Cadmium-resistant rhizobacterium Bacillus cereus M4 promotes the growth and reduces cadmium accumulation in rice (Oryza sativa L.)

Adsorption mechanism of Cd2+ on microbial inoculant and its potential for remediation Cd-polluted farmland soils

The adsorption characteristics and mechanism of Cd2+ on microbial inoculant (MI) mainly composed of Bacillus subtilis, Bacillus thuringiensis and Bacillus amyloliquefaciens, and its potential for remediation Cd polluted soils through batch adsorption and soil incubation experiments. It was found that the Freundlich isotherm model and the pseudo-second-order kinetics were more in line with the adsorption processes of Cd2+. The maximum adsorption capacity predicted by Langmuir isotherm model suggested that of MI was 57.38 mg g-1. Scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) images exhibited the surface structure of MI was damaged to varying degrees after adsorption, and Cd element was distributed on the surface of MI through ion exchange. X-ray diffraction (XRD) results showed that CdCO3 was formed on the surface of MI. Moreover, the functional groups (-OH, C-H, and -NH) involved in the adsorption of Cd2+ through fourier transform infrared spectroscopy (FTIR). After applying MI to Cd-contaminated soil, it was found that soil pH, conductivity (EC) and soil organic matter (SOM) increased by 0.84 %-2.43 %, 31.6 %-241.48 %, and 8.11 %-24.1 %, respectively, when compared with the control treatments. The content of DTPA-Cd in the soils was significantly (P < 0.05) reduced by 15.48 %-29.68 % in contrast with CK, and the Cd speciation was transformed into a more stable residual fraction. The activities of urease, phosphatase and sucrose were increased by 3.5 %-45.18 %, 57.00 %-134.18 % and 52.51 %-70.52 %, respectively, compared with CK. Therefore, MI could be used as an ecofriendly and sustainable material for bioremediation of Cd-contaminated soils.

Polyamine-producing bacteria inhibit the absorption of Cd by spinach and alter the bacterial community composition of rhizosphere soil

Polyamines (PAs) are small aliphatic nitrogenous bases with strong biological activity that participate in plant stress response signaling and the alleviation of damage from stress. Herein, the effects of the PA-producing bacterium Bacillus megaterium N3 and PAs on the immobilization of Cd and inhibition of Cd absorption by spinach and the underlying mechanisms were studied. A solution test showed that strain N3 secreted spermine and spermidine in the presence of Cd. Both strain N3 and the PAs (spermine+spermidine) immobilized Cd and increased the pH of the solution. Untargeted metabolomics results showed that strain N3 secreted PAs, N1-acetylspermidine, 3-indolepropionic acid, indole-3-acetaldehyde, cysteinyl-gamma-glutamate, and choline, which correlated with plant growth promotion and Cd immobilization. A pot experiment showed that rhizosphere soil inoculation with strain N3 and PAs improved spinach dry weight and reduced spinach Cd absorption compared with the control. These positive effects were likely due to the increase in rhizosphere soil pH and NH4+-N and PA contents, which can be attributed primarily to Cd immobilization. Moreover, inoculation with strain N3 more effectively inhibited the absorption of Cd by spinach than spraying PAs, mainly because strain N3 enabled a better relative abundance of bacteria (Microvirga, Pedobacter, Bacillus, Brevundimonas, Pseudomonas, Serratia, Devosid, and Aminobacter), that have been reported to have the ability to resist heavy metals and produce PAs. Strain N3 regulated the structure of rhizosphere functional bacterial communities and inhibited Cd uptake by spinach. These results provide a theoretical basis for the prevention of heavy metal absorption by vegetables using PA-producing bacteria.

