Remediation mechanism of high concentrations of multiple heavy metals in contaminated soil by Sedum alfredii and native microorganisms.

Pollution accident of nonferrous metallurgy industry often lead to serious heavy metal pollution of the surrounding soil. Phytoremediation of contaminated soil is an environmental and sustainable technology, and soil native microorganisms in the process of phytoremediation also participate in the remediation of heavy metals. However, the effects of high concentrations of multiple heavy metals (HCMHMs) on plants and native soil microorganisms remain uncertain. Thus, further clarification of the mechanism of phytoremediation of HCMHMs soil by plants and native soil microorganisms is required. Using the plant Sedum alfredii (S. alfredii) to restore HCMHM-contaminated soil, we further explored the mechanism of S. alfredii and native soil microorganisms in the remediation of HCMHM soils. The results showed that (i) S. alfredii can promote heavy metals from non-rhizosphere soil to rhizosphere soil, which is conducive to the effect of plants on heavy metals. In addition, it can also enrich the absorbed heavy metals in its roots and leaves; (ii) native soil bacteria can increase the abundance of signal molecule-synthesizing enzymes, such as trpE, trpG, bjaI, rpfF, ACSL, and yidC, and promote the expression of the pathway that converts serine to cysteine, then synthesize substances to chelate heavy metals. In addition, we speculated that genes such as K19703, K07891, K09711, K19703, K07891, and K09711 in native bacteria may be involved in the stabilization or absorption of heavy metals. The results provide scientific basis for S. alfredii to remediate heavy metals contaminated soils, and confirm the potential of phytoremediation of HCMHM contaminated soil.

Acid-modified hydrochar for higher biodegradation rate of atrazine in various conditions by Paenarthrobacter sp. KN0901: Higher cell viability and bacterial number.

Microbial remediation is a viable and eco-friendly approach for decontaminating pollution. However, its effectiveness can be limited by the microorganisms' survival and growth in changing environments. Hydrochar materials have been utilized in this study to increase the growth and atrazine degradation capabilities of Paenarthrobacter sp. KN0901, a strain capable of atrazine biodegradation. Acid-modified hydrochars exhibited a higher carbonation rate, specific surface area, and number of defect sites compared to raw hydrochar. Following three days of incubation at 15 °C, the atrazine degradation rate increased from 90.7 % to 98.2 % when utilizing H3PO4-modified hydrochar (PHC). Additionally, the addition of PHC resulted in an increase in both bacterial concentration and cell viability of strain KN0901, by 1.6 and 1.4 times, respectively. Under various conditions, including temperatures of 4 ºC and 35 ºC, as well as pH levels of 5 and 9, and dd·H2O media, PHC exhibited a significant enhancement in atrazine degradation and cell viability of strain KN0901. Furthermore, PHC demonstrated the ability to sustain high proliferation and viability of strain KN0901 over five cycles, indicating its remarkable stability and biocompatibility. This study offers a new perspective on the development and application of bioremediation approaches in restoring atrazine-polluted environments, even under challenging conditions.

Remediation of heavy metals polluted soil environment: A critical review on biological approaches.

Heavy metals (HMs) pollution is a globally emerging concern. It is difficult to cost-effectively combat such HMs polluted soil environments. The efficient remediation of HMs polluted soil is crucial to protect human health and ecological security that could be carried out by several methods. Amidst, biological remediation is the most affordable and ecological. This review focused on the principles, mechanisms, performances, and influential factors in bioremediation of HMs polluted soil. In microbial remediation, microbes can alter metallic compounds in soils. They transform these compounds into their metabolism through biosorption and bioprecipitation. The secreted microbial enzymes act as transformers and assist in HMs immobilization. The synergistic microbial effect can further improve HMs removal. In bioleaching, the microbial activity can simultaneously produce H2SO4 or organic acids and leach HMs. The production of acids and the metabolism of bacteria and fungi transform metallic compounds to soluble and extractable form. The key bioleaching mechanisms are acidolysis, complexolysis, redoxolysis and bioaccumulation. In phytoremediation, hyperaccumulator plants and their rhizospheric microbes absorb HMs by roots through absorption, cation exchange, filtration, and chemical changes. Then they exert different detoxification mechanisms. The detoxified HMs are then transferred and accumulated in their harvestable tissues. Plant growth-promoting bacteria can promote phytoremediation efficiency; however, use of chelants have adverse effects. There are some other biological methods for the remediation of HMs polluted soil environment that are not extensively practiced. Finally, the findings of this review will assist the practitioners and researchers to select the appropriate bioremediation approach for a specific soil environment.

