Abdelhafidh Dhouib

Salinity stress increases lipid, secondary metabolites and enzyme activity in Amphora subtropica and Dunaliella sp. for biodiesel production.

Amphora subtropica and Dunaliella sp. isolated from Tunisian biotopes were retained for their high lipid contents. Respective optimized parameters for rapid growth were: pH 9 and 10, light period 21 and 24h and temperature 31 and 34°C, respectively. After optimization, Amphora subtropica growth rate increased from 0.2 to 0.5day(-1) and Dunaliella sp. growth rate increased from 0.38 to 0.7day(-1). Amphora subtropica biomass production, productivity and lipid content increased from 0.3 to 0.7gL(-1)(dw), 69-100mgL(-1)d(-1)(dw) and 150-190gkg(-1)(dw), respectively, and Dunaliella sp. from 0.5 to 1.4gL(-1)(dw), 124-200mgL(-1)d(-1) (dw) and 190-280gkg(-1)(dw), respectively. Often to overcome trade-off between microalgae rapid growth and high lipid content which are often conflicting and very difficult to obtain at the same time, separation in a growth stage and a lipid accumulation stage is obvious. Salinity stress in a single stage of culture was studied. Compared to the optimal concentration of growth, excess or deficiency of NaCl engendered the same cellular responses by implication of oxidative stress systems and reactivation of defense and storage systems. Indeed, increasing salinity from 1M to 2M for Amphora subtropica or decreasing salinity from 3M to 2M for Dunaliella sp. have both increased lipids content from (220 and 280) to (350 and 430)gkg(-1), carotenoids from (1.8 and 2.4) to (2.3 and 3.7)pgcell(-1), TBARS amount from (10.4 and 5.3) to (12.1 and 10.7)nmolmg(-1) proteins and SOD activity from of (46.6 and 61.8) to (71.6 and 79.4)Umg(-1) proteins, respectively. With further improved fatty acids profile, the microalgae strains could be potent candidates for biofuel production.

Effect of Natural Mediators on the Stability of Trametes trogii Laccase during the Decolourization of Textile Wastewaters

The purpose of the present study was to determine the effect of natural mediators on the stability of the Trametes trogii crude laccase in the process of decolourization of textile effluents. Acetosyringone allowed the highest wastewaters decolourization rate of 25%. At higher concentrations of acetosyringone, the relative activity of laccase decreased approximately by between 38% and 88% after 5 days of incubation. T. trogii laccase was strongly inactivated at 3 mM syringaldehyde, after 3 days of incubation. However, laccase activity is more stable in the presence of the vanillin and m-coumarate. The T. trogii growth on solid effluent-based-medium was examined and evaluated by measuring the colony diameter in cm. T. trogii was completely inhibited on 100:0 and 80:20 effluent:water solid medium, however, colony diameter reached 5 cm on 60:40 effluent:water solid medium after 13-14 days incubation. When the textile effluent was pre-treated with laccase and laccase-acetosyringone system, the colony diameter of 2 cm of T. trogii on 80:20 effluent:water solid medium was reached after 14 and 10 days of incubation respectively.

Optimisation of the critical medium components for better growth of Picochlorum sp. and the role of stressful environments for higher lipid production.

BACKGROUND Coastal countries that suffer from a scarcity of water, such as Tunisia, have to cultivate marine microalgae on non-arable land in order to produce feedstock and overcome their demands of nutrition and energy. In this framework, a green microalga, CTM 20019, was isolated, identified as Picochlorum sp. and tested for its lipid production. RESULTS The dry weight of Picochlorum sp. is composed of 163 g kg(-1) lipids, 225 g kg(-1) total sugars, 440 g kg(-1) proteins and 112 g kg(-1) ash rich in potassium, calcium, iron, magnesium and zinc. Gas chromatography-mass spectrometry analysis showed that the main fatty acids were palmitic acid (29%), linolenic acid (26.5%), linoleic acid (23.5%), hexadecatrienoic acid (11%) and hexadecadienoic acid (8.5%). As it is known that culture conditions greatly influence the composition of microalgae, the experiments were designed to optimise the composition of the medium in order to increase Picochlorum sp. growth from OD680nm = 0.53 to OD680nm = 2.2 and lipid accumulation from 163 g kg(-1) to 190 g kg(-1) . The highest lipid contents of 570 and 585 g kg(-1) were achieved under phosphate starvation and sodium carbonate supplementation, respectively. Under these conditions, the fatty acid profile is dominated by mono-unsaturated and polyunsaturated acids, and is therefore suitable for aqua-culture feeding. However, under high salinity, growth and lipid synthesis are inhibited, and the fatty acids are saturate, and the product is therefore suitable for biodiesel. CONCLUSION This high lipid content rich in essential fatty acids, omega-6 and omega-3, endorses this wild strain of Picochlorum sp. as a promising feedstock for aqua-culture and human nutrition or for the production of biodiesel.

