leaves extract and derived fraction were tested for their capacity to inhibit bacterial and fungal proliferation in vitro and in vivo. The ethyl acetate fraction showed the most potent antibacterial and antifungal activities compared to the others extracts. Thus, the efficacy of this extract to inhibit the proliferation of Listeria monocytogenes in minced beef meat model was examined. This fraction eradicates the L. monocytogenes population in meat in a concentration- and time-dependent manner. A bio-guided purification of the Rt EtOAc fraction resulted in the isolation of the compound responsible for the observed antimicrobial activity. This compound was identified as luteolin by analysis of spectroscopic data. CHEMICAL COMPOUNDS ISOLATED IN THIS ARTICLE Luteolin (PubChem CID: 5280445); p-iodonitrotetrazolium chloride (PubChem CID: 64957); Amphotericin B (PubChem CID: 5280965); Gentamicin and (PubChem CID: 6419933); Hexane (PubChem CID: 8058); Methanol (PubChem CID: 887); Ethanol (PubChem CID: 702); Dimethylsulfoxide (PubChem CID: 679); Quercetin (PubChem CID: 5280343); Gallic acid (PubChem CID: 370).

Integrative Gene Cloning and Expression System for Streptomyces sp. US 24 and Streptomyces sp. TN 58 Bioactive Molecule Producing Strains

Streptomyces sp. US 24 and Streptomyces sp. TN 58, two strains producing interesting bioactive molecules, were successfully transformed using E. coli ET12567 (pUZ8002), as a conjugal donor, carrying the integrative plasmid pSET152. For the Streptomyces sp. US 24 strain, two copies of this plasmid were tandemly integrated in the chromosome, whereas for Streptomyces sp. TN 58, the integration was in single copy at the attB site. Plasmid pSET152 was inherited every time for all analysed Streptomyces sp. US 24 and Streptomyces sp. TN 58 exconjugants under nonselective conditions. The growth, morphological differentiation, and active molecules production of all studied pSET152 integrated exconjugants were identical to those of wild type strains. Consequently, conjugal transfer using pSET152 integration system is a suitable means of genes transfer and expression for both studied strains. To validate the above gene transfer system, the glucose isomerase gene (xylA) from Streptomyces sp. SK was expressed in strain Streptomyces sp. TN 58. Obtained results indicated that heterologous glucose isomerase could be expressed and folded effectively. Glucose isomerase activity of the constructed TN 58 recombinant strain is of about eighteenfold higher than that of the Streptomyces sp. SK strain. Such results are certainly of importance due to the potential use of improved strains in biotechnological process for the production of high-fructose syrup from starch.

The antifungal activity of the terrestrial Streptomyces US80 strain is induced by heat-killed fungi

Study of the influence of different concentrations of glucose, as carbon source, and magnesium, as chemical additive, on production by the Streptomyces sp. US80 strain of the three antifungal molecules (irumamycin, X-14952 B and 17-hydroxy-venturicidin A) showed that the highest antifungal activity was obtained at 5 g/L and 3.5 mM for glucose and magnesium, respectively. Environmental factors for maximum antifungal activity production are: temperature of growth 30 degrees C, pH 7, incubation time 72 h and agitation rate of 200 rpm. To further enhance the production of the three antifungal compounds, which possess a real potential application in the agriculture domain, and to explore the possibility of obtaining other active molecules from the Streptomyces sp. US80, we investigated the effect of the addition of heat-killed fungi to the culture media. Biochemical, microbiological and spectroscopic studies of the cultures of the Streptomyces sp. US80 strain in absence (control) and in presence of heat-killed fungus cells indicate an increase of 70% in the production of the three antifungal molecules, compared to the control culture.

