Absence of Nanoparticle-Induced Drought Tolerance in Nutrient Sufficient Wheat Seedlings.

Strategies to reduce crop losses due to drought are needed as climate variability affects agricultural productivity. Wheat (Triticum aestivum var. Juniper) growth in a nutrient-sufficient, solid growth matrix containing varied doses of CuO, ZnO, and SiO2 nanoparticles (NPs) was used to evaluate NP mitigation of drought stress. NP amendments were at fertilizer levels, with maxima of 30 Cu, 20 Zn, and 200 Si (mg metal/kg matrix). Seeds of this drought-tolerant cultivar were inoculated with Pseudomonas chlororaphis O6 (PcO6) to provide a protective root microbiome. An 8 day drought imposed on 14 day-old wheat seedlings decreased shoot and root mass, shoot water content, and the quantum yield of photosystem II when compared to watered plants. PcO6 root colonization was not impaired by drought or NPs. A dose-dependent increase in the Cu, Zn, and Si from the NPs was observed from analysis of the rhizosphere solution, and this process was not affected by drought. Consequently, fertilizer concentrations of the NPs did not further improve drought tolerance in wheat seedlings under the growth conditions of adequate mineral nutrition and the presence of a beneficial microbiome. These findings suggest that potential NP benefits in promoting plant drought tolerance occur only under certain environmental conditions.

Retrieved 16S rRNA and nifH sequences reveal co-dominance of Bradyrhizobium and Ensifer (Sinorhizobium) strains in field-collected root nodules of the promiscuous host Vigna radiata (L.) R. Wilczek.

In the present study, the relative distribution of endophytic rhizobia in field-collected root nodules of the promiscuous host mung bean was investigated by sequencing of 16S ribosomal RNA (rRNA) and nifH genes, amplified directly from the nodule DNA. Co-dominance of the genera Bradyrhizobium and Ensifer was indicated by 32.05 and 35.84% of the total retrieved 16S rRNA sequences, respectively, and the sequences of genera Mesorhizobium and Rhizobium comprised only 0.06 and 2.06% of the recovered sequences, respectively. Sequences amplified from rhizosphere soil DNA indicated that only a minor fraction originated from Bradyrhizobium and Ensifer strains, comprising about 0.46 and 0.67% of the total retrieved sequences, respectively. 16S rRNA gene sequencing has also identified the presence of several non-rhizobial endophytes from phyla Proteobacteria, Actinobacteria, Bacteroides, and Firmicutes. The nifH sequences obtained from nodules also confirmed the co-dominance of Bradyrhizobium (39.21%) and Ensifer (59.23%) strains. The nifH sequences of the genus Rhizobium were absent, and those of genus Mesorhizobium comprised only a minor fraction of the sequences recovered from the nodules and rhizosphere soil samples. Two bacterial isolates, identified by 16S rRNA gene sequence analysis as Bradyrhizobium strain Vr51 and Ensifer strain Vr38, successfully nodulated the original host (mung bean) plants. Co-dominance of Bradyrhizobium and Ensifer strains in the nodules of mung bean indicates the potential role of the host plant in selecting specific endophytic rhizobial populations. Furthermore, successful nodulation of mung bean by the isolates showed that strains of both the genera Bradyrhizobium and Ensifer can be used for production of inoculum.

New Arsenate Reductase Gene (arrA) PCR Primers for Diversity Assessment and Quantification in Environmental Samples.

