Disruption of the cell division protein ftsK gene changes elemental selenium generation, selenite tolerance, and cell morphology in Rahnella aquatilis HX2.

AIMS: Some studies have indicated that the alterations in cellular morphology induced by selenite [Se(Ⅳ)] may be attributed to its inhibitory effects on cell division. However, whether the genes associated with cell division are implicated in Se(Ⅳ) metabolism remains unclear. METHODS AND RESULTS: The ftsK gene in Rahnella aquatilis HX2 was mutated with an in-frame deletion strategy. The ftsK mutation strongly reduced the tolerance to selenite [Se(Ⅳ)] and the production of red elemental selenium [Se(0)] in R. aquatilis HX2, and this effect could not be attributed solely to the inhibition of cell growth. Deleting the ftsK gene also resulted in a significant decrease in bacterial growth of R. aquatilis HX2 during both exponential and stationary phases. The deletion of ftsK inhibited cell division, resulting in the development of elongated filamentous cells. Furthermore, the loss-of-function of FtsK significantly impacted the expression of seven genes linked to cell division and Se(Ⅳ) metabolism by at least 2-fold, as unveiled by real-time quantitative PCR (RT-qPCR) under Se(Ⅳ) treatment. CONCLUSIONS: These findings suggest that FtsK is associated with Se(Ⅳ) tolerance and Se(0) generation and is a key player in coordinating bacterial growth and cell morphology in R. aquatilis HX2.

Nitrate reductase involves in selenite reduction in Rahnella aquatilis HX2 and the characterization and anticancer activity of the biogenic selenium nanoparticles.

BACKGROUND: Biogenic selenium nanoparticles (SeNPs) show numerous advantages including their high stability, low toxicity, and high bioactivity. While metabolism of SeNPs remains not well studied and need more investigation to reveal the process. PURPOSE: The objective of the study was to investigate the relationship between nitrate reductase and selenite reduction in Rahnella aquatilis HX2, characterize the properties of HX2 produced SeNPs, and explore their potential applications, particularly their anticancer activity. PROCEDURES: Selenium species were measured by high-performance liquid chromatography coupled to inductively coupled plasma - Mass spectrometry (HPLC-ICP-MS). Transcription level of nitrate reductase was determined by Real-time quantitative PCR. Morphology, particle size, crystal structure and surface chemistry of SeNPs were determined by electron microscopy, dynamic light scattering method, Raman scattering, X-ray photoelectron spectroscopy, respectively. Anti cancer cell activity was measured by CCK-8 assay. MAIN FINDINGS: SeNP production in R. aquatilis HX2 was correlated with the cell growth. The products of selenite reduction in HX2 detected by HPLC-ICP-MS included SeNPs, selenocysteine (SeCys), Se-Methylselenocysteine (MeSeCys), and 7 unknown compounds. Nitrate addition experiments suggested the involvement of nitrate reductase in selenite reduction in HX2. Both the cellular membrane and cytoplasm of HX2 exhibited selenite-reducing ability, indicating that membrane-associated nitrate reductase was not the sole selenite reductase in HX2. Characterization of the biogenic SeNPs revealed a spherical morphology and amorphous structure of them. Surface chemistry analysis implicated the binding of extracellular polymeric substances to the biogenic SeNPs, and the presence of Se0, Se2-, and electron-rich Se atoms on the surface of SeNPs. Finally, the IC50 values of the biogenic SeNPs were 36.49 µM for HepG2 and 3.70 µM for HeLa cells. CONCLUSIONS: The study first revealed that the nitrate reductase is involving in selenite reduction in R. aquatilis HX2. The biogenic SeNPs coordinated with organic substances in the surface. And SeNPs produced by R. aquatilis HX2 showed excellent anticancer activities on HepG2 and HeLa cells.

Biochemical characterization of glutaminase-free L-asparaginases from Himalayan Pseudomonas and Rahnella spp. for acrylamide mitigation.

