Slim Abdelkafi

A newly high alkaline lipase: an ideal choice for application in detergent formulations

BackgroundBacterial lipases received much attention for their substrate specificity and their ability to function in extreme environments (pH, temperature...). Many staphylococci produced lipases which were released into the culture medium. Reports of thermostable lipases from Staphylococcus sp. and active in alkaline conditions are not previously described.ResultsA newly soil-isolated Staphylococcus sp. strain ESW secretes an induced lipase in the culture medium. The effects of temperature, pH and various components in a detergent on the activity and stability of Staphylococcus sp. lipase (SL1) were studied in a preliminary evaluation for use in detergent formulation solutions. The enzyme was highly active over a wide range of pH from 9.0 to 13.0, with an optimum at pH 12.0. The relative activity at pH 13.0 was about 60% of that obtained at pH 12.0. It exhibited maximal activity at 60°C. This novel lipase, showed extreme stability towards non-ionic and anionic surfactants after pre-incubation for 1 h at 40°C, and relative stability towards oxidizing agents. Additionally, the crude enzyme showed excellent stability and compatibility with various commercial solid and liquid detergents.ConclusionsThese properties added to the high activity in high alkaline pH make this novel lipase an ideal choice for application in detergent formulations.

Identification and biochemical characterization of a GDSL-motif carboxylester hydrolase from Carica papaya latex.

An esterase (CpEst) showing high specific activities on tributyrin and short chain vinyl esters was obtained from Carica papaya latex after an extraction step with zwitterionic detergent and sonication, followed by gel filtration chromatography. Although the protein could not be purified to complete homogeneity due to its presence in high molecular mass aggregates, a major protein band with an apparent molecular mass of 41 kDa was obtained by SDS-PAGE. This material was digested with trypsin and the amino acid sequences of the tryptic peptides were determined by LC/ESI/MS/MS. These sequences were used to identify a partial cDNA (679 bp) from expressed sequence tags (ESTs) of C. papaya. Based upon EST sequences, a full-length gene was identified in the genome of C. papaya, with an open reading frame of 1029 bp encoding a protein of 343 amino acid residues, with a theoretical molecular mass of 38 kDa. From sequence analysis, CpEst was identified as a GDSL-motif carboxylester hydrolase belonging to the SGNH protein family and four potential N-glycosylation sites were identified. The putative catalytic triad was localised (Ser(35)-Asp(307)-His(310)) with the nucleophile serine being part of the GDSL-motif. A 3D-model of CpEst was built from known X-ray structures and sequence alignments and the catalytic triad was found to be exposed at the surface of the molecule, thus confirming the results of CpEst inhibition by tetrahydrolipstatin suggesting a direct accessibility of the inhibitor to the active site.

In vitro stereoselective hydrolysis of diacylglycerols by hormone-sensitive lipase.

Hormone-sensitive lipase (HSL) contributes importantly to the mobilization of fatty acids in adipocytes and shows a substrate preference for the diacylglycerols (DAGs) originating from triacylglycerols. To determine whether HSL shows any stereopreference during the hydrolysis of diacylglycerols, racemic 1,2(2,3)-sn-diolein was used as a substrate and the enantiomeric excess (ee%) of residual 1,2-sn-diolein over 2,3-sn-diolein was measured as a function of DAG hydrolysis. Enantiomeric DAGs were separated by performing chiral-stationary-phase HPLC after direct derivatization from lipolysis product extracts. The fact that the ee% of 1,2-sn-diolein over 2,3-sn-diolein increased with the level of hydrolysis indicated that HSL has a preference for 2,3-sn-diolein as a substrate and therefore a stereopreference for the sn-3 position of dioleoylglycerol. The ee% of 1,2-sn-diolein reached a maximum value of 36% at 42% hydrolysis. Among the various mammalian lipases tested so far, HSL is the only lipolytic carboxylester hydrolase found to have a pronounced stereospecificity for the sn-3 position of dioleoylglycerol.

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.

Effect of treated and untreated domestic wastewater on seed germination, seedling growth and amylase and lipase activities in Avena sativa L

BACKGROUND Oats (Avena sativa L.) are a potential economically viable source of lipids and starch for use in foods. The aim of this study was to determine the effect of treated and untreated urban wastewater on seed germination, growth parameters and lipase and amylase activities in A. sativa. RESULTS Untreated wastewater was highly toxic in nature and had an inhibitory effect on seed germination and seedling growth. However, after bacterial treatment, its toxicity was significantly reduced and it showed improved seed germination. It was observed that treated wastewater had no inhibitory effect on seedling growth parameters. However, A. sativa seeds treated with untreated effluent showed reduced lipase and amylase activities. CONCLUSION Treated wastewater could be used for irrigation purposes provided that it satisfies other conditions fixed by legislation.

Isolation, identification and characterization of a new lipolytic Pseudomonas sp., strain AHD-1, from Tunisian soil

A novel, lipid‐degrading bacterium (strain AHD‐1) was isolated from soil regularly contaminated with washing‐machine wastewater in Sfax, Tunisia. When this strain was grown in a medium containing 2% triacylglycerol, the hydrolysis products were found to be diacylglycerols, monoacylglycerols and free fatty acids. This strain was an aerobic, mesophilic, Gram‐negative, motile, non‐sporulating bacterium, capable of growing optimally at pH 7 and 27 °C. The predominant fatty acids were found to be C16:1ω7c (31%), C16:0 (28.1%), C18:1ω7c (16.3%) and C17:0 (5.8%). Phylogenetic analysis of the 16S rRNA gene showed that this isolate is a new strain belonging to the genus Pseudomonas. Strain AHD‐1 was found to be closely related to Pseudomonas azotoformans IAM 1603T, Pseudomonas gessardii CIP 105469T and Pseudomonas libanensis CIP 105460T with 99.7%, 99.56% and 99.54% of similarity, respectively.