The extent of arsenic contamination in drinking water and its potential threat to human health have resulted in considerable research interest in the microbial species responsible for arsenic reduction. The arsenate reductase gene (arrA), an important component of the microbial arsenate reduction system, has been widely used as a biomarker to study arsenate-reducing microorganisms. A new primer pair was designed and evaluated for quantitative PCR (qPCR) and high-throughput sequencing of the arrA gene, because currently available PCR primers are not suitable for these applications. The primers were evaluated in silico and empirically tested for amplification of arrA genes in clones and for amplification and high-throughput sequencing of arrA genes from soil and groundwater samples. In silico, this primer pair matched (≥90% DNA identity) 86% of arrA gene sequences from GenBank. Empirical evaluation showed successful amplification of arrA gene clones of diverse phylogenetic groups, as well as amplification and high-throughput sequencing of independent soil and groundwater samples without preenrichment, suggesting that these primers are highly specific and can amplify a broad diversity of arrA genes. The arrA gene diversity from soil and groundwater samples from the Cache Valley Basin (CVB) in Utah was greater than anticipated. We observed a significant correlation between arrA gene abundance, quantified through qPCR, and reduced arsenic (AsIII) concentrations in the groundwater samples. Furthermore, we demonstrated that these primers can be useful for studying the diversity of arsenate-reducing microbial communities and the ways in which their relative abundance in groundwater may be associated with different groundwater quality parameters. IMPORTANCE: Arsenic is a major drinking water contaminant that threatens the health of millions of people worldwide. The extent of arsenic contamination and its potential threat to human health have resulted in considerable interest in the study of microbial species responsible for the reduction of arsenic, i.e., the conversion of AsV to AsIII In this study, we developed a new primer pair to evaluate the diversity and abundance of arsenate-reducing microorganisms in soil and groundwater samples from the CVB in Utah. We observed significant arrA gene diversity in the CVB soil and groundwater samples, and arrA gene abundance was significantly correlated with the reduced arsenic (AsIII) concentrations in the groundwater samples. We think that these primers are useful for studying the ecology of arsenate-reducing microorganisms in different environments.

Dehalococcoides and general bacterial ecology of differentially trichloroethene dechlorinating flow-through columns.

The diversity of Dehalococcoides mccartyi (Dhc) and/or other organohalide respiring or associated microorganisms in parallel, partial, or complete trichloroethene (TCE) dehalogenating systems has not been well described. The composition of Dhc populations and the associated bacterial community that developed over 7.5 years in the top layer (0-10 cm) of eight TCE-fed columns were examined using pyrosequencing. Columns biostimulated with one of three carbon sources, along with non-stimulated controls, developed into complete (ethene production, whey amended), partial (cis-dichloroethene (DCE) and VC, an emulsified oil with nonionic surfactant), limited (<5 % cis-DCE and 95 % TCE, an emulsified oil), and non- (controls) TCE dehalogenating systems. Bioaugmentation of one column of each treatment with Bachman Road enrichment culture did not change Dhc populations nor the eventual degree of TCE dehalogenation. Pyrosequencing revealed high diversity among Dhc strains. There were 13 OTUs that were represented by more than 1000 sequences each. Cornell group-related populations dominated in complete TCE dehalogenating columns, while Pinellas group related Dhc dominated in all other treatments. General microbial communities varied with biostimulation, and three distinct microbial communities were established: one each for whey, oils, and control treatments. Bacterial genera, including Dehalobacter, Desulfitobacterium, Sulfurospirillum, Desulfuromonas, and Geobacter, all capable of partial TCE dehalogenation, were abundant in the limited and partial TCE dehalogenating systems. Dhc strain diversity was wider than previously reported and their composition within the community varied significantly depending on the nature of the carbon source applied and/or changes in the Dhc associated partners that fostered different biogeochemical conditions across the columns.

Ag nanoparticles generated using bio-reduction and -coating cause microbial killing without cell lysis.

Cost-effective "green" methods of producing Ag nanoparticles (NPs) are being examined because of the potential of these NPs as antimicrobials. Ag NPs were generated from Ag ions using extracellular metabolites from a soil-borne Pythium species. The NPs were variable in size, but had one dimension less than 50 nm and were biocoated; aggregation and coating changed with acetone precipitation. They had dose-dependent lethal effects on a soil pseudomonad, Pseudomonas chlororaphis O6, and were about 30-fold more effective than Ag(+) ions. A role of reactive oxygen species in cell death was demonstrated by use of fluorescent dyes responsive to superoxide anion and peroxide accumulation. Also mutants of the pseudomonad, defective in enzymes that protect against oxidative stress, were more sensitive than the wild type strain; mutant sensitivity differed between exposure to Ag NPs and Ag(+) ions demonstrating a nano-effect. Imaging of bacterial cells treated with the biocoated Ag NPs revealed no cell lysis, but there were changes in surface properties and cell height. These findings support that biocoating the NPs results in limited Ag release and yet they retained potent antimicrobial activity.

Dehalococcoides abundance and alternate electron acceptor effects on large, flow-through trichloroethene dechlorinating columns.