L-asparaginase having low glutaminase activity is important in clinical and food applications. Herein, glutaminase-free L-asparaginase (type I) coding genes from Pseudomonas sp. PCH182 (Ps-ASNase I) and Rahnella sp. PCH162 (Rs-ASNase I) was amplified using gene-specific primers, cloned into a pET-47b(+) vector, and plasmids were transformed into Escherichia coli (E. coli). Further, affinity chromatography purified recombinant proteins to homogeneity with monomer sizes of ~37.0 kDa. Purified Ps-ASNase I and Rs-ASNase I were active at wide pHs and temperatures with optimum activity at 50 °C (492 ± 5 U/mg) and 37 °C (308 ± 4 U/mg), respectively. Kinetic constant Km and Vmax for L-asparagine (Asn) were 2.7 ± 0.06 mM and 526.31 ± 4.0 U/mg for Ps-ASNase I, and 4.43 ± 1.06 mM and 434.78 ± 4.0 U/mg for Rs-ASNase I. Circular dichroism study revealed 29.3 % and 24.12 % α-helix structures in Ps-ASNase I and Rs-ASNase I, respectively. Upon their evaluation to mitigate acrylamide formation, 43 % and 34 % acrylamide (AA) reduction were achieved after pre-treatment of raw potato slices, consistent with 65 % and 59 % Asn reduction for Ps-ASNase I and Rs-ASNase I, respectively. Current findings suggested the potential of less explored intracellular L-asparaginase in AA mitigation for food safety.

Uptake of Selenite by Rahnella aquatilis HX2 Involves the Aquaporin AqpZ and Na+/H+ Antiporter NhaA.

Microbial transformation of selenite [Se(IV)] to elemental selenium nanoparticles (SeNPs) is known to be an important process for removing toxic soluble selenium (Se) oxyanions and recovery of Se from the environment as valuable nanoparticles. However, the mechanism of selenite uptake by microorganisms, the first step through which Se exerts its cellular function, remains not well studied. In this study, the effects of selenite concentration, time, pH, metabolic inhibitors, and anionic analogues on selenite uptake in Rahnella aquatilis HX2 were investigated. Selenite uptake by R. aquatilis HX2 was concentration- and time-dependent, and its transport activity was significantly dependent on pH. In addition, selenite uptake in R. aquatilis HX2 was significantly inhibited by the aquaporin inhibitor AgNO3 and sulfite (SO32-), and partially inhibited by carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and 2,4-dinitrophenol (2,4-DNP) treatments. Three mutants with in-frame deletions of aqpZ, glpF, and nhaA genes were constructed. The transport assay showed that the water channel protein AqpZ, and not GlpF, was a key channel of selenite uptake by R. aquatilis HX2, and sulfite and selenite had a common uptake pathway. In addition, the Na+/H+ antiporter NhaA is also involved in selenite uptake in R. aquatilis HX2.

Hyphosphere interactions between Rhizophagus irregularis and Rahnella aquatilis promote carbon-phosphorus exchange at the peri-arbuscular space in Medicago truncatula.

Arbuscular mycorrhizal (AM) fungi form a continuum between roots and soil. One end of this continuum is comprised of the highly intimate plant-fungus interface with intracellular organelles for nutrient exchange, while on the other end the fungus interacts with bacteria to compensate for the AM fungus' inability to take up organic nutrients from soil. How both interfaces communicate in this highly complex tripartite mutualism is widely unknown. Here, the effects of phosphate-solubilizing bacteria (PSB) Rahnella aquatilis dwelling at the surface of the extraradical hyphae of Rhizophagus irregularis was analysed based on the expression of genes involved in C-P exchange at the peri-arbuscular space (PAS) in Medicago truncatula. The interaction between AM fungus and PSB resulted in an increase in uptake and transport of Pi along the extraradical hyphae and its transfer from AM fungus to plant. In return, this was remunerated by a transfer of C from plant to AM fungus, improving the C-P exchange at the PAS. These results demonstrated that a microorganism (i.e., a PSB) developing at the hyphosphere interface can affect the C-P exchange at the PAS between plant and AM fungus, suggesting a fine-tuned communication operated between three organisms via two distantly connected interfaces.

