Jacques Maury

Antibacterial action of essential oils from corsica

Abstract The antimicrobial activity of 28 essential oil samples isolated from local plants or plants cultivated in Corsica was evaluated against a large panel of human pathogenic bacteria, including Campylobacter jejuni which appeared as a good model for this purpose. The chemical composition of the 18 oils selected for their efficiency was determined by GC and GC/MS. Among them, the oils of Cistus ladaniferus, Crithmum maritimum, Daucus carota, Juniperus communis, Mentha aquatica and Santolina corsica showed compositions without components known as active, suggesting the presence of compounds not previously described as antibacterial agents.

Genetic relationships between cultivated and wild olives of Corsica and Sardinia using RAPD markers

In order to ensure the genetic diversity of the Olea europaea complex,it is necessary to characterize the cultivated varieties and the wildpopulations. In the present study, we focused on the olives growing on twoMediterranean islands, Corsica and Sardinia. On these two islands, there areolives with many denominations, as well as forests of oleasters. Here, it wasproposed to determine the relationships among cultivated and wild olives.Some Italian denominations were studied in addition to assess the influenceof the mainland on the two islands in this respect.The 59 RAPD markers obtained showed the existence of manysynonymous, and homonymous. A dendrogram was constructed using theUPGMA method and a FCA was carried out. The results of these twoanalyses showed the existence of a genetic divergence between the oleastersand the cultivated varieties. They suggest that some of the Corsicanvarieties were probably selected from local wild forms, contrary to theSardinian varieties. They also show that there are feral forms growing onboth islands, which result from hybridization between oleasters andvarieties.

A lipoxygenase with dual positional specificity is expressed in olives (Olea europaea L.) during ripening.

Plant lipoxygenases (LOXs) are a class of widespread dioxygenases catalysing the hydroperoxidation of polyunsaturated fatty acids. Although multiple isoforms of LOX have been detected in a wide range of plants, their physiological roles remain to be clarified. With the aim to clarify the occurrence of LOXs in olives and their contribution to the elaboration of the olive oil aroma, we cloned and characterized the first cDNA of the LOX isoform which is expressed during olive development. The open reading frame encodes a polypeptide of 864 amino acids. This olive LOX is a type-1 LOX which shows a high degree of identity at the peptide level towards hazelnut (77.3%), tobacco (76.3%) and almond (75.5%) LOXs. The recombinant enzyme shows a dual positional specificity, as it forms both 9- and 13-hydroperoxide of linoleic acid in a 2:1 ratio, and would be defined as 9/13-LOX. Although a LOX activity was detected throughout the olive development, the 9/13-LOX is mainly expressed at late developmental stages. Our data suggest that there are at least two Lox genes expressed in black olives, and that the 9/13-LOX is associated with the ripening and senescence processes. However, due to its dual positional specificity and its expression pattern, its contribution to the elaboration of the olive oil aroma might be considered.

Identification of putative residues involved in the accessibility of the substrate-binding site of lipoxygenase by site-directed mutagenesis studies

Lipoxygenases (LOXs) are a class of widespread dioxygenases catalyzing the hydroperoxidation of polyunsaturated fatty acids (PUFA). Recently, we isolated a cDNA encoding a LOX, named olive LOX1, from olive fruit of which the deduced amino acid sequence shows more than 50% identity with plant LOXs. In the present study, a model of olive LOX1 based on the crystal structure of soybean LOX-1 as template has been generated and two bulky amino acid residues highly conserved in LOXs (Phe277) and in plant LOXs (Tyr280), located at the putative entrance of catalytic site were identified. These residues may perturb accessibility of the substrate-binding site and therefore were substituted by less space-filling residues. Kinetic studies using linoleic and linolenic acids as substrates were carried out on wild type and mutants. The results show that the removal of steric bulk at the entrance of the catalytic site induces an increase of substrate affinity and of catalytic efficiency, and demonstrate that penetration of substrates into active site of olive LOX1 requires the movement of the side chains of the Phe277 and Tyr280 residues. This study suggests the involvement of these residues in the accessibility of the substrate-binding site in the lipoxygenase family.