Bioremediation Of Heavy Metals Research Articles

Engineered Cyanobacteria-Based Living Materials for Bioremediation of Heavy Metals Both In Vitro and In Vivo.

The pollution caused by heavy metals (HMs) represents a global concern due to their serious environmental threat. Photosynthetic cyanobacteria have a natural niche and the ability to remediate HMs such as cadmium. However, their practical application is hindered by a low tolerance to HMs and issues related to recycling. In response to these challenges, this study focuses on the development and evaluation of engineered cyanobacteria-based living materials for HMs bioremediation. Genes encoding phytochelatins (PCSs) and metallothioneins (MTs) were introduced into the model cyanobacterium Synechocystis sp. PCC 6803, creating PM/6803. The strain exhibited improved tolerance to multiple HMs and effectively removed a combination of Cd2+, Zn2+, and Cu2+. Using Cd2+ as a representative, PM/6803 achieved a bioremediation rate of approximately 21 μg of Cd2+/OD750 under the given test conditions. To facilitate its controllable application, PM/6803 was encapsulated using sodium alginate-based hydrogels (PM/6803@SA) to create "living materials" with different shapes. This system was feasible, biocompatible, and effective for removing Cd2+ under simulated conditions of zebrafish and mice models. Briefly, in vitro application of PM/6803@SA efficiently rescued zebrafish from polluted water containing Cd2+, while in vivo use of PM/6803@SA significantly decreased the Cd2+ content in mice bodies and restored their active behavior. The study offers feasible strategies for HMs bioremediation using the interesting biomaterials of engineered cyanobacteria both in vitro and in vivo.

Comparative study on the effect of SRB and Sporosarcina pasteurii on the MICP cementation and solidification of lead–zinc tailings

The production of tailings sand due to mining and smelting activities is one of the reasons for the accelerated environmental pollution caused by heavy metals, drawing social attention to the management of tailings sand. Microbially induced carbonate precipitation (MICP) is an environmentally friendly soil remediation technique that is gradually becoming the preferred method for soil stabilisation and heavy metal pollution control. To address the issues of heavy metal pollution release and the loose particle structure of lead–zinc tailings sand (LZTS), this study employs a layered MICP approach. The solidification effects of two typical mineralising bacteria, sulfate-reducing bacteria (SRB) and Sporosarcina pasteurii, on LZTS, were compared for the first time. The results show that the maximum unconfined compressive strength (UCS) of SRB cemented solidified lead–zinc tailings sand (SRB-CS-LZTS) specimens is 0.22 MPa, while that of S. pasteurii cemented solidified lead–zinc tailings sand (SP-CS-LZTS) specimens is 0.95 MPa. Compared with the UCS of SRB-CS-LZTS, the UCS of SP-CS-LZTS increased by 3.32 times. The effect of S. pasteurii on the improvement of UCS and immobilisation of heavy metal ions was greater than that of SRB. The immobilisation effect of SRB on SO42- in the LZTS was better than that of S. pasteurii. Compared with SRB, the biological CaCO3 formed by S. pasteurii exhibited stronger adhesion and was more suitable for the cementation and solidification of LZTS. This study uses MICP technology to treat LZTS, aligning with the green environmental concept and providing a reference for the bioremediation of multiple heavy metals in tailing areas.

Metagenomic analysis of bacterial communities in heavy metal leachate-contaminated soils at Jalan Lipis Sanitary Landfill, Pahang, Malaysia

A variety of bacterial communities can be found in heavy metal leachate-contaminated soil. These bacteria might have molecular defenses that allow them to endure a high heavy metal concentration. However, there aren't enough datasets on bacterial populations to be exploited for bioremediation, especially the biotreatment of leachate contaminated with heavy metals. This research examined the diversity of the bacterial population in heavy metal leachate-contaminated soil from the Jalan Lipis Sanitary Landfill in Pahang, Malaysia. The soil samples were taken from three (3) different locations. pH analysis showed that the heavy metal leachate-contaminated soil possesses alkaline pH. ICPMS analysis showed high concentration of nickel (112.96 mg/kg) followed by manganase (89.83 mg/kg), arsenic (43.84 mg/kg), and lead (3.62 mg/kg). The three most prevalent bacteria in the heavy metal leachate-contaminated soil from the site were Pseudomonas C (Proteobacteria), Flavobacterium (Bacteroidota), and Proteiniclasticum (Firmicutes), according to metagenomic sequencing of the 16 s rRNA gene. The alpha and beta bacterial diversity analysis indicate that each location with different heavy metal concentration differs significantly on its bacterial diversity providing a valuable information to be applied in heavy metal bioremediation exclusively from landfill leachate.