Two-component system in Rahnella aquatilis is impacted by the hyphosphere of the arbuscular mycorrhizal fungus Rhizophagus irregularis.

Two-component systems (TCS) are ubiquitous among bacteria, playing key roles in signalling events. However, to what extent the TCS of Rahnella aquatilis (a Phosphate solubilizing bacteria) is influenced by the hyphosphere of the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis is totally unknown. Here, the expression of 16 genes encoding the TCS of R. aquatilis (i.e. involved in carbon-sensing and nutrient-sensing) and of eight genes regulated by the PhoR TCS (i.e. involved in inorganic and organic phosphorus mobilization) were analysed at regular intervals in presence of hyphae of R. irregularis. The study was conducted under in vitro culture conditions with phytate as the unique source of phosphorus. In presence of the AM fungus, the expression of TCS genes involved in carbon-sensing and nutrient-sensing were stimulated. Only, BaeS at 30 and 120 min, and BaeR at 60 min were inhibited. In addition, the PhoR TCS stimulated the expression of genes encoding phosphatase but inhibited the expression of genes involved in gluconic acid production. As the mechanism of coupling environmental changes with cellular physiological changes, TCS plays a pivotal role in regulating specific gene expression in R. aquatilis, recognizing environmental signals. More importantly, TCS genes may regulate bacteria response to hyphal carbon to mobilize phosphorus efficiently in the hyphosphere.

Highly stable selenium nanoparticles: Assembly and stabilization via flagellin FliC and porin OmpF in Rahnella aquatilis HX2.

Microorganisms play a critical role in the reduction of the more toxic selenite and selenate to the less toxic elemental selenium. However, the assembly process and stability of selenium nanoparticles (SeNPs) remain understudied. The plant growth-promoting rhizobacterium Rahnella aquatilis HX2 can reduce selenite to biogenic SeNPs (BioSeNPs). Two main proteins, namely flagellin FliC and porin OmpF were identified in the BioSeNPs. The fliC and ompF gene mutation experiments demonstrated that the FliC and OmpF could control the assembly of BioSeNPs in vivo. At the same time, the expressed and purified FliC and OmpF could control the assembly of SeNPs in vitro. BioSeNPs produced by R. aquatilis HX2 exhibited high stability under various ionic strengths, while the chemically synthesized SeNPs (CheSeNPs) showed a high level of aggregation. The in vitro experiments verified that FliC and OmpF could prevent the aggregation of the CheSeNPs under various ionic strengths. This work reports the preparation of highly stable BioSeNPs produced by strain R. aquatilis HX2 and verifies that FliC and OmpF both could control the assembly and stability of BioSeNPs. BioSeNPs with high stability could be suitable as nutritional supplement to remedy selenium deficiency and in nanomedicine applications.

Three chlorotoluene-degrading bacterial strains: Differences in biodegradation potential and cell surface properties.

Pollution of the environment with chlorinated aromatic compounds is a problem of increasing importance, which has stimulated the search for efficient methods for the remediation of contaminated soil and water. Additionally, for better understanding of the significance of bioavailability to biodegradation, investigation of the cell surface properties is necessary. Hence, this study concerns the properties and possible application, in chlorotoluene removal, of three newly isolated environmental bacterial strains from the genera Pseudomonas, Raoultella and Rahnella. The results show the differences in the biochemical profiles of the isolated strains, their cellular fatty acid composition and their hemolytic properties. However, all three strains exhibit high biodegradation potential, degrading not less than 60% of each monochlorotoluene isomer in 21-day experiments. What is more, observations of changes in the cell surface properties indicate the possible adaptation mechanisms of the strains that enable efficient biodegradation of hydrophobic pollutants such as monochlorotoluenes.

Rahnella sp. LRP3 induces phosphate precipitation of Cu (II) and its role in copper-contaminated soil remediation.