Critical steps in the restoration of coal mine soils: Microbial-accelerated soil reconstruction.

Soil reconstruction is a critical step in the restoration of environments affected by mining activities. This paper provides a comprehensive review of the significant role that microbial processes play in expediting soil structure formation, particularly within the context of mining environment restoration. Coal gangue and flotation tailings, despite their low carbon content and large production volumes, present potential substrates for soil reclamation. These coal-based solid waste materials can be utilized as substrates to produce high-quality soil and serve as an essential carbon source to enhance poor soil conditions. However, extracting active organic carbon components from coal-based solid waste presents a significant challenge due to its complex mineral composition. This article offers a thorough review of the soilization process of coal-based solid waste under the influence of microorganisms. It begins by briefly introducing the primary role of in situ microbial remediation technology in the soilization process. It then elaborates on various improvements to soil structure under the influence of microorganisms, including the enhancement of soil aggregate structure and soil nutrients. The article concludes with future recommendations aimed at improving the efficiency of soil reconstruction and restoration, reducing environmental risks, and promoting its application in complex environments. This will provide both theoretical and practical support for more effective environmental restoration strategies.

Hg2+ removal characteristics of a strain of mercury-tolerant bacteria screened from heavy metal-contaminated soil in a molybdenum-lead mining area.

In this study, the mercury-tolerant strain LTC105 was isolated from a contaminated soil sample collected from a molybdenum-lead mine in Luanchuan County, Henan Province, China. The strain was shown to be highly resistant to mercury, with a minimum inhibitory concentration (MIC) of 32 mg·L-1. After a 24-h incubation in LB medium with 10 mg·L-1 Hg2+, the removal, adsorption, and volatilization rates of Hg2+ were 97.37%, 7.3%, and 90.07%, respectively, indicating that the strain had significant influence on mercury removal. Based on the results of Fourier infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), the investigation revealed that the primary function of LTC105 was to encourage the volatilization of mercury. The LTC105 strain also showed strong tolerance to heavy metals such as Mn2+, Zn2+, and Pb2+. According to the results of the soil incubation test, the total mercury removal rate of the LTC105 inoculation increased by 16.34% when the initial mercury concentration of the soil was 100 mg·L-1 and by 62.28% when the initial mercury concentration of the soil was 50 mg·kg-1. These findings indicate that LTC105 has certain bioremediation ability for Hg-contaminated soil and is a suitable candidate strain for microbial remediation of heavy metal-contaminated soil in mining areas.

Plant endophyte immobilization technology: A promising approach for chromium-contaminated water and soil remediation.

Microbial immobilization technology is considered an efficient bioremediation method for chromium (Cr) pollution. However, it is currently unclear which strain is more beneficial for the remediation of Cr-contaminated water and soil. Therefore, corn straw biochar was used as a carrier to prepare materials for fixing the endophytes Serratia sp. Y-13 (BSR1), Serratia nematodiphila (BSR2), Lysinibacillus sp. strain SePC-36 (BLB1), Lysinibacillus mangiferihumi strain WK63 (BLB2) and the commercial bacteria Shewanella oneidensis MR-1 (BSW). The results demonstrated that, compared with BSW, endophyte-loaded biochar (especially BSR1) was more effective at remediating Cr pollution in water and soil. Endophyte-loaded biochar reduced the abundance of soil pathogenic bacteria, enhanced the number of beneficial plant endophytes, reduced the soil Cr(VI) concentration, improved soil fertility, reduced the plant Cr concentration and improved the yield of lettuce. Redundancy analysis (RDA) and structural equation modelling (PLS-PM) suggested that soil microbes are closely related to soil Cr(VI), plant fresh weight and soil organic matter, whereas endophyte-loaded biochar directly influences plant cell motility pathways by altering plant microbes. This study represents a pioneering investigation into the efficacy of endophyte-loaded biochar as a remediation strategy for Cr pollution.