Biopreservative Efficacy of Bacteriocin BacFL31 in Raw Ground Turkey Meat in terms of Microbiological, Physicochemical, and Sensory Qualities

　The effect of the semi purified bacteriocin BacFL31 at 200 and 400 AU/g on the shelf life of refrigerated raw ground turkey meat was investigated. The microbiological, physicochemical, and sensory properties of the meat samples were examined during refrigerated storage. The findings indicated that BacFL31 treatments were effective (p<0.05) against the proliferation of various spoilage microorganisms and suppressed the growth of Listeria monocytogenes and Salmonella Typhimurium. The pH, % Met-MB, and TBA-RS values of the treated samples were lower (p<0.05) than those of their control samples. The addition of BacFL31 extended the shelf life and enhanced the sensory attributes of the turkey meat samples during refrigerated storage. These results suggest that BacFL31 could be considered a promising candidate for future application as an additive to preserve the raw turkey meat during storage at 4℃.

Identification and characterization of single nucleotide polymorphism markers in FADS2 gene associated with olive oil fatty acids composition

BackgroundGenotyping of the FAD2.1 and FAD2.3 polymorphisms in the fatty acid desaturase 2 gene (FADS2) shows that they are associated with the fatty acids composition of olive oil samples. However, these associations require further confirmation in the Tunisian olive oil cultivars, and little is known about the effect of polymorphisms in fatty acid-related genes on olive oil mono- and poly- unsaturated fatty acids distribution.MethodsA set of olive oils from 12 Tunisian cultivars was chosen. The fatty acid composition of each olive oil sample was determined by gas chromatography. Statistical and modeling Bayesian analyses were used to assess whether the FAD2.1 and FAD2.3 genotypes were associated with fatty acids composition.ResultsThe TT-FAD2.1 and the GG-FAD2.3 genotypes were found to be associated with a lower proportion of oleic acid (C18:1) (r = −0.778, p = 0.003; r = −0.781, p= 0.003) as well as higher proportion of linoleic (C18:2) (r = 0.693, p = 0.012; r = −0.759, p= 0.004) and palmitic acids (C16:0) (r = 0.643, p = 0.024; r = −0.503, p= 0.095), making varieties with this haplotype (i.e. Chemlali Sfax and Meski) producing more saturated (C16: 0) and polyunsaturated acids than oleic acid. The latter plays a major role in preventing several diseases.ConclusionThe two associations FADS2 FAD2.1 and FADS2 FAD2.3 with the fatty acid compositions of olive oil samples were identified among the studied olive cultivars. These associations differed between studied cultivars, which might explain variability in lipidic composition among them and consequently reflecting genetic diversity through differences in gene expression and biochemical pathways. FADS2 locus would constitute thus a good marker for detecting interesting lipidic chemotypes among commercial olive oils.

Bioactive secondary metabolites from new terrestrial Streptomyces sp. TN82 strain: Isolation, structure elucidation and biological activity

An actinomycete strain designated TN82 was isolated from Tunisian Sahara soil and selected for its interesting antimicrobial activity against Gram positive and Gram negative bacteria and fungi. Based on the results of cultural characteristic, the 16S rRNA gene nucleotide sequence (1434 bp, accession n° LT608133) and the phylogenetic analysis, this new isolate was assigned as Streptomyces sp. TN82 strain. Two active compounds, 3-phenylpyrazin-2(1H)-one (1) and 3-O-methylviridicatin (2), described for the first time as natural product and bacterial compound respectively, together with four known bacterial metabolites; cyclo-(Leu, Pro) (3), anthranilic acid (4), indole-3-carbaldehyde (5) and p-hydroxybenzoic acid (6) were isolated from the culture broth of this strain. Structure of the natural compound (1) was confirmed by extensive 1D and 2D NMR and EI MS and ESI HR mass measurements, and by comparison with literature data. Minimum inhibitory concentrations of the two compounds (1) and (2) against the tested human pathogenic bacteria S. aureus, L. monocytogenes and S. typhimurium were significantly lower than those of kanamycin. For the natural compound 3-phenylpyrazin-2(1H)-one (1), MICs values were very interesting especially that against L. monocytogenes (1.0 μg/mL) which is 2 and 12 times lower than those of ampicillin (2.0 μg/mL) and kanamycin (12.50 μg/mL), respectively.