Strains Of Rhizobium Leguminosarum Research Articles

Defining the requirements for the conjugative transfer of Rhizobium leguminosarum plasmid pRleVF39b.

Rhizobium leguminosarum strain VF39 contains a plasmid, pRleVF39b, which encodes a distinctive type of conjugation system (rhizobial type IVa) that is relatively widespread among rhizobial genomes. The cluster of genes encoding the transfer functions lacks orthologs to genes such as traCD, traF and traB, but contains 15 conserved genes of unknown function. We determined the importance of these genes in conjugation by constructing marked and unmarked mutations in each gene, and established that six genes, now designated trcA-F, played a significant role in plasmid transfer. Like the relaxase gene, traA, and the genes encoding the MPF system (trb genes), five of these genes, located in two divergently transcribed operons, are regulated by the Xre family repressor TrbR. The other gene, trcF encodes a protein with similarity to histidinol phosphatases, and its role in conjugation is unclear, but mutations in trcF are severely impaired for conjugation. TrcF does not play a role in regulation of other conjugation genes.

Airborne exposure of Rhizobium leguminosarum strain E20-8 to volatile monoterpenes: Effects on cells challenged by cadmium

Volatile organic compounds (VOCs) are produced by plants, fungi, bacteria and animals. These compounds are metabolites originated mainly in catabolic reactions and can be involved in biological processes. In this study, the airborne effects of five monoterpenes (α-pinene, limonene, eucalyptol, linalool, and menthol) on the growth and oxidative status of the rhizobial strain Rhizobium leguminosarum E20-8 were studied, testing the hypothesis that these VOCs could influence Rhizobium growth and tolerance to cadmium. The tested monoterpenes were reported to have diverse effects, such as antibacterial activity (linalool, limonene, α-pinene, eucalyptol), modulation of antioxidant response or antioxidant properties (α-pinene and menthol). Our results showed that non-stressed cells of Rhizobium E20-8 have different responses (growth, cell damage and biochemistry) to monoterpenes, with α-pinene and eucalyptol increasing colonies growth. In stressed cells the majority of monoterpenes failed to minimize the detrimental effects of Cd and increased damage, decreased growth and altered cell biochemistry were observed. However, limonene (1 and 100 mM) and eucalyptol (100 nM) were able to increase the growth of Cd-stressed cells. Our study evidences the influence at-a-distance that organisms able to produce monoterpenes may have on the growth and tolerance of bacterial cells challenged by different environmental conditions.

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In silico structural and functional characterization and phylogenetic study of alkaline phosphatase in bacterium, Rhizobium leguminosarum (Frank 1879)

Phosphorus is one of the primary macronutrient of plants, which is present in soil. It is essential for normal growth and development of plants. Plants use inorganic form of phosphate but organic form can also be assimilated with the help of soil inhabiting bacteria. Alkaline phosphatase is an enzyme present in Rizobium bacteria. This enzyme is responsible for solubilization and mineralization of organic phosphate and makes it readily available for plants. In the present study, nine different strains of Rhizobium leguminosarum were selected for a detailed computational structural and functional characterization and phylogenetic studies of alkaline phosphatase. Amino acid sequences were retrieved from UniProt and saved in FASTA format for use in analysis. Phylogenetic analysis of these strains was done by using MEGA7. 3D structure prediction was performed by using online server I-Tasser. Galaxy Web and 3D Refine were used for structure refinement. The refined structures were evaluated using two validation servers, QMEAN and SAVES. Protein-protein interaction analysis was done by using STRING. For detailed functional characterization, Cofactor, Coach, RaptorX, PSORT and MEME were used. Overall quality of predicted protein models was above 80%. Refined and validated models were submitted into PMDB. Seven out of nine strains were closely related and other two were distantly related. Protein-Protein interaction showed no significant co-expression among the interaction partners.

