Economic production and biocontrol efficiency of lipopeptide biosurfactants from Bacillus mojavenis A21.

In the wake of an increased attention on the eco-friendly biopesticidal products and the rising market requirements for organic agents, lipopeptides compounds have been described as biological control agents which improve the overall health growth and development of plants. Nevertheless, their high production cost constitue the major flaw in their wide use to control plant diseases. The present article aims to formulate an economic media for lipopeptides production by Bacillus mojavensis A21 for application as natural fungicides for plant disease treatment. We herein demonstrated the suitability of the potato waste, as low cost substrate, for lipopeptides production. Moreover, sea water  was found to be a good mineral salts sources. In the second part of this study, we investigate the inhibitory activity of A21 lipopeptides against the phtopathogenic Fusarium sp. The in vitro test showed a minimal inhibitory concentration of about 0.3 mg/ml. The microscopic examination, of the treated Fusarium revealed an excessive lysis of the mycelia ultrastructure with destructed spores. The in vivo antagonist activity was confirmed towards the infected potato tubers. A21 lipopeptides are effective in decreasing by about 78.26% and 60.68% when applied as preventive and curative treatments, respectively, as compared to the untreated tubers.

Isolation and biochemical characterisation of a bacteriocin-like substance produced by Bacillus amyloliquefaciens An6.

This study focuses on the isolation and characterisation of a peptide with bacteriocin-like properties from Bacillus amyloliquefaciens An6. Incubation conditions were optimised, and the effects of the incubation period and of carbon and nitrogen sources were investigated. The produced bacteriocin was partially purified with ammonium sulphate precipitation, dialysis and ultrafiltration and was then biochemically characterised. Maximum bacteriocin production was achieved after 48h of incubation in a culture medium containing 20g/L starch and 10g/L yeast extract, with an initial pH 8.0 at 30°C under continuous agitation at 200rpm. The bacteriocin was sequentially purified and its molecular weight was determined to be 11kDa by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The bacteriocin was relatively heat-resistant and was not sensitive to acid and alkaline conditions (pH 4.0-10.0). Its inhibitory activity was sensitive to proteinase K but was resistant to the proteolytic action of alcalase, trypsin, chymotrypsin and pepsin. In conclusion, bacteriocin An6, owing its wide spectrum of activity as well as its high tolerance to acidic and alkaline pH values, temperature and proteases shows great potential for use as a food biopreservative.

Structural, physicochemical and antioxidant properties of sodium alginate isolated from a Tunisian brown seaweed.

An original sodium alginate from Tunisian seaweed (Cystoseira barbata) was purified and characterized by circular dichroism (CD) and ATR-FTIR spectroscopies. ATR-FTIR spectrum of C. barbata sodium alginate (CBSA) showed the characteristic bands of mannuronic (M) and guluronic acids (G). The M/G ratio was estimated by CD (M/G = 0.59) indicating that CBSA was composed of 37% mannuronic acid and 63% guluronic acid. The analysis of viscosity of CBSA showed evidence of pseudoplastic fluid behaviour. The emulsifying capacity of CBSA was evaluated at different concentrations (0.25-3%), temperatures (25-100 °C) and pH (3.0-11.0). Compared to most commercial emulsifiers, the emulsion formulated by CBSA was found to be less sensitive to temperature changes and more stable at acidic pH. CBSA was examined for antioxidant properties using various antioxidant assays. CBSA exhibited important DPPH radical-scavenging activity (74% inhibition at a concentration of 0.5 mg/ml) and considerable ferric reducing potential. Effective hydroxyl-radical scavenging activity (82% at a concentration of 5 mg/ml) and potent protection activity against DNA breakage were also recorded for CBSA. However, in the linoleate-ß-carotene system, CBSA exerted moderate antioxidant activity (60% at a concentration of 1.5 mg/ml). Therefore, CBSA can be used as a natural ingredient in food industry or in the pharmaceutical field.

Physical, structural, antioxidant and antimicrobial properties of gelatin-chitosan composite edible films.

Physico-chemical and mechanical properties of cuttlefish skin gelatin (G), chitosan (C) from shrimp (Penaeus kerathurus) and composite films (G75/C25, G50/C50, G25/C75) plasticized with glycerol were investigated. The results indicated that chitosan film had higher tensile strength and lower elongation at break when compared with the other films. Composite films show no significant difference in tensile strength (TS), thickness and transparency. The structural properties evaluated by FTIR and DSC showed total miscibility between both polymers. DSC scans showed that the increase of chitosan content in the composite films increases the transition temperature (Tg) and enthalpy (ΔHg) of films. The morphology study of gelatin, chitosan and composite films showed a compact and homogenous structure. In addition, gelatin and G75/C25 films demonstrated a high antioxidant activities monitored by ß-carotene bleaching, DPPH radical-scavenging and reducing power activities, while films contained chitosan exhibited higher antimicrobial activity against Gram-positive than Gram-negative bacteria.