Microbially induced phosphate precipitation (MIPP) is an advanced bioremediation technology to immobilize heavy metals in soil. In this study, an indigenous bacterial strain LRP3, identified as Rahnella sp., was isolated from Cu-contaminated dark brown soil in the mining area. Strain LRP3 could produce phytase and alkaline phosphatase to degrade phytic acid, which released soluble phosphate to the bacterial culture. Due to the metabolism of bacterial growth, the pH value of bacterial culture was increased. The minimum inhibitory concentration of Cu (II) to bacterial growth in solution was up to 130 mg/L. The bacterial culture could rapidly precipitate Cu (II) in solution through MIPP. The analysis results of Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS), Fourier Transform-Infrared Spectrometer (FTIR), and X-ray Diffraction (XRD) revealed that the precipitate form by bacterial culture was rod-shaped Cu3(OH)3PO4 crystal with a diameter of 10 µm. The bacterial culture decreased the content of DTPA-Cu of 83 mg/kg soil in the soil by 58.2%, 61.5% and 75.8% after 5, 10 and 30 days of incubation, respectively, at the temperature of 25 °C. The results indicate that MIPP-based bioremediation by Rahnella sp. LRP3 is a practical, environmental friendly technology for the cleaning-up of copper-contaminated soil.

Disruption of acdS gene reduces plant growth promotion activity and maize saline stress resistance by Rahnella aquatilis HX2.

Rahnella aquatilis HX2 was isolated from Beijing vineyard soil and used as a plant growth-promoting rhizobacterium in the field. Previous studies have shown that it has a broad in vitro antimicrobial spectrum and could inhibit a variety of plant pathogenic bacteria and fungi. In this study, a gene, acdS, encoding 1-aminocyclopropane-1-carboxylic acid-deaminase was disrupted by in-frame deletion in the HX2 strain. Compared to the wild-type, the acdS-mutant had higher rates of nitrogen fixation, reduced indole-3-acetic acid production, lowered efficacy as a biological control agent against the grape crown gall pathogen Agrobacterium vitis. Under saline stress conditions, plant height, above-ground fresh weight, root fresh weight of corn plants were increased by treatment with HX2 but this increase was compromised by the disruption of acdS gene. Our data confirmed the function of HX2 on plant growth promoting and demonstrated that acdS gene plays a major role in its PGPR activities.

The arbuscular mycorrhizal fungus Rhizophagus irregularis MUCL 43194 induces the gene expression of citrate synthase in the tricarboxylic acid cycle of the phosphate-solubilizing bacterium Rahnella aquatilis HX2.

An increasing number of studies have demonstrated that arbuscular mycorrhizal fungi can cooperate with other soil microorganisms, e.g., bacteria, which develop near or on the surface of the extraradical hyphae where they perform multiple functions. However, the mechanisms involved in this privileged relationship are still poorly known. In the present study, we investigated how the arbuscular mycorrhizal fungus Rhizophagus irregularis MUCL 43194 influences the three pace-making enzymes (i.e., citrate synthase, isocitrate dehydrogenase, and α-oxoglutarate dehydrogenase) of the tricarboxylic acid (TCA) cycle in the phosphate-solubilizing bacterium Rahnella aquatilis HX2. The study was conducted under strict in vitro culture conditions and analysis made at the transcriptional level. Results showed that R. irregularis induced the expression of the gene-encoding citrate synthase (gltA), the pace-making enzyme involved in the first step of the TCA cycle, in R. aquatilis at all time points of observation (i.e., 1, 6, 12, 24, 48, and 72 h). The expression of the gene-encoding isocitrate dehydrogenase (icd) significantly decreased at 6, 12, 24, 48, and 72 h and the expression of the gene-encoding α-oxoglutarate dehydrogenase E1 component (kgdhc) significantly increased at 1, 6, and 48 h. The above results suggested that R. irregularis may influence the level of adenosine triphosphate production in R. aquatilis and thus the metabolism of the bacterium by stimulating the expression of gltA involved in the TCA cycle. Our results suggest a fine-tuned dialog between R. irregularis MUCL 43194 and R. aquatilis HX2 and emphasize the complexity of the interactions that might take place at the hyphal surface of arbuscular mycorrhizal fungi hosting communities of microbes.