Pilot-scale field studies on activated microbial remediation of petroleum-contaminated soil.

Soil contamination by petroleum, including crude oil from various sources, is increasingly becoming a pressing global environmental concern, necessitating the exploration of innovative and sustainable remediation strategies. The present field-scale study developed a simple, cost-effective microbial remediation process for treating petroleum-contaminated soil. The soil treatment involves adding microbial activators to stimulate indigenous petroleum-degrading microorganisms, thereby enhancing the total petroleum hydrocarbons (TPH) degradation rate. The formulated microbial activator provided a growth-enhancing complex of nitrogen and phosphorus, trace elements, growth factors, biosurfactants, and soil pH regulators. The field trials, involving two 500 m3 soil samples with the initial TPH content of 5.01% and 2.15%, were reduced to 0.41% and 0.02% in 50 days, respectively, reaching the national standard for cultivated land category II. The treatment period was notably shorter than the commonly used composting and bioaugmentation methods (typically from 8 to 12 weeks). The results indicated that the activator could stimulate the functional microorganisms in the soil and reduce the phytotoxicity of the contaminated soil. After 40 days of treatment, the germination rate of rye seeds increased from 20 to 90%, indicating that the microbial activator could be effectively used for rapid on-site remediation of oil-contaminated soils.

An insight on the plausible biological and non-biological detoxification of heavy metals in tannery waste: A comprehensive review.

A key challenge for the tannery industries is the volume of tannery waste water (TWW) generated during the processing of leather, releasing various forms of toxic heavy metals resulting in uncontrolled discharge of tannery waste (TW) into the environment leading to pollution. The pollutants in TW includes heavy metals such as chromium (Cr), cadmium (Cd), lead (Pb) etc, when discharged above the permissible limit causes ill effects on humans. Therefore, several researchers have reported the application of biological and non-biological methods for the removal of pollutants in TW. This review provides insights on the global scenario of tannery industries and the harmful effects of heavy metal generated by tannery industry on micro and macroorganisms of the various ecological niches. It also provides information on the process, advantages and disadvantages of non-biological methods such as electrochemical oxidation, advanced oxidation processes, photon assisted catalytic remediation, adsorption and membrane technology. The various biological methods emphasised includes strategies such as constructed wetland, vermitechnology, phytoremediation, bioaugmentation, quorum sensing and biofilm in the remediation of heavy metals from tannery wastewater (TWW) with special emphasize on chromium.

Detoxification of phoxim by a gut bacterium of Delia antiqua.

The presence of certain associated bacteria has been reported to increase pest resistance to pesticides, which poses a serious threat to food security and the environment. Researches on the above microbe-derived pesticide resistance would bring innovative approaches for pest management. Investigations into the phoxim resistance of Delia antiqua, one Liliaceae crop pests, revealed the contribution of a phoxim-degrading gut bacterium, D39, to this resistance. However, how the strain degraded phoxim was unknown. In this study, the role of D39 in phoxim degradation and resistance was first confirmed. DT, which had an identical taxonomy but lacked phoxim-degrading activity, was analyzed alongside D39 via comparative genomics to identify the potential phoxim degrading genes. In addition, degradation metabolites were identified, and a potential degradation pathway was proposed. Furthermore, the main gene responsible for degradation and the metabolites of phoxim were further validated via prokaryotic expression. The results showed that D39 contributed to resistance in D. antiqua larva by degrading phoxim. Phoxim was degraded by an enzyme encoded by the novel gene phoD in D39 to O,O-diethyl hydrogen phosphorothioate and 2-hydroxyimino-2-phenylacetonitrile. Finally, downstream products were metabolized in the tricarboxylic acid cycle. Further analysis via prokaryotic expression of phoD confirmed its degradation activity. The mechanisms through which gut microbes promote pesticide resistance are elucidated in this study. These results could aid in the development of innovative pest control methods. In addition, this information could also be used to identify microbial agents that could be applied for the remediation of pesticide contamination.