Study of Multiple Metal Resistant Citrobacter sp. Isolated From Industrial Effluent

The pollution of the environment with toxic heavy metals is spreading throughout the world along with industrial progress. Microbe related technologies may provide an alternative or addition to conventional method of metal removal or metal recovery. The present study deals with isolation, identification and characterization of heavy metal resistant bacteria from industrial effluent. a total58 isolates were screened for heavy metal resistant from industrial effluent. The GOZPRN isolate show multiple metal resistant and antibiotic resistances. On the basis of morphological, biochemical, partial 16S rRNA gene sequencing revealed that this isolates belongs to Citrobacter sp.. The isolate showed optimum growth at 30°C and pH 7.0. This isolate was found to be resistant to nickel (Ni), lead (Pb), zinc (Zn), Chromium (Cr). The minimal tolerance concentration (MTC) of this isolate against Cr, Ni, Pb, and Zn was 2.8 mM, 80 mM, 800 mM, and 500 mM respectively. It also exhibited resistance against tetracycline. This Citrobacter Sp. has potential to be useful for the bioremediation of heavy metals.

Selective Isolation and Identification of Microorganisms with Dual Capabilities: Leather Biodegradation and Heavy Metal Resistance for Industrial Applications.

Tanning, crucial for leather production, relies heavily on chromium yet poses risks due to chromium's oxidative conversion, leading to significant wastewater and solid waste generation. Physico-chemical methods are typically used for heavy metal removal, but they have drawbacks, prompting interest in eco-friendly biological remediation techniques like biosorption, bioaccumulation, and biotransformation. The EU Directive (2018/850) mandates alternatives to landfilling or incineration for industrial textile waste management, highlighting the importance of environmentally conscious practices for leather products' end-of-life management, with composting being the most researched and viable option. This study aimed to isolate microorganisms from tannery wastewater and identify those responsible for different types of tanned leather biodegradation. Bacterial shifts during leather biodegradation were observed using a leather biodegradation assay (ISO 20136) with tannery and municipal wastewater as the inoculum. Over 10,000 bacterial species were identified in all analysed samples, with 7 bacterial strains isolated from tannery wastewaters. Identification of bacterial genera like Acinetobacter, Brevundimonas, and Mycolicibacterium provides insights into potential microbial candidates for enhancing leather biodegradability, wastewater treatment, and heavy metal bioremediation in industrial applications.

Bioremediation potential of Bacillus sp. and Paenebacillus sp. novel lead-resistant isolates: Identification, characterization, and optimization studies

Environmental pollution by heavy metals and other toxic substances has increasingly become a global health concern. Lead is a hazardous environmental contaminant that is been released to the surface causing deleterious health effects to man. Various strategies have been employed such as excavation, precipitation, and vitrification to remove lead from polluted sites. However, bioremediation of heavy metal contaminated sites has served as a cost-effective and ecofriendly tool for detoxifying and restoration of ecological entities. In this study, we reported the isolation and optimization of two novel lead-resistant isolates from active goldmine contaminated site of Anka, Zamfara state Nigeria. Results of Atomic Absorption Spectroscopy (AAS) showed higher lead concentration from the sampled sites (p<0.05) than the USEPA standard (400 mg/Kg). Paenebacillus sp. strain BUK_BCH_BTE 3 (MT160418) and Bacillus sp. strain BUK_BCH_BTE 4 (MT160452) were identified based on the 16 S rRNA partial gene sequencing of the locally isolated microorganisms. Characterization of the two isolates revealed optimum growth at 37 °C, a pH of 7.0 over 48 hrs while utilizing inoculum volumes of 100 µL each. The two isolates utilized optimum sucrose concentrations at 10–20 g/L, while 5 g/L nitrogen source and 5 g/L of urea were optimum for Paenebacillus sp. as well as Bacillus sp. respectively. An optimal lead concentration of 1000 g/L was obtained by both isolates. Furthermore, the two isolates tolerated up to 3000 mg/L lead nitrate. Mercury, a toxic heavy metal, was noticed to hinder the growth of both isolates significantly at p<0.05. Hence, the locally isolated Paenebacillus sp. and Bacillus sp. could be used as promising tools for bioremediation of lead-contaminated environment.