Improving radish phosphorus utilization efficiency and inhibiting Cd and Pb uptake by using heavy metal-immobilizing and phosphate-solubilizing bacteria

Phosphate-solubilizing bacteria play a key role in increasing plant growth as potential suppliers of soluble phosphorus and have great potential for the remediation of heavy metal-polluted soils. However, the soil and microbiological mechanisms by which phosphate-solubilizing bacteria prevent heavy metal absorption in radish have not been adequately studied. Here, the mechanisms of phosphorus solubilization, Cd and Pb immobilization, and the inhibition of heavy metal absorption by phosphate-solubilizing bacteria were studied in radish through solution adsorption and pot experiments. Two phosphate-solubilizing bacteria with high Cd and Pb removal rates (46.9-97.12 %), Klebsiella sp. M2 and Kluyvera sp. M8, were isolated. The soluble phosphorus content released by strains M2 and M8 was 265-277 mg L^-1, achieved by secreting oxalic acid, ascorbic acid, citric acid, and succinic acid in an inorganic phosphorus medium containing 3 mg L^-1 Cd and 5 mg L^-1 Pb. Furthermore, these two functional strains induced the formation of Pb₂(PO₄)₂, Cd(PO₃)₂, Fe₂Pb₃(PO₄)₂, CdS, and PbS precipitates that immobilized Cd and Pb in the solution. In general, strains M2 and M8 inhibited the absorption of Cd and Pb by radish by the following mechanisms: i) bacterial cell wall adsorption, ii) induction of Pb₂(PO₄)₂, Cd(PO₃)₂, Fe₂Pb₃(PO₄)₂, CdS, and PbS precipitation in the solution/soil, iii) increases in the Ca₂P and FeP contents in the radish rhizosphere, and iv) the promotion of bacterial community enrichment toward phosphorus-solubilizing and plant growth-promoting properties (Ramlibacter, Enterobacter, Bacillus, Gemmatimonas, and Lysinibacillusin) in the radish rhizosphere. These results provide bacterial resources and technical approaches to heavy metal pollution amelioration and efficient phosphorus fertilizer use in farmland.

Cadmium-absorptive Bacillus vietnamensis 151-6 reduces the grain cadmium accumulation in rice (Oryza sativa L.): Potential for cadmium bioremediation

Microbial bioremediation of heavy metal-polluted soil is a promising technique for reducing heavy metal accumulation in crops. In a previous study, we isolated Bacillus vietnamensis strain 151-6 with a high cadmium (Cd) accumulation ability and low Cd resistance. However, the key gene responsible for the Cd absorption and bioremediation potential of this strain remains unclear. In this study, genes related to Cd absorption in B. vietnamensis 151-6 were overexpressed. A thiol-disulfide oxidoreductase gene (orf4108) and a cytochrome C biogenesis protein gene (orf4109) were found to play major roles in Cd absorption. In addition, the plant growth-promoting (PGP) traits of the strain were detected, which enabled phosphorus and potassium solubilization and indole-3-acetic acid (IAA) production. Bacillus vietnamensis 151-6 was used for the bioremediation of Cd-polluted paddy soil, and its effects on growth and Cd accumulation in rice were explored. The strain increased the panicle number (114.82%) and decreased the Cd content in rice rachises (23.87%) and grains (52.05%) under Cd stress, compared with non-inoculated rice in pot experiments. For field trials, compared with the non-inoculated control, the Cd content of grains inoculated with B. vietnamensis 151-6 was effectively decreased in two cultivars (low Cd-accumulating cultivar: 24.77%; high Cd-accumulating cultivar: 48.85%) of late rice. Bacillus vietnamensis 151-6 encoded key genes that confer the ability to bind Cd and reduce Cd stress in rice. Thus, B. vietnamensis 151-6 exhibits great application potential for Cd bioremediation.

