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Miscanthus has good tolerance to multi-metal(loid)s and has received increasing attention in remediated studies of metal(loid)s-contaminated soil. In this study, we conducted phytoextraction techniques to investigate the synergic effects of remediation of multi-metal(loid)s-contaminated soil by Miscanthus floridulus (Lab.) and two plant growth-promoting bacteria (PGPB), TS8 and MR2, affiliated to Enterobacteriaceae. The results exhibited a decrease of arsenic (15.27-21.50%), cadmium (8.64-15.52%), plumbum (5.92-12.76%), and zinc (12.84-24.20%) except for copper contents in the soil in bacterial inoculation groups, indicating that MR2 and TS8 could enhance the remediation of metal(loid)s. Moreover, increased fresh/dry weight and height indicated that inoculated bacteria could promote Miscanthus growth. Although the activities of antioxidant enzymes and the content of chlorophyll in the overground tissues showed no significant increase or even decrease, the activities of antioxidant enzymes in the underground tissues and soil were elevated by 48.95-354.17%, available P by 19.07-23.02%, and available K by 15.34-17.79% (p < 0.05). Bacterial inoculants could also decrease the soil pH. High-throughput sequencing analysis showed that the bacterial inoculant affected the rhizosphere bacterial community and reduced community diversity, but the relative abundance of some PGPB was found to increase. Phylogenetic molecular ecological networks indicated that bacterial inoculants reduced interactions between rhizosphere bacteria and thereby led to a simpler network structure but increased the proportion of positive-correlation links and enhanced the metabiosis and symbiosis of those bacteria. Spearman's test showed that OTUs affiliated with Enterobacteriaceae and soil nutrients were critical for metal(loid) remediation and Miscanthus growth. The results of this study provide a basis for the synergic remediation of multi-metal(loid)s-contaminated soils by Miscanthus and PGPB and provide a reference for the subsequent regulation of Miscanthus remediation efficiency by the other PGPB or critical bacteria., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Cadmium (Cd)-contaminated soil poses a severe threat to crop production and human health, while also resulting in a waste of land resources. In this study, two types of organic fertilizer (ZCK: Low-content available iron; Z2: High-content available iron) were applied to Cd-contaminated soil for rice cultivation, and the effects of the fertilizer on rice growth and Cd passivation were investigated in conjunction with soil microbial analysis. Results showed that Z2 could alter the composition, structure, and diversity of microbial communities, as well as enhance the complexity and stability of the microbial network. Both 2% and 5% Z2 significantly increased the fresh weight and dry weight of rice plants while suppressing Cd absorption. The 2% Z2 exhibited the best Cd passivation effect. Gene predictions suggested that Z2 may promote plant growth by regulating microbial production of organic acids that dissolve phosphorus and potassium. Furthermore, it is suggested that Z2 may facilitate the absorption and immobilization of soil cadmium through the regulation of microbial cadmium efflux and uptake systems, as well as via the secretion of extracellular polysaccharides. In summary, Z2 can promote rice growth, suppress Cd absorption by rice, and passivate soil Cd by regulating soil microbial communities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The issue of heavy metal pollution caused by human production and living activities is progressively worsening. This study explored the effect of iron-rich organic fertilizer on the growth, quality, and cadmium (Cd) absorption of Chinese cabbage under Cd stress. The results showed that iron-rich organic fertilizer could increase the soluble protein content and root length of Chinese cabbage. Meanwhile, it could change the form of Cd to inhibit the enrichment of Cd in Chinese cabbage. The alkali hydrolyzed nitrogen (AN), total potassium (TK), organic matter (OM), and moisture content (MC) of the Z3 treatment group (2 % ferrous sulfate heptahydrate) were significantly higher than those of other treatment groups. The microbial network of Z3 was more complex than the other three groups. PICRUSt analysis and correlation analysis showed that the genes related to protein synthesis (e.g., glutathione S-transferase, zinc and Cd transporter, outer membrane protein, ArsR family transcriptional regulator, catalase, etc.) can also promote microbial absorption. This study aims to provide theoretical insights into soil Cd pollution immobilization techniques., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Phytoremediation technology is an important approach applied to heavy metal remediation, and how to improve its remediation efficiency is the key. In this study, we compared the rhizospheric bacterial communities and metals contents in Miscanthus floridulus (M. floridulus) of four towns, including Huayuan Town (HY), Longtan Town (LT), Maoer Village (ME), and Minle Town (ML) around the lead-zinc mining area in Huayuan County, China. The roles of rhizospheric bacterial communities in assisting the phytoremediation of M. floridulus were explored. It was found that the compositions of the rhizospheric bacterial community of M. floridulus differed in four regions, but majority of them were heavy metal-resistant bacteria that could promote plant growth. Results of bioconcentration factors showed the enrichment of Cu, Zn, and Pb by M. floridulus in these four regions were significantly different. The Zn enrichment capacity of ML was the strongest for Cu and stronger than LT and ME for Pb. The enrichment capacity of LT and ML was stronger than HY and ME. These bacteria may influence the different heavy metals uptake of M. floridulus by altering the soil physiochemical properties (e.g., soil peroxidase, pH and moisture content). In addition, co-occurrence network analysis also showed that LT and ML had higher network stability and complexity than HY and ME. Functional prediction analysis of the rhizospheric bacterial community showed that genes related to protein synthesis (e.g., zinc-binding alcohol dehydrogenase/oxidoreductase, Dtx R family transcriptional regulators and ACC deaminase) also contributed to phytoremediation in various ways. This study provides theoretical guidance for selecting suitable microorganisms to assist in the phytoremediation of heavy metals., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Inc.)

