Bioremediation Options for Heavy Metal Pollution

The quorum sensing SinI/SinR-TraI/TraR systems promote Pb stabilization by Ensifer adhaerens S24 in the Pb-polluted aquatic environment

In this study, the Pb-resistant Ensifer adhaerens strain S24, which contains quorum sensing (QS) systems responsible for N-acyl homoserine lactone (AHL) production, was investigated for QS system-mediated Pb stabilization and the underlying mechanisms. Whole-genome sequence analysis revealed the QS SinI/R and TraI/R systems in strain S24. Subsequently, strains S24 and the S24∆sinI/R, S24∆traI/R, S24∆traI/R/sinR, and S24∆sinI/R-traI/R/sinR mutants were constructed and compared for QS SinI/SinR-TraI/TraR system-mediated Pb stabilization in the solution and the mechanisms involved. After 5 days of incubation, strain S24 significantly decreased the Pb concentration in the Pb-contaminated solution compared with the mutants. The S24∆sinI/R-traI/R/sinR mutant exhibited reduced Pb stabilization and AHL activity than the other mutants. The S24∆sinI/R-traI/R/sinR mutant had significantly greater Pb concentrations in the solution and lower cell surface-adsorbed and extracellular precipitated Pb (PbS) contents as well as lower expression of H2S-producing genes of metC and sseA than did strain S24. Furthermore, the S24∆sinI/R-traI/R/sinR mutant displayed reduced interactions between the hydroxyl, amino, carboxyl, and ether groups and Pb, compared with strain S24. These findings implied the vital role of the SinI/SinR-TraI/TraR systems in strain S24 for Pb stabilization through enhanced cell surface adsorption and extracellular precipitation in Pb-polluted aquatic environments.

Sustainable approaches for removing toxic heavy metal from contaminated water: A comprehensive review of bioremediation and biosorption techniques

In this comprehensive study, highlights emerging environmentally friendly methods to eliminating hazardous heavy metals from contaminated water, with an emphasis on bioremediation and biosorption. Breakthroughs, such as the combination of biological remediation and nanotechnology to improve the elimination of metals effectiveness and the use of genetically modified microbes for targeted pollutant breakdown. Developing biosorption materials made from agricultural waste and biochar, this indicates interesting areas for future research and emphasizes the necessity of sustainable practices in tackling heavy metal contamination in water systems. There seems to be a surge in enthusiasm for the utilization of biological remediation and biosorption methods as sustainable and viable options for eliminating heavy metals from contaminated water in the past couple of decades. The present review intends to offer an in-depth review of the latest understanding and advances in the discipline of biological remediation methods like bioaccumulation, biofiltration, bio-slurping, and bio-venting. Biosorption is specifically explained and includes waste biomass as biosorbent with the removal mechanisms and the hindrances caused in the process are detailed. Advances in biosorption like microbes as biosorbents and the mechanism involved in it. Additionally, novel enhancement techniques like immobilization, genetic modification, and ultrasound-assisted treatment in microbial sorbent are clarified. However, the review extended with analyzing the future advances in the overall biological methods and consequences of heavy metal pollution.

Perspectives of pteridophytes microbiome for bioremediation in agricultural applications

The microbiome is the synchronised congregation of millions of microbial cells in a particular ecosystem. The rhizospheric, phyllospheric, and endospheric microbial diversity of lower groups of plants like pteridophytes, which includes the Ferns and Fern Allies, have also given numerous alternative opportunities to achieve greener and sustainable agriculture. The broad-spectrum bioactivities of these microorganisms, including bioremediation of heavy metals (HMs) in contaminated soil, have been drawing the attention of agricultural researchers for the preparation of bioformulations for applications in climate-resilient and versatile agricultural production systems. Pteridophytes have an enormous capacity to absorb HMs from the soil. However, their direct application in the agricultural field for HM absorption seems infeasible. At the same time, utilisation of Pteridophyte-associated microbes having the capacity for bioremediation have been evaluated and can revolutionise agriculture in mining and mineral-rich areas. In spite of the great potential, this group of microbiomes has been less studied. Under these facts, this prospective review was carried out to summarise the basic and applied research on the potential of Pteridophyte microbiomes for soil bioremediation and other agricultural applications globally. Gaps have also been indicated to present scopes for future research programmes.