Trichloroethene (TCE) in groundwater is a major health concern and biostimulation/bioaugmentation-based strategies have been evaluated to achieve complete reductive dechlorination with varying success. Different carbon sources were hypothesized to stimulate different extents of TCE reductive dechlorination. Ecological conditions that developed different dechlorination stages were investigated by quantitating Dehalococcoides 16S rRNA (Dhc) and reductive dehalogenase gene abundance, and by describing biogeochemical properties of laboratory columns in response to this biostimulation. Eight large columns (183 cm × 15.2 cm), packed with aquifer material from Hill AFB, Utah, that were continuously fed TCE for 7.5 years. Duplicate columns were biostimulated with whey or one of two different Newman Zone® emulsified oil formulations containing either nonionic surfactant (EOLN) or standard surfactant (EOL). Two columns were non-stimulated controls. Complete (whey amended), partial (EOLN amended), limited (EOL), and non-TCE dehalogenating systems (controls) developed over the course of the study. Bioaugmentation of half of the columns with Bachman Road culture 3 years prior to dismantling did not influence the extent of TCE dehalogenation. Multivariate analysis clustered samples by biostimulation treatments and extent of TCE dehalogenation. Dhc, tceA, and bvcA gene concentrations did not show a consistent relationship with TCE dehalogenation but the vcrA gene was more abundant in completely dehalogenating, whey-treated columns. The whey columns developed strongly reducing conditions producing Fe(II), sulfide, and methane. Biostimulation with different carbon and energy sources can support high concentrations of diverse Dhc, but carbon addition has a major influence on biogeochemical processes effecting the extent of TCE dehalogenation.

Bioaccumulation of copper, lead, and zinc in six macrophyte species grown in simulated stormwater bioretention systems.

Stormwater bioretention (BR) systems collect runoff containing heavy metals, which can concentrate in soil environments and potentially leach into groundwater. This greenhouse experiment evaluated differences among six plant species undergoing three varying hydraulic and pollutant loads in their bioaccumulation potential when subjected to continual application of low metal concentrations as a means of preventing copper, lead, and zinc accumulation in the BR soil. Results show that >92% of metal mass applied to the treatments via synthetic stormwater was removed from the exfiltrate within 27 cm of soil depth. Compacted soil conditions of unplanted controls retained significantly more Cu, Pb, and Zn than Carex praegracilis, and Carex microptera treatments. Differences in above and below ground plant tissue concentrations differed among species, resulting in significant differences in mass accumulation. In the above ground tissue, from highest to lowest, Phragmites australis accumulated 8 times more Cu than Scirpus acutus, and C. microptera accumulated 18 times more Pb, and 6 times more Zn than Scirpus validus. These results, and differences among species in mass distribution of the metals recovered at the end of the study, reveal various metal accumulation mechanisms.

The phytotoxicity of ZnO nanoparticles on wheat varies with soil properties.

Zn is an essential element for plants yet some soils are Zn-deficient and/or have low Zn-bioavailability. This paper addresses the feasibility of using ZnO nanoparticles (NPs) as soil amendments to improve Zn levels in the plant. The effects of soil properties on phytotoxicity and Zn bioavailability from the NPs were studied by using an acidic and a calcareous alkaline soil. In the acid soil, the ZnO NPs caused dose-dependent phytotoxicity, observed as inhibition of elongation of roots of wheat, Triticum aestivum. Phytotoxicity was mitigated in the calcareous alkaline soil although uptake of Zn from the ZnO NPs occurred doubling the Zn level compared to control plants. This increase occurred with a low level of Zn in the soil solution as expected from the interactions of Zn with the soil components at the alkaline pH. Soluble Zn in the acid soil was 200-fold higher and shoot levels were tenfold higher than from the alkaline soil correlating with phytotoxicity. Mitigation of toxicity was not observed in plants grown in sand amended with a commercial preparation of humic acid: growth, shoot uptake and solubility of Zn from the NPs was not altered by the humic acid. Thus, variation in humic acid between soils may not be a major factor influencing plant responses to the NPs. These findings illustrate that formulations of ZnO NPs to be used as a soil amendment would need to be tuned to soil properties to avoid phytotoxicity yet provide increased Zn accumulations in the plant.

Nano-CuO and interaction with nano-ZnO or soil bacterium provide evidence for the interference of nanoparticles in metal nutrition of plants.