Efficiency of bacterial fertilizers in peas agrocoenosis under the conditions of the northeastern Forest-Steppe of Ukraine

Peas (Pisum sativum L.) is an appreciable annual leguminous crop which can solve the problem of phytoalbumin, improve nitrogen balance of soil and increase the production of food products.
 The important role in cultivation method of leguminous crops, pea in particular, plays the realization of productive potential due to energy-saving techniques, namely seed inoculation. One of the ways to supply pea agrocoenosis with beneficial microflora is the use of bacterial fertilizers which can supply the plants with essential complex of microorganisms, good nutrition and as a result it can help to realize its genetic potential as for yielding capacity and protein content.
 The aim of the research is to define the influence of bacterial fertilizers on pea productivity by different level of mineral nutrition. The researches have been conducted on the base of educational and scientific centre of Sumy National Agrarian University according to generally accepted methods during 2015–2017.
 The research variants were the following: without inoculation by bacterial fertilizer and with seed treatment with Rhyzohumin and Polymyxobakteryn. Inoculation of peas seed was conducted according to the method of the Institute of Agricultural Microbiology and Agro-Industrial Production of NAAS (Chernihiv).
 On the control the seed inoculation has not been done. The backgrounds of mineral nutrition were P60K60 and N60P60K60. The application of bacterial fertilizers which contain new, highly effective, culturally specific variety of rhizobial bacteria with the increased viability in high concentrations ensures the development of maximal amount of tubers on root system of plants. The highest efficiency in forming symbiotic apparatus and intensity of its activity was stipulated by combination of presowing seed inoculation with Rhezohumin and application of phosphate-potassium fertilizers in the doze of P60K60. The maximal amount and weight of nodules was 50.3 unit per plant and 2.06 g per plant. The level of peas yielding capacity is defined by individual plant productivity which is multiplied by its amount and characterizes the cro productivity under the certain conditions of growing.
 It was determined that the combination of seed inoculation by bacterial fertilizers through using of nitrogen fixing (Rhizobium leguminosarum strain 31) and phosphorus mobilizing (Bacillus polymyxa KB) bacteria and mineral fertilizers favours to raising of peas productivity under the conditions North-East Forest-Steppe zone of Ukraine. The most effective result was obtained in the variant with peas seed inoculation by Rhyzohumin and application of mineral fertilizer in the doze N60P60K60 (yield has increased on 33.7 % comparing with the control).

Effects of Rhizobium Strain on the Growth, Nodulation, N2 Fixation and Ions Accumulation in Vicia Faba Plant Under Salt Stress

Vicia faba L.-rhizobia symbiosis is utilized in different biological ways to improve the productivity of faba beans. This research aims to analyze the effects of the Rhizobium strain on nodulation, N2 fixation, growth, and ion accumulation under salt stress in Viciafaba. The commercial cultivar of faba beans (Viciafaba L. var. minor) was inoculated with the Rhizobium leguminosarumbiovar, by considering viciae strains S10 and S16, after 15 days of growth. This inoculation was carried out in the solution culture consisting of two salt concentrations; 0 mmole l-1NaCl and 50 mmole l-1NaCl. The results revealed that under saline and non-saline conditions, S10 and S16 strains of Rhizobium leguminosarum resulted in the formation of ineffective and effective symbiosis with faba beans. However, the presence of salt stress resulted in increasing the biomass of nodule and nitrogen content. The concentrations of sodium and chloride, in shoot and root, were increased in the presence of salinity. However, potassium concentration was only increased in the shoot. With and without salinity, phosphorus concentration in the shoots was not modified. The results revealed that the salt tolerance of faba beans, inoculated with two strains of Rhizobium were found to possess association with their stable growth. Moreover, the salt tolerance of faba beans inoculated with two salts tolerant rhizobia was also associated with an increment in the capacity of faba beans to increase nodulation and the concentration of shoot N2, Na and Cl-content. In addition, salt tolerance of this variety, inoculated with Rhizobium strains was associated with a decrement in the concentration of K+ in shoot under the salt constraints.

