Mosbah Mahdhi - Academia.edu (original) (raw)

Papers by Mosbah Mahdhi

International Journal of Systematic and Evolutionary Microbiology, 2009

Nine isolates from Argyrolobium uniflorum, Lotus creticus, Medicago sativa (Tunisia) and Lotus ar... more Nine isolates from Argyrolobium uniflorum, Lotus creticus, Medicago sativa (Tunisia) and Lotus arabicus (Senegal) were analysed by multilocus sequence analysis (MLSA) of five housekeeping genes (recA, atpD, glnA, gltA and thrC), the 16S rRNA gene and the nodulation gene nodA. Analysis of the individual and concatenated gene sequences demonstrated that the nine new strains constituted three stable, well-supported (bootstrap and gene sequence similarity values) monophyletic clusters, A, B and C, all belonging to the branch of the genus Ensifer, regardless of the phylogenetic reconstruction method used (maximum likelihood, maximum-parsimony, neighbour-joining). The three groups were further characterized by API 100 auxanographic tests, host specificity and nodA gene sequence analysis. On the basis of these data, clusters A and C are suggested as representing two novel species within the genus Ensifer, for which the names Ensifer numidicus sp. nov. (type strain ORS 1407T=LMG 24690T=CIP ...

Agriculture, Ecosystems & Environment, 2012

ABSTRACT Wild legumes (herbs, shrubs or trees) play a critical role in natural ecosystems, agricu... more ABSTRACT Wild legumes (herbs, shrubs or trees) play a critical role in natural ecosystems, agriculture, and agroforestry, where their ability to fix nitrogen in symbiosis makes them excellent colonizers of low-N environments, and hence an economic and environmentally friendly species. The field natural nodulation of the wild Tunisian legumes, the genetic diversity and symbiotic-efficiency of their root nodulating bacteria (RNB) and the dynamics of soil fertility under symbiotic association in arid regions of Tunisia were investigated during this study. Natural nodulation varied according to the species and site. Morphologically, nodules were spindle-shaped (Trigonella maritima, Hedysarum spinosissimum, Argyrolobium uniflorum, Genista saharae, Retama reteam, Vicia sativa). The colour of the nodules was not related to that of the roots, but depends on soil quality and colour, and on the presence of leghaemoglobin. Based on molecular techniques (16S rRNA sequencing) and phenotypic characteristics, the root-nodule bacteria isolated from the Tunisian wild legumes were classified into four genera (Rhizobium, Mesorhizobium, Sinorhizobium). No Bradyrhizobium genus was recovered in our results. Non-nodulating bacteria considered as endophytic to nodules were also reported in our results and four genera belonging to Phyllobacterium, Starkeya, Pseudomonas, and Kocuria were taxonomically defined, for Lotus sp. and H. spinosissimum. Bacteria belonging to Sinorhizobium genus were widely distributed in area under study. Wild legumes belonging to Lotus spp., Vicia spp. and Hedysarum spp. were nodulated by this genus. Mesorhizobium genus was restricted to Lotus sp., and Rhizobium genus nodulated Vicia and Lotus. Phenotypically, our results showed that the root nodulating bacteria belonging to the genus Sinorhizobium exhibited higher tolerance to salt stress and elevated temperatures. Based on symbiotic properties, our reports indicated that the wild-legume rhizobia formed effective and successful symbioses with their legume hosts. The diversity and effectiveness of the nitrogen-fixing wild legumes are of major significance to soil fertility dynamics in the arid regions. Effects on enzyme activities, microbial biomass and respiration, were evaluated in different agricultural soils and in the presence of different wild legumes such as G. saharae and R. raetam. Results showed that legumes–rhizobia symbiosis improves enzyme activities, microbial biomass and respiration of field soils and regenerate microbiological properties and the microflora activity involved in the decomposition of organic matter.

