Phylogenetic analysis of 16S rRNA, nodC, and nifH genes of four bacterial strains isolated from root nodules of Phaseolus vulgaris grown in Morocco soils were identified as Burkholderia phymatum. All four strains formed N 2 -fixing nodules on P. vulgaris and Mimosa, Acacia, and Prosopis species and reduced acetylene to ethylene when cultured ex planta.Until 2001 all known bacteria involved in root nodule symbioses with leguminous plants were classified as members of the order Rhizobiales of the Alphaproteobacteria, including Azorhizobium, Bradyrhizobium, Mesorhizobium, Rhizobium, and Sinorhizobium (28,36,38). Moulin et al. (21), however, described two Burkholderia nodule-forming strains isolated from Machaerium lunatum in French Guiana and Aspalathus carnosa in South Africa, respectively, this being the first report on the presence of a betaproteobacterium within root nodules of legumes. Later, the strains were formally classified as Burkholderia phymatum STM815T and Burkholderia tuberum STM678 T , respectively (33). Burkholderia species are the predominant isolates from nodules of mimosoid legumes from Panama (2), Costa Rica (3), Taiwan (4, 6), Brazil (5, 7), Venezuela (5), and Madagascar (24), which indicates a high affinity of Burkholderia for forming effective symbioses with Mimosa. Diazotrophy is well represented in Burkholderia; among the more than 55 species presently classified as Burkholderia, 9 have been shown to fix N 2 ex planta by using either the acetylene reduction activity (ARA) assay or the presence of nifH genes encoding nitrogenase reductase (3,5,11,24) and more recently by 15 N 2 isotopic dilution experiments (17). Common bean (Phaseolus vulgaris) is an herbaceous leguminous plant which establishes N 2 -fixing symbiosis with at least 5 species of the genus Rhizobium. Rhizobium etli is the predominant species in America (29) and is also detected in Europe and Africa (13,20). Rhizobium leguminosarum bv. phaseoli is commonly found in Europe (13) and has also been reported to be present in Tunisia (20) and Colombia (10). Rhizobium tropici is found in acid soils of South America and is also present in Europe and several African countries (18). Rhizobium giardinii has been detected only in European and Tunisian soils (1,20), and Rhizobium gallicum has been found nodulating beans in Europe, North Africa, and Mexico (1, 13). In this study we report on the isolation and characterization of B. phymatum from root nodules of P. vulgaris grown in alkaline soils from Morocco. Our results show that strains formed effective nodules on species of Mimosa, Acacia, and Prosopis and fixed atmospheric N 2 under free-living conditions.Soil was taken from a field near Oulade Mansour (34°47ЈN, 2°15ЈW, Oujda province, Morocco) where maize and common bean have traditionally been grown as rotational crops without N fertilization. Soil had a sandy-clay texture and the following characteristics: pH (in water), 8.1; 55.18% sand; 17.17% silt; 27.65% clay; 6.1% carbonates; 7.69% organic carbon; 0.069 total nitrogen. Seeds o...
A modABC gene cluster that encodes an ABC-type, high-affinity molybdate transporter from Bradyrhizobium japonicum has been isolated and characterized. B. japonicum modA and modB mutant strains were unable to grow aerobically or anaerobically with nitrate as nitrogen source or as respiratory substrate, respectively, and lacked nitrate reductase activity. The nitrogen-fixing ability of the mod mutants in symbiotic association with soybean plants grown in a Mo-deficient mineral solution was severely impaired. Addition of molybdate to the bacterial growth medium or to the plant mineral solution fully restored the wild-type phenotype. Because the amount of molybdate required for suppression of the mutant phenotype either under free-living or under symbiotic conditions was dependent on sulphate concentration, it is likely that a sulphate transporter is also involved in Mo uptake in B. japonicum. The promoter region of the modABC genes has been characterized by primer extension. Reverse transcription and expression of a transcriptional fusion, P modA -lacZ, was detected only in a B. japonicum modA mutant grown in a medium without molybdate supplementation. These findings indicate that transcription of the B. japonicum modABC genes is repressed by molybdate.