Signal beyond nutrient, fructose, exuded by an arbuscular mycorrhizal fungus triggers phytate mineralization by a phosphate solubilizing bacterium.

Cooperation is a prevalent phenomenon in nature and how it originates and maintains is a fundamental question in ecology. Many efforts have been made to understand cooperation between individuals in the same species, while the mechanisms enabling cooperation between different species are less understood. Here, we investigated under strict in vitro culture conditions if the exchange of carbon and phosphorus is pivotal to the cooperation between the arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis and the phosphate solubilizing bacterium (PSB) Rahnella aquatilis. We observed that fructose exuded by the AMF stimulated the expression of phosphatase genes in the bacterium as well as the rate of phosphatase release into the growth medium by regulating its protein secretory system. The phosphatase activity was subsequently increased, promoting the mineralization of organic phosphorus (i.e., phytate) into inorganic phosphorus, stimulating simultaneously the processes involved in phosphorus uptake by the AMF. Our results demonstrated for the first time that fructose not only is a carbon source, but also plays a role as a signal molecule triggering bacteria-mediated organic phosphorus mineralization processes. These results highlighted the molecular mechanisms by which the hyphal exudates play a role in maintaining the cooperation between AMF and bacteria.

The replication protein of pHW126 auto-controls its expression.

pHW126 belongs to a small group of rolling circle plasmids. So far, the region mediating autonomous replication has been identified and it was shown that the rep gene is required for replication. However, the regulation of rep expression remained elusive. Here evidence is presented that expression of the replication gene rep is auto-regulated. Sequence analysis revealed a conserved stretch in the rep promoter consisting of three imperfect direct repeats (DR2.1, DR2.2 and DR2.3). Assays for promoter activity showed that these direct repeats act as an enhancer of transcriptional activity. Interestingly, the activating effect was reduced in the presence of Rep protein. Electrophoretic mobility shift assays demonstrated that the Rep protein can directly bind to direct repeats DR2.1 and DR2.3 while DR2.2 is not bound but places DR2.1 and DR2.3 in an appropriate distance. These results show that the synthesis of Rep protein is auto-regulated. In the absence of Rep protein the promoter is, due to the presence of the direct repeats acting as a transcriptional enhancer, highly active. Binding of Rep to the direct repeats reduces the transcription rate significantly. Since this regulation mechanism is independent of a specialised regulator protein it is presumably a very economic strategy.

Rahnella sp. strain EK12: Cell surface properties and diesel oil biodegradation after long-term contact with natural surfactants and diesel oil.

The changes in cell surface properties of Rahnella sp. strain EK12 and modifications in genetic material after long-term contact with saponins and rhamnolipids, were investigated. Rhamnolipids caused a decrease of hydrophobicity in liquid cultures compared with saponins. On the other hand, in cultures with rhamnolipids, the addition of diesel oil results in a rapid rise of cell surface hydrophobicity. The similar effect was not so significant in the presence of saponins. For the bacteria grown in the presence of saponins or rhamnolipids, but without diesel oil, the ratio of unsaturated to saturated fatty acids decreased, in comparison to the control culture. The differences observed in hydrophobicity, zeta potential and fatty acids profiles, indicated various mechanisms of an interaction between a surfactant and a bacterial cells. The results have also shown an impact of the long-term contact on changes in genetic material of Rahnella sp. strain EK12 cells. Moreover, the presence of saponins led to significant increase of diesel oil biodegradation.

Inoculation of Lens culinaris with Pb-resistant bacteria shows potential for phytostabilization.