The expansion of nanotechnology raises concerns about the consequences of nanomaterials in plants. Here, the effects of nanoparticles (NPs; 100-500 mg/kg) on processes related to micronutrient accumulation were evaluated in bean (Phaseolus vulgaris) exposed to CuO NPs, a mixture of CuO and ZnO (CuO:ZnO) NPs, and in CuO NP-exposed plants colonized by a root bacterium, Pseudomonas chlororaphis O6 (PcO6) in a sand matrix for 7 days. Depending on exposure levels, the inhibition of growth by CuO NPs was more apparent in roots (10-66 %) than shoots (9-25 %). In contrast, CuO:ZnO NPs or root colonization with PcO6 partially mitigated growth inhibition. At 500 mg/kg exposure, CuO NPs increased soluble Cu in the growth matrix by 23-fold, relative to the control, while CuO:ZnO NPs increased soluble Cu (26-fold), Zn (127-fold) and Ca (4.5-fold), but reduced levels of Fe (0.8-fold) and Mn (0.75-fold). Shoot accumulations of Cu (3.8-fold) and Na (1-fold) increased, while those of Fe (0.4-fold), Mn (0.2-fold), Zn (0.5-fold) and Ca (0.5-fold) were reduced with CuO NP (500 mg/kg) exposure. CuO:ZnO NPs also increased shoot Cu, Zn and Na levels, while decreasing that of Fe, Mn, Ca and Mg. Root colonization reduced shoot uptake of Cu and Na, 15 and 24 %, respectively. CuO NPs inhibited ferric reductase (up to 49 %) but stimulated cupric (up to 273 %) reductase activity; while CuO:ZnO NPs or root colonization by PcO6 altered levels of ferric, but not copper reductase activity, relative to CuO NPs. Cu ions at the level released from the NPs did not duplicate these effects. Our findings demonstrate that in addition to the apparent phytotoxic effects of NPs, NP exposure may also have subtle impacts on secondary processes such as metal nutrition.

Arsenic(V) reduction in relation to Iron(III) transformation and molecular characterization of the structural and functional microbial community in sediments of a basin-fill aquifer in Northern Utah.

Basin-fill aquifers of the Southwestern United States are associated with elevated concentrations of arsenic (As) in groundwater. Many private domestic wells in the Cache Valley Basin, UT, have As concentrations in excess of the U.S. EPA drinking water limit. Thirteen sediment cores were collected from the center of the valley at the depth of the shallow groundwater and were sectioned into layers based on redoxmorphic features. Three of the layers, two from redox transition zones and one from a depletion zone, were used to establish microcosms. Microcosms were treated with groundwater (GW) or groundwater plus glucose (GW+G) to investigate the extent of As reduction in relation to iron (Fe) transformation and characterize the microbial community structure and function by sequencing 16S rRNA and arsenate dissimilatory reductase (arrA) genes. Under the carbon-limited conditions of the GW treatment, As reduction was independent of Fe reduction, despite the abundance of sequences related to Geobacter and Shewanella, genera that include a variety of dissimilatory iron-reducing bacteria. The addition of glucose, an electron donor and carbon source, caused substantial shifts toward domination of the bacterial community by Clostridium-related organisms, and As reduction was correlated with Fe reduction for the sediments from the redox transition zone. The arrA gene sequencing from microcosms at day 54 of incubation showed the presence of 14 unique phylotypes, none of which were related to any previously described arrA gene sequence, suggesting a unique community of dissimilatory arsenate-respiring bacteria in the Cache Valley Basin.

Silver nanoparticles disrupt wheat (Triticum aestivum L.) growth in a sand matrix.

Hydroponic plant growth studies indicate that silver nanoparticles (Ag NPs) are phytotoxic. In this work, the phytotoxicity of commercial Ag NPs (10 nm) was evaluated in a sand growth matrix. Both NPs and soluble Ag were recovered from water extracts of the sand after growth of plants challenged with the commercial product; the surface charge of the Ag NPs in this extract was slightly reduced compared to the stock NPs. The Ag NPs reduced the length of shoots and roots of wheat in a dose-dependent manner. Furthermore, 2.5 mg/kg of the NPs increased branching in the roots of wheat (Triticum aestivum L.), thereby affecting plant biomass. Micron-sized (bulk) Ag particles (2.5 mg/kg) as well as Ag ions (63 µg Ag/kg) equivalent to the amount of soluble Ag in planted sand with Ag NPs (2.5 mg/kg) did not affect plant growth compared to control. In contrast, higher levels of Ag ions (2.5 mg/kg) reduced plant growth to a similar extent as the Ag NPs. Accumulation of Ag was detected in the shoots, indicating an uptake and transport of the metal from the Ag NPs in the sand. Transmision electron microscopy indicated that Ag NPs were present in shoots of plants with roots exposed to the Ag NPs or high levels of Ag ions. Both of these treatments caused oxidative stress in roots, as indicated by accumulation of oxidized glutathione, and induced expression of a gene encoding a metallothionein involved in detoxification by metal ion sequestration. Our findings demonstrate the potential effects of environmental contamination by Ag NPs on the metabolism and growth of food crops in a solid matrix.