Annals of Microbiology, 2006

ABSTRACT Thirty-five isolates of rhizobia were picked up fromRetama raetam root nodules growing i... more ABSTRACT Thirty-five isolates of rhizobia were picked up fromRetama raetam root nodules growing in arid lands of Tunisia. A genotypic approach including PCR-RFLP of 16S rDNA and 16S–23S rDNA was used to study their diversity and their relationships with te n reference strains of rhizobia. Four distinct clusters were defined in numerical analysis of RFLP of 16S rDNA, which related at the 78% similarity level to distinct species ofMesorhizobium, Agrobacterium, Rhizobium andSinorhizobium. More greater variability was detected by analysis of Intergenic Spacers 16S–23S rDNA. The results from both methods used in this study, showed that among all newsolates only three were found to be closely related to species of the genusSinorhizobium.

ABSRACT Fifteen endophytic bacterial isolates associated to root nodules of Vicia sativa growing ... more ABSRACT Fifteen endophytic bacterial isolates associated to root nodules of Vicia sativa growing in arid zone of Tunisia were examined by phenotypic characterization and 16S rDNA analysis. Measured phenotypic characteristics included growth rate, colony morphology, and tolerances to extremes temperature, salt and pH. The isolates were very diverse phenotypically. All isolates were fast-growing rhizobia with generation time of 2-6 hours. The majority of isolates tolerated high concentration of Nacl (2 %), alkaline pH and grew at 37°C. Numerical analysis of PCR-RFLP of 16S rDNA showed that only one isolate (ViB15) was closely related to Sinorhizobium meliloti type species. New isolates grouped separately from reference strains and formed two clusters at 80 % of similarity, which indicates that new isolates were genetically very diverse.

In the context of climate change, increasing earth population and burst of energy cost, legumes s... more In the context of climate change, increasing earth population and burst of energy cost, legumes should contribute more to both food security and sustainable management of natural resources (water, soils) in the next years. A collaborative work with research groups in several developing countries during the past 20 years focused on investigation and sampling of local wild legumes (herbs, shrubs and trees) having environmental/agronomic/forestry potential in West Africa and in the Mediterranean region. New symbiotic systems were discovered, resulting in new models for fundamental research, and new applications. This is, for one part, due to their associated microsymbionts, often belonging to unexpected bacterial groups with original physiological / metabolic properties i.e. photosynthesis, freeliving nitrogen fixation, methylothrophy, tolerance to extreme environmental conditions (salinity, aridity, heavy metals, hydrocarbon breakdown), stem nodulation, beneficial associations with no...

Most regions of Saudi Arabia are frequently subjected to high temperature and drought spells whic... more Most regions of Saudi Arabia are frequently subjected to high temperature and drought spells which destroy natural vegetation and lead to soil erosion and the advance of sand dunes. The use of legume plants may help to preserve these ecosystems and to slow down desertification processes. Legumes produce extensive, deep root systems with a capacity to develop mycorrhizal and rhizobial symbioses facilitating the plant’s nutrition via enhanced soil nutrients absorption and atmospheric nitrogen fixation, respectively. These associations play a vital role in preserving and even restoring the fertility of poor and eroded soils. Research on tripartite associations of Arbuscular mycorrhizal fungi (AMF), rhizobia and legumes is rare in Saudi Arabia. Little is known about the diversity of these beneficial symbioses in Saudi ecosystems and their beneficial role for the sustainable management of range land. We attempted to explore the present status of research on rhizobia and AMF associated w...

Geoderma

Abstract Drylands are highly susceptible to degradation and climate change, which has important e... more Abstract Drylands are highly susceptible to degradation and climate change, which has important ecological and socio-economic consequences worldwide. To halt drylands degradation, plant species selection for restoration is starting to include also a functional approach, but does not integrate belowground functional traits yet. Therefore we tested the use of mycorrhizal traits to identify native plant species which host guilds of beneficial microbes and therefore enhance multiple soil functions simultaneously – soil multifunctionality. We used a soil organic matter (SOM) gradient (0.9–1.9%) and evaluated the effect of 14 common and abundant native herbaceous plant species (+bare soil) on soil functionality. We measured several soil functions (soil microbial biomass, metabolic quotient, and enzymatic activities – dehydrogenase, β-glucosidase and phosphatase) and built a soil multifunctionality index. Soil multifunctionality was strongly associated with mycorrhizal traits across the analysed SOM gradient. Bare soils and soils under non- or low-mycorrhizal plant species displayed the lower soil functionality (both individual functions and multifunctionality), while soils under Fabaceae species (Medicago truncatula, Astragalus corrugatus and Lotus halophilus) displayed the highest. For each plant species, the highest soil multifunctionality was observed at the SOM-richer site. Soil multifunctionality was strongly associated with all the mycorrhizal traits but mycorrhizal intensity and AMF spores abundance were more correlated with soil multifunctionality than mycorrhizal frequency. Our data show that: i) AM traits can be good indicators of simultaneous multiple soil functions in drylands; and ii) soil multifunctionality in drylands can be improved by management practices promoting SOM accumulation and favouring specific native plant species.

