A novel peptidoglycan cross-linking enzyme for a beta-lactam-resistant transpeptidation pathway

The beta-lactam antibiotics remain the most commonly used to treat severe infections. Because of structural similarity between the beta-lactam ring and the d-alanyl(4)-d-alanine(5) extremity of bacterial cell wall precursors, the drugs act as suicide substrates of the dd-transpeptidases that catalyze the last cross-linking step of cell wall assembly. Here, we show that this mechanism of action can be defeated by a novel type of transpeptidase identified for the first time by reverse genetics in abeta-lactam-resistant mutant of Enterococcus faecium. The enzyme, Ldt(fm), catalyzes in vitro the cross-linking of peptidoglycan subunits in a beta-lactam-insensitive ld-transpeptidation reaction. The specificity of Ldt(fm) for the l-lysyl(3)-d-alanine(4) peptide bond of tetrapeptide donors accounts for resistance because the substrate does not mimic beta-lactams in contrast to d-alanyl(4)-d-alanine(5) in the pentapeptide donors required for dd-transpeptidation. Ldt(fm) homologues are encountered sporadically among taxonomically distant bacteria, indicating that ld-transpeptidase-mediated resistance may emerge in various pathogens.     

Pathogénie comparée de 4 espèces d'Helminthosporium Obtenues à Partir des Plantes Malades du Riz au Maroc

A comparative study into the pathogenicity of four Helminthosporiumspp. towards rice cultivars in Marocco In this paper, the behaviour of four Helminthosporium species on nine rice cultivars widely cultivated in Morocco, permit the classification of this species according to their virulence. Helminthosporium oryzae and Helminthosporium sativum are the most virulent and the best equipped to sporule on all varieties of tested lesions. The level of pathogenicity of Helminthosporium spiciferum and Helminthosporium australiensis and their capacity to sporule on host plant depend on the rice variety used. At the same time, each Helminthosporium induces characteristics symptoms on rice leaves.     

Isolation, structure elucidation and biological activity of metabolites from Sch-642305-producing endophytic fungus Phomopsis sp. CMU-LMA

Eight polyketide compounds were isolated from the cultivation broth of Phomopsis sp. CMU-LMA. We have recently described LMA-P1, a bicyclic 10-membered macrolide, obtained as a bioconversion derivative of Sch-642305, the major compound isolated in this study. Benquinol is the ethyl ester derivative of the 13-dihydroxytetradeca-2,4,8-trienoic acid produced by Valsa ambiens. This compound is concomitantly produced with the 6,13-dihydroxytetradeca-2,4,8-trienoic acid (DHTTA) previously isolated from Mycosphaerellarubella. The absolute configuration of the new compound, (2R,3R,4S,5R)-3-hydroxy-2,4-dimethyl-5-[(S,Z)-3-methylpentenyl]-tetrahydro-pyranone LMA-P2 was confirmed by X-ray crystallography. The δ-lactone 2,3-dihydroxytetradecan-5-olide (DHTO) was previously isolated from Seiridium unicorne. This compound may form through the cyclization of the methyl-2,3,5-trihydroxytridecanoate LMA-P3, a new linear polyketide isolated in this study. Benquoine, a new 14-membered lactone generated from the cyclization of benquinol, is proposed as the key precursor for the biosynthesis of Sch-642305. Antimicrobial activity and cancer cell viability inhibition by the new compounds were investigated. Benquoine exhibits antimicrobial activity against Gram positive bacteria, and cytotoxicity against HCT-116 cancer cell line.     

Synthesis of hydantoin analogues of (2S,3R,4S)-4-hydroxyisoleucine with insulinotropic properties

The first synthesis of an optically pure (2R,3R,4S)-hydantoin 2, analogue of (2S,3R,4S)-4-hydroxyisoleucine, was achieved in two steps in un-optimized 35% overall yield from previously reported aldehyde synthon 1. (2R,3R,4S)-Hydantoin is stable at acidic pH. This solves the major drawback of (2S,3R,4S)-4-hydroxyisoleucine that easily cyclizes into inactive lactone. Furthermore, (2R,3R,4S)-hydantoin stimulates the insulin secretion by 150% at 25 μM compared with 4-hydroxyisoleucine and insulin secretagogue drug repaglinide. In view of its stability and biological activity, (2R,3R,4S)-hydantoin represents a good candidate for type-2 diabetes management and control.     