Expression of Serratia and Pseudomonas Chitinase Genes in Rhizobium Via Horizontal Gene Transfer

This study aimed to transfer chitinase genes into Rhizobium leguminosarum bv. vicia in order to enhance the defense of faba bean plants against soil pathogens, in addition to , improving symbiotic nitrogen fixation, as well. Toward this target, 12 transconjugants resulted from conjugation between Pseudomonas flurocescens and Serratia marcescence as a donors against four strains of Rhizobium leguminosarum. The donar strains were tested for chitinolytic activity depending on chitin hydrolysis zone appeared on chitin agar medium. Six out of eight matings between Pseudomonas and Serratia against Rhizobium were successeded. Some recombinants expressed significant amount of IAA production in both complete and minimal media. Some of Rhizobium transcojugants showed significant performance for chitinase activity above the mid-parent. Cell culture and cell – free filterate of some Rhizobium transconjugants showed higher antagonistic activity against Rhizoctonia solani in relation to the mid-parent, because they were able to produce higher amounts of antifungal metabolites. These transcojugants may inhibit the growth of various soil-born pathogens with a higher efficiency than their parents.

Rhizobial symbiosis modifies root hydraulic properties in bean plants under non-stressed and salinity-stressed conditions.

Rhizobial symbiosis improved the water status of bean plants under salinity-stress conditions, in part by increasing their osmotic root water flow. One of the main problems for agriculture worldwide is the increasing salinization of farming lands. The use of soil beneficial microorganisms stands up as a way to tackle this problem. One approach is the use of rhizobial N2-fixing, nodule-forming bacteria. Salinity-stress causes leaf dehydration due to an imbalance between water lost through stomata and water absorbed by roots. The aim of the present study was to elucidate how rhizobial symbiosis modulates the water status of bean (Phaseolus vulgaris) plants under salinity-stress conditions, by assessing the effects on root hydraulic properties. Bean plants were inoculated or not with a Rhizobium leguminosarum strain and subjected to moderate salinity-stress. The rhizobial symbiosis was found to improve leaf water status and root osmotic water flow under such conditions. Higher content of nitrogen and lower values of sodium concentration in root tissues were detected when compared to not inoculated plants. In addition, a drop in the osmotic potential of xylem sap and increased amount of PIP aquaporins could favour higher root osmotic water flow in the inoculated plants. Therefore, it was found that rhizobial symbiosis may also improve root osmotic water flow of the host plants under salinity stress.

Analysis of metal tolerance in Rhizobium leguminosarum strains isolated from an ultramafic soil.

Natural habitats containing high amounts of heavy metals provide a valuable source of bacteria adapted to deal with metal toxicity. A functional analysis of the population of legume endosymbiotic bacteria in an ultramafic soil was undertaken by studying a collection of Rhizobium leguminosarum bv viciae (Rlv) isolates obtained using pea as trap plant. One of the isolates, Rlv UPM1137, was selected on the basis of its higher tolerance to nickel and cobalt and presence of inducible mechanisms for such tolerance. A random transposon mutagenesis of Rlv UPM1137 allowed the generation of 14 transposant derivatives with increased nickel sensitivity; five of these transposants were also more sensitive to cobalt. Sequencing of the insertion sites revealed that one of the transposants (D2250) was affected in a gene homologous to the cation diffusion facilitator gene dmeF first identified in the metal-resistant bacterium Cupriavidus metallidurans CH34. The symbiotic performance of D2250 and two other transposants bearing single transposon insertions was unaffected under high-metal conditions, suggesting that, in contrast to previous observations in other Rlv strain, metal tolerance in UPM1137 under symbiotic conditions might be supported by functional redundancy between several mechanisms.

Molecular diversity and phylogeny of indigenous Rhizobium leguminosarum strains associated with Trifolium repens plants in Romania.

