Nihed Ben Halima

Poly(vinyl alcohol): review of its promising applications and insights into biodegradation

Poly(vinyl alcohol) (PVA) is a water soluble synthetic polymer, with a backbone composed only of carbon atoms and is biodegradable under both aerobic and anaerobic conditions. This polymer can be prepared by the hydrolysis of polyvinylacetate and is one of the most important synthetic polymers used in commercial, industrial, medical and nutraceutical applications. The environmental issues caused by PVA industrial practice have increased globally. Several methods have been used to treat PVA industrial discharge including in particular physicochemical methods such as electrocoagulation. Nowadays, use of bioremediation for PVA release, which has caused serious pollution problems in the natural environment, has attracted much interest. The bioremediation ability of microorganisms and their PVA degrading enzymes, especially PVA oxidases/hydrolases, has long been perceived. These enzymes as well as symbiotic microorganisms could be an effective means for biodegradation of PVA.

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.

Identification of a new oat β-amylase by functional proteomics.

Oat (Avena sativa L.) seed extracts exhibited a high degree of catalytic activity including amylase activities. Proteins in the oat seed extracts were optimized for their amylolytic activities. Oat extract with amylolytic activity was separated by SDS-PAGE and a major protein band with an apparent molecular mass of 53 kDa was subjected to tryptic digestion. The generated amino acid sequences were analyzed by liquid chromatography–tandem mass spectrometry (LC/ESI/MS/MS) and database searches. These sequences were used to identify a partial cDNA from expressed sequence tags (ESTs) of A. sativa L. Based upon EST sequences, a predicted full-length gene was identified, with an open reading frame of 1464 bp encoding a protein of 488 amino acid residues (AsBAMY), with a theoretical molecular mass of 55 kDa identified as a β-amylase belonging to the plant β-amylase family. Primary structure of oat β-amylase (AsBAMY) protein indicated high similarity with other β-amylase from other cereals such as wheat (Triticum aestivum), barley (Hordeum vulgare), and rye (Secale cereale) with two conserved Glu residues (E184 and E378) assigned as the “putative” catalytic residues which would act as an acid and base pair in the catalytic process. In addition, a 3D-model of AsBAMY was built from known X-ray structures and sequence alignments. A similar core (β/α)8-barrel architecture was found in AsBAMY like the other cereal β-amylases with a specific location of the active site in a pocket-like cavity structure made at one end of this core (β/α)8-barrel domain suggesting an accessibility of the non-reducing end of the substrate and thus confirming the results of AsBAMY exo-acting hydrolase.

Oat (Avena sativa L.): Oil and Nutriment Compounds Valorization for Potential Use in Industrial Applications

Oat is a promising plant for the future. It is edible and beneficial thanks to its nutritional, medicinal and pharmaceutical uses and, hence, recognized to be useful for a healthier world. The assessment of the vital functions of oat components is important for industries requiring correct health labelling, valid during the shelf life of any product. Oil, enzymes and other biomolecules of nutraceutic or dietary usage from oats would be valorized for this purpose. Although oats have a unique and versatile composition including antioxidants and biomolecules indispensable for health, they are undervalued in comparison with other staple cereals such as wheat, barley and rice. Furthermore, oats, apart from maize, comprise a high oil content used for a wide range of beneficial purposes. In addition, they contain beta glucan that has proven to be very helpful in reducing blood cholesterol levels and other cardiovascular diseases risks. In fact, there is diversity in the composition and content of the beneficial oat components within their genotypes and the different environmental conditions and, thus, oats are amenable to be enhanced by agronomic practices and genetic approaches.

Structural and functional characterisation of two novel durum wheat annexin genes in response to abiotic stress

Abiotic stress results in massive loss of crop productivity throughout the world. Understanding the plant gene regulatory mechanisms involved in stress responses is very important. Annexins are a conserved multigene family of Ca-dependent, phospholipid-binding proteins with suggested functions in response to environmental stresses and signalling during plant growth and development. Annexins function to counteract oxidative stress, maintain cell redox homeostasis and enhance drought tolerance. A full-length cDNA of two genes (TdAnn6 and TdAnn12) encoding annexin proteins were isolated and characterised from Tunisian durum wheat varieties (Triticum turgidum L. subsp. durum cv. Mahmoudi). Analyses of the deduced proteins encoded by annexin cDNAs (TdAnn6 and TdAnn12) indicate the presence of the characteristic four repeats of 70-75 amino acids and the motifs proposed to be involved in Ca2+ binding. Gene expression patterns obtained by real-time PCR revealed differential temporal and spatial regulation of the two annexin genes in durum wheat under different abiotic stress conditions such as salt (NaCl 150mM), osmotic (10% polyethylene glycol 8000), ionic (LiCl 10mM), oxidative (H2O2), ABA (100µM), salicylic acid (10mM), cold (4°C) and heat (37°C) stress. The two annexin genes were not regulated by heavy metal stress (CdCl2 150µM). Moreover, heterologous expression of TdAnn6 and TdAnn12 in yeast improves its tolerance to abiotic stresses, suggesting annexins involvement in theses stress tolerance mechanisms. Taken together, our results show that the two newly isolated wheat annexin might play an active role in modulating plant cell responses to abiotic stress responses.

The LmSAP gene isolated from the halotolerant Lobularia maritima improves salt and ionic tolerance in transgenic tobacco lines

The A20/AN1 zinc-finger domain-containing proteins of the stress-associated proteins (SAPs) family are fast emerging as potential candidates for biotechnological approaches to improve abiotic stress tolerance in plants. We identified LmSAP, one of the SAPs genes in Lobularia maritima (L.) Desv., a halophyte brassicaceae, through its transcript accumulation in response to salinity and ionic stresses. Sequence homology analysis revealed that LmSAP contains two conserved zinc-finger domains A20 and AN1. Phylogeny analyses showed that LmSAP exhibited high amino acid sequence identity to other plant SAPs. Heterologous expression of LmSAP in yeast increased cell tolerance to salt and osmotic stress. In addition, the overexpression of LmSAP conferred high salt and ionic tolerance to transgenic tobacco plants. Transgenic tobacco seedlings showed higher survival rates and antioxidant activities under salt and ionic stresses. Enhanced antioxidant activities paralleled lower malondialdehyde and superoxide anion O2- levels in the LmSAP transgenic seedlings. Overall, our results suggest that overexpression of LmSAP enhanced salt tolerance by maintaining ionic balance and limiting oxidative and osmotic stresses.