A critical review on the ecotoxicity of heavy metal on multispecies in global context: A bibliometric analysis

Heavy metals (HMs) have become a significant concern in the current era, with deleterious effects on diverse living organisms when exposed beyond threshold concentrations. Both nature and human beings have been constantly casting out HMs into environmental matrices through various activities. Innumerable cases of threatened diseases such as cancer, respiratory ailments, reproductive defects, skin diseases, and several others have been a cause of significant concern for humans as the number of instances has been increasing with each decade. HMs migrates via several pathways to infiltrate biological organisms and amass within them. Even though numerous treatment approaches are available for remediating HM pollution, however, they are expensive, along with other setbacks. Due to such constraints, combating HM contamination requires environmentally conscious strategies like bioremediation, which employs an array of biological systems to remove HMs from the environment. Nonetheless, to address the current global HM pollution situation, it is critical to comprehend not only how these hazardous HMs cause toxicity in various living organisms but also the knowledge gaps that currently exist concerning the subject of HM ecotoxicity. In the present investigation, data was extracted from Google Scholar using software program called Harzing's Publish or Perish. The collected information has been subsequently displayed as a network file using the VOSViewer software tool. Thus, the current review presents a significant insight with the inclusion of a readily accessible bibliometric analysis to comprehend the present status of HMs research, global research trends, existing knowledge discrepancies, and research challenges. Further, it also provides an in-depth review of HMs ecotoxicity, with a focus on arsenic (As), cadmium (Cd), and lead (Pb). Thus, as indicated by the bibliometric study, the present review will assist future investigators studying HMs ecotoxicity by providing baseline data concerning a wide range of living organisms and by addressing research gaps.

Microbial assisted multifaceted amelioration processes of heavy-metal remediation: a clean perspective toward sustainable and greener future

Rapidly increasing heavy metal waste has adversely affected the environment and the Earth's health. The lack of appropriate remediation technologies has worsened the issue globally, especially in developing countries. Heavy-metals contaminants have severely impacted the environment and led to devastating conditions owing to their abundance and reactivity. As they are nondegradable, the potential risk increases even at a low concentration. However, heavy-metal remediation has increased with the up-gradation of technologies and integration of new approaches. Also, of all the treatment methodologies, microbial-assisted multifaceted approach for ameliorating heavy metals is a promising strategy for propagating the idea of a green and sustainable environment with minimal waste aggregation. Microbial remediation combined with different biotechniques could aid in unraveling new methods for eradicating heavy metals. Thus, the present review focuses on various microbial remediation approaches and their affecting factors, enabling recapitulation of the interplay between heavy-metals ions and microorganisms. Additionally, heavy-metals remediation mechanisms adapted by microorganisms, the role of genetically modified (GM) microorganisms, life cycle assessment (LCA), techno-economic assessment (TEA) limitations, and prospects of microbial-assisted amelioration of heavy-metals have been elaborated in the current review with focus toward "sustainable and greener future."

Biosorption of arsenic (III) from aqueous solution using calcium alginate immobilized dead biomass of Acinetobacter sp. strain Sp2b

This study presents a novel biosorbent developed by immobilizing dead Sp2b bacterial biomass into calcium alginate (CASp2b) to efficiently remove arsenic (AsIII) from contaminated water. The bacterium Sp2b was isolated from arsenic-contaminated industrial soil of Punjab, a state in India. The strain was designated Acinetobacter sp. strain Sp2b as per the 16S rDNA sequencing, GenBank accession number -OP010048.The CASp2b was used for the biosorption studies after an initial screening for the biosorption capacity of Sp2b biomass with immobilized biomass in both live and dead states. The optimum biosorption conditions were examined in batch experimentations with contact time, pH, biomass, temperature, and AsIII concentration variables. The maximum biosorption capacity (qmax = 20.1 ± 0.76 mg/g of CA Sp2b) was obtained at pH9, 35 ̊ C, 20 min contact time, and 120 rpm agitation speed. The isotherm, kinetic and thermodynamic modeling of the experimental data favored Freundlich isotherm (R2 = 0.941) and pseudo-2nd-order kinetics (R2 = 0.968) with endothermic nature (ΔH° = 27.42) and high randomness (ΔS° = 58.1).The scanning electron microscopy with energy dispersive X-ray (SEM-EDX) analysis indicated the As surface binding. The reusability study revealed the reasonable usage of beads up to 5 cycles. In conclusion, CASp2b is a promising, efficient, eco-friendly biosorbent for AsIII removal from contaminated water.