Land Degradation & Development, 2014

The objectives of this study, conducted in Bou-Hedma National Park, were to quantify the effects ... more The objectives of this study, conducted in Bou-Hedma National Park, were to quantify the effects of the dominant legume Acacia tortilis subsp. raddiana on soil properties. Three sites with differing soil texture were studied; the first with a gravelly-sand texture, the second with a sandy-loam texture and the third with a loam texture. At each study site, two subhabitats were distinguished, under Acacia canopies (canopied soil) and open areas (uncanopied soil). Soil organic carbon, microbial biomass and microbial coefficient were found to be significantly greater in canopied soil, compared with uncanopied soil. The lower metabolic quotient under this legume indicated a higher carbon use efficiency of microorganisms in soil. The enzyme activities (dehydrogenase, phosphatase and b-glucosidase) expressing soil microbial activity were significantly higher under Acacia canopies. Therefore, A. raddiana planting can be considered an effective and applicable measure to restore vegetation and control desertification in arid regions. On account of the variability of soil texture in the park, three sites were studied: gravelly-sand, sandy-loam and loam soils. The highest microbial density and activity were registrated in sandy-loam soil. Microbial biomass and activity increased gradually and significantly to a maximum at 20-30 cm and subsequently decreased at 30-50 cm. The results allow us to conclude that soil texture and soil depth can play an important role in the extent of soil properties.

Canadian Journal of Microbiology, 2012

A collection of rhizobia isolated from Acacia tortilis subsp. raddiana nodules from various arid ... more A collection of rhizobia isolated from Acacia tortilis subsp. raddiana nodules from various arid soils in Tunisia was analyzed for their diversity at both taxonomic and symbiotic levels. The isolates were found to be phenotypically diverse. The majority of the isolates tolerated 3% NaCl and grew at 40 °C. Genetic characterization emphasized that most of the strains (42/50) belong to the genus Ensifer , particularly the species Ensifer meliloti , Ensifer garamanticus , and Ensifer numidicus . Symbiotic properties of isolates showed diversity in their capacity to nodulate their host plant and to fix atmospheric nitrogen. The most effective isolates were closely related to E. garamanticus. Nodulation tests showed that 3 strains belonging to Mesorhizobium genus failed to renodulate their host plant, which is surprising for symbiotic rhizobia. Furthermore, our results support the presence of non-nodulating endophytic bacteria belonging to the Acinetobacter genus in legume nodules.

Asian Journal of Crop Science

Notulae Botanicae Horti Agrobotanici Cluj-Napoca

Seeds of three sorghum (Sorghum bicolor (L.) Moench.) varieties from Southwest Saudi Arabia were ... more Seeds of three sorghum (Sorghum bicolor (L.) Moench.) varieties from Southwest Saudi Arabia were used to investigate the potential of osmopriming with polyethylene glycol (PEG 8000) to improve germination performance, seed reserve utilization and early seedling growth and drought stress tolerance. The primed (PS) and unprimed (UPS) seeds of the three sorghum varieties were germinated for 8 days under increasing PEG-induced osmotic stress. The treatments were arranged in a completely randomized design, in a factorial arrangement, with three sorghum cultivars (‘Zaydia’, ‘Shahbi’ and ‘Ahmar’) and four osmotic potentials (0.0; -0.4; -0.8 and -1.2 MPa) with four replicates of 50 seeds each. The results showed that drought stress affected seed germination and seedling emergence and establishment, but increased the activity of the antioxidant enzyme catalase (CAT). The strongest inhibition of germination and growth occurred at the highest PEG concentration and a significant difference was ...