Contribution of Cd passivating functional bacterium H27 to tobacco growth under Cd stress.

The cadmium (Cd) embedded in tobacco not only affects yield and quality but also harms human health. Microbial remediation has attracted widespread attention due to its low cost and minimal risk of secondary pollution. Therefore, researching microbes capable of inhibiting crop absorption of heavy metals or removing heavy metals from the environment has significant practical implications. This study screened a strain named H27 with a Cd immobilization efficiency of up to 76.60%. Static cultivation experiments showed that immobilization of Cd by H27 is achieved through intracellular absorption, hydroxyl, carboxyl, and phosphate group reactions on the cell wall. The bacterium can also secrete extracellular substances to adsorb Cd and increase the environmental pH, reducing the bioavailability of Cd. H27 reduced the accumulation of Cd in the stems of hydroponically grown tobacco by 55.23% and decreased the expression of three Cd transport genes, HAM2, IRT1, and NRAMP1, in the roots. Additionally, H27 increased the mineralization rate of organic matter, increased the content of humic acid in the soil, promoted the formation of smaller soil particles, and enhanced the adsorption and fixation of Cd by soil components while simultaneously raising the pH of rhizosphere and non-rhizosphere soils in tobacco growth environments. Both hydroponic and potted experiments showed that H27 alleviated the inhibitory effect of Cd on tobacco growth, significantly reducing Cd accumulation in various parts of tobacco and lowering the transfer coefficient of Cd within the tobacco plant. This study aims to effectively reduce the Cd content in tobacco using microbes, mitigate the harm of heavy metals in cigarettes to human health, and provide theoretical and practical basis for the application of microbial techniques to control heavy metal absorption in tobacco.

The role and mechanisms of microbes in dichlorodiphenyltrichloroethane (DDT) and its residues bioremediation.

Environmental contamination with dichlorodiphenyltrichloroethane (DDT) has sever effects on the ecosystem worldwide. DDT is a recalcitrant synthetic chemical with high toxicity and lipophilicity. It is also bioaccumulated in the food chain and causes genotoxic, estrogenic, carcinogenic, and mutagenic effects on aquatic organisms and humans. Microbial remediation mechanism and its enzymes are very important for removing DDT from environment. DDT and its main residues dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD) can biodegrade slowly in soil and water. To enhance this process, a number of strategies are proposed, such as bio-attenuation, biostimulation, bioaugmentation and the manipulation of environmental conditions to enhance the activity of microbial enzymes. The addition of organic matter and flooding of the soil enhance DDT degradation. Microbial candidates for DDT remediation include micro-algae, fungi and bacteria. This review provide brief information and recommendation on microbial DDT remediation and its mechanisms.

A review of phyto- and microbial-remediation of indoor volatile organic compounds.

Volatile organic compounds (VOCs) are crucial air pollutants in indoor environments, emitted from building materials, furniture, consumer products, cleaning products, smoking, fuel combustion, cooking, and other sources. VOCs are also emitted from human beings via breath and whole-body skin. Some VOCs cause dermal/ocular irritation as well as gastrointestinal, neurological, cardiovascular, and/or carcinogenic damage to human health. Because people spend most of their time indoors, active control of indoor VOCs has garnered attention. Phytoremediation and microbial remediation, based on plant and microorganism activities, are deemed sustainable, cost-effective, and public-friendly technologies for mitigating indoor VOCs. This study presents the major sources of VOCs in indoor environments and their compositions. Various herbaceous and woody plants used to mitigate indoor VOCs are summarized and their VOCs removal performance is compared. Moreover, this paper reviews the current state of active phytoremediation and microbial remediation for the control of indoor VOCs, and discusses future directions.

Toward the development of a molecular toolkit for the microbial remediation of per-and polyfluoroalkyl substances.

