Phytoplankton distribution in the upwelling areas of the Moroccan Atlantic coast localized between 32°30'N and 24°N

Marine phytoplankton was studied in January and July 2002 along of four transects: 32°30′N, 29°N, 24°30′N and 24°N. A total of 142 taxa were recorded in this area. The maximal specific richness, both in summer and in winter, was registered around Dakhla (24°N). The global spatiotemporal variability of species richness and specific diversity showed that the most structured and species-rich populations are situated in the coastal areas. The vertical variation of the two parameters showed homogeneity between depth levels. The maximal phytoplanktonic densities are recorded in the southern transects due to the permanent upwelling activity in the southern Atlantic coast. The bathymetric distribution of densities was more heterogeneous during summer, characterized by a high intensity of upwelling. The species Thalassionema nitzschioides, Asterionellopsis glacialis, Melosira, Chaetoceros and Leptocylindrus minimus are indicators of upwelling.     

Increased trehalose biosynthesis improves <Emphasis Type="Italic">Mesorhizobium ciceri</Emphasis> growth and symbiosis establishment in saline conditions

Cicer arietinum (chickpea) is a legume very sensitive to salinity, and so are most of its rhizobial symbionts belonging to the species Mesorhizobium ciceri. We observed that exogenous trehalose (i.e., added to the growth medium) can significantly improve growth of M. ciceri strain Rch125 under moderate salinity. In order to test if endogenous trehalose (i.e., synthesized by the cell) could also enhance salt tolerance, strain Rch125 was genetically modified with various trehalose biosynthesis genes from Sinorhizobium meliloti 1021 (otsA, treS, treY) and Mesorhizobium loti MAFF 303099 (otsAB). We found that overexpression of otsA or otsAB, but not treS or treY, significantly improved M. ciceri Rch125 growth in saline media. This growth improvement correlated with enhanced trehalose accumulation in otsA- and otsAB-modified cells, suggesting that increased trehalose synthesis via trehalose-6-phosphate can enhance bacterial salt tolerance. Chickpea plants inoculated with M. ciceri Rch125 derivatives carrying extra otsAB or otsA genes formed more nodules and accumulated more shoot biomass than wild type inoculated plants when grown in the presence of NaCl. These results support the notion that improved salt tolerance of the bacterial symbiont can alleviate the negative effects of salinity on chickpeas, and that such improvement in M. ciceri can be achieved by manipulating trehalose metabolism.     

Rhizobium laguerreae is the main nitrogen-fixing symbiont of cultivated lentil (Lens culinaris) in Morocco

Genetic diversity and population structure of 268 Lens culinaris symbiotic rhizobia collected from 40 cultivated fields in the main lentil production regions in Morocco were estimated. Three chromosomal housekeeping genes (recA, glnII and atpD) and one common symbiotic gene (nodC) were sequenced and analyzed in order to identify the local symbionts of lentil. The molecular phylogeny of the concatenated housekeeping genes clustered more than 95% of the isolates in one main clade together with Rhizobium laguerreae species. R. laguerreae represents the main symbiont of cultivated lentil in Morocco and, for the first time, a large sample of individuals is obtained for this species. There is a significant and high genetic differentiation of bacterial populations among the four regions for their symbiotic gene, and much lower for their housekeeping genes. The reasons why R. laguerreae is so frequently recovered in our study is discussed.     

Phenotypic and molecular characterization of chickpea rhizobia isolated from different areas of Morocco

AIMS: To determine the biodiversity of rhizobial strains nodulating Cicer arietinum L. in representative soils from various areas of Morocco. METHODS AND RESULTS: Symbiotic traits, utilization of 49 carbohydrate sources, resistance to antibiotics and heavy metals, tolerance to salinity, to extreme temperatures and pH were studied as phenotypic markers. In addition, restriction fragment length polymorphism (RFLP) of PCR-amplified 16S rDNAs were compared with those of reference strains. Numerical analysis of the phenotypic characteristics showed that the 48 strains studied fell into three distinct groups. RFLP analysis of 16S rRNA genes revealed an additional heterogeneity and four ribotypes were identified. CONCLUSIONS: Chickpea rhizobia isolated from Moroccan soils are both phenotypically and genetically diverse. Most of these rhizobia belong to the Mesorhizobium genus. However, some strains originating from a particular soil appeared to have 16S rRNA genes similar to Sinorhizobium as well as very distinct auxanographic characteristics compared with Mesorhizo- bium isolates. SIGNIFICANCE AND IMPACT OF THE STUDY: A well characterized collection of chickpea-nodulating rhizobia in representative soils of Morocco has been generated, which can be used to develop efficient inoculants for this crop. This is the first report evidencing that chickpeas may be nodulated by bacteria from the Sinorhizobium genus.     