The symbiotic nitrogen fixing legumes play an essential role in sustainable agriculture. White clover (Trifolium repens L.) is one of the most valuable perennial legumes in pastures and meadows of temperate regions. Despite its great agriculture and economic importance, there is no detailed available information on phylogenetic assignation and characterization of rhizobia associated with native white clover plants in South-Eastern Europe. In the present work, the diversity of indigenous white clover rhizobia originating in 11 different natural ecosystems in North-Eastern Romania were assessed by a polyphasic approach. Initial grouping showed that, 73 rhizobial isolates, representing seven distinct phenons were distributed into 12 genotypes, indicating a wide phenotypic and genotypic diversity among the isolates. To clarify their phylogeny, 44 representative strains were used in sequence analysis of 16S rRNA gene and IGS fragments, three housekeeping genes (atpD, glnII and recA) and two symbiosis-related genes (nodA and nifH). Multilocus sequence analysis (MLSA) phylogeny based on concatenated housekeeping genes delineated the clover isolates into five putative genospecies. Despite their diverse chromosomal backgrounds, test strains shared highly similar symbiotic genes closely related to Rhizobium leguminosarum biovar trifolii. Phylogenies inferred from housekeeping genes were incongruent with those of symbiotic genes, probably due to occurrence of lateral transfer events among native strains. This is the first polyphasic taxonomic study to report on the MLSA-based phylogenetic diversity of indigenous rhizobia nodulating white clover plants grown in various soil types in South-Eastern Europe. Our results provide valuable taxonomic data on native clover rhizobia and may increase the pool of genetic material to be used as biofertilizers.

Structural and functional organization of the plasmid regulons of Rhizobium leguminosarum symbiotic genes

The structure of the plasmid locus containing the sym-genes (nod-, nif-, and fix-operons) was investigated in eight Rhizobium leguminosarum strains differing in their origin and host specificity, including five strains of the viciae biovar—symbionts of pea (3), forage beans (1), and Vavilovia (1)—as well as three strains of the biovar trifolii (clover symbionts). Strains of R. leguminosarum bv. viciae, which possess the nodX gene (controlling acetylation of the Nod factor, which is responsible for the ability of rhizobia to form symbioses with a broad spectrum of hosts, including the “Afghan” pea lines, homozygous by the allele sym2A), are characterized by a less compact location of the sym-genes than the strains lacking the nodX gene. The size of the symbiotic cluster in the strains possessing nodX was 94.5 ± 3.5 kb, with the share of the sym-genes of 36.5 ± 1.5%, while for the strains lacking nodX these values were 61.7 ± 3.7 kb and 56.3 ± 1.4%, respectively (significant difference at P0 < 0.01). Syntenic structures were revealed in the symbiotic regions of strains Vaf12, UPM1131, and TOM, as well as syntenic structures of non-symbiotic regions in strains Vaf12, TOM, and WSM1689. The correlation coefficients between the matrices of genetic distances in the analyzed strains for the nodABC, nifHDK, and fixABC operons were on average 0.993 ± 0.002, while their values for the plasmid sites located between the sym-genes were considerably less (0.706 ± 0.010). In these regions, 21 to 27% of the genes were involved in amino acid transport and metabolism, which was substantially higher than the average for the genome of R. leguminosarum bv. viciae (11–12%). These data suggest that the evolution of R. leguminosarum bv. viciae, defined by narrowing of the host specificity (associated with a loss of the nodX gene), was accompanied by reduction of the regions of plasmids located between the sym-genes, as well as by specialization of these areas to perform the functions related to symbiotic nitrogen fixation. The observed increase of density in the cluster of sym-genes may be associated with intensification of their horizontal transfer in the populations of rhizobia, which determines the speed of evolution of the symbiotic system.

Response of Pea Plant (Pisum sativum L.) for Levels of Nitrogen, Rhizobium Inoculation and Spraying of Molybdenum on Growth, Green Pods, Dry Seed Yield and its Components

