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Drought tolerant rhizobacteria of the genus Bacillus, Enterobacter, Moraxella and Pseudomonas colonizing the root system of Acacia arabica were isolated to mitigate the drought stress of wheat (Triticum aestivum L.). In vitro auxin production by rhizobacteria was quantified by Ultra High Performance Liquid Chromatography (UPLC). Analysis of the crude extracts detected the indole-3-acetic acid (IAA), indole-3-carboxylic acid (ICA) and indole-3-lactic acid (ILA). Highest IAA production of 25.9 µg ml−1 was observed for Bacillus amyloliquefaciens S-134. Pot trials were conducted to evaluate the role of rhizobacteria to enhance the growth of wheat at different water regimes. At highest water stress i.e. 10% field capacity (FC), significant improvement of shoot length was observed with B. amyloliquefaciens S-134. For yield parameters, B. muralis D-5 and E. aerogenes S-10 recorded 34% and 1 fold increases for spike length and seed weight, over respective control at 10% FC. Mixed culture combinations of M-2 (B. thuringiensis S-26, D-2, B. amyloliquefaciens S-134, B. simplex D-11) and M-3 (M. pluranimalium S-29, B. simplex D-1, B. muralis D-5, P. stutzeri S-80) showed significant improvement for tillers and number of spikelets. In conclusion, application of the drought tolerant rhizobacteria can help to overcome productivity losses in drought prone areas. [ABSTRACT FROM AUTHOR]

Four pairs of strains were isolated from four individual root nodules collected from different plants of the Miocene-Pliocene relict legumeOxytropis triphyllagrowing in the Baikal region (one nodule – one pair of strains). Identification of these strains by the 16S rRNA gene sequencing showed that one strain of each pair was fast-growing and phylogenetically closest to the type strainsPhyllobacterium endophyticumPEPV15T(98.8–99.5% 16S rDNA similarity) andPhyllobacterium bourgognenseSTM 201T(98.8–99.3% 16S rDNA similarity). The other strain was slow-growing and closely related to the type strainsBosea vestrisii34635TandBosea eneae34614T(99.5–99.8% 16S rDNA similarity). Results of theatpD gene sequencing suggested thatPhyllobacterium-related isolates most probably belong to a new species ofPhyllobacterium.It is known that none of the currently described strains ofP. endophyticum,P. bourgognense(familyPhyllobacteriaceae),B. vestrisiiandB. eneae(familyBradyrhizobiaceae) can induce root nodules, but several symbiotic genes were found in the representatives of these two genera.Thus we hypothesize that the pairs of strains isolated fromO. triphyllaroot nodules can be co-microsymbionts having complementary sets of symbiotic genes and their simultaneous presence in roots is required for efficient nodulation of the host plant. The whole genome sequencing of the studied strains is in progress to find and compare symbiotic genes. [ABSTRACT FROM AUTHOR]

The present report aimed to better understand the mechanisms of plant co-tolerance to various toxic metals, and relationships between metal tolerance and metal accumulation. The pea ( Pisum sativum L.) line SGE and its mutant SGECd t , having increased tolerance to and accumulation of Cd, but decreased tolerance to and accumulation of Hg, were cultivated in hydroponics at a range of toxic concentrations of heavy metals (Cd, Co, Cr, Hg, La, Ni, Pb and Zn), as well as Al, Fe, Mn, NaCl and H + ions. The SGECd t mutant showed increased tolerance to Co (increased root biomass at 12 and 25 μM Co and shoot biomass at 25, 50 and 100 μM Co), but similar root and shoot Co contents as SGE. No significant differences between SGE and SGECd t in biomass response to other metals and low pH were detected. However at particular metal concentrations, SGECd t tended to (Student's t test, P < 0.05) have increased: (i) shoot biomass (34%) in the presence of 400 μM Zn; (ii) root and shoot biomass (32%) in the presence of 100 μM Fe; (iii) root Mn or Zn contents (65% or 8%, respectively) in the presence 400 μM Mn or Zn, compared to SGE plants. No genotypic differences in the content of other toxic metals were observed, except for the previously reported increased Cd content and decreased Hg content in SGECd t . Generally, metal toxicity decreased macro- and micro-element (nutrient) concentrations in plants, however opposite effects were also observed particularly on Hg-treated plants. SGECd t had increased root Ca, Fe, Mg, Mn and S content and shoot B, Ca, Mg, Mn, Na and Zn content in Cd-treated plants. In the presence of toxic Hg the mutant contained less root and shoot Ca, K, Mg and S, but had increased root Co, Cr and Cu contents. Genotypic differences in individual nutrient elements were also observed following Ag, Al, La, Mn, Ni or Zn treatment. Taken together, the results indicate high specificity in phenotypic responses of SGECd t exposed to toxic metals and that the mutation might affect some regulatory genes, which could modulate nutrient (particularly Ca) homeostasis and regulation of ion transporters. [ABSTRACT FROM AUTHOR]