Sources, effects and present perspectives of heavy metals contamination: Soil, plants and human food chain

Heavy metal (HM) poisoning of agricultural soils poses a serious risk to plant life, human health, and global food supply. When HM levels in agricultural soils get to dangerous levels, it harms crop health and yield. Chromium (Cr), arsenic (As), nickel (Ni), cadmium (Cd), lead (Pb), mercury (Hg), zinc (Zn), and copper (Cu) are the main heavy metals. The environment contains these metals in varying degrees, such as in soil, food, water, and even the air. These substances damage plants and alter soil characteristics, which lowers crop yield. Crop types, growing circumstances, elemental toxicity, developmental stage, soil physical and chemical properties, and the presence and bioavailability of heavy metals (HMs) in the soil solution are some of the factors affecting the amount of HM toxicity in crops. By interfering with the normal structure and function of cellular components, HMs can impede various metabolic and developmental processes. Humans are exposed to numerous serious diseases by consuming these affected plant products. Exposure to certain metals can harm the kidneys, brain, intestines, lungs, liver, and other organs of the human body. This review assesses (1) contamination of heavy metals in soils through different sources, like anthropogenic and natural; (2) the effect on microorganisms and the chemical and physical properties of soil; (3) the effect on plants as well as crop production; and (4) entering the food chain and associated hazards to human health. Lastly, we identified certain research gaps and suggested further study. If people want to feel safe in their surroundings, there needs to be stringent regulation of the release of heavy metals into the environment.

Factors influencing cadmium accumulation in plants after inoculation with rhizobacteria: A meta-analysis

Rhizobacteria have the potential to enhance phytoremediation by generating substances that stimulate plant development and influence the effectiveness of cadmium (Cd) remediation by adjusting Cd availability via metal solubilization. Furthermore, rhizobacterial inoculation affects plants' metal tolerance and uptake by controlling the expression of several metal transporters, channels, and metal chelator genes. A meta-analysis was conducted to quantitatively assess the effects of rhizobacteria on Cd accumulation in plants using 207 individual observations from 47 articles. This meta-analysis showed an average Cd concentration increase of 8.09 % in plant cells under rhizobacteria treatment. The effects of different plant-microbial interactions on the bioaccumulation of Cd in plants varied. Selecting the proper rhizobacteria-plant association is essential to affect Cd buildup in plant roots and shoots. A more extended planting period (>30 days) and a suitable soil pH (<6, 7-8) would aid in the phytoextraction of Cd from the soil. This study comprehensively and quantitatively investigated the effects of plants, rhizobacteria, soil pH, planting period, experimental sites, and plant organs on plant Cd accumulation. According to the analysis of explanatory factors, plant species, planting period, soil pH, and rhizobacteria species have a more decisive influence on Cd accumulation than other factors. The results provide information for future research on the successful remediation of soils contaminated with Cd. More investigations are required to elucidate the intricate interactions between plant roots and microorganisms.

Bioremediation of hazardous heavy metals by marine microorganisms: a recent review

Heavy metals (HMs) like Zn, Cu, Pb, Ni, Cd, and Hg, among others, play a role in several environmental problems. The marine environment is polluted by several contaminants, such as HMs. A variety of physico-chemical methods usually available for sanitation HMs remediation suffer from either limitation. Bioremediation is a promising way of dealing with HMs pollution. Microbes have the ability with various potencies to resist HMs tension. The current review discusses the main sources and influences of HMs, the role of marine microorganisms in HMs bioremediation, as well as the microbial mechanisms for HMs detoxification and transformation. This review paper aims to provide an overview of the bioremediation technologies that are currently available for the removal of HMs ions from industrial and urban effluent by aquatic organisms such as bacteria, fungi, and microalgae, particularly those that are isolated from marine areas. The primary goals are to outline various studies and offer helpful information about the most important aspects of the bioelimination techniques. The biotreatment practices have been primarily divided into three techniques based on this topic. They are biosorption, bioaccumulation, bioleaching, and biotransformation. This article gives the brief view on the research studies about bioremediation of HMs using marine microorganisms. The current review also deals with the critical issues and recent studies based on the HMs biodetoxification using aquatic microorganisms.