Detoxification of olive mill wastewaters by Moroccan yeast isolates

A total of 105 yeast strains were isolated from Moroccan olive oil production plants and evaluated for their ability to grow in olive oil mill wastewaters (OMW). The 9 isolates that grew best on OMW were selected for further study to evaluate their effect on removal of organic pollutants and OMW phytotoxicity (barley seed germination test). The results showed that at least four yeast isolates effectively lowered the toxicity of this effluent in addition to providing very useful materials in terms of both yeast biomass (6 g/l DW) and an irrigation fluid. This group of yeast isolates significantly reduced the concentration of total phenols (44% removal) and Chemical Oxygen Demand, COD (63% removal). The best germination rate of 80% for undiluted OMW was obtained for strain Candida holstii that also increased the pH from 4.76 to 6.75. Principal component analysis of the results obtained for the best yeast strains confirmed the importance of COD and total phenol reduction along with increase of organic nitrogen and final pH for the improvement of germination rates and phytotoxic reduction. This study has highlighted the potential of indigenous yeasts in detoxification of olive mill wastewaters.     

Biotransformation of natural compounds. Oxido-reduction of Sch-642305 by Aspergillus ochraceus ATCC 1009

Sch-642305 is the major compound produced by the endophytic fungi Phomopsis sp. CMU-LMA. Incubation of Sch-642305 with Aspergillus ochraceus ATCC 1009 resting cells leads to three new derivatives through an oxido-reduction of the six-membered ring of the molecule. Reduction of the double bound leads to compound (1), which subsequently undergoes carbonyl reduction to (2) and ring hydroxylation to (3). According to the previously solved crystal structure of Sch-642305 coupled with ¹H NMR NOE correlation and the crystal structure of compound 1, the absolute configurations of the new derivatives were established. In contrast to the parent compound Sch-642305, compound (1) exhibits antimicrobial activity against Gram-negative bacteria. Furthermore, while all derivatives exhibit cytotoxic activity against various cancer cell lines, compound (2) achieved an IC₅₀ of 4 nM against human myelogenous leukemia K 562, compared to 20 nM for the parent Sch-642305.     

Phytostabilization of polymetallic contaminated soil using Medicago sativa L. in combination with powdered marble: Sustainable rehabilitation

This study uses an ecotoxicology approach to evaluate the effectiveness of combining powdered marble as an amendment, with phytostabilization by Medicago sativa L. on the neutralization of acidic mine tailings, and the stabilization of heavy metals. The mine tailings were collected from an abandoned polymetallic mine in Southern Morocco, and mixed with powdered marble as the following proportions, 25%, 50%, and 75%. Laboratory immobilization/stabilization tests showed that the application of powdered marble in the treatments led to a significant increase in pH, and significant reductions of Cu, Zn (99%), Pb (98%), and Fe (45%). Greenhouse experiments showed that plant growth in all treatments was significantly (p ≤ 0.05) less than growth in agricultural soil. Plant growth significantly (p ≤ 0.05) decreased as the proportion of powdered marble increased. The concentration of metals in plant roots were significantly (p ≤ 0.05) higher than those of shoots. Combining immobilization by powdered marble with phytostabilization by M. sativa L. could represent a viable method of rehabilitating acidic polymetallic mine tailings.     

Asymmetric synthesis ofα-aminophosphonic acids

Summary The enantiospecific synthesis of several-aminophosphonic esters starting from enantiomerically pure derivatives of phosphonic analogues of homoserine is reported.     

Verticillium Wilt of Pepper (Capsicum annuum) in Morocco

Pepper crops in Morocco formerly thought to be free from attack by Verticillium were found to be susceptible to this pathogen. Verticillium wilt of pepper was observed in plots where the crop was cultivated in rotation with tomatoes. Strains of Verticillium isolated from pepper possessed different morphological and pathogenic characteristics.