A fungus (Trametes pubescens) resists cadmium toxicity by rewiring nitrogen metabolism and enhancing energy metabolism

As a primary goal, cadmium (Cd) is a heavy metal pollutant that is readily adsorbed and retained in rice, and it becomes a serious threat to food safety and human health. Fungi have attracted interest for their ability to remove heavy metals from the environment, although the underlying mechanisms of how fungi defend against Cd toxicity are still unclear. In this study, a Cd-resistant fungus Trametes pubescens (T. pubescens) was investigated. Pot experiments of rice seedlings colonized with T. pubescens showed that their coculture could significantly enhance rice seedling growth and reduce Cd accumulation in rice tissues. Furthermore, integrated transcriptomic and metabolomic analyses were used to explore how T. pubescens would reprogram its metabolic network against reactive oxygen species (ROS) caused by Cd toxicity. Based on multi-omic data mining results, we postulated that under Cd stress, T. pubescens was able to upregulate both the mitogen-activated protein kinase (MAPK) and phosphatidylinositol signaling pathways, which enhanced the nitrogen flow from amino acids metabolism through glutaminolysis to α-ketoglutarate (α-KG), one of the entering points of tricarboxylic acid (TCA) cycle within mitochondria; it thus increased the production of energy equivalents, adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) for T. pubescens to resist oxidative damage. This study can enable a better understanding of the metabolic rewiring of T. pubescens under Cd stress, and it can also provide a promising potential to prevent the rice paddy fields from Cd toxicity and enhance food safety.

Endophyte colonization enhanced cadmium phytoremediation by improving endosphere and rhizosphere microecology characteristics

This study investigated the phytoremediation efficiency of Cd-contaminated soils by hyperaccumulator P. acinosa and its endophyte B. cereus, and evaluated the variation of rhizosphere/endosphere microecology characteristics. The result showed that endophyte PE31, which could successfully colonize on P. acinosa root, increased plant Cd uptake by 42.90% and 28.85% in low and high Cd contaminated soils by promotion of plant biomass and Cd concentration in plant tissues. The improved phytoremediation may attribute to the endophyte inoculation, which significantly improved the bioavailable heavy metal (HM) percentage, nutrient cycling related enzyme activities and nutrient contents including available potassium, phosphorus and organic matter. Additionally, the relative abundance beneficial bacteria Bacillus (significantly increased by 81.23% and 34.03% in the endosphere, and by 4.86% and 8.54% in rhizosphere in low and high Cd contaminated soils) and Lysobacter, showed positive and close correlation with plant growth and HM accumulation. These results indicated that endophyte inoculation could reshape rhizosphere and endosphere microecology characteristics, which enhanced the potential for phytoremediation of Cd contaminated soils.

Application of a newly recorded diazotrophic cyanobacterium in acidified and Cd contaminated paddy soil: Promotes rice yield and decreases Cd accumulation

Acidification caused by excessive fertilization and heavy metals contamination are two prominent problems of agricultural soils. Diazotrophic cyanobacteria play important role in nitrogen (N) input in agricultural ecosystem. However, the effects of diazotrophic cyanobacteria on the growth of rice and heavy metal uptake by rice grain in acidified and heavy metal contaminated paddy soil remain unknown. In this study, a newly recorded diazotrophic cyanobacterium Aliinostoc sp. YYLX235 was isolated from acidified paddy soil. The results of pot experiment and in situ field plot experiment demonstrated that Aliinostoc sp. YYLX235 could promote rice grain yield and decrease cadmium (Cd) accumulation in rice grain. Nitrogen input by N₂-fixation and increase of bio-available phosphorus (P) by promotion of activity of soil phosphatase may be the main mechanisms for growth-promoting effects of Aliinostoc sp. YYLX235 on rice. Binding and immobilization of Cd through hydroxyl, carboxyl, and amino groups may be the reason for decrease of Cd accumulation in rice grain by Aliinostoc sp. YYLX235 inoculation. The results presented in this study suggest that diazotrophic cyanobacteria have great potential in safe cropping in acidified and Cd contaminated paddy soils.

