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...

No abstract

Sugarcane is an important crop around the world. Burkholderia genus has emerged as an important plant associated bacteria in the last years. In this study, the occurrence of Burkholderia species associated with two sugarcane varieties cultivated in Mexico was assessed. Burkholderia species were isolated with and without diazotrophs enrichment from sugarcane. Burkholderia strains were identified using a semi-selective set of primers and clustered by restriction analysis of 16S rRNA. The isolates were characterized by 16S rRNA, recA and nifH sequence analysis, whole-cell protein patterns, and plant-growth promotion (PGP) characteristics. Diazotrophic B. unamae and B. tropica were predominant using diazotroph enrichment method. Non-diazotrophic B. cepacia complex (Bcc) species were predominant without enrichment. Among non-diazotrophs, B. tropica was identified. The diazotrophic Burkholderia species exhibit in vitro PGP activities: biosynthesis of indolic compounds, phosphate solubilization, siderophores production and acdS gene presence, which encodes the enzyme ACC (1-aminocyclopropane-1-carboxylate) deaminase. The present study confirms the broad environmental and geographic distribution of diazotrophic B. unamae and B. tropica, and reveals the riches of Bcc and other Burkholderia species associated with sugarcane field-grown in Mexico. This work also shows the potential activities in PGP.

The use of biosensors for biomonitoring environmental health has gained much attention in the last decades. The environment is continuously loaded with xenobiotics released by anthropogenic activities that pollute ecosystems, putting their integrity at risk. Therefore, there is an urgent need to study the negative effects of xenobiotics, specifically chemical agents. Biosensors or organisms that integrate exposure to pollutants in their environment and which respond in some measurable and predictable way are useful tools to study the extent of chemical pollution and its consequences across levels of biological organization. Among chemical pollutants, heavy metals are among the most toxic elements to nearly all living organisms. Wildlife is chronically exposed to complex metal mixtures in which effects on ecosystem health are difficult to assess. Therefore, different organisms may serve as biosensors to estimate detrimental effects of metal pollution. In this chapter, we will analyze bacteria, small mammals, some plant species, and lichens as biosensors for environmental metal pollution. Also, we will assess the importance of using different biomarkers on biosensors.