The current study was carried out at Qaha Vegetable Research Farm (Qalubia Governorate), Horticulture Research Institute, Agriculture Research Center (A. R. C.), Egypt, during the two consecutive winter seasons of 2014/2015 and 2015/2016 to study the influence of different nitrogen fertilization levels i.e. 20, 35 and 50 Kg N/ fed., an inoculation of pea seeds (Pisum sativum L.) cv. Master B with compatible strain of the nodule bacteria Rhizobium leguminosarum,foliar spraying with molybdenum twice at the rate of 10 Mg/ L. and its combinations on vegetative growth, total fresh green pod and dry seed yield (ton/ fed.). Increasing nitrogen fertilization levels from 20 to 50 Kg N/fed. alone led to significant increased plant pea growth, fresh green pod yield, green pod characters, dry seed yield, nitrogen, protein, phosphorus and potassium (%) presenting contents for dry seed. However, the earliest germination rate (days) were obtained with adding 35 Kg N/fed. during the two winter seasons, as compared with the other two levels (20 and 50 Kg N/fed.).Results showed that the Rhizobium inoculation gave better pea growth, green pods yield, dry seed yield and its quality as well as germination ratio, rate (days) and sprout length (cm) with adding 35 Kg N/fed. compared with the same treatments with other two N fertilization levels(20 and 50 kg N/fed). But the foliar spraying by molybdenum twice at the rate of 10 Mg/ L. led to significant increased with nitrogen level from 20 up to 50 Kg N/fed. for all traits under this study. On the other hand, adding 50 Kg N/fed. with the foliar spraying by molybdenum gave significant increased on all parameters for this study compared with other treatments. The results showed that adding 35 Kg N/fed. with Rhizobium inoculation and molybdenum foliar spraying twice at the rate of 10 Mg/L. led to significant increased for total green and dry pea seed yield as well as its characters compared with the same combination under other two nitrogen levels (20 and 50 kg N/fed). In generally, the combination between adding 35 kg N/fed, Rhizobium inoculation and molybdenum foliar spraying twice at the rate of 10 Mg/L was the highest economic return and led to provide 30% of nitrogen fertilization. Fedan = 4200 m2.

Local genetic structure and worldwide phylogenetic position of symbiotic Rhizobium leguminosarum strains associated with a traditional cultivated crop, Vicia ervilia, from Northern Morocco

A total of 212 symbiotic bacteria were isolated from nodules of Vicia ervilia, a traditional crop cultivated in Northern Morocco. The isolates were recovered from 10 different sites, trapped each time with the local cultivar grown in the same field. Four loci were sequenced in order to characterize the isolates, including two housekeeping genes (recA and glnII), one plasmidic symbiotic gene (nodC) and one locus from another plasmid (prL11). In several isolates, two different copies of glnII were detected and sequenced, suggesting a unique duplication event, which has never been reported previously. There was no correlation between the genetic differentiation among cultivars and among bacteria, showing that the evolution of the bacterial population was independent, at least partially, from the host plant. By placing the haplotypes in a wide-ranging phylogenetic reconstruction, it was shown that the diversity detected in Morocco was spread throughout the different clades detected worldwide. The differentiation between areas relied on frequency variations of haplotypes rather than a presence/absence pattern. This finding raises new questions concerning bacterial genetic resource preservation, and confirms the old tenet “everything is everywhere but the environment selects”.

Inoculation with indigenous rhizobium strains increases yields of common bean (Phaseolus vulgaris L.) in northern Spain, although its efficiency is affected by the tillage system

Common bean (Phaseolus vulgaris L.) crops hold the potential to obtain higher yields by enhancing their biological nitrogen fixation (BNF) with Rhizobium. However in contrast to other legumes, common bean has shown a lack of positive response to inoculation with Rhizobium in many cases. This has led to a limited use of rhizobial inoculants in this crop, especially in Europe. The adaptation of bacterial strains to the rhizosphere is a key factor in the success of any inoculant, especially in a promiscuous legume such as common bean. This research aimed at increasing common bean yields via inoculation with effective indigenous Rhizobium leguminosarum strains. Three highly effective strains (LCS0306, LBM1123 and ZBM1008) which were selected according to their effectiveness at BNF in hydroponic conditions were separately inoculated onto common bean in a field experiment. The experiment was carried out under three environments and three tillage systems: conventional-tillage (CONVT), no-tillage (NT) and a cover-crop (CC). The grain yield observed with seed inoculation was significantly higher than the yield obtained with uninoculated seed under CONVT and CC. However, under NT inoculation had no effect. Furthermore, under CONVT and CC, inoculation with R. leguminosarum LCS0306 produced even higher yields than those obtained in nitrogen-fertilised or control plots. This is the first attempt to explain the inoculation performance of common bean under different tillage systems in Europe. A gene–based hypothesis has been used to explain the effectiveness of indigenous common bean rhizobia as nitrogen fixers in this crop.