Evaluation of the cadmium phytoextraction potential of tobacco (Nicotiana tabacum) and rhizosphere micro-characteristics under different cadmium levels

In this study, a field-scale and pot experiment were performed to evaluate the remedial efficiency of Cd contaminated soil by tobacco and explore rhizosphere micro-characteristics under different cadmium levels, respectively. The results indicated that tobacco could remove 12.9 % of Cd from soil within a short growing period of 80 d. The pot experiment revealed that tobacco could tolerate soil Cd concentrations up to 5.8 mg kg-1 and bioaccumulate 68.1 and 40.8 mg kg-1 Cd in shoots and roots, respectively. The high Cd bioaccumulation in tobacco might be attributed to strong acidification in the rhizosphere soil and the increase in Cd bioavailability. Rhizobacteria did not appear to be involved in Cd mobilization. In contrast, tobacco tended to enrich sulfate-reducing bacteria (such as Desulfarculaceae) under high Cd treatment (5.8 mg kg-1) but enrich plant growth-promoting bacteria (such as Bacillus, Dyadobacter, Virgibacillus and Lysobacter) to improve growth under low Cd treatment (0.2 mg kg-1), suggesting that tobacco employed different microbes for responding to Cd stress. Our results demonstrate the advantages of using tobacco for bioremediating Cd contaminated soil and clarify the rhizosphere mechanisms underlying Cd mobilization and tolerance.

Alleviation of salinity and metal stress using plant growth-promoting rhizobacteria isolated from semiarid Moroccan copper-mine soils

Phytoremediation is an eco-friendly method for rehabilitation of mine tailing. Some heavy metals and salt-tolerant plant growth-promoting rhizobacteria (PGPR) could be beneficial in alleviating soil salinity and heavy metal stress during plant growth. The aim of this work is to select PGPR that could be used in phytoremediation process. Twenty-nine rhizobacteria are examined for their ability to grow at increasing concentrations of NaCl, Zn, Pb, Cu, and Cd. The results showed that seventeen rhizobacteria displayed high salinity and metal tolerance up to 100 g L^-1 of NaCl, 5 mM of Cd, 9 mM of Pb, 10 mM of Zn, and 6 mM of Cu. Moreover, almost all tested bacteria maintained their PGP traits under 10% of NaCl and multi-metal stress. Based on seedling bioassay under metallic and salt stress, using Peganum harmala L. and Lactuca sativa L., beneficial effects of seed inoculation with bacterial consortia (Mesorhizobium tamadayense, Enterobacter xiangfangensis, Pseudomonas azotifigens, and Streptomyces caelestis) have been observed in terms of root and shoot elongation. Our results show that the stress-tolerant consortium used has a great potential to sustain plants establishment in heavily disturbed soils.

Biomineralization of Cd2+ and inhibition on rhizobacterial Cd mobilization function by Bacillus Cereus to improve safety of maize grains

Reducing cadmium (Cd) bioavailability and rhizobacterial Cd mobilization functions in the rhizosphere via the inoculation of screened microbial inoculum is an environmental-friendly strategy to improve safety of crop grains. In this study, Bacillus Cereus, a model Cd resistant strain, was selected to explore its effects on Cd bioavailability and uptake, bacterial metabolic functions related to Cd mobilization. Results indicated that inoculation of Bacillus Cereus in maize roots of sand pot with water-soluble Cd (0.06-0.15 mg/kg) and soil pot with high Cd-contaminated soil (total Cd: 2.33 mg/kg; Cd extracted by NH₄NO₃: 38.6 μg/kg) could decrease water-soluble Cd ion concentration by 7.7-30.1% and Cd extracted with NH₄NO₃ solution by 7.8-22.5%, inducing Cd concentrations in maize grains reduced by 10.6-39.9% and 17.4-38.6%, respectively. Even for a single inoculation in soil, Cd concentration in maize grains still satisfy food safety requirements (Cd content: 0.1 mg/kg dry weight) due to its successful colonization on root surface of maize. Bacillus Cereus could enrich more plant growth promotion bacteria (PGPB) and down-regulate the expression of genes related to bacterial motility, membrane transports, carbon and nitrogen metabolism in the rhizosphere soil, decreasing Cd bioavailability in soil. Approximately 80% Cd²⁺ in media was transferred into intracellular, meanwhile Cd salts (sulfide and/or phosphate) were produced in Bacillus Cereus through biomineralization process. Overall, this study could provide a feasible method for improving safety of maize grains via the inoculation of Bacillus Cereus under Cd pollution.