Fate of CuO and ZnO nano- and microparticles in the plant environment.

The environmental fate of metal oxide particles as a function of size was assessed by comparing the behavior of CuO or ZnO nanoparticles (NPs) to that of the corresponding microparticles (MPs) in a sand matrix, with and without wheat (Triticum aestivum L.) growth. After 14 days of incubation in the planted sand, the CuO and ZnO NPs were increased from their nominal sizes of <50 nm and <100 nm, to ~317 nm and ~483 nm, respectively. Accordingly, the negative surface charge of colloids present in aqueous extracts from the sand amended with CuO (-27.0 mV) and ZnO (-10.0 mV) NPs was reduced by the presence of plants, to -19.8 mV and -6.0 mV, respectively. The surface charge of the MPs was not influenced by plants. Plant growth increased dissolution of NPs and MPs of both metal oxides in the sand from <0.3 mg/kg to about 1.0 mg/kg for the CuO products, and from ≤0.6 mg/kg to between 1.0 and 2.2 mg/kg for the Zn products. The NP or MP products reduced wheat root length by ~60% or ~50% from control levels; CuO was more toxic than ZnO. X-ray absorption spectroscopy (XAS) analysis showed that treatments with MPs or NPs of ZnO led to similar accumulations of Zn-phosphate species in the shoots, likely from dissolution of ZnO. Exposure to CuO NPs or MPs resulted in similar XAS spectra for Cu in the shoots explained by plant accumulation of both CuO and Cu(I)-sulfur complexes. These findings demonstrate the similarities between commercial NPs and MPs of CuO or ZnO in wheat plants, with greater root toxicity correlating with smaller particle size. Factors from the sand and the plant modified the aggregation or dissolution of both types of particles, thus, influencing their environmental fates.

Antifungal activity of ZnO nanoparticles and their interactive effect with a biocontrol bacterium on growth antagonism of the plant pathogen Fusarium graminearum.

Fungal plant pathogens such as Fusarium graminearum cause severe global economic losses in cereals crops, and current control measures are limited. This work addresses the potential for ZnO nanoparticles (NPs) and biocontrol bacteria to be used in plant fungal control strategies. Growth of F. graminearum was significantly (p = 0.05) inhibited by inclusion of the NPs in a mung bean broth agar and in sand. Suspension in mung bean broth medium modified the surface charge, dissolution, and aggregation state of the ZnO NPs, in comparison to processes occurring in water suspension. The ZnO NPs were significantly more inhibitory to fungal growth than micro-sized particles of ZnO, although both types of particles released similar levels of soluble Zn, indicating size-dependent toxicity of the particles. Zn ions produced dose-dependent inhibition, noticeable at the level of soluble Zn released from NPs after seven-day suspension in medium; inhibitory levels caused acidification of the growth medium. Transfer of fungal inoculum after exposure to the ZnO NPs to fresh medium did not indicate adaptation to the stress because growth was still inhibited by the NPs. The ZnO NPs did not prevent metabolites from a biocontrol bacterium, Pseudomonas chlororaphis O6, from inhibiting Fusarium growth: no synergism was observed in the mung bean agar. Because other studies find that soil amendment with ZnO NPs required high doses for inhibition of plant growth, the findings of pathogen growth control reported in this paper open the possibility of using ZnO NP-based formulations to complement existing strategies for improving crop health in field settings.

Changes in Metal-Chelating Metabolites Induced by Drought and a Root Microbiome in Wheat.

The essential metals Cu, Zn, and Fe are involved in many activities required for normal and stress responses in plants and their microbiomes. This paper focuses on how drought and microbial root colonization influence shoot and rhizosphere metabolites with metal-chelation properties. Wheat seedlings, with and without a pseudomonad microbiome, were grown with normal watering or under water-deficit conditions. At harvest, metal-chelating metabolites (amino acids, low molecular weight organic acids (LMWOAs), phenolic acids, and the wheat siderophore) were assessed in shoots and rhizosphere solutions. Shoots accumulated amino acids with drought, but metabolites changed little due to microbial colonization, whereas the active microbiome generally reduced the metabolites in the rhizosphere solutions, a possible factor in the biocontrol of pathogen growth. Geochemical modeling with the rhizosphere metabolites predicted Fe formed Fe-Ca-gluconates, Zn was mainly present as ions, and Cu was chelated with the siderophore 2'-deoxymugineic acid, LMWOAs, and amino acids. Thus, changes in shoot and rhizosphere metabolites caused by drought and microbial root colonization have potential impacts on plant vigor and metal bioavailability.

