Khalid Oufdou

Allelopatic effects of cyanobacteria extracts containing microcystins on Medicago sativa–Rhizobia symbiosis

The eutrophication of water leads to massive blooms of cyanobacteria potentially producers of highly toxic substances: cyanotoxins, especially microcystins (MC). The contamination of water used for irrigation by these toxins, can cause several adverse effects on plants and microorganisms. In this work, we report the phytotoxic effects of microcystins on the development of symbiosis between the leguminous plant Medicago sativa (Alfalfa) and rhizobia strains. The exposure of rhizobial strains to three different concentrations 0.01, 0.05 and 0.1 μg MC ml(-1) led to decrease on the bacteria growth. The strains of rhizobia Rh L1, Rh L2, Rh L3 and Rh L4 reduced their growth to, respectively, 20.85%, 20.80%, 33.19% and 25.65%. The chronic exposure of alfalfa seeds and seedlings to different MC concentrations affects the whole stages of plant development. The germination process has also been disrupted with an inhibition, which reaches 68.34% for a 22.24 μg MC ml(-1). Further, seedlings growth and photosynthetic process were also disrupted. The toxins reduced significantly the roots length and nodule formation and leads to an oxidative stress. Thus, the MCs contained in lake water and used for irrigation affect the development of symbiosis between M. sativa and Rhizobia.

Identification at the species and symbiovar levels of strains nodulating Phaseolus vulgaris in saline soils of the Marrakech region (Morocco) and analysis of the otsA gene putatively involved in osmotolerance

Salinity is an increasing problem in Africa affecting rhizobia-legume symbioses. In Morocco, Phaseolus vulgaris is cultivated in saline soils and its symbiosis with rhizobia depends on the presence of osmotolerant strains in these soils. In this study, 32 osmotolerant rhizobial strains nodulating P. vulgaris were identified at the species and symbiovar levels by analysing core and symbiotic genes, respectively. The most abundant strains were closely related to Rhizobium etli and R. phaseoli and belonged to symbiovar phaseoli. A second group of strains was identified as R. gallicum sv gallicum. The remaining strains, identified as R. tropici, belonged to the CIAT 899(T) nodC group, which has not yet been described as a symbiovar. In representative strains, the otsA gene involved in the accumulation of trehalose and putatively in osmotolerance was analysed. The results showed that the phylogeny of this gene was not completely congruent with those of other core genes, since the genus Ensifer was more closely related to some Rhizobium species than others. Although the role of the otsA gene in osmotolerance is not well established, it can be a useful protein-coding gene for phylogenetic studies in the genus Rhizobium, since the phylogenies of otsA and other core genes are coincident at the species level.

Nodule phosphorus requirement and O2 uptake in common bean genotypes under phosphorus deficiency

Abstract The effect of P deficiency on nodulation, nodule P content, nodule O2 permeability and N fixation rates in Phaseolus vulgaris–rhizobia symbiosis was studied under glasshouse conditions. Four recombinant inbred lines (L34, L83, L115 and L147) and one variety cultivated in Morocco (Concesa) were inoculated with Rhizobium tropici CIAT 899 in hydroaeroponic culture. Two P levels i.e. 75 (deficient level) and 250 µmol plant−1 week−1 P (sufficient level) were applied and the trial was assessed 42 days after transplanting that coincide with plant flowering stage. Under P-deficiency, decrease of plant growth (18%) and nodule biomass (19%) was detected and significantly pronounced in the sensitive line L147 compared with the remaining genotypes. Additionally, under P-deficiency, the efficiency in use of rhizobial symbiosis, estimated by the slope of the regression model of shoot biomass as a function of nodule biomass, was significantly increased in the four lines. This constraint did not significantly influence nodule P content in Concesa, but it was 24 and 41% lower in the tolerant and in the sensitive lines, respectively. Nodule P content was positively correlated to nodule biomass, r=0.75, and shoot N, r=0.92. These genotypic variations were associated with variability in nodule O2 permeability that was significantly affected by the P level-bean genotype interaction. Under P-deficiency, nodule O2 permeability was significantly reduced in the tested genotypes and accompanied with a decrease in shoot N content, especially in the sensitive lines (35%). Moreover, the ratios plant N fixed: nodule P content and plant N fixed:nodule dry weight were affected under P-deficiency in four lines with an exception observed in Concesa. Depending on the observed data we concluded that N2 fixation efficiency could be influenced by nodulation and level of nodule P requirement which depend on both bean genotypes and P level.