Recent trends on bioremediation of heavy metals; an insight with reference to the potential of marine microbes

Recent trends on bioremediation of heavy metals; an insight with reference to the potential of marine microbes

Assessment of Effects of Amended Bioremediation of Toxic Metal-polluted Soil using Organic Composites and Bacillus sp on Plant Growth Parameters

It has become pertinent to develop improved bioremediation techniques, to avert the deleterious effects of heavy metal pollution on agricultural productivity, and safety of its produce. In this study, cow dung, poultry wastes and their composites used as organic amendments were collected and processed, while Bacillus sp used as plant growth promoting rhizosphere was isolated and identified. Then 24 kg of fertile soil was polluted by introducing 20 mL of 0.1M lead acetate solution, before bagging 5 kg of polluted soil into ten perforated nylons. Soil sample was then analyzed before and after treatment. After mixing with Bacillus sp suspension, two of the pot experiments were amended with each of 0.5 kg cow dung only, 0.5 kg poultry wastes only and 1:1 ratio of their composites. Control samples were set up without amendment, and they were bioremediated for 25 days. Following germination of sown corn seedlings, heights of their shoots and number of leaves were monitored on day 4, weeks 2, 4 and 7, before harvesting for analysis together with soil samples. Results obtained revealed that seedlings grown on treated samples as well as properties of treatment of soil were generally better than those of control samples. Highest percentage increase in organic matter content of soil was recorded in treatment with mixture of cow dung only and Bacillus sp, with 9.28% and 7.63% increase at 33.75 mg/kg and 52.55 mg/kg of lead (Pb) pollution. Seedlings grown on samples treated with poultry wastes only, recorded the highest protein content of 161.25±5.5 mg/g, 104.99±4.95 mg/g and 79.75±3.2 mg/g protein contents, at 32.75 mg/kg, 42.02 mg/kg and 52.44 mg/kg levels of Pb pollution, respectively. The amendments also reduced bioaccumulation of Pb in corn seedlings, which was in the order; stem&lt;leaf&lt;root. Therefore, these amendments can be exploited for improved bioremediation of heavy metals.

Omics technology draws a comprehensive heavy metal resistance strategy in bacteria.

The rapid industrial revolution significantly increased heavy metal pollution, becoming a major global environmental concern. This pollution is considered as one of the most harmful and toxic threats to all environmental components (air, soil, water, animals, and plants until reaching to human). Therefore, scientists try to find a promising and eco-friendly technique to solve this problem i.e., bacterial bioremediation. Various heavy metal resistance mechanisms were reported. Omics technologies can significantly improve our understanding of heavy metal resistant bacteria and their communities. They are a potent tool for investigating the adaptation processes of microbes in severe conditions. These omics methods provide unique benefits for investigating metabolic alterations, microbial diversity, and mechanisms of resistance of individual strains or communities to harsh conditions. Starting with genome sequencing which provides us with complete and comprehensive insight into the resistance mechanism of heavy metal resistant bacteria. Moreover, genome sequencing facilitates the opportunities to identify specific metal resistance genes, operons, and regulatory elements in the genomes of individual bacteria, understand the genetic mechanisms and variations responsible for heavy metal resistance within and between bacterial species in addition to the transcriptome, proteome that obtain the real expressed genes. Moreover, at the community level, metagenome, meta transcriptome and meta proteome participate in understanding the microbial interactive network potentially novel metabolic pathways, enzymes and gene species can all be found using these methods. This review presents the state of the art and anticipated developments in the use of omics technologies in the investigation of microbes used for heavy metal bioremediation.