Per- and polyfluoroalkyl substances (PFAS) are highly fluorinated synthetic organic compounds that have been used extensively in various industries owing to their unique properties. The PFAS family encompasses diverse classes, with only a fraction being commercially relevant. These substances are found in the environment, including in water sources, soil, and wildlife, leading to human exposure and fueling concerns about potential human health impacts. Although PFAS degradation is challenging, biodegradation offers a promising, eco-friendly solution. Biodegradation has been effective for a variety of organic contaminants but is yet to be successful for PFAS due to a paucity of identified microbial species capable of transforming these compounds. Recent studies have investigated PFAS biotransformation and fluoride release; however, the number of specific microorganisms and enzymes with demonstrable activity with PFAS remains limited. This review discusses enzymes that could be used in PFAS metabolism, including haloacid dehalogenases, reductive dehalogenases, cytochromes P450, alkane and butane monooxygenases, peroxidases, laccases, desulfonases, and the mechanisms of microbial resistance to intracellular fluoride. Finally, we emphasize the potential of enzyme and microbial engineering to advance PFAS degradation strategies and provide insights for future research in this field.

Microecological characteristics of water bodies/sediments and microbial remediation strategies after 50 years of pollution exposure in ammunition destruction sites in China.

The effects of long-term ammunition pollution on microecological characteristics were analyzed to formulate microbial remediation strategies. Specifically, the response of enzyme systems, N/O stable isotopes, ion networks, and microbial community structure/function levels were analyzed in long-term (50 years) ammunition-contaminated water/sediments from a contamination site, and a compound bacterial agent capable of efficiently degrading trinitrotoluene (TNT) while tolerating many heavy metals was selected to remediate the ammunition-contaminated soil. The basic physical and chemical properties of the water/sediment (pH (up: 0.57-0.64), nitrate (up: 1.31-4.28 times), nitrite (up: 1.51-5.03 times), and ammonium (up: 7.06-70.93 times)) were changed significantly, and the significant differences in stable isotope ratios of N and O (nitrate nitrogen) confirmed the degradability of TNT by indigenous microorganisms exposed to long-term pollution. Heavy metals, such as Pb, Zn, Cu, Cd, Cs, and Sb, have synergistic toxic effects in ammunition-contaminated sites, and significantly decreased the microbial diversity and richness in the core pollution area. However, long-term exposure in the edge pollution area induced microorganisms to use TNT as a carbon and nitrogen sources for life activities and growth and development. The Bacteroidales microbial group was significantly inhibited by ammunition contamination, whereas microorganisms such as Proteobacteria, Acidobacteriota, and Comamonadaceae gradually adapted to this environmental stress by regulating their development and stress responses. Ammunition pollution significantly affected DNA replication and gene regulation in the microecological genetic networks and increased the risk to human health. Mg and K were significantly involved in the internal mechanism of microbial transport, enrichment, and metabolism of TNT. Nine strains of TNT-utilizing microbes were screened for efficient TNT degradation and tolerance to typical heavy metals (copper, zinc and lead) found in contaminated sites, and a compound bacterial agent prepared for effective repair of ammunition-contaminated soil significantly improved the soil ecological environment.

[The application of molecular biology-based microbial remediation technologies in petroleum polluted environments].

Owing to human activities and industrial production, petroleum pollution has become a serious environmental issue. Microbial remediation technology, characterized by its eco-friendly characteristics, has drawn significant attention in petroleum pollution remediation. The application of molecular biology technology has led to a drastic revolution in microbial remediation technology, providing resources for the development of highly efficient degrading agents. However, limitations such as the lack of precision in species annotation and the limited detection sensitivity still exist. Other microbial remediation technologies also have substantial potential in enhancing the degradation efficiency of petroleum pollutants and reducing their environmental harm, especially biosurfactants and bio-stimulants, which offer relatively shorter remediation periods and lower costs, promising large-scale application in the future. Moreover, the combination of molecular biology and other microbial remediation technologies may become an effective tool for petroleum pollutant degradation. This review summarized the application of molecular biology methods in petroleum polluted environments, reviewed the recent research progress on microbial remediation techniques for petroleum-contaminated sites, discussed the remediation effects of these microbial remediation techniques, and proposed the future development direction of microbial remediation technology.