Phytoremediation comprises a set of plant and microbe-based technologies for remediation of soil heavy metal contamination. In this work, four Pb-resistant bacteria (Agrobacterium tumefaciens, Rahnella aquatilis, and two Pseudomonas sp.) were selected among a collection of isolates from root nodule of Lens culinaris. They had a high degree of bioaccumulation ability in nutrient medium containing 2 mM Pb, and the maximum Pb accumulation of whole cell was found after 48-h incubation. These Pb-resistant bacteria synthesized plant growth promoting substances such as indole acetic acid and siderophore. The presence of the Pb resistance genes (pbrA) in these bacteria has been confirmed by PCR. L. culinaris cultivated in two experimental soils with different levels of contamination showed that Pb contamination affected plant growth; therefore, it's co-inoculation with the consortium of Pb-resistant bacteria improved plant biomass. The present study demonstrated that lentil accumulated Pb primarily in their roots and poorly in their shoots; in addition, it's co-inoculation in moderately Pb-contaminated soil induced a reduction in Pb accumulation in roots and shoots by 22 and 80 %, respectively. Whereas in highly Pb-contaminated soil, we registered a diminution in concentration of Pb in shoots (66 %) and an augmentation in roots (21 %). The contamination of soil by Pb caused an oxidative stress in lentil plant, inducing modulation in antioxidant enzymes activities, essentially in superoxide dismutase (SOD) and peroxidase (GPOX) activities which were more pronounced in lentil cultivated in highly Pb-contaminated soil, in addition, co-inoculation enhanced these activities, suggesting the protective role of enzymatic antioxidant against Pb-induced plant stress.Thus, the present study demonstrated that co-inoculation of lentil with A. tumefaciens, R. aquatilis, and Pseudomonas sp. formed a symbiotic system useful for phytostabilization of highly and moderately Pb-contaminated soils.

Uncovering potential 'herbal probiotics' in Juzen-taiho-to through the study of associated bacterial populations.

Juzen-taiho-to (JTT) is an immune-boosting formulation of ten medicinal herbs. It is used clinically in East Asia to boost the human immune functions. The active factors in JTT have not been clarified. But, existing evidence suggests that lipopolysaccharide (LPS)-like factors contribute to the activity. To examine this possibility, JTT was subjected to a series of analyses, including high resolution mass spectrometry, which suggested the presence of structural variants of LPS. This finding opened a possibility that JTT contains immune-boosting bacteria. As the first step to characterize the bacteria in JTT, 16S ribosomal RNA sequencing was carried out for Angelica sinensis (dried root), one of the most potent immunostimulatory herbs in JTT. The sequencing revealed a total of 519 bacteria genera in A. sinensis. The most abundant genus was Rahnella, which is widely distributed in water and plants. The abundance of Rahnella appeared to correlate with the immunostimulatory activity of A. sinensis. In conclusion, the current study provided new pieces of evidence supporting the emerging theory of bacterial contribution in immune-boosting herbs.

Interactions of three soil bacteria species with phyllosilicate surfaces in hybrid silica gels.

To simulate iron consumption in soils, iron leaching from silicate minerals due to three heterotrophic bacterial strains and a chemical treatment was studied using hybrid silica gel (HSG) doped with two phyllosilicates, nontronite (NAu-2) or low-iron-content montmorillonite (SWy-2). HSG methodology, a novel way of separating bacteria cells from a colloidal mineral source, consisted in embedding colloidal mineral particles into an amorphous porous silica matrix using a classical sol-gel procedure. Pantoae agglomerans PA1 and Rahnella aquatilis RA1 were isolated from silicate-rich soils, that is, beech and wheat rhizospheres (Vosges, France); Burkholderia sp. G5 was selected from acidic and nutrient-poor podzol soils (Vosges, France). Fe release from clay minerals and production of bacterial metabolites, that is, low molecular weight organic acids (LMWOA) and siderophores, were monitored. Two LMWOA profiles were observed with major gluconate production (> 9000 µM) for Burkholderia sp. G5 and moderate production of lactate, acetate, propionate, formate, oxalate, citrate, and succinate (< 300 µM) for R. aquatilis RA1 and P. agglomerans PA1. HSG demonstrated its usefulness in revealing clay mineral-microorganisms interactions. The effect of bacterial exsudates was clearly separated from physical contact effect.

Bioweathering of nontronite colloids in hybrid silica gel: implications for iron mobilization.