Evaluating the efficiency of indigenous soil bacterial strains for heavy metal removal

Significant quantities of toxic heavy metals are regularly deposited into soil environments every day as a result of industrial and human activities, as well as natural emissions. Today, biological methods for reducing heavy metal pollution are becoming increasingly common as an innovative approach to combating heavy metal pollution. The purpose of this study was to identify soil bacteria capable of removing heavy metals and to explore the potential of native bacteria in the bioremediation process. During this experiment, various soil samples were collected from several sites (river bank Rvs1, bus station Bt2, agricultural site Ag3, landfill Gr4 and construction site Cn5). Five bacterial strains were isolated from soil samples using a conventional serial plate dilution method. Morphologically distinct colonies were selected and purified during incubation. Pure cultures of bacterial colonies were established and maintained as slant cultures. Depending on preliminary physical, chemical and morphological characteristics, isolates RvsS1, Bt2, Ag3, Gr4 and Cn5 were compared with the bacterial species: “Proteus”, “Staphylococcus”, “Pseudomonas”, “Bacilli” and “Klebsiella” respectively. Bacterial isolates were examined for their uptake of Cu, Cd and Pb in flask bioreactors. Strains RV1, Bt2, Ag3 and Gr4 removed 48.7%, 25.6%, 59.8% and 23.5% of lead, respectively. The removal efficiency of isolate Cn5 was 35.68% for lead and 48.53% for copper. Thus, the data demonstrate that the use of indigenous bacteria is potentially effective in the bioremediation of heavy metals. Keywords: BIOREMEDIATION, MICROORGANISMS, HEAVY METALS, LOCAL BACTERIA, ISOLATES, STRAINS, ABSORPTION

Exploring Microalgae Diversity in Indonesia: Harnessing Potential for Lead Bioremediation

Background: Indonesia's biodiverse microalgae, numbering 2060 species, thrive in diverse environments, offering potential in pharmaceuticals, cosmetics, fuel, and heavy metal bioremediation. Lead pollution from mining poses risks, prompting stringent government contamination limits. Microalgae-based bioremediation, notably Chlamydomonas reinhardtii and Chlorella vulgaris removing up to 90% of lead, suggests further exploring Indonesia's microalgae diversity. Methods: Data sourcing (2013-2023) employed Google and Google Scholar using specific keyword combinations across Indonesian provinces. Seventy-eight sources underwent analysis and visualization via Microsoft Excel 2021. Results: Microalgae's potential as lead bioremediation was explored across classes like Chlorophyceae, Cyanophyceae, and Bacillariophyceae. Chlorophyceae, exemplified by Chlorella and Scenedesmus, exhibit varied cell sizes and complex cell walls, aiding metal ion binding. Cyanophyceae like Cyanospira capsulata and N. commune synthesize diverse EPS compositions, indicating their potential in lead remediation. Conclusions: Indonesia's microalgae diversity across habitats, especially in the Chlorophyceae and Cyanophyceae classes, suggests a significant role in lead bioremediation. Their adaptability and diverse compositions highlight their potential for sustainable practices in combatting environmental lead contamination.

APPLICATION OF BIOREMEDIATION IN MITIGATION OF HEAVY METAL STRESS ON PLANTS

Heavy metals are toxic metals which are persistent in nature due to their nondegradable nature.Due to increase in industrialization and urbanization heavy metals are being added to theenvironment and consequently causing heavy metal pollution of water and soil. These heavy metals cause significant stress on crop plants and effect various parameters such as growth and yield. Manymethods like physical, chemical and biological methods are available to degrade these heavymetals. Recently, bioremediation is being widely used because of its cost-effective andenvironment friendly approach. Bioremediation is a biological process which makes use ofmicroorganisms to remove hazardous substances or environmental pollutants from air, water,soil, industrial effluents etc. Bacteria and fungi are mostly employed for bioremediation.These organisms are genetically engineered for effective use in bioremediation. This not onlydiscussed about the importance of bacteria for bioremediation of heavy metals but alsodiscussed about the challenges and limitations of bacteria for bioremediation. In this chapter, a variety of mechanisms responsible for adaptation of microorganisms to high heavy metal concentrations, e.g. metal sorption, uptake and accumulation, extracellular precipitation and enzymatic oxidation or reduction, will be reported. Moreover, molecular mechanisms responsible for their metal tolerance will be described.