The endophytic bacterium Bacillus koreensis 181-22 promotes rice growth and alleviates cadmium stress under cadmium exposure

Recently, cadmium (Cd) contamination in paddy soils has become a highly concerning pollution problem. Endophytic microbes in rice not only affect the plant growth but also contribute to ion absorption by the roots. Therefore, they are a promising, ecologically sound means of reducing the Cd transport from soils to shoots and grains of the plant. In this study, a Cd-resistant endophytic bacterium, named 181-22, with high Cd absorption capacity (90.8%) was isolated from the roots of rice planting in heavily Cd-contaminated paddy soils and was identified as Bacillus koreensis CGMCC 19,468. The strain significantly increased fresh weight of roots and shoots (44.4% and 42.7%) and dry weight of roots and shoots (71.3% and 39.9%) and decreased Cd content in the rice roots (12.8%), shoots (34.3%), and grains (39.1%) under Cd stress compared to uninoculated plant by colonizing rice roots via seed inoculation. Moreover, colonization of 181-22 reprogrammed rice physiology to alleviate Cd stress by increasing pigment and total protein content, regulating Cd-induced oxidative stress enzymes such as superoxide dismutase and catalase and reducing malondialdehyde. Thus, B. koreensis 181-22 has the potential to protect rice against Cd stress and can be used as a biofertilizer to bioremediate paddy soils contaminated with Cd. KEY POINTS: • Bacillus koreensis 181-22 colonized the inside of rice roots at high numbers via seed inoculation. • B. koreensis 181-22 promoted rice growth and decreased Cd accumulation in grains. • B. koreensis 181-22 regulated the physiological response to alleviated Cd stress in rice.

Cadmium-resistant and arginine decarboxylase-producing endophytic Sphingomonas sp. C40 decreases cadmium accumulation in host rice (Oryza sativa Cliangyou 513)

In this study, an cadmium (Cd)-immobilizing and arginine decarboxylase-producing endophytic Sphingomonas sp. strain C40 obtained from the seeds of Oryza sativa Cliangyou 513 was characterized for its Cd availability and Cd uptake in host rice using hydroponic and soil experiments. The Cd concentration decreased by 51-95% compared to the control, while the spermidine concentration increased by 19-25% with Cd compared with no Cd in the strain C40-inoculated solution. Strain C40 decreased the above-ground tissue Cd content by 27-37% and increased spermine and spermidine contents by 28-67% and the expression levels of genes involved in spermine and spermidine production by 29-217% in rice roots compared to the controls. Furthermore, correlation analyses showed the significantly negative correlation between rice root spermine and spermidine contents and above-ground tissue Cd content. In the Cd-added soil, strain C40 promoted the rice biomass by 29-36% and decreased rice root, above-ground tissue, and grain Cd contents by 18, 16, and 33% and total grain Cd uptake by 14% compared with the controls at the maturity stage. Strain C40 decreased the exchangeable Cd content by 27% and increased the Fe and Mn oxides-bound Cd content by 45% in the rice rhizosphere soils at the maturity stage compared with the controls. These results suggested that the endophytic bacterial strain C40 increased rice root polyamine production and their related gene expression and the transformation of available Cd to unavailable Cd, leading to reduced Cd accumulation and translocation from the rice roots to grains.

Potential of Bacterial Strains Isolated from Ironstone Outcrops Bromeliads to Promote Plant Growth Under Drought Conditions