In this study, the effects of two plant growth-promoting bacteria Klebsiella michiganensis TS8 and Lelliottia Jeotgali MR2 on the growth and cadmium (Cd) uptake of Arabidopsis thaliana under Cd stress were explored. A wild-type Arabidopsis thaliana was selected as the experimental plant and was planted at different Cd concentrations. MR2 and TS8 bacterial suspensions were sprayed onto the rhizospheric soil during the planting process. The initial Cd concentration of the bought soil was 14.17 mg/kg, which was used as the pot soil of the low-concentration Cd treatment group (LC). The concentration of soil Cd at high-concentration Cd treatment group (HC) were 200 mg/kg higher than that at LC group. Compared with the control group, MR2 suspension significantly promoted the growth of A . thaliana at both low and high concentrations, while TS8 strain and MR2&#95;TS8 mixture only exhibited growth-promoting effect at high concentration. However, it was noteworthy that, TS8 suspension significantly reduced the Cd content in the underground parts of A . thaliana (60% and 59%), and significantly improved the Cd content in the aboveground parts of A . thaliana (234% and 35%) at both low and high concentrations. In addition, at low concentration, both single strain and mixed strains significantly improved the transformation from reducible Cd to acid-extractable Cd in soil, promoted Cd intake, and thereby reduced the total Cd content in soil. Therefore, the rational application of plant growth-promoting bacteria may improve crop yield and remediate Cd contamination in soil.

A major challenge in radically alleviating the threats posed by Cd-contaminated paddy fields to human health is to reduce the Cd levels in both soils and rice grains. In this study, the microbial extraction (ME) treatment using a mixotrophic acidophilic consortium was used for the bioremediation of Cd-contaminated soils. The results showed that the ME treatment enhanced the total Cd (40%) and diethylenetriamine pentaacetic acid-soluble Cd (DTPA-Cd, 64%) removal efficiencies in contaminated soils. In addition, ME treatment decreased the levels of Cd acid-soluble and reducible fractions and thereby reduced Cd uptake in rice tissues. Microbial community analysis indicated that the indigenous soil microbial diversity and composition were not changed after the ME treatment, but the relative abundance of functional microbes associated with Cd removal was improved. Notably, soil available nutrient levels were elevated upon inoculation with mixotrophic acidophiles, resulting in an increase in rice growth and grain weight. This study provides a scientific basis for the potential application and evaluation of ME treatment in the field for remediating Cd-contaminated paddy soils., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Soil lead (Pb) contamination has caused severe environmental threats and is in urgent need of remediation. This study was aimed to explore the feasibility of using the Miscanthus-microbe combination to reduce Pb pollution in the farmland surrounding a lead-zinc mining area. We have screened three heteroauxin (IAA)-producing microbes ( Lelliottia jeotgali MR2, Klebsiella michiganensis TS8, and Klebsiella michiganensis ZR1) with high Pb tolerance. The IAA-producing ability of the mixed-species was stronger than that of the single bacterium. In pot experiments, the mixed-species of MR2-ZR1 and MR2-TS8 had better performance in enhancing the weight of Miscanthus grass (increased by 22.2-53.6% compared to the control group without inoculating microbes). The remediation efficiency of Pb was significantly higher in the MR2 (30.79%), MR2-TS8 (24.96%), and TS8-ZR1 (21.10%) groups than that in the control group (6.75%). We speculated that MR2 and mixed species of MR2-TS8 and TS8-ZR1 could promote the percentages of activated Pb fractions in soils and increase the Pb uptake of M. floridulus (Lab.). These results implied that the MR2-TS8 mixed-species might be selected as the effective microbial agent to simultaneously enhance the remediation efficiency of Pb-contaminated soils and the biomass of M. floridulus (Lab.).