Effects of simulated acid rain on hydrochemical factors and microbial community structure in red soil aquifers

Acid rain can lower the pH of groundwater and affect its hydrogeochemistry and microbial ecology. However, the effects of acid rain on the hydrogeochemistry and microbial ecology of red soil groundwater systems in southern China are poorly understood. Previous research had mainly investigated the sources and patterns of groundwater acidification, but not the microbial mechanisms that contribute to this process and their associations with hydrochemical factors. To address this knowledge gap, we conducted a soil column experiment to simulate the infiltration of acid rain through various filter materials (coarse, medium, and fine sand) and to examine the hydrochemical and microbial features of the infiltrate, which can reveal how simulated acid rain (pH 3.5-7.0) alters the hydrochemistry and microbial community composition in red soil aquifers. The results showed that the pH of the leachate decreased due to simulated acid rain, and that the leaching efficiency of nitrogen and metal ions was influenced by the particle size of the filter media. Illumina 16S rRNA gene sequencing revealed that the leachate was dominated by Proteobacteria, Patescibacteria, Actinobacteria, and Acidobacteria, with Proteobacteria accounting for 67.04-74.69% of the bacterial community and containing a high proportion of nitrifying and denitrifying bacteria. Additionally, several genera with heavy metal tolerance, such as Burkholderia-Caballeronia-Paraburkholderia, Delftia, Methylversatilis, Aquicella, and Ralstonia, were widely distributed in the leachate, indicating the strong adaptive capacity of the microbial population. A correlation analysis between the hydrochemical factors and the microbial community structure revealed that pH was the most influential factor, followed by NO2--N, Fe, Al, Cu, Mn, and others. These results indicate that acidification modifies the hydrochemical conditions of the aquifer, creating an environment that is unfavorable for microbial growth and survival. However, some microorganisms may acquire resistance genes to cope with environmental changes.

Microbially Induced Calcium Carbonate Precipitation as a Bioremediation Technique for Mining Waste

Mining waste represents a global issue due to its potential of generating acidic or alkaline leachate with high concentrations of metals and metalloids (metal(loid)s). Microbial-induced calcium carbonate precipitation (MICP) is an engineering tool used for remediation. MICP, induced via biological activity, aims to precipitate calcium carbonate (CaCO3) or co-precipitate other metal carbonates (MCO3). MICP is a bio-geochemical remediation method that aims to immobilize or remove metal(loid)s via enzyme, redox, or photosynthetic metabolic pathways. Contaminants are removed directly through immobilization as mineral precipitates (CaCO3 or MCO3), or indirectly (via sorption, complexes, or inclusion into the crystal structure). Further, CaCO3 precipitates deposited on the surface or within the pore spaces of a solid matrix create a clogging effect to reduce contaminant leachate. Experimental research on MICP has shown its promise as a bioremediation technique for mining waste. Additional research is required to evaluate the long-term feasibility and potential by-products of MICP-treated/stabilized waste.

High-resolution temporal profiling of E. coli transcriptional response

Understanding how cells dynamically adapt to their environment is a primary focus of biology research. Temporal information about cellular behavior is often limited by both small numbers of data time-points and the methods used to analyze this data. Here, we apply unsupervised machine learning to a data set containing the activity of 1805 native promoters in E. coli measured every 10 minutes in a high-throughput microfluidic device via fluorescence time-lapse microscopy. Specifically, this data set reveals E. coli transcriptome dynamics when exposed to different heavy metal ions. We use a bioinformatics pipeline based on Independent Component Analysis (ICA) to generate insights and hypotheses from this data. We discovered three primary, time-dependent stages of promoter activation to heavy metal stress (fast, intermediate, and steady). Furthermore, we uncovered a global strategy E. coli uses to reallocate resources from stress-related promoters to growth-related promoters following exposure to heavy metal stress.

