Heavy metals multi-tolerant Bradyrhizobium isolated from mercury mining region in Algeria

Investigation of Cd and Pb enrichment capacities of Erigeron sumatrensis across three polluted regions: Insights into soil parameters and microbial communities

Erigeron sumatrensis is a vigorously growing invasive plant in mining areas and has been the subject of research for its potential in the phytoremediation of heavy metals. In this study, the bioconcentration factor (BCF) and translocation factor (TF) of E. sumatrensis were assessed to evaluate its phytoaccumulation potential for cadmium (Cd) and lead (Pb) across three distinct zinc mining regions with different degrees of contamination, including Huayuan (HY), Yueyang (YY), and Liuyang (LY) areas. The region of HY is identified as having the most severe Cd contamination, while the most pronounced Pb pollution characterizes the LY area. The findings indicate that E. sumatrensis demonstrated a stronger ability to enrich Cd and Pb in less contaminated areas. To elucidate the underlying mechanisms, high-throughput sequencing of 16S rRNA and internal transcribed spacer (ITS) regions was employed to analyze the rhizosphere bacterial and fungal communities across the three areas. The results revealed significant variations in the microbial community structure, function, and composition, suggesting a complex interplay between the plant and its associated microorganisms. Correlation analysis identified several soil properties, including soil pH, total nitrogen (TN), available nitrogen (AN), organic matter (OM), and available phosphorus (AP), as pivotal factors that may influence the heavy metal enrichment capabilities of the plant. Notably, some microorganisms (e.g., Burkholderia, Brevundimonas, Paraglomus, and Trichoderma) and enzymes (e.g., P-type ATPases, citrate synthase, catalase) of microorganisms were found to be potentially involved in facilitating the accumulation of Cd and Pb by E. sumatrensis. This research contributes to understanding how invasive alien plants can be utilized to remedy contaminated environments. It highlights the importance of modulating critical soil factors to enhance the phytoremediation potential of E. sumatrensis, which could aid in developing strategies to manage invasive plants and mitigate heavy metal pollution in ecosystems.

Study on Plant-blanket to reduce heavy metal migration caused by precipitation and to improve the soil environment of pyritic tailings

The increasing demand for mineral resources due to industrial development has led to significant tailings pollution during the mineral extraction process. In the southwestern region of China, a large amount of pyritic tailings containing pyrite cinder easily leaches heavy metals and other pollutants when exposed to precipitation, resulting in widespread soil contamination. Effective remediation methods are urgently needed to address this issue. This study utilized naturally occurring Plant-blanket formed by the symbiosis of moss and herbaceous plants on pyritic tailings as restoration material. Through leaching experiments and staining tracer techniques, the study investigated the ability of Plant-blanket to reduce the migration of heavy metals from pyrite cinder to soil under the influence of precipitation and its role in improving the soil environment. The results showed that within 12 h, the Plant-blanket could absorb water equivalent to 206.9 % of its own weight and had good water retention ability. It reduced the stained area ratio of soil horizontal and vertical profiles after precipitation leaching by a maximum of 76.08 % and 46.41 %, respectively, and improved the pH, cation exchange capacity (CEC), bulk density, and water content of soil at different depths. In addition, after being covered by Plant-blanket, the migration of Cd and Cu was reduced by a maximum of 44.35 % and 55.77 % respectively, and it increased the diversity and abundance of bacterial communities, promoting the recovery of soil microbial ecological functions. These findings indicate that Plant-blanket can regulate water and improve soil environment, and has certain control ability on the migration of Cd and Cu produced by pyritic tailings. Meanwhile, Plant-blanket plays an important role in improving the soil environment in mining areas and promoting ecosystem restoration, providing valuable reference for further exploration of ecological restoration of tailings.

Distinct adaptive strategies and microbial interactions of soil viruses under different metal(loid) contaminations

Viruses, as the most abundant organisms, significantly influence ecological function and microbial survival in soils, yet little was known about how viruses and virus-microbe interactions respond to environmental stresses induced by metal(loid) contaminations. Here, we conducted the metagenomic analysis to investigate the adaptative mechanisms of soil viruses under different metal(loid) contamination levels. By capturing a catalogue of 23,066 viruses, we found that viral communities exhibited the increased richness, diversity, and the temperate to lytic ratio in facing the highest metal(loid) contaminations. Meanwhile, viruses displayed obvious lineage-specific infection modes to distinct dominant hosts under different pollution levels. Viral functions linking to the inhibition of transcription and the enhancement of DNA repairment as well as multiple resistance not only contributed to coping with elevated multiple metal(loid) stresses, but also facilitated the adaptation and functioning of viral hosts. Moreover, the harmonious coexistence of viruses and resistant/pathogenic bacteria under the heaviest contaminations potentially exacerbated disseminating resistance and pathogenicity, while viruses under the lightest contaminations might be natural predators of resistant/pathogenic bacteria through lysing host cells. Overall, this study highlights the ecological importance of viral adaptation and the interactions between viruses and resistant/pathogenic bacteria in contaminated environments, contributing to developing virus-based approaches to soil restoration.