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The efficiency of eight Rhizobium leguminosarum strains isolated from root nodules of Faba bean plants which were collected from different Governorate in Egypt has been examined. After inoculation of faba bean seeds with each Rhizobium strain individually, we measured the growth promotion, nodule formation and plant protein profile under different concentration of sodium chloride salt stress. The interactions between salt tolerant and sensitive faba bean cultivars and Rhizobium strains under NaCl stress were found to be significant. Nitrogen fixation efficiency varied among the eight Rhizobium strains. The protein profile using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for both faba bean cultivars revealed that Rhizobium strains numbers RL1, 2, 4 and RL 8 showed high level of salt tolerance under 40 and 80 mM NaCl in both faba bean cultivars. Rhizobium strains improved the salt tolerance, as is clearly observed in number of nodules and the amount of N 2 fixation. It is known that stress affects the growth, metabolic activity and symbiotic efficiency of Rhizobium with faba bean plant but in this study we found that Rhizobium strains numbers RL2 and RL 3 showed high efficiency of N 2 fixation and growth promotion in both faba bean cultivar. Keywords: Faba bean, Rhizobium , nodulation efficiency, salt stress, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) protein profile. African Journal of Biotechnology , Vol 13(41) 4081-4092

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Our previous studies showed that living and heat-killed cells of the Rhizobium leguminosarum strain P.SOM induce in pea roots systemic resistance to infection by Orobanche crenata. To better understand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heat stable bacterial surface carbohydrates such as exopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for recognition in the symbiotic interaction between Rhizobium and legumes, their role in the R. leguminosarum-pea interaction was studied. EPS and LPS were extracted from bacterial cultures, applied to pea roots, and tested for activity as an inducer of plant resistance to broomrape. Whereas EPS did not affect O. crenata infection, LPS reduced Orobanche infection significantly in concentrations as low as 1 and 0.5 mg ml-1. In contrast these compounds did not influence parasite germination induced by the artificial stimulant, GR24. Our results show that soil treatments with LPS resulted in a highly significant reduction of O. crenata infection of pea roots. The results clearly showed that LPS of R. leguminosarum P.SOM act as the inducing agent of systemic resistance in pea roots against Orobanche. Key words: Rhizobium leguminosarum, Lipopolysaccharides, Exopolysaccharides, Induced resistance, Orobanche crenata, Pea.

Use of Rhizobium leguminosarum as a potential biofertilizer for Lactuca sativa and Daucus carota crops

AbstractMicrobial biofertilizers are becoming an effective tool for sustainable agriculture by means of the reduction of the use of chemical fertilizers. However, the knowledge of each specific plant–microorganism interaction is essential for a correct application. In this study, we analyzed the in vitro plant‐growth‐promotion mechanisms of a Rhizobium leguminosarum strain named PEPV16 isolated from Phaseolus vulgaris nodules. This strain was able to produce siderophores and indole acetic acid and to solubilize phosphate. Confocal microscopy showed that this strain was able to colonize the roots of two horticultural crops, Lactuca sativa L. (lettuce) and Daucus carota L. (carrot). Strain PEPV16 was also able to promote the plant growth of both plant species increasing the dry matter of shoots and roots of lettuce and carrots, respectively, as well as to increase the uptake of N and P in the edible parts of both plant species. These data confirmed the suitability of Rhizobium as biofertilizer for nonlegumes.