Plant growth-promoting bacteria (PGPB) are bacteria that have mechanisms that facilitate plant growth in stress conditions such as drought. The objective of this study was to characterize bacterial strains isolated from bromeliads roots in ironstone outcrops (Urucum Residual Plateau, Mato Grosso do Sul, Brazil) for plant growth-promoting under drought conditions. Firstly, we screened isolates with the presence of 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. Then, all isolates were tested for tolerance to drought, exopolysaccharides (EPS) production, indole-3-acetic acid (IAA)-producing abilities, phosphate and zinc solubilization, production of catalase and hydrolytic enzymes (amylase, cellulase, and protease). Germination assay and a pot experiment with maize plants submitted to well-watered and drought conditions were performed with the strains most promising (VBN11 and VBE23). Briefly, Bacillus cereus VBE23 showed in vitro higher ACC deaminase activity (3.83 and 2.52 µmol α-KB mg^-1 h^-1 in non-drought and drought conditions, respectively), tolerance to drought, EPS production and other mechanisms of plant growth promotion: solubilization of phosphate and zinc, ammonia production, catalase activity and production of hydrolytic enzymes (amylase, cellulase, and protease). Inoculation of strain VBE23 in maize seeds submitted to drought conditions showed higher germination concerning uninoculated seeds and inoculated with VBN11. Also, the results indicated that the isolate VBE23 provided higher values of fresh and dry biomass compared to the control of uninoculated treatment and inoculated with VBN11 under drought conditions. This is the first report on the PGPB from ironstone outcrops of Urucum Residual Plateau, Mato Grosso do Sul, Brazil. Thus, this bacterial isolate could be used as a strategy for the facilitation of plant growth in drought environments.

Priming Strategies for Benefiting Plant Performance under Toxic Trace Metal Exposure

Combating environmental stress related to the presence of toxic elements is one of the most important challenges in plant production. The majority of plant species suffer from developmental abnormalities caused by an exposure to toxic concentrations of metals and metalloids, mainly Al, As, Cd, Cu, Hg, Ni, Pb, and Zn. However, defense mechanisms are activated with diverse intensity and efficiency. Enhancement of defense potential can be achieved though exogenously applied treatments, resulting in a higher capability of surviving and developing under stress and become, at least temporarily, tolerant to stress factors. In this review, I present several already recognized as well as novel methods of the priming process called priming, resulting in the so-called “primed state” of the plant organism. Primed plants have a higher capability of surviving and developing under stress, and become, at least temporarily, tolerant to stress factors. In this review, several already recognized as well as novel methods of priming plants towards tolerance to metallic stress are discussed, with attention paid to similarities in priming mechanisms activated by the most versatile priming agents. This knowledge could contribute to the development of priming mixtures to counteract negative effects of multi-metallic and multi-abiotic stresses. Presentation of mechanisms is complemented with information on the genes regulated by priming towards metallic stress tolerance. Novel compounds and techniques that can be exploited in priming experiments are also summarized.

Bacillus cereus liquid fertilizer was produced from Agaricus bisporus industrial wastewater

During the Agaricus bisporus canning processes, a large number of water-soluble elements were dissolved into the processing hot water. This study was conducted to use the industrial wastewater of A. bisporus to prepare agricultural microbial fertilizer. In the work, the influence of 6 different liquid fermentation factors on the total biomass of living Bacillus cereus was evaluated with the one-factor-at-a-time method and the Plackett-Burman design. The total biomass of living B. cereus was most influenced by fermentation temperature, shaking speed, and inoculation volume, which were identified as the most critical independent variables for the B. cereus biomass. The approximate ranges of optimal fermentation conditions for the three key factors were identified by the path of steepest ascent. The center point of these factors were 24 ℃ of temperature, 250 rpm of shaking speed and 12 % inoculum amount, respectively. The Box-Behnken design was applied to derive a statistical model for optimizing the three fermentation factors for B. cereus biomass. After further optimizations based on statistical predictions, the optimum fermentation parameters for B. cereus cultured in the A. bisporus industrial wastewater were fermentation temperature of 24.8 °C, shaking speed of 234 rpm, inoculum dose of 12.2 % (v:v, %), industrial wastewater concentration of 4%, initial pH values of 6.5, loading liquid of 60 mL/250 mL, and culture time of 24 h. Culturing with the optimal fermentation conditions resulted in the biomass of B. cereus of 1.35 ± 0.02 × 10⁹ Obj/mL (N = 3), which was consistent with the predicted values (1.32 × 10⁹ Obj/mL) predicted by the corresponding regression models (p < 0.05), and more, was also far higher than that of the standard of agricultural bacterial fertilizers in People's Republic of China. Further, the results of field trial indicated that the of B. cereus liquid fertilizer can remarkably enhance the yield of Brassica chinensis L. It is practicable to make use of the industrial wastewater of A. bisporus to prepare the microbial fertilizer.