AIMS: This study aimed to study biotic iron dissolution using a new hybrid material constituted of well-dispersed mineral colloids in a silica gel matrix. This permitted to prevent adsorption of colloidal mineral particles on bacteria. Hybrid silica gel (HSG) permitted to study bioweathering mechanisms by diffusing molecules. METHODS AND RESULTS: Hybrid silica gel was synthesized through a classical sol-gel procedure in which mineral colloidal particles (NAu-2) were embedded in a porous silica matrix. Rahnella aquatilis RA1, isolated from a wheat rhizosphere was chosen for its ability to dissolve minerals by producing various organic acids and siderophores. Pyruvic, acetic and lactic acids were the major organic acids produced by R. aquatilis RA1 followed by oxalic and citric acids at the end of incubation. Comparison of abiotic and biotic experiments revealed a high efficiency of R. aquatilis RA1 for iron dissolution suggesting an optimized action of different ligands that solubilized or mobilized iron. CONCLUSIONS: Hybrid silica gel allowed focusing on the colloidal mineral weathering by metabolites diffusion without mineral adsorption on bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: Hybrid silica gels are new and efficient tools to study colloidal mineral bioweathering. Adjusting HSG porosity and hydrophobicity should permit to precise the influence of limiting diffusion of siderophores or aliphatic organic acids on mineral weathering.

Enhancement of Cd phytoextraction by two Amaranthus species with endophytic Rahnella sp. JN27.

Microbe-assisted phytoextraction shows a potential for the remediation of metal-contaminated soils. The aim of this study was to isolate, characterize, and evaluate the potential of endophytic bacteria in improving plant growth and metal uptake by Cd-hyperaccumulators-Amaranthus hypochondriacus and Amaranthus mangostanus. An endophytic bacterial strain JN27 isolated from roots of Zea mays displayed high tolerance and mobilization to Cd, and was identified as Rahnella sp. based on 16S rDNA sequencing. The strain also exhibited multiple plant growth beneficial features including the production of indole-3-acetic acid, siderophore, 1-aminocyclopropane-1-carboxylic acid deaminase and solubilization of insoluble phosphate. Subsequently, a pot trial was performed to elucidate the effects of inoculation with JN27 on plant growth and Cd uptake by A. hypochondriacus, A. mangostanus, Solanum nigrum and Z. mays grown in soils with different levels of Cd (25, 50, 100 mg Cd kg(-1)). The results revealed that inoculation with JN27 significantly increased the biomasses of all the tested plants and the Cd concentrations of all the tested plants except Z. mays in both above-ground and root tissues. Moreover, strain JN27 could successfully re-colonized in rhizosphere soils of all the tested plants and root interior of A. hypochondriacus and Z. mays. The present results indicated that the symbiont of A. hypochondriacus (or A. mangostanus) and strain JN27 can effectively improve the Cd uptake by plants and would be a new strategy in microbe-assisted phytoextraction for metal-contaminated soils.

Exploring metal effects and synergistic interactions of ferric stimulation on azo-dye decolorization by new indigenous Acinetobacter guillouiae Ax-9 and Rahnella aquatilis DX2b.

The first-attempt study deciphered metal-interacting effects on dye-decolorizing capabilities of indigenous bioelectricity-generating strains, Acinetobacter guillouiae Ax-9 and Rahnella aquatilis DX2b. Most of the metallic ions were inhibitory to color removal capabilities of these strains. However, with supplementation of 5 mM ferric chloride, specific decolorization rate (SDR) of Ax-9 increased by 55.48% compared to Fe(3+)-free conditions. In contrast, SDR of DX2b decreased 75.35% due to the inhibition of ferric chloride. On the other hand, ferric citrate could stimulate SDR of DX2b for 21.5% at same dosage. Enzymatic assay indicated that Fe reductase activity was consistent with synergistic effects of ferric chloride on Ax-9, and ferric citrate on DX2b. Protein analysis via SDS-PAGE and identification of Tandem MS/MS afterwards showed that outer membrane protein (Omp) primarily deals with decolorization as a channeling regulation. Moreover, molecular modeling and bioinformatics data also provided detailed evidences to confirm the biological significance of Omp.