Antibiotic photocatalysis and antimicrobial activity of low-cost multifunctional Fe3O4@HAp nanocomposites.

Water contamination by multiple pollutants is a serious environmental issue originating from the many diverse sources of pollution. It has worsened with the appearance of new contaminants, named emerging micropollutants, such as drug residues which are considered a potential threat to human health and/or ecosystems. These require prior treatment before release into the environment. Simultaneous adsorption and photocatalysis as well as solid-liquid separation are promising technologies for water treatment. In order to obtain low cost photoactive nanocomposites, porous and magnetic Fe3O4-hydroxyapatite (wFeHAp) nanocomposites were prepared by soft chemistry from the dissociation of natural phosphate into Ca2+ and H3PO4 precursors, further neutralized by ammonia in the presence of preformed Fe3O4 particles. The magnetic nanocomposites were characterized and examined as effective antibacterial agents. Fe3O4 association with apatite modifies the surface properties of the wFeHAp nanocomposite materials, yielding efficient antimicrobial activity for S. aureus, B. subtilis, E. coli and K. pneumoniae strains. The photocatalytic removal of ciprofloxacin (CPF) and oxytetracyclin (OXT) antibiotics in water was also evaluated. The wFeHAp nanocomposites adsorbed and degraded the selected antibiotics successfully. Toxicity evaluation of the treated water after photodegradation using the four strains demonstrates the absence of toxic by-products at the end of the reaction. Therefore, Fe3O4@HAp nanoparticles are valuable for antimicrobial and photocatalysis applications.

Characterisation of Phaseolus symbionts isolated from Mediterranean soils and analysis of genetic factors related to pH tolerance.

The ultimate objective of PhIMED, in which two European (Germany, Italy) and two Mediterranean (Morocco, Egypt) countries collaborate, is to improve the cultivation of French bean (Phaseolus vulgaris) under arid and semi-arid conditions by analysing and enhancing stress tolerance of the nitrogen fixing rhizobial microsymbionts. Rhizobial strains nodulating P. vulgaris (RP strains) isolated from areas in Morocco frequently subjected to drought were analysed for their salt and pH tolerance and their phylogenetic relationship. Strain RP163, exhibiting high nodulation efficiency and a broad pH tolerance was mutagenised by Tn5 and mutants unable to grow on extreme pH media were isolated. Some of the mutants affected in low pH tolerance were found to be mutated in genes related to cobalmin biosynthesis and in succinate dehydrogenase (sdhA). In a parallel approach, promoters and genes inducible under extreme pH values were identified in Rhizobium leguminosarum bv. viciae VF39, among them gabT, which encodes the GABA transaminase and which is induced under acidic conditions. The same gene is present and similarly regulated in RP163. The actSR gene region was cloned from VF39, sequenced and mutants generated in this region were found to be impaired in growth at low pH, but also under neutral conditions. The Agrobacterium rhizogenes 'promintron' promoter, reported to be activated in stationary phase, was found to be also strongly induced under acidic conditions in rhizobia and it is currently being characterised to construct a system allowing the expression of stress tolerance genes in bacteroids and free-living bacteria.

An interdisciplinary research strategy to improve symbiotic nitrogen fixation and yield of common bean (Phaseolus vulgaris) in salinised areas of the Mediterranean basin.

The main findings of a cooperative research group of agronomists, plant breeders, microbiologists, physiologists and molecularists to improve the symbiotic nitrogen fixation (SNF) and N2-dependent yield of common bean under moderate salinity in the Mediterranean basin are summarised. Agronomic surveys in reference production areas show large spatial and temporal variations in plant nodulation and growth, and in efficiency of utilisation of the rhizobial symbiosis. The latter was associated with a large rhizobial diversity, including new bean nodulating species. Macrosymbiont diversity in SNF and adaptation to NaCl was found. However, contrasts between plant genotypes could be altered by specific interactions with some native rhizobia. Therefore, variations in soil rhizobial population, in addition to agronomic practices and environmental constraints, may have contributed to erratic results observed in field inoculations. At the mechanistic level, nodule C and N metabolisms, and abcissic acid content, were related to SNF potential and tolerance to NaCl. Their relation with nodule conductance to O2 diffusion was addressed by in situ hybridisation of candidate carbonic anhydrase and aquaporin genes in nodule cortex. The limits and prospects of the cooperative strategy are discussed.

Phenotypic characteristics of rhizobia isolates nodulating acacia species in the arid and Saharan regions of Morocco.

The phenotypic characteristics of 48 isolates obtained from root nodules of four Acacia species (Acacia cyanophylla, A. gummifera, A. horrida and A. raddiana) growing in soils collected from the arid and Saharan regions of Morocco were studied. The rhizobia were very diverse with respect to their cross-nodulation patterns, as well as their physiological and biochemical properties. Dendrograms obtained through computer numerical analysis of 52 phenotypic characteristics showed that isolates could fit into four clusters below the boundary level of 0.85 average distance and that they were very distinct from the reference strains. Some interesting isolates for inoculation trials have been identified. They were able to grow at pH ranging from 4 to 9, tolerate a high salt concentration (3% NaCl) and grew at a maximum temperature between 35 and 40 degrees C.

Tolerance ofRhizobium leguminosarum bv.phaseoli to acidity and drought.

Ten strains ofRhizobium leguminosarum bv.phaseoli isolated from soils of Morocco were more tolerant than three culture collection strains to acid conditions in culture media or in sterile soil. The survival rate of a tolerant strain in a sandy acid soil was greater than a sensitive strain at different humidity levels. These properties should give locally selected strains an advantage in nodulatingPhaseolus vulgaris roots in soils similar to those used here.