Effects of domestic wastewater toxicity on anaerobic membrane‐bioreactor (MBR) performances

An anaerobic membrane bioreactor (MBR) was operated for 367 days to treat domestic wastewater originating from the Sfax wastewater treatment plant. The results showed that the MBR was not very efficient because of the considerable fluctuations in the domestic wastewater composition and the presence of toxic compounds resulting from the industrial effluents in the Sfax region. The acute toxicity tests used for this purpose were the LUMIStox test with the luminescent marine bacterium Vibrio fischeri and the phytotoxicity test with Lepidium sativum. The results of these tests showed that the Sfax wastewaters were highly toxic. The rate of inhibition of Vibrio fischeri ranged from 11.7% to 95%. In all the samples tested, the germination index was less than 15%, as compared with the 100% germination index obtained with distilled water. In addition, the fact that the tendency towards microtoxicity and the chemical oxygen demand (COD) increased during the day, when industrial activities are most intense, confirms that these wastewaters are particularly toxic during the day.

Myrtus communis Essential Oil: Chemical Composition and Antimicrobial Activities against Food Spoilage Pathogens

Myrtus communis is a typical plant of the Mediterranean area, which is mainly used as animal and human food and, in folk medicine, for treating some disorders. In the present study, we evaluated in vitro antibacterial and antifungal properties of the essential oils of Myrtus communis (McEO), as well as its phytochemical composition. The GC/MS analysis of the essential oil revealed 17 compounds. Myrtenyl acetate (20.75%), 1,8‐cineol (16.55%), α‐pinene (15.59%), linalool (13.30%), limonene (8.94%), linalyl acetate (3.67%), geranyl acetate (2.99%), and α‐terpineol (2.88%) were the major components. The antimicrobial activity of the essential oil was also investigated on several microorganisms. The inhibition zones and minimal inhibitory concentration (MIC) values of bacterial strains were in the range of 16–28 mm and 0.078–2.5 mg/ml, respectively. The inhibitory activity of the McEO against Gram‐positive bacteria was significantly higher than against Gram‐negative. It also exhibited remarkable activity against several fungal strains. The investigation of the mode of action of the McEO by the time‐kill curve against Listeria monocytogenes (food isolate) showed a drastic bactericidal effect after 5 min using a concentration of 312 μg/ml. These results evidence that the McEO possesses antimicrobial properties, and it is, therefore, a potential source for active ingredients for food and pharmaceutical industries.

Olive fermentation brine: biotechnological potentialities and valorization

Olive fermentation brine causes an important local environmental problem in Mediterranean countries. Valorization is a relatively new concept in the field of industrial residue management, promoting the principle of sustainable development. One of the valorization objectives regarding food processing by-products is the recovery of fine chemicals and the production of value metabolites via chemical and biotechnological processes. In this article, recent research studies for the valorization of olive fermentation brine performed by several authors were reviewed. Special attention was paid to the metabolic products produced during table olive preparation. The selection of the corresponding valorization process will depend on the agricultural or industrial environment of the olive fermentation brine. Although some methods are strongly consolidated in this sector, other options, more respectful to the environment, should also be considered.

Desulfovibrio tunisiensis sp. nov., a novel weakly halotolerant, sulfate-reducing bacterium isolated from exhaust water of a Tunisian oil refinery

A novel weakly halotolerant, sulfate-reducing bacterium, designated strain RB22(T), was isolated from exhaust water of a Tunisian oil refinery. Cells of strain RB22(T) were Gram-negative, motile, vibrio-shaped or sigmoid and non-spore-forming, and occurred singly or in chains. Strain RB22(T) grew between 15 and 45 degrees C (optimum, 37 degrees C) and at pH 4.5 to 9 (optimum, pH 7). NaCl was not required for growth, but the strain tolerated high NaCl concentrations (up to 70 g l(-1)) with an optimum of 40 g l(-1). Sulfate, thiosulfate, sulfite and elemental sulfur served as electron acceptors, but not fumarate. Nitrate and nitrite were not reduced. Strain RB22(T) utilized lactate, formate, fumarate, succinate, glycerol, H(2)+CO(2) and methanol as substrates. The DNA G+C content was found to be 59.6 mol%. Phylogenetic analysis based on the 16S rRNA gene revealed that the isolate was a member of the genus Desulfovibrio, with no close relatives at the species level (16S rRNA gene sequence similarity of less than 95 %). Strain RB22(T) exhibited levels of 16S rRNA gene sequence similarity of 94.6 and 94.12 % to the type strains of the closely related species Desulfovibrio aespoeensis and Desulfovibrio dechloracetivorans, respectively. On the basis of genotypic and phylogenetic characteristics, and significant phenotypic differences, we suggest that strain RB22(T) represents a novel species, for which the name Desulfovibrio tunisiensis sp. nov. is proposed. The type strain is RB22(T) (=NCIMB 14400(T)=JCM 15076(T)=DSM 19275(T)).