Bioremoval of Co(II) by a novel halotolerant microalgae Dunaliella sp. FACHB-558 from saltwater.

Cobalt pollution is harmful to both the aquatic ecosystem and human health. As the primary producer of aquatic ecosystems in hypersaline environments, unicellular planktonic Dunaliella microalgae is considered to be a low-energy and eco-friendly biosorbent that removes excess cobalt and enhances the vitality of coastal and marine ecosystems. In this study, we found that the halotolerant microalga named Dunaliella sp. FACHB-558 could grow under a salinity condition with 0.5-4.5 M NaCl. A phylogenetic analysis based on the rbcL gene revealed that Dunaliella sp. FACHB-558 is a close relative of Dunaliella primolecta TS-3. At lab-scale culture, Dunaliella sp. FACHB-558 exhibited high tolerance to heavy metal stresses, including cobalt, nickel, and cadmium. Treatment with 60 μM cobalt delayed its stationary phase but ultimately led to a higher population density. Furthermore, Dunaliella sp. FACHB-558 has the ability to adsorb the cobalt ions in the aquatic environment, which was evidenced by the decreased amount of cobalt in the culture medium. In addition, the tolerance of Dunaliella sp. FACHB-558 to cobalt stress was correlated with enhanced nitric oxide content and peroxidase activity. The autophagy inhibitor 3-MA enhanced nitric oxide burst, increased peroxidase activity, and accelerated the bioremoval of cobalt, suggesting that the autophagy pathway played a negative role in response to cobalt stress in Dunaliella sp. FACHB-558. In summary, our study identified a novel microalga possessing high cobalt tolerance and provided a promising natural biosorbent for the research and application of heavy metal bioremediation technology.

Bioremediation of Pb contaminated water using a novel Bacillus sp. strain MHSD_36 isolated from Solanum nigrum.

The Pb bioremediation mechanism of a multi-metal resistant endophytic bacteria Bacillus sp. strain MHSD_36, isolated from Solanum nigrum, was characterised. The strain tested positive for the presence of plant growth promoters such as indoleacetic acid, 1-aminocyclopropane-1-carboxylate deaminase, siderophores, and phosphate solubilization. The experimental data illustrated that exopolysaccharides and cell hydrophobicity played a role in Pb uptake. The data further showed that the cell wall biosorbed a significant amount (71%) of the total Pb (equivalent to 4 mg/L) removed from contaminated water, compared to the cell membrane (11%). As much as 11% of the Pb was recovered from the cytoplasmic fraction, demonstrating the ability of the strain to control the influx of toxic heavy metals into the cell and minimize their negative impacts. Pb biosorption was significantly influenced by the pH and the initial concentration of the toxic ions. Furthermore, the presence of siderophores and biosurfactants, when the strain was growing under Pb stress, was detected through liquid chromatography mass spectrometry. The strain demonstrated a multi-component based Pb biosorption mechanism and thus, has a great potential for application in heavy metal bioremediation.

Cadmium biosorption: Lake waters in Bengaluru-mitigation of cadmium-induced oxidative stress by Selaginella bryopteris

ABSTRACT Heavy metals cause alarming levels of environmental and health problems and among them Cadmium has become a threat to organisms and natural resources like soil and water alike. It accumulates in living systems thereby causing oxidative stress. Efforts are made for bioremediation of heavy metals by employing biosorption, which is a well-known economic method for removal and in the current study Selaginella bryopteris was used as biosorbent. The biosorption capacity was optimized by its physicochemical parameters such as pH, dosage, contact time, and temperature. Cadmium-induced Reactive Oxygen Species levels and the antioxidant potential of S. bryopteris in ameliorating them were studied in Drosophila melanogaster. Water-quality analysis was performed using Chemical Oxygen Demand(COD) and Biological Oxygen Demand (BOD) and effect of S.bryopteris on these parameters were also analyzed. Further the concentration of Cadmium via colorimetric assay and Atomic Absorption Spectroscopy(AAS) was employed to quantify the Cadmium in lake water samples before and after treatment with biosorbent. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscope (SEM) were performed to characterize the surface properties for adsorptive removal of metal ions, and antioxidant studies were conducted to assess the role of S. bryopteris in suppressing oxidative stress.