Although plant salt tolerance has been improved by soil inoculation with rhizobacteria containing the enzyme 1-aminocyclopropane-l-carboxylate (ACC) deaminase (which metabolises ACC, the immediate precursor of the phytohormone ethylene), it is not always clear whether ion homeostasis and plant water relations are affected. When pea (Pisum sativum L. cv. Alderman) was grown with 70 and 130 mM NaCl, the ACC-deaminase containing rhizobacterium Variovorax paradoxus 5C-2 increased total biomass by 25 and 54% respectively. Nutrient flow modelling showed that V. paradoxus 5C-2 increased K uptake and root to shoot K flow, but decreased Na flow and increased Na deposition in roots. Thus, shoot K[sup +]: Na[sup +] ratio increased following V.paradoxus 5C-2 inoculation. At 70 and 130 mMNaCl, rhizobacterial inoculation decreased stomatal resistance by 14 and 31 % and decreased xylem balancing pressure by 7 and 21 % respectively. Furthermore, rhizobacterial inoculation improved photo synthetic efficiency (F[sub v]F[sub m]) by 12 and 19% and increased maximal electron transport rate (ETR) by 18 and 22% at 70 and 130mM NaCl respectively. Thus V. paradoxus 5C-2 mitigates salt stress by improving water relations, ion homeostasis and photosynthesis of pea plants, and may provide an economic means of promoting growth of plants exposed to salt stress. [ABSTRACT FROM AUTHOR]

Heavy metals have multiple effects on plant growth and physiology, including perturbation of plant water status. These effects were assessed by exposing the unique Cd-tolerant and Cd-accumulating pea (Pisum sativum L.) mutant SGECdt and its wild-type (WT) line SGE to either cadmium (1, 4 μM CdCl2) or mercury (0.5, 1, 2 μM HgCl2) in hydroponic culture for 12 days. When exposed to Cd, SGECdt accumulated more Cd in roots, xylem sap, and shoot, and had considerably more biomass than WT plants. WT plants lost circa 0.2 MPa turgor when grown in 4 μM CdCl2, despite massive decreases in whole-plant transpiration rate and stomatal conductance. In contrast, root Hg accumulation was similar in both genotypes, but WT plants accumulated more Hg in leaves and had a higher stomatal conductance, and root and shoot biomass compared with SGECdt. Shoot excision resulted in greater root-pressure induced xylem exudation of SGECdt in the absence of Cd or Hg and following Cd exposure, whereas the opposite response or no genotypic differences occurred following Hg exposure. Exposing plants that had not been treated with metal to 50 μM CdCl2 for 1 h increased root xylem exudation of WT, whereas 50 μM HgCl2 inhibited and eliminated genotypic differences in root xylem exudation, suggesting differences between WT and SGECdt plants in aquaporin function. Thus, root water transport might be involved in mechanisms of increased tolerance and accumulation of Cd in the SGECdt mutant. However, the lack of cross-tolerance to Cd and Hg stress in the mutant indicates metal-specific mechanisms related to plant adaptation. [ABSTRACT FROM AUTHOR]

Many plant-growth-promoting rhizobacteria (PGPR) associated with plant roots contain the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase and can metabolize ACC, the immediate precursor of the plant hormone ethylene, thereby decreasing plant ethylene production and increasing plant growth. However, relatively few studies have explicitly linked ethylene emission and/or action to growth promotion in these plant-microbe interactions. This study examined effects of the PGPR Variovorax paradoxus 5C-2 containing ACC deaminase on the growth and development of Arabidopsis thaliana using wild-type (WT) plants and several ethylene-related mutants (etr1-1, ein2-1, and eto1-1). Soil inoculation with V. paradoxus 5C-2 promoted growth (leaf area and shoot biomass) of WT plants and the ethylene-overproducing mutant eto1-1, and also enhanced floral initiation of WT plants by 2.5 days. However, these effects were not seen in ethylene-insensitive mutants (etr1-1 and ein2-1) even though bacterial colonization of the root system was similar. Furthermore, V. paradoxus 5C-2 decreased ACC concentrations of rosette leaves of WT plants by 59% and foliar ethylene emission of both WT plants and eto1-1 mutants by 42 and 37%, respectively. Taken together, these results demonstrate that a fully functional ethylene signal transduction pathway is required for V. paradoxus 5C-2 to stimulate leaf growth and flowering of A thaliana. [ABSTRACT FROM AUTHOR]

We present the genome sequence of Ensifer aridi strain RCAM05007 obtained from long reads. The strain was isolated from the root nodule of Cyamopsis tetragonoloba (L.) Taub. plant inoculated with a soil sample from India. The assembly contains one chromosome and two megaplasmids totalling ~6.7 Mbp with 61.6% GC content.