Sulfur-containing iron carbon nanocomposites activate persulfate for combined chemical oxidation and microbial remediation of petroleum-polluted soil.

In this study, sulfur-containing iron carbon nanocomposites (S@Fe-CN) were synthesized by calcining iron-loaded biomass and utilized to activate persulfate (PS) for the combined chemical oxidation and microbial remediation of petroleum-polluted soil. The highest removal efficiency of total petroleum hydrocarbons (TPHs) was achieved at 0.2% of activator, 1% of PS and 1:1 soil-water ratio. The EPR and quenching experiments demonstrated that the degradation of TPHs was caused by the combination of 1O2,·OH, SO4·-, and O2·-. In the S@Fe-CN activated PS (S@Fe-CN/PS) system, the degradation of TPHs underwent two phases: chemical oxidation (days 0 to 3) and microbial degradation (days 3 to 28), with kinetic constants consistent with the pseudo-first-order kinetics of chemical and microbial remediation, respectively. In the S@Fe-CN/PS system, soil enzyme activities decreased and then increased, indicating that microbial activities were restored after chemical oxidation under the protection of the activators. The microbial community analysis showed that the S@Fe-CN/PS group affected the abundance and structure of microorganisms, with the relative abundance of TPH-degrading bacteria increased after 28 days. Moreover, S@Fe-CN/PS enhanced the microbial interactions and mitigated microbial competition, thereby improving the ability of indigenous microorganisms to degrade TPHs.

Uranium removal in groundwater by Priestia sp. isolated from uranium-contaminated mining soil.

Priestia sp. WW1 was isolated from a uranium-contaminated mining soil and identified. The uranium removal characteristics and mechanism of Priestia sp. WW1 were investigated. The results showed that the removal efficiency of uranium decreased with the increase of initial uranium concentration. When the uranium initial concentration was 5 mg/L, the uranium removal efficiency achieved 92.1%. The increase of temperature could promote the uranium removal. Carbon source could affect the removal rate of uranium, which was the fastest when the methanol was used as carbon source. The solution pH had significant effect on the uranium removal efficiency, which reached the maximum under solution pH 5.0. The experimental results and FTIR as well as XPS demonstrated that Priestia sp. WW1 could remove uranium via both adsorption and reduction. The common chloride ions, sulfate ions, Mn(II) and Cu(II) enhanced the uranium removal, while Fe(III) depressed the uranium removal. The Priestia sp. WW1 could effectively remove the uranium in the actual mining groundwater, and the increase of initial biomass could improve the removal efficiency of uranium in the actual mining groundwater. This study provided a promising bacterium for uranium remediation in the groundwater.

Transcriptome analysis reveals diverse Curvularia tsudae strategies in response to cadmium stress.

Cadmium (Cd) is a highly toxic heavy metal that poses significant threats to living organisms. Curvularia tsudae has demonstrated remarkable survival capabilities in the presence of high Cd concentrations, exhibiting its exceptional Cd tolerance. Although some physiological studies have been conducted, the molecular mechanisms underlying Cd tolerance in C. tsudae is largely unknown. In this study, a comparative transcriptome analysis was performed to explore the molecular mechanisms of C. tsudae under Cd stress. Among the 10,498 identified unigenes, 2526 differentially expressed genes (DEGs) were identified between the Cd-free and Cd-treated samples. Functional annotation and enrichment analysis of these DEGs identified several key biological processes involved in coping with Cd stress. Genes related to cell wall modification and organic acid metabolism contributes to Cd binding or chelation. Fourier transform infrared spectroscopy (FTIR) analysis further highlighted the modifications in functional groups with the cell wall under Cd stress. Furthermore, the transporters tended to be modulated in response to Cd stress, and up-regulated genes involved in antioxidants likely contributes to high Cd tolerance. The processes from DNA to protein metabolism appeared to responsive to the presence of Cd stress as well. These results contribute to the advance of the current knowledge about the response of C. tsudae to Cd stress and lay the foundation for further advancements in using fungi for the remediation of Cd-polluted environments.