INTERACTIONS BETWEEN COMMON BEAN GENOTYPES AND RHIZOBIA STRAINS ISOLATED FROM MOROCCAN SOILS FOR GROWTH, PHOSPHATASE AND PHYTASE ACTIVITIES UNDER PHOSPHORUS DEFICIENCY CONDITIONS

The improvement of common bean production requires the selection of effective rhizobia strains and Phaseolus vulgaris genotypes adapted to available soil phosphorus limitations. The interactions between bean genotypes and rhizobia were studied in hydroponic culture using six genotypes and four strains, CIAT899 as reference and three strains isolated from nodule of farmers fields in the Marrakech region. The phosphorus (P) sub-deficiency caused a significant reduction on shoot biomass in some bean genotype-rhizobia combinations. Nodule biomass is significantly more reduced under P limitation for several combinations tested. Bean plants inoculated with these local rhizobial strains showed higher nodulation and an increase of nodules phytase and phosphatase activities under phosphorus sub-deficiency especially for RhM11 strain. It was concluded that the studied bean-rhizobia symbiosis differ in their adaptation to phosphorus sub-deficiency and the nodule phosphatases and phytases activities may constitute a strategy of nodulated bean plants to adapt their nitrogen fixation to P deficiency.

Antibiotic resistance and serotype distribution of nasopharyngeal isolates of Streptococcus pneumoniae from children in Marrakech region (Morocco).

Monitoring of Streptococcus pneumoniae antibiotic resistance is of great importance due to the frequency of strains becoming increasingly resistant to antibiotics. In this study, we report the antibiotic susceptibility of the serotypes of S. pneumoniae strains isolated from healthy children aged 1-24 months in the Marrakech region of Morocco. Resistance to penicillin (38.7%) was frequently associated with resistance to other antibiotics. The highest rates of resistance were to cotrimoxazole (trimethoprim/sulfamethoxazole) (49.3%), erythromycin (48.7%), tetracycline (37.3%), lincomycin (35.3%), chloramphenicol (32.7%) and ciprofloxacin (24%). Prisitinamycin and vancomycin were effective against all isolated pneumococcal strains (100% sensitive strains). Gentamycin demonstrated good efficacy on S. pneumoniae, with 98.7% of strains being sensitive. Multidrug resistance characterized 43.33% of all studied strains. Of the multidrug-resistant strains, 36.92% were resistant to erythromycin (E), tetracycline (T) and cotrimoxazole (Co: sulfamethoxazole-trimethoprim) (phenotype ETCo, n = 24), and 20% had decreased susceptibility to beta-lactams, erythromycin and cotrimoxazole (phenotype PECo, n = 13). A total of 29.23% of S. pneumoniae strains exhibited combined resistance to four antibiotics (phenotype PETCo, n = 19). This study reports the status of resistance and multiresistance of S. pneumoniae strains in the Marrakech region of Morocco.

Microbiote shift in the Medicago sativa rhizosphere in response to cyanotoxins extract exposure.

The bloom-containing water bodies may have an impact due to cyanotoxins production on other microorganisms and aquatic plants. Where such water is being used for crops irrigation, the presence of cyanotoxins may also have a toxic impact on terrestrial plants and their rhizosphere microbiota. For that purpose, PCR-based 454 pyrosequencing was applied to phylogenetically characterize the bacterial community of Medicago sativa rhizosphere in response to cyanotoxins extract. This analysis revealed a wide diversity at species level, which decreased from unplanted soil to root tissues indicating that only some populations were able to compete for nutrients and niches in this selective habitat. Gemmatimonas, Actinobacteria, Deltaproteobacteria and Opitutae mainly inhabited the bulk soil, whereas, the root-adhering soil and the root tissues were inhabited by Gammaproteobacteria and Alphaproteobacteria. The proportion of these populations fluctuated in response to cyanotoxins extract exposure. Betaproteobacteria proportion increased in the three studied compartments, whereas Gammaproteobacteria proportion decreased except in the bulk soil. This study revealed the potential toxicity of cyanotoxins extract towards Actinobacteria, Gemmatimonas, Deltaproteobacteria, and Gammaproteobacteria, however Clostridia, Opitutae and bacteria related with Betaproteobacteria, were stimulated denoting their tolerance. Altogether, these data indicate that crop irrigation using cyanotoxins containing water might alter the rhizosphere functioning.

Determination of several potential virulence factors in non-O1 Vibrio cholerae, Pseudomonas aeruginosa, faecal coliforms and streptococci isolated from Marrakesh groundwater.