Accumulation of heavy metals in agricultural soils due to human production activities-mining, fossil fuel combustion, and application of chemical fertilizers/pesticides-results in severe environmental pollution. As the transmission of heavy metals through the food chain and their accumulation pose a serious risk to human health and safety, there has been increasing attention in the investigation of heavy metal pollution and search for effective soil remediation technologies. Here, we summarized and discussed the basic principles, strengths and weaknesses, and limitations of common standalone approaches such as those based on physics, chemistry, and biology, emphasizing their incompatibility with large-scale applications. Moreover, we explained the effects, advantages, and disadvantages of the combinations of common single repair approaches. We highlighted the latest research advances and prospects in phytoremediation-chemical, phytoremediation-microbe, and phytoremediation-genetic engineering combined with remediation approaches by changing metal availability, improving plant tolerance, promoting plant growth, improving phytoextraction and phytostabilization, etc. We then explained the improved safety and applicability of phytoremediation combined with other repair approaches compared to common standalone approaches. Finally, we established a prospective research direction of phytoremediation combined with multi-technology repair strategy.

Endophytic bacteria are generally helpful for plant growth and protection. We isolated from tobacco seeds three Pseudomonas strains (K03, Y04, and N05) that could produce siderophores, indole-3-acetic acid, and 1-aminocyclopropane-1-carboxylate deaminase, fix nitrogen, dissolve phosphorus and potassium, and tolerate heavy metals. In pot experiments, the three isolated strains significantly promoted root growth and increased the root enzyme activity in Nicotiana tobacum K326. Furthermore, bacterial inoculations increased the proportion of residual lead (Pb) by 8.36%-51.63% and decreased the total Pb content by 3.28%-6.38% in the contaminated soil during tobacco planting, compared with uninoculated soils. An effective decrease in Pb content was also found in tobacco leaves with bacterial inoculations. K03 inoculation decreased the Pb content in the upper leaves by 49.80%, and Y04 inoculation had the best effect, decreasing the Pb content in the middle leaves by 70.12%. Additionally, soil pH and root activity had significant effects on transformation and translocation of Pb. The study suggested that in response to Pb pollution in soil, a reasonable application of endophytes (e.g., Pseudomonas) might be a promising approach in promoting tobacco growth and reducing Pb content in tobacco, while simultaneously enhancing Pb stabilization in soils.

The aim of this study is to explore the impact of cadmium (Cd) and arsenic (As) stress on physiological indexes and Cd/As uptake ability of Miscanthus, including Miscanthus sacchariflorus A0104, Miscanthus sinensis C0424 and C0640. Cd and As concentration showed significant hormesis effects on some physiological indexes, such as chlorophyll content, net photosynthetic rate, and MDA content. Compared with control group, Cd uptake can be most greatly enhanced by above fourfold with 150 mg/kg Cd treatment. As uptake of A0104 was increased by 3 ~ 33 folds with 200 mg/kg As treatment, C0424 was increased by 7-12 folds with 100 mg/kg As treatment, while C0640 was increased 1 ~ 6 folds with 250 mg/kg As treatment. The results also showed that C0640 was relatively better for the Cd remediation in the high Cd concentration (150 mg/kg) contaminated soil, while A0104 and C0424 were relatively better for the As remediation in the high As concentration (100 ~ 200 mg/kg) contaminated soil. Additionally, significantly (p < 0.05) close correlations were found among physiological indexes (except MDA content), while physiological indexes showed no significant relationship with the heavy metal contents in root, stem, and leaf.

Due to the persistence of metals in the ecosystem and their threat to all living organisms, effects of heavy metal on soil microbial communities were widely studied. However, little was known about the interactions among microorganisms in heavy metal-contaminated soils. In the present study, microbial communities in Non (CON), moderately (CL) and severely (CH) contaminated soils were investigated through high-throughput Illumina sequencing of 16s rRNA gene amplicons, and networks were constructed to show the interactions among microbes. Results showed that the microbial community composition was significantly, while the microbial diversity was not significantly affected by heavy metal contamination. Bacteria showed various response to heavy metals. Bacteria that positively correlated with Cd, e.g. Acidobacteria&#95;Gp and Proteobacteria&#95;thiobacillus, had more links between nodes and more positive interactions among microbes in CL- and CH-networks, while bacteria that negatively correlated with Cd, e.g. Longilinea, Gp2 and Gp4 had fewer network links and more negative interactions in CL and CH-networks. Unlike bacteria, members of the archaeal domain, i.e. phyla Crenarchaeota and Euryarchaeota, class Thermoprotei and order Thermoplasmatales showed only positive correlation with Cd and had more network interactions in CH-networks. The present study indicated that (i) the microbial community composition, as well as network interactions was shift to strengthen adaptability of microorganisms to heavy metal contamination, (ii) archaea were resistant to heavy metal contamination and may contribute to the adaption to heavy metals. It was proposed that the contribution might be achieved either by improving environment conditions or by cooperative interactions., (Copyright © 2017 Elsevier Ltd. All rights reserved.)