Health Effects of Heavy Metal Contamination in Drinking Water

Water is essential for life, be it the life of animals, plants or human beings. It’s our prime duty to protect, manage and preserve the quality of water. Uncontrolled anthropogenic activities have resulted in contamination of fresh water resources thereby affecting the health of living beings. Rampant industrialization is a major environmental problem on the global scale for the pollution of fresh water with toxic effluents containing heavy metals. Contamination of surface water by heavy metals is the greatest quality issues because of their toxic nature, increased release and negative impact on the health of human beings. Water-borne diseases remain one of the major health concerns in the world. Heavy metals are individual metals and metal compounds that can impact human health. Exposure of humans to metals such as antimony, arsenic, barium, cadmium, chromium, cobalt, copper, iron, lead, manganese, mercury, nickel, selenium, silver, tin, zinc, etc results in chronic and acute toxicities. The toxicity of heavy metals depends on their concentration, period of exposure and route of exposure. Humans are exposed to heavy metals either by inhalation from the atmosphere, intake through drinking water, or by ingestion through the skin by dermal contact. The present review describes the analysis of ‘heavy metal contamination in drinking water’ with reference to definition, sources, health effects on humans and preventive measures. This study suggests that, the best way to get rid of heavy metal contamination in drinking water is to remove toxic heavy metals by using the best water purification system. Also, the ground water resources must be monitored for quality assessment, source identification and bioremediation of heavy metals.

Health effects of heavy metal contaminants Vis-à-Vis microbial response in their bioremediation

Toxic heavy metals are currently significant environmental pollutants as their growing ecotoxicity becomes a serious public health concern. Their multiple application in several fields such as the mining industry, agriculture, medicine, technology and many others, leads to a widespread distribution into the environmental systems. Since toxic metals are not biodegradable, their accumulation in soil, water and air contaminates the food chain, which poses a danger to human health. Because of extensive damage caused by metal intoxication on various organs of the human body, the search for therapeutic methods is very important. Removal of heavy metals from the body is usually carried out by the most common and conventional chelation therapy methods. However, for removal from environment the use of chemical methods is often expensive and can lead to the production of secondary pollutants. There is a remarkable attentiveness with respect to recent progress in heavy metals remediation over the past few decades with special emphasis on bioremediation utilized in various environmental areas. The present review is focused to throw light on the possible sources and related intake routes of the harmful metals, the symptoms of poisoning, their impact on the environment and health and the molecular mechanisms, which threaten human health effects. It also aims to provide an overview of the available studies on microbial bioremediation of heavy metals from the environment, including the mechanisms involved in metal removal and some future directions in microbial biodegradation technology.

OPTIMISATION OF TECHNOLOGY AND SELECTION OF BIOSORBENTS BASED ON HAWTHORN, MOUNTAIN ASH AND MOTHERWORT TO IMPROVE THE QUALITY OF FERMENTED MILK PRODUCT

The accelerated development of urbanisation brings with it environmental problems and adverse effects on human health. Air pollution, water pollution and limited access to natural resources are becoming serious challenges. However, innovative products incorporating enterosorption technologies present a potential solution to improve public health. These products contribute to the effective removal of toxic substances from the body, mitigating the negative health effects of urbanisation.In the context of yoghurt with LABR, it has been found to be more stable to whey separation and moisture retention. Prebiotics have a positive effect on water retention, although this effect may diminish over time. The optimal concentration of LABR bacteria also emphasises the importance of a precise balance, after which additional increases do not bring significant improvements. These results can be used to optimise the production of yoghurt, taking into account its structure and properties over its shelf life.Considering the study data, it can be concluded that an optimal combination of L. acidophilus bacterial concentration and metal concentration, reached on the fourth day after the addition of prebiotics, is necessary to maximise the efficiency of heavy metal bioremediation. These results have practical implications for heavy metal removal processes in aqueous media, providing a basis for optimising bioremediation conditions in industrial and environmental applications.