Evaluation of copper-tolerant fungi isolated from Sarcheshmeh copper mine of Iran

Mycoremediation, a subset of bioremediation, is considered an advanced method to eliminate environmental contaminations. To identify tolerant fungi to copper contamination and study the related gene expression, sampling was carried out from the soil of "Sarcheshmeh Copper Mine," which is one of the biggest open-cast copper mines in the world. A total of 71 fungal isolates were obtained and purified. Afterward, the inhibitory effect of different concentrations (1000, 1500, 3500, 4000, and 5500 ppm) of copper sulfate on mycelial growth was evaluated. Results indicated that only 5500 ppm of copper sulfate inhibited fungal growth compared to the control. Based on the bioassay experiments, three isolates including S3-1, S3-21, and S1-7, which were able to grow on solid and broth medium containing 5500 ppm of copper sulfate at different pH conditions, were selected and identified using molecular approaches. Also, laccase and metallothionein gene expression has been assessed in these isolates. According to the molecular identification using ITS1-5.8S- ITS2 region, isolates S3-1 and S1-7 were identified as Pleurotus eryngii, and isolate S3-21 belonged to the genus Sarocladium. In addition, P. eryngii showed laccase gene expression reduction after 8 days of exposure to copper sulfate. While in the genus Sarocladium, it increased (almost 2 times) from 6 to 8 days. Besides, metallothionein gene expression has increased from 6 to 8 days of copper sulfate treatment compared to the control which reveals its role in copper tolerance of all studied isolates. In this study, Pleurotus eryngii and Sarocladium sp. are introduced as heavy metal tolerant fungi and the related gene expression to copper tolerance was studied for the first time in Iran.

Pseudomonas putida Metallothionein: Structural Analysis and Implications of Sustainable Heavy Metal Detoxification in Madinah

Heavy metals, specifically cadmium (Cd) and lead (Pb), contaminating water bodies of Madinah (Saudi Arabia), is a significant environmental concern that necessitates prompt action. Madinah is exposed to toxic metals from multiple sources, such as tobacco, fresh and canned foods, and industrial activities. This influx of toxic metals presents potential hazards to both human health and the surrounding environment. The aim of this study is to explore the viability of utilizing metallothionein from Pseudomonas putida (P. putida) as a method of bioremediation to mitigate the deleterious effects of pollution attributable to Pb and Cd. The use of various computational approaches, such as physicochemical assessments, structural modeling, molecular docking, and protein-protein interaction investigations, has enabled us to successfully identify the exceptional metal-binding properties that metallothionein displays in P. putida. The identification of specific amino acid residues, namely GLU30 and GLN21, is crucial in understanding their pivotal role in facilitating the coordination of lead and cadmium. In addition, post-translational modifications present opportunities for augmenting the capacity to bind metals, thereby creating possibilities for focused engineering. The intricate web of interactions among proteins serves to emphasize the protein's participation in essential cellular mechanisms, thereby emphasizing its potential contributions to detoxification pathways. The present study establishes a strong basis for forthcoming experimental inquiries, offering potential novel approaches in bioremediation to tackle the issue of heavy metal contamination. Metallothionein from P. putida presents a highly encouraging potential as a viable remedy for environmental remediation, as it is capable of proficiently alleviating the detrimental consequences related to heavy metal pollution.

Recent Advances in the Treatment of Industrial Wastewater from Different Celluloses in Continuous Systems

There are numerous studies on water care methods featured in various academic and research journals around the world. One research area is cellulose residue coupled with continuous systems to identify which are more efficient and easier to install. Investigations have included mathematical design models that provide methods for developing and commissioning industrial wastewater treatment plants, but nothing is provided on how to size and start these treatment systems. Therefore, the objective is to determine recent advances in the treatment of industrial wastewater from different celluloses in continuous systems. The dynamic behavior of the research results with cellulose biomasses was analyzed with the mass balance model and extra-particle and intraparticle dispersion, evaluating adsorption capacities, design variables, and removal constants, and making a size contribution for each cellulose analyzed using adsorption capacities. A mathematical model was also developed that feeds on cellulose reuse, determining new adsorption capacities and concluding that the implementation of cellulose waste treatment systems has a high feasibility due to low costs and high adsorption capacities. Furthermore, with the design equations, the companies themselves could design their systems for the treatment of water contaminated with heavy metals with cellulose.