Impact de la méthode de segmentation dans la caractérisation des adénocarcinomes pulmonaires en TEP-TDM au 18FDG

ObjectiveThe treatment of lung adenocarcinomas is conditioned by the presence of certain genetic abnormalities. Certain quantitative parameters obtained from FDG PET-CT, at the voxel scale, provide tumour shape and texture characteristics and might predict their mutational status. Our objective was to determine the impact of the segmentation method in the characterization of lung adenocarcinomas in FDG PET-CT.MethodsForty-nine patients with pulmonary adenocarcinomas were retrospectively included, with their initial FDG PET-CT image. The studied tumours were big, heterogeneous and difficult to segment automatically. The automatic FLAB algorithm was used with and without manual adjustment. The parameters were extracted and compared to the ALK, PDL1, and KRAS status, in order to compare the performances of the two segmentation methods. Their performance was determined by the ROC curve method.ResultsSeveral parameters were significant to predict genetic status (AUC > 0.65). The best performing parameters were different according to the genes studied and according to the resampling methods used. The results were less dependent on resampling in automatic segmentation without manual adjustment. The best performing parameters were volume dependent parameters for segmentation with manual adjustment, and texture parameters for automatic segmentation without adjustment.ConclusionThe study of texture parameters is more efficient in automatic segmentation that is not manually adjusted, and it is advantageous to use a manual adjustment when studying volume-dependent parameters in the case of very heterogeneous tumors.     

Copepods distribution in relation to a Cape Ghir upwelling filament (Moroccan Atlantic coast)

The study of the Cape Ghir upwelling filament (31°N) focalizes to describe the dispersive mechanism, caused by the upwelling. The zooplankton was sampled during five oceanographic cruises conducted between 2008 and 2009. Surface temperature and chlorophyll “a” were also measured along with sampling. The distribution of environmental parameters accused extensions that show the path of the filament. Copepods constitute the largest fraction of zooplankton community and represented by 86 species, majorly dominated by Acartia clausi and Oncaea venusta. A number of species of deep or cold waters have been recorded in the area corresponding to a net resurgence of cold water. The analysis of the copepods distribution allowed to view the path of the filament at different times of the year. The distribution of the species A. clausi, neritic specie was observed in the open ocean, shows a result of this dynamic.     

Iron requirement and siderophore production in Rhizobium ciceri during growth on an iron-deficient medium

Under conditions of iron limitation many rhizospheric bacteria produce siderophores, ferric iron-specific ligands, which may enhance plant growth by increasing the availability of iron near the roots. Thirty-five strains of Rhizobium ciceri, specific to chickpea (Cicer arietinum L.), were screened for their ability to grow on iron-deficient medium and to produce siderophores. Maximal growth of all strains previously depleted in iron was obtained in medium containing 5 to 10 m of ferric iron. When iron limitation was achieved by the addition of 2,2-bipyridyl or EDDHA [ethylene diamine di(o-hydroxyphenyl) acetic acid] to the medium, only two strains were able to scavenge iron and grow. Siderophore production by these two strains was detected by the Chrome Azurol S assay (CAS), a universal test for siderophores. No hydroxamate-type siderophores were detected in the supernatants of Rhizobium ciceri cultures. However, some strains secreted salicylic acid and 2,3-dihydroxybenzoic acid as phenolate-type siderophores. Addition of ferric iron to the culture medium increased growth yield significantly but depressed the production of siderophores. Although these compounds are produced in response to iron deficiency, nutritive components of the culture medium significantly affected their production. It seems that CuII, MoVI and MnII ions bound competitively with iron to siderophores, resulting in a 34 to 100% increase in production.     

Isolation of salt-tolerant mutants of <Emphasis Type="Italic">Mesorhizobium ciceri</Emphasis> strain Rch125 and identification of genes involved in salt sensitivity

Mesorhizobium ciceri Rch125 is a salt-sensitive strain isolated from root nodules of chickpea (Cicer arietinum L.). The aim of this work was to investigate the genes responsible for the sensitivity to salinity. Twelve Rch125 salt-tolerant mutants were isolated after random Tn5 mutagenesis and selected using a medium containing 300 mM NaCl, where growth of the wild-type is totally inhibited. In addition to this NaCl tolerance, the mutants also displayed higher tolerance to LiCl, CaCl₂ and sucrose. Genes that were disrupted in the salt-tolerant mutants were in one of three functional categories: membrane transporters, outer membrane proteins, and genes of unknown function. Genetic complementation experiments demonstrated that the genes identified were involved in the salt sensitivity of the Rch125 strain. In most cases, disruption of the salt-sensitivity genes did not negatively affect the free-living or the symbiotic capabilities of Rch125 under non-saline conditions.