Production of indole-3-acetic acid via the indole-3-acetamide pathway in the plant-beneficial bacterium Pseudomonas chlororaphis O6 is inhibited by ZnO nanoparticles but enhanced by CuO nanoparticles.

The beneficial bacterium Pseudomonas chlororaphis O6 produces indole-3-acetic acid (IAA), a plant growth regulator. However, the pathway involved in IAA production in this bacterium has not been reported. In this paper we describe the involvement of the indole-3-acetamide (IAM) pathway in IAA production in P. chlororaphis O6 and the effects of CuO and ZnO nanoparticles (NPs). Sublethal levels of CuO and ZnO NPs differentially affected the levels of IAA secreted in medium containing tryptophan as the precursor. After 15 h of growth, CuO NP-exposed cells had metabolized more tryptophan than the control and ZnO NP-challenged cells. The CuO NP-treated cells produced higher IAA levels than control cultures lacking NPs. In contrast, ZnO NPs inhibited IAA production. Mixing of CuO and ZnO NPs resulted in an intermediate level of IAA production relative to the levels in the separate CuO and ZnO NP treatments. The effect of CuO NPs on IAA levels could be duplicated by ions at the concentrations released from the NPs. However, ion release did not account for the inhibition caused by the ZnO NPs. The mechanism underlying changes in IAA levels cannot be accounted for by effects on transcript accumulation from genes encoding a tryptophan permease or the IAM hydrolase in 15-h cultures. These findings raise the issue of whether sublethal doses of NPs would modify the beneficial effects of association between plants and bacteria.

Nanospecific inhibition of pyoverdine siderophore production in Pseudomonas chlororaphis O6 by CuO nanoparticles.

CuO nanoparticles (NPs) exhibit dose-dependent toxicity to bacteria, whereas sublethal concentrations of these NPs change bacterial metabolism. Siderophores are model metabolites to study the impact of sublethal levels of metallic NPs on bacteria because they are involved in survival and interaction with other organisms and with metals. We report that a sublethal level of CuO NPs modify the production of the fluorescent siderophore pyoverdine (PVD) in a soil beneficial bacterium, Pseudomonas chlororaphis O6. The production of PVD was inhibited by CuO NPs but not by bulk CuO nor Cu ions at concentrations equivalent to those released from the NPs. The cell responses occurred despite the NPs forming near micrometer-sized aggregates. The CuO NPs reduced levels of periplasmic and secreted PVD and impaired expression from genes encoding proteins involved in PVD maturation in the periplasm and export through cell membranes. EDTA restored the fluorescence of PVD quenched by Cu ions but did not generate fluorescence with cultures of NP-challenged cells, confirming the absence of PVD. Consequently, depending on the bacterium, this nanoparticle-specific phenomenon mediating cellular reprogramming through effects on secondary metabolism could have an impact on critical environmental processes including bacterial pathogenicity.

Cost-benefit analysis of nanofertilizers and nanopesticides emphasizes the need to improve the efficiency of nanoformulations for widescale adoption.

Nanotechnology-based approaches have demonstrated encouraging results for sustainable agriculture production, particularly in the field of fertilizers and pesticide innovation. It is essential to evaluate the economic and environmental benefits of these nanoformulations. Here we estimate the potential revenue gain/loss associated with nanofertilizer and/or nanopesticide use, calculate the greenhouse gas emissions change from the use of nanofertilizer and identify feasible applications and critical issues. The cost-benefit analysis demonstrates that, while current nanoformulations show promise in increasing the net revenue from crops and lowering the environmental impact, further improving the efficiency of nanoformulations is necessary for their widescale adoption. Innovating nanoformulation for targeted delivery, lowering the greenhouse gas emissions associated with nanomaterials and minimizing the content of nanomaterials in the derived nanofertilizers or pesticides can substantially improve both economic and environmental benefits.