Selection of native Tunisian microalgae for simultaneous wastewater treatment and biofuel production

This paper focuses on the selection of native microalgae strains suitable for wastewater treatment and biofuel production. Four Chlorophyceae strains were isolated from North-eastern Tunisia. Their performances were compared in continuous mode at a 0.3 1/day dilution rate. The biomass productivity and nutrient removal capacity of each microalgae strain were studied. The most efficient strain was identified as Scenedesmus sp. and experiments at different dilution rates from 0.2 to 0.8 1/day were carried out. Maximal biomass productivity of 0.9 g/L day was obtained at 0.6 1/day. The removal of chemical oxygen demand (COD), ammonium and phosphorus was in the range of 92-94%, 61-99% and 93-99%, respectively. Carbohydrates were the major biomass fraction followed by lipids and then proteins. The saponifiable fatty acid content was in the 4.9-13.2% dry biomass range, with more than 50% of total fatty acids being composed of saturated and monosaturated fatty acids.

Nitrogen or phosphorus repletion strategies for enhancing lipid or carotenoid production from Tetraselmis marina

The objective of this study was to investigate the accumulation of lipid and photosynthetic pigments from Tetraselmis marina. When the cells were grown in F/2-medium for seven days in the first stage, the carotenoid and lipid contents, and productivity were 44g/kg (DW), 27% and 31mg/L/d, respectively. After second stage of cultivation of T. marina for further 3-days under N-replete condition (4.41mM NaNO3) increased biomass concentration of 1900mg/L and lipid content of 50% were observed, with an enhanced lipid productivity of 86.36mg/L/d and SFA and MUFA fractions of 70.76 and 13.14%, respectively. However, under P-repletion (2.08mM NaH2PO4), its carotenoid content increased to 89.23g/kg and its PUFA for 65% of total lipids. Results showed that N and P-replete conditions decreased SOD activity and increased H2O2 and TBARS levels of T. marina. Thus, this native microalga strain could be a potent candidate for feed,  food or biofuel production.

Enzymatic oxidative transformation of phenols by Trametes trogii laccases

The removal of toxic phenolic compounds from industrial wastewater is an important issue to be addressed. Their presence in water and soil has become a great environmental concern, and effective methods for their removal need to be addressed. The feasibility of applying laccases for the degradation of phenolic compounds has received increasing attention. In the present work, the transformation of five phenolic compounds (catechol, hydroxytyrosol, tyrosol, guaiacol and p-coumaric acid), the main constituents of a typical wastewater derived from an olive oil factory, by Trametes trogii laccases was studied at concentrations ranging between 0.2 and 1.6 mM. High-performance liquid chromatography analysis showed high degradation rates of phenolic compounds by T. trogii laccases. Independently of the used concentration, a complete transformation of guaiacol, p−coumaric acid, hydroxytyrosol and tyrosol occurred after 1 h of incubation. The transformation of catechol depends on its initial concentration. The liquid chromatography-mass spectrometry analysis showed that laccases catalysed transformation of p-coumaric acid and tyrosol, resulting in the formation of phenolic dimers. No reduction of enzyme activity has been observed during the oxidation of all phenolic compounds. These results suggest that the studied laccases were capable of efficiently removing phenolic compounds, as well as catalysing the production of novel phenolic dimers.

Effect of hydroxytyrosol‐rich preparations on phenolic‐linked antioxidant activity of seeds