Diversity

Arbuscular mycorrhizal fungi (AMF) are determinant for the performance of plant communities and f... more Arbuscular mycorrhizal fungi (AMF) are determinant for the performance of plant communities and for the functionality of terrestrial ecosystems. In natural ecosystems, grazing can have a major impact on mycorrhizal fungi and consequently on plant growth. The objective of this study was to evaluate the statements referred above in Mediterranean arid areas in Tunisia. Root samples and rhizosphere soils of five dominant herbaceous plants were studied at six distinct arid sites differing on soil proprieties and grazing intensity. At each site, chemical and dynamic properties of the soil were characterized as well as the AMF colonization intensity and the soil functionality. Results showed that the mycorrhizal frequency and intensity and spore density, varied between plants in the same site and, for each plant, between sites and evidenced a positive effect of mycorrhized plants on soil microbial activity. Grazing and soil properties strongly affected AMF composition and the soil microbia...

Acta Scientiarum Polonorum Hortorum Cultus

The tripartite associations of arbuscular mycorrhizal fungi (AMF), rhizobia and legumes play a vi... more The tripartite associations of arbuscular mycorrhizal fungi (AMF), rhizobia and legumes play a vital role in preserving and even restoring fertility of poor and eroded soils. The present study attempted to quantify relationship between legumes and symbiotic microorganisms (rhizobia and mycorrhizal fungi) by describing the mycorrhizal status and the occurrence of nodualtion of legumes growing in different areas of Jazan. The effect of legume species on soil microbial biomass was also investigated. Mycorrhizal and nodulation intensity varied greatly between legume species. The higher number of nodules (14 nodules per plant) and mycorrhization intensity (54%) were registered in root of Argyrolobium arabicum. Rhizosphere soils of all legume species harbored higher AMF fungal spores than bulk soils. Our results suggest also a significant effect of legumes species on soil microbial biomass. Thus, legume species investigated in this study are potentially useful for replanting and soil protection of most degraded regions of Saudi Arabia.

Journal of Soil Science and Plant Nutrition

Evidence-Based Complementary and Alternative Medicine

For a long time, the people of Saudi Arabia have been using medicinal plants (MPs) as conventiona... more For a long time, the people of Saudi Arabia have been using medicinal plants (MPs) as conventional medicine to heal diverse human and livestock diseases. The present work is the first study on ethnobotanical uses of 124 MPs species used by the local tribal communities of Jazan province in the Southwest of Saudi Arabia. Ethnobotanical data were collected by interviewing 174 local informants using semistructured interviews. Informants of different ages, from several settlements belonging to several tribal communities, were interviewed. It is worth noticing that the age of informants and their knowledge of MPs were positively correlated, whereas the educational level and MP knowledge of participants were negatively correlated. To find out if there was agreement in the use of certain plants in the treatment of given ailments, we used Informant Consensus Factor (ICF). To determine the most frequently used plant species for treating a particular ailment category by local people we used th...

Journal of Water and Health

Drinking water quality plays a remarkable role in human infections and diseases. This study used ... more Drinking water quality plays a remarkable role in human infections and diseases. This study used polymerase chain reaction (PCR) techniques to detect bacterial pathogens. In addition, a physicochemical analysis was performed on drinking water samples from several sources. A total of 123 drinking water samples were collected from different areas in the Jazan region in Saudi Arabia: ground water (40 samples), bottled water (15 samples), tap water (52 samples), and water purification shops (16 samples). To isolate the bacterial pathogens, the water samples were spread on Nutrient and MacConkey agar media, and the grown pathogens were then identified by the 16S ribosomal RNA technique. In 87 (70.7%) of the 123 drinking water samples, there was no pathogen growth on the two-culture medium. However, 36 (29.3%) of the samples were found to be contaminated with bacteria. The physicochemical analysis indicated that the water samples were within the Saudi drinking water standards. The bacteri...

Soil Science and Plant Nutrition