Effect of the Combination of Phosphate-Solubilizing Bacteria with Orange Residue-Based Activator on the Phytoremediation of Cadmium by Ryegrass

Amendments with activators or microorganisms to enhance phytoremediation in toxic-metal-polluted soils have been widely studied. In this research, the production of indoleacetic acid, siderophore, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase by phosphate-solubilizing bacteria was investigated during a pure culture experiment. Pot experiments were performed using Cd-polluted soil with the following treatments: control (CK, only ultrapure water), orange-peel-based activator (OG), and a combination of phosphate-solubilizing bacteria (Acinetobacter pitti) and OG (APOG). Ryegrass plant height and fresh weight, Cd content in ryegrass, total and available Cd soil content, soil enzyme activity, and soil bacterial diversity were determined in this work. The findings showed that the height of ryegrass in OG and APOG increased by 14.78% and 21.23%. In the APOG group, a decreased ratio of Cd was 3.37 times that of CK, and the bioconcentration factor was 1.28 times that of CK. The neutral phosphatase activity of APOG was 1.33 times that of CK and catalase activity was 1.95 times that of CK. The activity of urease was increased by 35.48%. APOG increased the abundance of beneficial bacteria and Proteobacteria was the dominant bacterium, accounting for 57.38% in APOG. Redundancy analysis (RDA) showed that nutrient elements were conducive to the propagation of the dominant bacteria, the secretion of enzymes, and the extraction rate of Cd in the soil. The possible enhancement mechanism of phytoremediation of cadmium by A. pitti combined with OG was that, on the one hand, APOG increased soil nutrient elements and enzyme activities promoted the growth of ryegrass. On the other hand, APOG activated Cd and boosted the movement of Cd from soil to ryegrass. This research offers insight for the combination of phosphate-solubilizing bacteria with an orange-peel-based activator to improve phytoremediation of Cd-contaminated soils and also provides a new way for the resource utilization of fruit residue.

A new strategy for treating Pb2+ and Zn2+ pollution with industrial waste derivatives Humin

Metal pollution caused by industrial waste accumulation is a long-term and far-reaching problem. Humin (HM), as a highly condensed organic component insoluble in alkaline or water solution, is often discarded as humic acid industrial waste. However, the abundant active functional groups in HM reported by some researches make it possible for HM to remove metals. In this study, a waste reuse strategy was proposed to reduce the pressure of industrial metal pollution on the environment. HM was obtained from lignite waste residue. Scanning electron microscopy, energy spectrum and Fourier infrared spectroscopy, combined with the adsorption models were employed to reveal the mechanism of HM adsorption. The results showed that HM had multiple adsorption mechanism and high biological stability. The adsorption capacity of HM to Zn²⁺ and Pb²⁺ were 194.88 mg/g and 289.59 mg/g respectively. HM adsorbed Zn²⁺ mainly by physical multilayer adsorption. And the adsorption of Pb²⁺ by HM was mainly a monolayer chemical reaction, which depended on its active functional groups and the exchange of valence electrons. Notably, HM could simultaneously remove Pb²⁺ and Zn²⁺ and almost did not affect its original adsorption capacity to single ions. These results will provide a new strategy for the treatment of metal pollution in the future and alleviate the pressure of multiple metal pollution of the environment.

Nickel mine soil is a potential source for soybean plant growth promoting and heavy metal tolerant rhizobia

Mine soil is not only barren but also contaminated by some heavy metals. It is unclear whether some rhizobia survived under extreme conditions in the nickel mine soil. Therefore, this study tries to isolate some effective soybean plant growth promoting and heavy metal resistant rhizobia from nickel mine soil, and to analyze their diversity. Soybean plants were used to trap rhizobia from the nickel mine soil. A total of 21 isolates were preliminarily identified as rhizobia, which were clustered into eight groups at 87% similarity level using BOXA1R-PCR fingerprinting technique. Four out of the eight representative isolates formed nodules on soybean roots with effectively symbiotic nitrogen-fixing and plant growth promoting abilities in the soybean pot experiment. Phylogenetic analysis of 16S rRNA, four housekeeping genes (atpD-recA-glnII-rpoB) and nifH genes assigned the symbiotic isolates YN5, YN8 and YN10 into Ensifer xinjiangense and YN11 into Rhizobium radiobacter, respectively. They also showed different tolerance levels to the heavy metals including cadmium, chromium, copper, nickel, and zinc. It was concluded that there were some plant growth promoting and heavy metal resistant rhizobia with the potential to facilitate phytoremediation and alleviate the effects of heavy metals on soybean cultivation in nickel mine soil, indicating a novel evidence for further exploring more functional microbes from the nickel mine soil.