Inhibitory effects of Pseudomonas sp. W112 on cadmium accumulation in wheat grains: Reduced the bioavailability in soil and enhanced the interception by plant organs

Microorganisms play an important role in heavy metal bioremediation and soil fertility. The effects of soil inoculation with Pseudomonas sp. W112 on Cd accumulation in wheat were investigated by analyzing the transport, subcellular distribution and speciation of Cd in the soil and plants. Pseudomonas sp. W112 application significantly decreased Cd content in the roots, internode and grains by 10.2%, 29.5% and 33.0%, respectively, and decreased Cd transfer from the basal nodes to internodes by 63.5%. Treatment with strain W112 decreased the inorganic and water-soluble Cd content in the roots and increased the proportion of residual Cd in both the roots and basal nodes. At the subcellular level, the Cd content in the root cell wall and basal node cytosol increased by 19.6% and 61.8%, respectively, indicating that strain W112 improved the ability of the root cell wall and basal node cytosol to fix Cd. In the rhizosphere soil, strain W112 effectively colonized and significantly decreased the exchangeable Cd, carbonate-bound Cd and iron-manganese oxide-bound Cd content by 43.5%, 27.3% and 17.6%, respectively, while it increased the proportion of residual Cd by up to 65.2%. Moreover, a 3.1% and 23.5% increase in the pH and inorganic nitrogen content in the rhizosphere soil, respectively, was recorded. Similarly, soil bacterial community sequencing revealed that inoculating with strain W112 increased the abundance of Pseudomonas, Thauera and Azoarcus, which are associated with inorganic nitrogen metabolism, and decreased that of Acidobacteria, which is indicative of soil alkalinization. Hence, root application of Pseudomonas sp. W112 improved soil nitrogen availability and inhibited Cd accumulation in the wheat grains in a two-stage process: by reducing the Cd availability in the rhizosphere soil and by improving Cd interception and fixation in the wheat roots and basal nodes. Pseudomonas sp. W112 may be a suitable bioremediation agent for restoring Cd-contaminated wheat fields.

Bioindicator responses to extreme conditions: Insights into pH and bioavailable metals under acidic metal environments

Acid mine drainage (AMD) caused environmental risks from heavy metal pollution, requiring treatment methods such as chemical precipitation and biological treatment. Monitoring and adapting treatment processes was crucial for success, but cost-effective pollution monitoring methods were lacking. Using bioindicators measured through 16S rRNA was a promising method to assess environmental pollution. This study evaluated the effects of AMD on ecological health using the ecological risk index (RI) and the Risk Assessment Code (RAC) indices. Additionally, we also examined how acidic metal stress affected the diversity of bacteria and fungi, as well as their networks. Bioindicators were identified using linear discriminant analysis effect size (LEfSe), Partial least squares regression (PLS-R), and Spearman analyses. The study found that Cd, Cu, Pb, and As pose potential ecological risks in that order. Fungal diversity decreased by 44.88% in AMD-affected areas, more than the 33.61% decrease in bacterial diversity. Microbial diversity was positively correlated with pH (r = 0.88, p = 0.04) and negatively correlated with bioavailable metal concentrations (r = −0.59, p = 0.05). Similarly, microbial diversity was negatively correlated with bioavailable metal concentrations (bio_Cu, bio_Pb, bio_Cd) (r = 0.79, p = 0.03). Acidiferrobacter and Thermoplasmataceae were prevalent in acidic metal environments, while Puia and Chitinophagaceae were identified as biomarker species in the control area (LDA>4). Acidiferrobacter and Thermoplasmataceae were found to be pH-tolerant bioindicators with high reliability (r = 1, P < 0.05, BW > 0.1) through PLS-R and Spearman analysis. Conversely, Puia and Chitinophagaceae were pH-sensitive bioindicators, while Teratosphaeriaceae was a potential bioindicator for Cu–Zn–Cd metal pollution. This study identified bioindicator species for acid and metal pollution in AMD habitats. This study outlined the focus of biological monitoring in AMD acidic stress environments, including extreme pH, heavy metal pollutants, and indicator species. It also provided essential information for heavy metal bioremediation, such as the role of omics and the effects of organic matter on metal bioavailability.