Identification of soil bacteria expressing a symbiotic plasmid from Rhizobium leguminosarum bv. trofolii

Confluence of montmorillonite and Rhizobium towards the adsorption of chromium(vi) from aqueous medium

Chromium in its hexavalent oxidation state is carcinogenic and wastewater from the electroplating industry is one of the principal sources of pollution. To reduce this toxicity and pave way towards environmental safety, a combination of environmental microbiology and chemistry is quite efficient for developing biosorbents to sequester chromium from waste water. Immobilization of Rhizobium in sodium montmorillonite provides a conducive environment to capture hexavalent chromium. Various characterization techniques such as FTIR, XPS and SEM-EDAX were performed and batch parameters such as pH variation, adsorbent dosage, concentration of metal ion and temperature were optimized. Pseudo second order kinetics coupled with a higher regression coefficient for Freundlich isotherm and a Langmuir adsorption capacity of 22.22 mg g⁻¹ was achieved for the adsorption process. The adsorption was enhanced by the charge interactions between the protonated clay-Rhizobium surface and Cr(vi) ions in acidic medium. The biosorbent was stable and easily regenerated using NaOH. Preliminary column studies were performed to test the efficiency of the developed biosorbent at higher volumes on a laboratory scale.

Chromium in its hexavalent oxidation state is carcinogenic and wastewater from the electroplating industry is one of the principal sources of pollution.

Potential Application of Saccharomyces cerevisiae and Rhizobium Immobilized in Multi Walled Carbon Nanotubes to Adsorb Hexavalent Chromium

The presence of harmful contaminants in the waste stream is an important concern worldwide. The convergence of biotechnology and nanoscience offers a sustainable alternative in treating contaminated waters. Hexavalent chromium, being carcinogenic deserves effective and sustainable methods for sequestration. Here in, we report the immobilization of a prokaryote (Rhizobium) and eukaryote (Saccharomyces cerevisiae) in multiwalled carbon nanotubes (MWCNTs) for the effective adsorption of hexavalent chromium. The carboxylic groups were introduced into the MWCNTs during oxidation using potassium permanganate and were subjected to EDC-HOBT coupling to bind with microbial cell surface. FTIR, TGA, BET, FESEM-EDAX, HRTEM, XPS and confocal microscopy were the investigative techniques used to characterize the developed biosorbents. Experimental variables such as pH, adsorbent dosage, kinetics, isotherms and thermodynamics were investigated and it was observed that the system follows pseudo second order kinetics with a best fit for Langmuir isotherm. Electrostatic interactions between the functional groups in the microbial cell wall and hydrochromate anion at pH 2.0 propel the adsorption mechanism. The lab scale column studies were performed with higher volumes of the Cr(VI) contaminated water. Sodium hydroxide was used as the desorbing agent for reuse of the biosorbents. The sustainable biosorbents show prospects to treat chromium contaminated water.

Apparent incompatibility of plasmid pSfrYC4b of Sinorhizobium fredii with two different plasmids in another strain

Sinorhizobium fredii YC4B is a spontaneous mutant derivative of strain YC4 that is unable to nodulate soybeans. The second-largest plasmid of strain YC4B, termed pSfrYC4b (810 kb), was transferred to S. fredii HN01SR, a strain which contains three large indigenous plasmids (pSfrHN01a, pSfrHN01b and pSfrHN01c). Surprisingly, two stable indigenous plasmids (pSfrHN01a and pSfrHN01b) of strain HN01SR were cured simultaneously by the introduction of pSfrYC4b. Furthermore, a novel, unstable plasmid (pHY4) became visible in agarose gels. The electrophoretic mobility of plasmid pHY4 was slower than that shown by the cured plasmids, indicating that the molecular weight of the former is higher than that of plasmids pSfrYC4b and pSfrHN01b. Replication gene repC-like sequences were detected by polymerase chain reaction (PCR) on pSfrHN01a and pSfrYC4b, but not on pSfrHN01b. Sau3AI and PstI restriction patterns of the PCR-amplified repC-like sequences from HN01SR and YC4B were very similar.

PCR primers based on different portions of insertion elements can assist genetic relatedness studies, strain fingerprinting and species identification in rhizobia

Using the sequence of an insertion element originally found in Rhizobium sullae, the nitrogen-fixing bacterial symbiont of the legume Hedysarum coronarium, we devised three primer pairs (inbound, outbound and internal primers) for the following applications: (a) tracing genetic relatedness within rhizobia using a method independent of ribosomal inheritance, based on the presence and conservation of IS elements; (b) achieve sensitive and reproducible bacterial fingerprinting; (c) enable a fast and unambiguous detection of rhizobia at the species level. In terms of taxonomy, while in line with part of the 16S rRNA gene- and glutamine synthetase I-based clustering, the tools appeared nonetheless more coherent with the actual geographical ranges of origin of rhizobial species, strengthening the European-Mediterranean connections and discerning them from the asian and american taxa. The fingerprinting performance of the outward-pointing primers, designed upon the inverted repeats, was shown to be at least as sensitive as BOX PCR, and to be functional on a universal basis with all 13 bacterial species tested. The primers designed on the internal part of the transposase gene instead proved highly species-specific for R. sullae, enabling selective distinction from its most related species, and testing positive on every R. sullae strain examined, fulfilling the need of PCR-mediated species identification. A general use of other IS elements for a combined approach to rhizobial taxonomy and ecology is proposed.

Description of new Ensifer strains from nodules and proposal to transfer Ensifer adhaerens Casida 1982 to Sinorhizobium as Sinorhizobium adhaerens comb. nov. Request for an opinion

A group of four diverse rhizobial isolates and two soil isolates that are highly related to Ensifer adhaerens were characterized by a polyphasic approach. On the basis of DNA-DNA hybridizations and phenotypic features, these strains cannot be distinguished clearly form Ensifer adhaerens, a soil bacterium that was described in 1982, mainly on the basis of phenotypic characteristics. Phylogenetically, Ensifer and Sinorhizobium form a single group in the 16S rDNA dendrogram of the alpha-Proteobacteria, as well as in an analysis of partial recA gene sequences. They may therefore be regarded as a single genus. Because Sinorhizobium was proposed in 1988, according to the Bacteriological Code (1990 Revision) the older name, Ensifer, has priority. However, there are several reasons why a change from Sinorhizobium to Ensifer may not be the best solution and making an exception to Rule 38 may be more appropriate. We therefore propose the species Sinorhizobium adhaerens comb. nov. and put forward a Request for an Opinion to the Judicial Commission regarding the conservation of Sinorhizobium adhaerens over Ensifer adhaerens.