Acinetobacter sp. SG-5 inoculation alleviates cadmium toxicity in differentially Cd tolerant maize cultivars as deciphered by improved physio-biochemical attributes, antioxidants and nutrient physiology

Cadmium is a phytotoxic metal which threatens the global food safety owing to its higher retention rates and non-biodegradable nature. Optimal study of microbe-assisted bioremediation is a potential way to minimize the adversities of Cd on plants. Current study was aimed to isolate, identify and characterize Cd tolerant PGPBs from industrially contaminated soil and to evaluate the potential of plant-microbe synergy for the growth augmentation and Cd remediation. The Acinetobacter sp. SG-5, identified through 16S rRNA gene sequence analysis, was able to tolerate 1000 mg/l of applied Cd stress and ability of in vitro indole-3-acetic acid production, phosphate solubilization, as well as 1-aminocyclopropane-1-carboxylic acid deaminase activity. A Petri plate experiment was designed to investigate the impact of Acinetobacter sp. SG-5 on applied Cd toxicity (0, 6, 12, 18, 24, 30 μM) in maize cultivars (3062-Cd tolerant, 31P41-Cd susceptible). Results revealed that non-inoculated maize plants were drastically affected with applied Cd treatments for growth, antioxidants and mineral ions acquisition predominantly in susceptible cultivar (31P41). PGPB inoculation positively influenced the maize growth by enhanced anti-oxidative potential coupled with optimum level of nutrients (K, Ca, Mg, Zn). Analysis of morpho-physio-biochemical traits after PGPB application revealed that substantial Cd tolerance was acquired by susceptible cv. 31P41 than tolerant cv. 3062 under applied Cd regimes. Research outcomes may be important for understanding the growth responses of Cd susceptible and tolerant maize cultivars under Acinetobacter sp. SG-5 inoculation and likely to provide efficient approaches to reduce Cd retention in edible plant parts and/or Cd bioremediation.

Burkholderia sp. Y4 inhibits cadmium accumulation in rice by increasing essential nutrient uptake and preferentially absorbing cadmium

Microbial remediation of heavy metal-polluted soil is a commonly used method. Burkholderia sp. Y4, isolated from cadmium (Cd)-contaminated rice rhizosphere soil, was investigated for its direct and indirect effects on Cd accumulation in rice by SEM-EDS, FITR and sequencing analysis of the soil bacterial community. Burkholderia sp. Y4 inoculation reduced Cd accumulation in rice roots, rachises, and grains of the two rice varieties T705 and X24 and increased levels of essential elements, especially Fe and Mn, which competitively inhibited Cd transport through cationic channels. Living Burkholderia sp. Y4 cells, rather than non-living ones, could colonize the surface of rice roots and accumulated more Cd through direct biosorption associated with -CO and -NH/-CO bonds of amino acids and proteins. The results of soil microbial community showed that the colonization of externally added Burkholderia sp. Y4 could be maintained over some time to impact the total rhizospheric environment. Burkholderia sp. Y4 inoculation decreased the abundance of microbes involved in the iron cycle (Acidobacteria) as well as of those mediating the transformation of ammonium nitrogen to nitrate nitrogen (Nitrosomonadaceae and Nitrospira). So Burkholderia sp. Y4 inoculation may indirectly change the availability of micronutrients and Cd in rice rhizosphere soil through iron-nitrogen coupled cycles to increase essential nutrient uptake and inhibit Cd accumulation in rice by preferential Cd-biosorption. Therefore, Burkholderia sp. Y4 is potentially suitable for the bioremediation of Cd-contaminated paddy soil.