ACC deaminase producing Pseudomonas putida strain PSE3 and Rhizobium leguminosarum strain RP2 in synergism improves growth, nodulation and yield of pea grown in alluvial soils

Plant growth promoting rhizobacteria affects the overall performance of plants by one or combination of mechanisms. However, little information is available on how ACC deaminase secreting bacteria enhance crop production. The present study aimed at identifying ACC deaminase producing and phosphate solubilizing bacterial strains and to assess their plant growth promoting activities. Additionally, the effect of two ACC deaminase positive bacterial strains Pseudomonas putida and Rhizobium leguminosarum on pea plants was determined to find a novel and compatible bacterial pairing for developing efficient inoculants for enhancing legume production and reducing dependence on chemical fertilizers. The isolated bacterial cultures were characterized biochemically and by 16S rRNA sequence analysis. The plant growth promoting activities was determined using standard microbiological methods. The impact of P. putida and R. leguminosarum, on pea plants was determined both in pots and in field environments. Of the total 40 bacterial strains, strain PSE3 isolated from Mentha arvenss rhizosphere and RP2 strain from pea nodules produced ACC deaminase, solubilized insoluble phosphate, synthesized indole acetic acid, ammonia, cyanogenic compounds, exopolysaccharides and had antifungal activity. The dual inoculation of P. putida strain PSE3 and R. leguminosarum strain RP2 had largest positive effect and markedly increased the growth, symbiotic characteristics, nutrient pool and quantity and quality of pea seeds. The measured parameters were further augmented when inoculated pea plants were grown in soils treated with urea or DAP. A significant variation in the measured parameters of pea plants was observed under both pot and field trials following microbial inoculation but the bacterial cultures did not differ significantly in growth promoting activities. The results suggest that ACC deaminase positive bacterial cultures endowed with multiple potential can be targeted to develop mixed inoculants for enhancing pea production and hence, to reduce dependence on synthetic fertilizers.

Nodule occupancy by Rhizobium leguminosarum strain WSM1325 following inoculation of four annual Trifolium species in Canterbury, New Zealand

The genotype of nodule occupants in four annual clovers – balansa (Trifolium michelianum), Persian (Trifolium resupinatum), gland (Trifolium glanduliferum) and arrowleaf (Trifolium vesiculosum) – was investigated. The clovers were inoculated with the ALOSCA® group C granule preparation of strain WSM1325. A total of 224 strains were recovered from root nodules with between 55 and 58 strains for each clover species. Genotyping showed that no strains had fingerprints identical to strain WSM1325. The nodule occupants were diverse with 26, 35, 31 and 32 genotypes identified on arrowleaf, balansa, gland and Persian clovers, respectively. Arrowleaf clover had some specificity for genotype A with 43% of nodules occupied by this strain. The most dominant strain for the other three clovers ranged between 13%–18% occupancy. This work demonstrates a high diversity of naturalized rhizobia strains in New Zealand soils that had the ability to nodulate these top flowering annual clover species.

The role of GSTs in the tolerance of Rhizobium leguminosarum to cadmium

A high intraspecific difference in cadmium (Cd) tolerance exits among Rhizobium leguminosarum strains. The higher tolerance to Cd appeared to be related to the efficiency of the glutathione (GSH)-Cd chelation mechanism, but it is not known how efficiency is influenced. Thus, in this work it was intended to investigate the traits behind the efficiency of intracellular Cd chelation by GSH. Glutathione-S-transferases (GST; EC 2.5.1.18) are a family of multi-functional dimeric proteins, found in both prokaryotes and eukaryotes, which are implicated in a variety of stress conditions. The common feature of these enzymes is to catalyze the conjugation of the sulfur atom of GSH with a large variety of hydrophobic toxic compounds of both endogenous and exogenous origin. Taking into account the reactions catalyzed by GSTs, it was hypothesized that they could be involved in the GSH-Cd complex formation in R. leguminosarum. Differences in GSTs activity between strains could explain variation in Cd chelation efficiency detected among strains and, consequently, discrepancy in tolerance to Cd. Thus, GST isoforms of R. leguminosarum strains with distinct tolerances to Cd were purified and their activity investigated. The relationship between chelation efficiency and enzymatic activity of GSTs was demonstrated, supporting the hypothesis that GSTs, in particular one isoform, was involved in the formation of GSH-Cd complexes and in the tolerance of Rhizobium to Cd.