In this article, we report the complete genome sequence of Microbacteriun strain A8/3-1 isolated from the root nodule of Oxytropis tragacanthoides Fisch. ex DC., growing in the Altai region, Russia. The sequence was obtained using Oxford Nanopore Technologies MinION., Competing Interests: The authors declare no conflict of interest.

This study reports the whole-genome sequence of an endosymbiotic bacteria Bosea sp. strain 685, which was isolated from the root nodule of Astragalus umbellatus Bunge. in the Kamchatka Peninsula, Russia. The genome consists of one chromosome and one plasmid with a total length of 6,795,213 bp and 65.37% of GC content., Competing Interests: The authors declare no conflict of interest.

Cadmium (Cd) is one of the most widespread and toxic soil pollutants that inhibits plant growth and microbial activity. Polluted soils can be remediated using plants that either accumulate metals (phytoextraction) or convert them to biologically inaccessible forms (phytostabilization). The phytoremediation potential of a symbiotic system comprising the Cd-tolerant pea ( Pisum sativum L.) mutant SGECd t and selected Cd-tolerant microorganisms, such as plant growth-promoting rhizobacterium Variovorax paradoxus 5C-2, nodule bacterium Rhizobium leguminosarum bv. viciae RCAM1066, and arbuscular mycorrhizal fungus Glomus sp. 1Fo, was evaluated in comparison with wild-type pea SGE and the Cd-accumulating plant Indian mustard (Brassica juncea L. Czern.) VIR263. Plants were grown in pots in sterilized uncontaminated or Cd-supplemented (15 mg Cd kg -1 ) soil and inoculated or not with the microbial consortium. Cadmium significantly inhibited growth of uninoculated and particularly inoculated SGE plants, but had no effect on SGECd t and decreased shoot biomass of B. juncea. Inoculation with the microbial consortium more than doubled pea biomass (both genotypes) irrespective of Cd contamination, but had little effect on B. juncea biomass. Cadmium decreased nodule number and acetylene reduction activity of SGE by 5.6 and 10.8 times, whereas this decrease in SGECd t was 2.1 and 2.8 times only, and the frequency of mycorrhizal structures decreased only in SGE roots. Inoculation decreased shoot Cd concentration and increased seed Cd concentration of both pea genotypes, but had little effect on Cd concentration of B. juncea . Inoculation also significantly increased concentration and/or accumulation of nutrients (Ca, Fe, K, Mg, Mn, N, P, S, and Zn) by Cd-treated pea plants, particularly by the SGECd t mutant. Shoot Cd concentration of SGECd t was twice that of SGE, and the inoculated SGECd t had approximately similar Cd accumulation capacity as compared with B. juncea . Thus, plant-microbe systems based on Cd-tolerant micro-symbionts and plant genotypes offer considerable opportunities to increase plant HM tolerance and accumulation., Competing Interests: The authors declare no conflict of interest.

Plant growth-promoting rhizobacteria (PGPR) improve plant productivity and stress resistance. The mechanisms involved in plant-microbe interactions include the modulation of plant hormone status. The Novosphingobium sp. strain P6W was previously described as the bacterium capable of abscisic acid (ABA) degradation, and its inoculation decreased ABA concentrations in planta. The metabolic pathway for the ABA degradation in bacteria is still unknown. Here we present transcriptome data of Novosphingobium sp. P6W grown in the medium supplemented with ABA or fructose as the carbon source. Cleaned FASTQ files for the RNA-seq libraries are deposited in the NCBI Sequence Read Archive (SRA, Identifier: SRP189498) and have been assigned BioProject accession PRJNA529223., (© 2019 The Author(s).)

Although plant salt tolerance has been improved by soil inoculation with rhizobacteria containing the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase (which metabolises ACC, the immediate precursor of the phytohormone ethylene), it is not always clear whether ion homeostasis and plant water relations are affected. When pea (Pisum sativum L. cv. Alderman) was grown with 70 and 130mM NaCl, the ACC-deaminase containing rhizobacterium Variovorax paradoxus 5C-2 increased total biomass by 25 and 54% respectively. Nutrient flow modelling showed that V. paradoxus 5C-2 increased K uptake and root to shoot K flow, but decreased Na flow and increased Na deposition in roots. Thus, shoot K+:Na+ ratio increased following V. paradoxus 5C-2 inoculation. At 70 and 130mM NaCl, rhizobacterial inoculation decreased stomatal resistance by 14 and 31% and decreased xylem balancing pressure by 7 and 21% respectively. Furthermore, rhizobacterial inoculation improved photosynthetic efficiency (Fv/Fm) by 12 and 19% and increased maximal electron transport rate (ETR) by 18 and 22% at 70 and 130mM NaCl respectively. Thus V. paradoxus 5C-2 mitigates salt stress by improving water relations, ion homeostasis and photosynthesis of pea plants, and may provide an economic means of promoting growth of plants exposed to salt stress.