Hydroxytyrosol‐rich extract (HRE) and hydroxytyrosol‐rich olive mill wastewater (HROMW) were used as exogenous growth enhancers to stimulate tomato seedling vigor. The tomato seeds soaking in 10% w/v HROMW or HRE solutions were optimum in maximally enhancing seedling performance according to biochemical seed vigor parameters. Biochemical parameters as the average glucose‐6‐phosphate dehydrogenase (G6PDH) activity in HRE‐treated seeds (915.11 nmoles min−1 mg−1 protein) was higher than control (629.58 nmoles min−1 mg−1 protein) and correlated with the increased phenolic content (3530 μg g−1 fw) and 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH)‐based antioxidant activity (70.60%), respectively. Some key enzymes, guaiacol peroxidase (GPX) (6100.65 nmoles min−1 mg−1 protein) and catalase (2.04 μmoles min−1 mg−1 protein), were also higher in response to treatments and correlated with enhanced phenolic content and antioxidant activity. This study supports the hypothesis that the exogenous phenolic application stimulates the pentose phosphate pathway through an over‐expression of endogenous phenolic synthesis and an increase in free‐radical scavenging antioxidant activity. Therefore, the current study indicates the enhancement of seed vigor by HRE especially and HROMW as reflected by the stimulation of biochemical responses.

Protective effect of Dunaliella sp., lipid extract rich in polyunsaturated fatty acids, on hepatic and renal toxicity induced by nickel in rats

Abstract Aims: The present study was undertaken to investigate the protective effect of lipid extract of Dunaliella sp. (LE) rich in polyunsaturated fatty acids (PUFA), against oxidative stress induced by nickel in experimental rats. Methods: Our investigation evaluated the antioxidant activity of LE using both DPPH and NBT assays. Twenty female albino Wistar rats, randomly allocated into four experimental groups, namely (C): control, (Nit): nickel-treated rats with 5 mg/kg/d of NiCl2 during 30 days, (LEa): lipid extract-administered rats with 5  mg/kg BW/d during 30 days and (Nit + LEa): rats treated with Ni and LE-administered during 30 days. Results: The in vitro antioxidant activity demonstrated that LE presents an important antioxidant potential. In vivo, the (Nit + LEa) cotreatment decreased the level of malondialdehyde and restored the antioxidant enzyme activities (superoxide dismutase, catalase and glutathione peroxidase) in livers and kidneys in comparison with those treated with Ni only. LE administration to rats treated with Ni also ameliorated biochemical and histological parameters as compared to only Ni-treated group. LE of Dunaliella sp., rich in polyunsaturated fatty acids showed a significant hepato- and reno-protective effect against metal-induced toxicity. Conclusion: LE of Dunaliella sp., rich in PUFA has been proven to be effective in protection against Ni-induced toxicity.

Two Isorhamnetin Glycosides from Arthrocnemum glaucum that Inhibit Adipogenesis in 3T3-L1 Adipocytes

In our search for bioactive compounds from North African plants [1, 2], we found that the Tunisian medicinal plant Arthrocnemum glaucum Delile inhibited adipogenesis in 3T3-L1. A. glaucum, which belongs to the Chenopodiaceae, is a densely branched robust plant that grows wild in the Sahara Desert of Tunisia, especially in the Mediterranean Coastal region. It was previously reported that some alkaloids and some sterols were isolated from A. glaucum [3–6]. In this research, the bioassay-guided fractionation of this plant implied that the bioactive components are two isorhamnetin glycosides, isorhamnetin-3-O-[apiosyl(1 6)]glucosyl-7-O-rhamnoside (1) and isorhamnetin-3-O-rutinoside (2). In this paper, we report the isolation and structure elucidation of the two isorhamnetin glycosides 1 and 2 from aerial parts of this plant and their antiadipogenesis activity. The aerial part of A. glaucum was collected at the Sahara Desert of Tunisia. The voucher specimen (TPM-20080401) is maintained at Alliance for Research on North Africa (ARENA), University of Tsukuba and Environmental Bioprocesses Laboratory at Biotechnology Center of Sfax. The leaves were dried in the shade at 25 C. The dried leaves of A. glaucum (100 g) were extracted with MeOH. The MeOH extracts were partitioned between EtOAc and H2O, and the H2O layer was partitioned with n-BuOH. The n-BuOH-soluble portion (1.33 g) was subjected to ODS column chromatography and purified by reversed-phase HPLC or gel-filtration HPLC to afford two known flavonol glycosides, isorhamnetin-3-O[apiosyl(1 6)]glucosyl-7-O-rhamnoside (1, 0.0085%) and isorhamnetin-3-O-rutinoside (2, 0.0027%). Structure elucidation of 1 and 2 was through spectroscopic data, mainly 1H and 13C NMR spectra and ESI-MS spectra. Full assignment of signals in the NMR spectra of 1 and 2 was confirmed by 2D NMR experiments (1H–1H COSY, NOESY, HMQC, and HMBC) and comparison with reported data [7, 8].