Illumina sequencing of 16S rRNA tag shows disparity in rhizobial and non-rhizobial diversity associated with root nodules of mung bean (Vigna radiata L.) growing in different habitats in Pakistan.

In Rhizobium-legume symbiosis, the nodule is the most frequently studied compartment, where the endophytic/symbiotic microbiota demands critical investigation for development of specific inocula. We identified the bacterial diversity within root nodules of mung bean from different growing areas of Pakistan using Illumina sequencing of 16S rRNA gene. We observed specific OTUs related to specific site where Bradyrhizobium was found to be the dominant genus comprising of 82-94% of total rhizobia in nodules with very minor fraction of sequences from other rhizobia at three sites. In contrast, Ensifer (Sinorhizobium) was single dominant genus comprising 99.9% of total rhizobial sequences at site four. Among non-rhizobial sequences, the genus Acinetobacter was abundant (7-18% of total sequences), particularly in Bradyrhizobium-dominated nodule samples. Rhizobia and non-rhizobial PGPR isolated from nodule samples include Ensifer, Bradyrhizobium, Acinetobacter, Microbacterium and Pseudomonas strains. Co-inoculation of multi-trait PGPR Acinetobacter sp. VrB1 with either of the two rhizobia in field exhibited more positive effect on nodulation and plant growth than single-strain inoculation which favors the use of Acinetobacter as an essential component for development of mung bean inoculum. Furthermore, site-specific dominance of rhizobia and non-rhizobia revealed in this study may contribute towards decision making for development and application of specific inocula in different habitats.

CuO and ZnO Nanoparticles Modify Interkingdom Cell Signaling Processes Relevant to Crop Production.

As the world population increases, strategies for sustainable agriculture are needed to fulfill the global need for plants for food and other commercial products. Nanoparticle formulations are likely to be part of the developing strategies. CuO and ZnO nanoparticles (NPs) offer potential as fertilizers, as they provide bioavailable essential metals, and as pesticides, because of dose-dependent toxicity. Effects of these metal oxide NPs on rhizosphere functions are the focus of this review. These NPs at doses of ≥10 mg metal/kg change the production of key metabolites involved in plant protection in a root-associated microbe, Pseudomonas chlororaphis O6. Altered synthesis occurs in the microbe for phenazines, which function in plant resistance to pathogens, the pyoverdine-like siderophore that enhances Fe bioavailability in the rhizosphere and indole-3-acetic acid affecting plant growth. In wheat seedlings, reprogramming of root morphology involves increases in root hair proliferation (CuO NPs) and lateral root formation (ZnO NPs). Systemic changes in wheat shoot gene expression point to altered regulation for metal stress resilience as well as the potential for enhanced survival under stress commonly encountered in the field. These responses to the NPs cross kingdoms involving the bacteria, fungi, and plants in the rhizosphere. Our challenge is to learn how to understand the value of these potential changes and successfully formulate the NPs for optimal activity in the rhizosphere of crop plants. These formulations may be integrated into developing practices to ensure the sustainability of crop production.

Biofilms Benefiting Plants Exposed to ZnO and CuO Nanoparticles Studied with a Root-Mimetic Hollow Fiber Membrane.

Plants exist with a consortium of microbes that influence plant health, including responses to biotic and abiotic stress. While nanoparticle (NP)-plant interactions are increasingly studied, the effect of NPs on the plant microbiome is less researched. Here a root-mimetic hollow fiber membrane (HFM) is presented for generating biofilms of plant-associated microbes nurtured by artificial root exudates (AREs) to correlate exudate composition with biofilm formation and response to NPs. Two microbial isolates from field-grown wheat, a bacillus endophyte and a pseudomonad root surface colonizer, were examined on HFMs fed with AREs varying in N and C composition. Bacterial morphology and biofilm architecture were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM) and responses to CuO and ZnO NP challenges of 300 mg/L evaluated. The bacillus isolate sparsely colonized the HFM. In contrast, the pseudomonad formed robust biofilms within 3 days. Dependent on nutrient sources, the biofilm cells produced extensive extracellular polymeric substances (EPS) and large intracellular granules. Pseudomonad biofilms were minimally affected by ZnO NPs. CuO NPs, when introduced before biofilm maturation, strongly reduced biofilm formation. The findings demonstrate the utility of the HFM root-mimetic to study rhizoexudate influence on biofilms of root-colonizing microbes but without active plant metabolism. The results will allow better understanding of how microbe-rhizoexudate-NP interactions affect microbial and plant health.