fThe genus Burkholderia is composed of functionally diverse species, and it can be divided into several clusters. One of these, designated the plant-beneficial-environmental (PBE) Burkholderia cluster, is formed by nonpathogenic species, which in most cases have been found to be associated with plants. It was previously established that members of the PBE group share an N-acyl-homoserine lactone (AHL) quorum-sensing (QS) system, designated BraI/R, that produces and responds to 3-oxo-C 14 -HSL (OC14-HSL). Moreover, some of them also possess a second AHL QS system, designated XenI2/R2, producing and responding to 3-hydroxy-C 8 -HSL (OHC8-HSL). In the present study, we performed liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) analysis to determine which AHL molecules are produced by each QS system of this group of bacteria. The results showed that XenI2/R2 is mainly responsible for the production of OHC8-HSL and that the BraI/R system is involved in the production of several different AHLs. This analysis also revealed that Burkholderia phymatum STM815 produces greater amounts of AHLs than the other species tested. Further studies showed that the BraR protein of B. phymatum is more promiscuous than other BraR proteins, responding equally well to several different AHL molecules, even at low concentrations. Transcriptome studies with Burkholderia xenovorans LB400 and B. phymatum STM815 revealed that the BraI/R regulon is species specific, with exopolysaccharide production being the only common phenotype regulated by this system in the PBE cluster. In addition, BraI/R was shown not to be important for plant nodulation by B. phymatum strains or for endophytic colonization and growth promotion of maize by B. phytofirmans PsJN.
To investigate the involvement of Rhizobium etli cbb(3) oxidase in the response of Phaseolus vulgaris to drought, common bean plants were inoculated with the R. etli strain, CFNX713, overexpressing this oxidase in bacteroids (cbb(3)(+)) and subjected to drought conditions. The negative effect of drought on plant and nodule dryweight, nitrogen content, and nodule functionality was more pronounced in plants inoculated with the wild-type (WT) strain than in those inoculated with the cbb(3)(+) strain. Regardless of the plant treatment, bacteroids produced by the cbb(3)(+) strain showed higher respiratory capacity than those produced by the WT strain. Inoculation of plants with the cbb(3)(+) strain alleviated the negative effect of a moderate drought on the respiratory capacity of bacteroids and the energy charge of the nodules. Expression of the FixP and FixO components of the cbb(3) oxidase was higher in bacteroids of the cbb(3)(+) strain than in those of the WT strain under all experimental conditions. The decline in sucrose synthase activity and the decrease in dicarboxylic acids provoked by moderate drought stress were more pronounced in nodules from plants inoculated with the WT strain than in those inoculated with the cbb(3)(+) strain. Taken together, these results suggest that inoculation of plants with a R. etli strain having enhanced expression of cbb(3) oxidase in bacteroids reduces the sensitivity of P. vulgaris-R. etli symbiosis to drought and can modulate carbon metabolism in nodules.
Coronavirus disease 2019 (COVID-19) is an infectious disease caused by severe acute respiratory syndrome Corona virus 2 (SARS-CoV-2), declared as a pandemic due to its rapid spread worldwide. In this study, we investigate the genetic diversity and genomic epidemiology of SARS-CoV-2, using 22 virus genome sequences reported by three different laboratories in Morocco till 07/06/2020, as well as 40,366 virus genomes from all around the world. The SARS-CoV-2 genomes from Moroccan patients revealed 62 mutations, of which 30 were mis-sense mutations. The mutations Spike_D614G and NSP12_P323L were present in all the 22 analyzed sequences, followed by N_G204R and N_R203K, which occurred in 9 among the 22 sequences. The mutations NSP10_R134S, NSP15_D335N, NSP16_I169L, NSP3_L431H, NSP3_P1292L and Spike_V6F occurred once in Moroccan sequences, with no record in other sequences worldwide. Phylogenetic analyses revealed that Moroccan SARS-CoV-2 genomes included 9 viruses belonging to clade 20A, 9 to clade 20B and 2 to clade 20C, suggesting that the epidemic spread in Morocco did not display a predominant SARS-CoV-2 route. Therefore, multiple and unrelated introductions of SARS-CoV-2 into Morocco through different routes have occurred, giving rise to the diversity of virus genomes in the country. Further, in all probability, the SARS-CoV-2 circulated in a cryptic way in Morocco, starting from January 15, 2020 before the first case was officially discovered on March 2, 2020.
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