The dynamic, hemolytic and hemagglutination activities and the antibiotic resistance of non-O1 Vibrio cholerae, Pseudomonas aeruginosa, faecal coliforms (FC) and faecal streptococci (FS), isolated by standard membrane filtration methods from suburban and rural groundwater supplies, were carried out. Detectable non-O1 V. cholerae and P. aeruginosa was present in 81% and 88% of samples. The total occurrence of FC and FS during the period of study was 94%. The annual average densities of non-O1 V. cholerae were 4,903 MPN/100 mL. While, they were 206, 1,891 and 1,246 cfu/100 mL for P. aeruginosa, FC and FS respectively. Non-O1 V. cholerae strains had the highest percentage of hemolytic activities (alpha + beta) (71.29%), whereas 20.71% of FS, 16.88% of FC and 9.13% of P. aeruginosa strains produced hemolysin. Bacterial strains isolated were found to be adhesive, with percentages of 63.09%, 65.09%, 84.06% and 87.98% respectively for non-O1 V. cholerae, FS, FC and P. aeruginosa. As for antibiotic resistance, the overall resistance of non-O1 V. cholerae strains was 79%, whereas it was 100% for the other bacteria. Non-O1 V. cholerae resistance was expressed towards sulfamethoxazole (75%), streptomycin (62%) and cephalothin (60%). Obtained results indicated correlation between bacteriological pollution and their public health implications.

Occurrence and Antibiotic Resistance of Pseudomonas aeruginosa and Faecal Indicator Bacteria: Risk Assessment for Groundwater Supplies (Marrakesh, Morocco)

The dynamic and antibiotic resistance of faecal coliforms, faecal streptococci and Pseudomonas aeruginosa , isolated by standard membrane filtration methods from suburban and rural untreated groundwater supplies, were scrutinized in this study. The annual average densities of these bacteria were respectively 1891 colony forming units (c.f.u.)/100 mL, 1246 c.f.u./100 mL and 206 c.f.u./100 mL. The total occurrence of faecal coliforms and faecal streptococci during the period of study was 94%. Detectable P. aeruginosa was present in 88% of samples. A total of 320 faecal coliforms, 338 faecal streptococci and 208 P. aeruginosa strains, were examined for their resistance to eighteen antibiotics. The overall resistance (resistance to at least one antibiotic) of these bacteria was 100%. The multiresistance (resistance to at least two antibiotics) of faecal coliforms and faecal streptococci was 94%, whereas 100% of P. aeruginosa strains were multiresistant. The monoresistance (resistance to one antibiotic) of fae...

Occurrence, Antibiotic Resistance and Pathogenicity of Non-O1 Vibrio cholerae in Moroccan Aquatic Ecosystems: A Review

The problem of water scarcity is becoming more pronounced especially in countries with arid and semi-arid climates such as Morocco. Wastewaters discharge into different aquatic ecosystems (groundwater, sea water, river, lake water...), are draining different types of microorganisms and hazardous chemicals. The microbiological risk is not negligible, especially in areas where wastewater or other contaminated water, are reused for irrigation without preliminary treatment or for direct consumption by human and animals.

Phenotypic and genetic diversity of Moroccan rhizobia isolated from Vicia faba and study of genes that are likely to be involved in their osmotolerance

Rhizobia are symbiotic nitrogen-fixing bacteria in root nodules of legumes. In Morocco, faba bean (Vicia faba L.), which is the main legume crop cultivated in the country, is often grown in marginal soils of arid and semi-arid regions. This study examines the phenotypic diversity of rhizobia nodulating V. faba isolated from different regions in Morocco for tolerance to some abiotic stresses. A total of 106 rhizobia strains isolated from nodules were identified at the species level by analysing 16S rDNA. Additionally, for selected strains recA, otsA, kup and nodA fragments were sequenced. 102 isolates are likely to belong to Rhizobium leguminosarum or R. laguerreae and 4 isolates to Ensifer meliloti. All strains tolerating salt concentrations of 428 or 342mM NaCl as well as 127 or 99mM Na2SO4 were highly resistant to alkaline conditions (pH 10) and high temperature (44°C). Three strains: RhOF4 and RhOF53 (both are salt-tolerant) and RhOF6 (salt-sensitive) were selected to compare the influence of different levels of salt stress induced by NaCl on growth and on trehalose and potassium accumulation. We find a direct correlation between the trehalose contents of the rhizobial strains and their osmotolerance.