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The aim of this study is to evaluate the efficacy of the strain Bacillus subtilis V26, a local isolate from the Tunisian soil, to control potato black scurf caused by Rhizoctonia solani. The in vitro antifungal activity of V26 significantly inhibited R. solani growth compared to the untreated control. Microscopic observations revealed that V26 caused considerable morphological deformations of the fungal hyphae such as vacuolation, protoplast leakage and mycelia crack. The most effective control was achieved when strain V26 was applied 24h prior to inoculation (protective activity) in potato slices. The antagonistic bacterium V26 induced significant suppression of root canker and black scurf tuber colonization compared to untreated controls with a decrease in incidence disease of 63% and 81%, respectively, and promoted plant growth under greenhouse conditions on potato plants. Therefore, B. subtilis V26 has a great potential to be commercialized as a biocontrol agent against R. solani on potato crops.

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BackgroundThis study aimed to maximize biomass concentration, biomass productivity and biochemical composition of the marine microalga Tetraselmis sp.MethodsIn the current study, Box-Behnken Design was used to model the effect of NaNO3, NaH2PO4, metals and vitamins in the F/2 medium on the growth, total chlorophylls, carotenoids and starch contents. The total chlorophylls content was quantified by spectrophotometry. The FT-IR spectroscopy was used to estimate the biochemical compositions of Tetraselmis sp. grown under both optimized medium culture for starch production and standard culture medium.ResultsFinalized NaNO3 (1.76 mM), NaH2PO4 (0.018 mM), metals (1500 μL.L−1) and vitamins (312.5 μL.L−1) concentrations, generated an increase in biomass concentration up to 5.72 g.L−1 which contributed to an increase about 2.4-fold than that of the standard conditions of biomass productivity (408.57 mg.L−1.day−1). The maximum value of carotenoids content (0.3 mg.g DW−1) was achieved at the highest level of all factors. The total chlorophylls content reached also its maximum (5.18 mg.g DW−1) at high nitrate (1.76 mM), phosphate (0.054 mM), metals and vitamins concentrations, while the maximum starch content (42% DW) was achieved with low nitrate and phosphate concentrations (0.58 mM and 0.027 mM) and with metals and vitamins limitations. Thus, the nitrogen, phosphorus, metals and vitamins limitations led to divert the metabolism for the starch biosynthesis.ConclusionsThe high biomass concentration productivity and starch production make Tetraselmis sp. strain a good candidate for biotechnological applications.

The endocrine-disrupting chemical bisphenol A (BPA) has attracted much attention because of its estrogenic activity and widespread environmental contamination. In this study, we investigated the BPA biodegradation abilities of various bacterial strains isolated from deserts and arid soils from southern Tunisia. Ten bacterial strains that belong to Pseudomonas putida, Pseudomonas aeruginosa, Enterobacter cloacae, Klebsiella sp. and Pantoea sp. showed high BPA removal potential in mineral salt medium (MSM) containing 1 mM BPA. BPA removal rates varied between strains and ranged from 36 to 97%. The strain G320 (P. putida) presented the highest BPA removal rate with 97% within 4 days at 30 °C. The half-life when increasing the BPA concentration to 3 mM was 2 days for strain G320, while total degradation was achieved within 8 days. BPA biodegradation products were identified by GC-MS, and their toxicity was assessed by an algal toxicity test. BPA detoxification was confirmed by evaluating the effect of its biodegradation metabolites on algal growth (dry weight), cells morphology and chlorophylls levels of Tetraselmis sp. strain V2. Results showed the interesting potential of desert soil's bacteria in BPA detoxification as well as the eventual use of the algal specie in toxicity assessment.

Microalgae have been used as natural ingredients to produce functional and nutritional food products. The impact of the addition of Chlorella minutissima, Isochrysis galbana, and Picochlorum sp. at concentrations of 0.5, 1, and 1.5% w/v on the texture and sensory attributes of canned burgers were investigated. The results show that carp formulations containing 1% microalgae show significantly better classification performance for many textural and sensory parameters compared to the rest of the formulations. Also, these treatments had higher swelling ability as well as water and oil holding capacities, thanks to the important dietary fiber and polysaccharide contents found in microalgae. Moreover, microalgae-supplemented burgers were characterized as having low a* and b* values, which made the color appear to be pale orange. Additionally, thanks to its richness in pigments and polysaccharides, microalgae considerably ameliorated the antioxidant activities of the new prepared fish burgers. Thus, microalgae could be used as natural and nutritious ingredient to develop new fish-based products.

BackgroundThe increasing demand for microalgae lipids as an alternative to fish has encouraged researchers to explore oleaginous microalgae for food uses. In this context, optimization of growth and lipid production by the marine oleaginous V2-strain-microalgae is of great interest as it contains large amounts of mono-unsaturated (MUFAs) and poly-unsaturated fatty acids (PUFAs).MethodsIn this study, the isolated V2 strain was identified based on 23S rRNA gene. Growth and lipid production conditions were optimized by using the response surface methodology in order to maximize its cell growth and lipid content that was quantified by both flow cytometry and the gravimetric method. The intracellular lipid bodies were detected after staining with Nile red by epifluorescence microscopy. The fatty acid profile of optimal culture conditions was determined by gas chromatography coupled to a flame ionization detector.ResultsThe phenotypic and phylogenetic analyses showed that the strain V2 was affiliated to Tetraselmis genus. The marine microalga is known as an interesting oleaginous species according to its high lipid production and its fatty acid composition. The optimization process showed that maximum cell abundance was achieved under the following conditions: pH: 7, salinity: 30 and photosynthetic light intensity (PAR): 133 μmol photons.m−2.s−1. In addition, the highest lipid content (49 ± 2.1% dry weight) was obtained at pH: 7, salinity: 37.23 and photosynthetic light intensity (PAR): 188 μmol photons.m−2.s−1. The fatty acid profile revealed the presence of 39.2% and 16.1% of total fatty acids of mono-unsaturated fatty acids (MUFAs) and poly-unsaturated fatty acids (PUFAs), respectively. Omega 3 (ω3), omega 6 (ω6) and omega 9 (ω9) represented 5.28%, 8.12% and 32.8% of total fatty acids, respectively.ConclusionsThis study showed the successful optimization of salinity, light intensity and pH for highest growth, lipid production and a good fatty acid composition, making strain V2 highly suitable for food and nutraceutical applications.