Research progress on using biological cathodes in microbial fuel cells for the treatment of wastewater containing heavy metals

Various types of electroactive microorganisms can be enriched to form biocathodes that reduce charge-transfer resistance, thereby accelerating electron transfer to heavy metal ions with high redox potentials in microbial fuel cells. Microorganisms acting as biocatalysts on a biocathode can reduce the energy required for heavy metal reduction, thereby enabling the biocathode to achieve a lower reduction onset potential. Thus, when such heavy metals replace oxygen as the electron acceptor, the valence state and morphology of the heavy metals change under the reduction effect of the biocathode, realizing the high-efficiency treatment of heavy metal wastewater. This study reviews the mechanisms, primary influencing factors (e.g., electrode material, initial concentration of heavy metals, pH, and electrode potential), and characteristics of the microbial community of biocathodes and discusses the electron distribution and competition between microbial electrodes and heavy metals (electron acceptors) in biocathodes. Biocathodes reduce the electrochemical overpotential in heavy metal reduction, permitting more electrons to be used. Our study will advance the scientific understanding of the electron transport mechanism of biocathodes and provide theoretical support for the use of biocathodes to purify heavy metal wastewater.

A Comparative Study of Cr(VI) Sorption by Aureobasidium pullulans AKW Biomass and Its Extracellular Melanin: Complementary Modeling with Equilibrium Isotherms, Kinetic Studies, and Decision Tree Modeling

Melanin as a natural polymer is found in all living organisms, and plays an important role in protecting the body from harmful UV rays from the sun. The efficiency of fungal biomass (Aureobasidium pullulans) and its extracellular melanin as Cr(VI) biosorbents was comparatively considered. The efficiency of Cr(VI) biosorption by the two sorbents used was augmented up to 240 min. The maximum sorption capacities were 485.747 (fungus biomass) and 595.974 (melanin) mg/g. The practical data were merely fitted to both Langmuir and Freundlich isotherms. The kinetics of the biosorption process obeyed the pseudo-first-order. Melanin was superior in Cr(VI) sorption than fungal biomass. Furthermore, four independent variables (contact time, initial concentration of Cr(VI), biosorbent dosage, and pH,) were modeled by the two decision trees (DTs). Conversely, to equilibrium isotherms and kinetic studies, DT of fungal biomass had lower errors compared to DT of melanin. Lately, the DTs improved the efficacy of the Cr(VI) removal process, thus introducing complementary and alternative solutions to equilibrium isotherms and kinetic studies. The Cr(VI) biosorption onto the biosorbents was confirmed and elucidated through FTIR, SEM, and EDX investigations. Conclusively, this is the first report study attaining the biosorption of Cr(VI) by biomass of A. pullulans and its extracellular melanin among equilibrium isotherms, kinetic study, and algorithmic decision tree modeling.

An In Silico Bioremediation Study to Identify Essential Residues of Metallothionein Enhancing the Bioaccumulation of Heavy Metals in Pseudomonas aeruginosa

Microorganisms are ubiquitously present in the environment and exert significant influence on numerous natural phenomena. The soil and groundwater systems, precipitation, and effluent outfalls from factories, refineries, and waste treatment facilities are all sources of heavy metal contamination. For example, Madinah, Saudi Arabia, has alarmingly high levels of lead and cadmium. The non-essential minerals cadmium (Cd) and lead (Pb) have been linked to damage to vital organs. Bioremediation is an essential component in the process of cleaning up polluted soil and water where biological agents such as bacteria are used to remove the contaminants. It is demonstrated that Pseudomonas aeruginosa (P. aeruginosa) isolated from activated sludge was able to remove Cd and Pb from water. The protein sequence of metallothionein from P. aeruginosa was retrieved to explore it for physicoparameters, orthologs, domain, family, motifs, and conserved residues. The homology structure was generated, and models were validated. Docking of the best model with the heavy metals was carried out to inspect the intramolecular interactions. The target protein was found to belong to the "metallothionein_pro" family, containing six motifs, and showed a close orthologous relationship with other heavy metal-resistant bacteria. The best model was generated by Phyre2. In this study, three key residues of metallothionein were identified that participate in heavy metal (Pb and Cd) binding, viz., Ala33, Ser34, and Glu59. In addition, the study provides an essential basis to explore protein engineering for the optimum use of metallothionein protein to reduce/remove heavy metals from the environment.

Safe Production Strategies for Soil-Covered Cultivation of Morel in Heavy Metal-Contaminated Soils

Morel is a popular edible mushroom with considerable medicinal and economic value which has garnered global popularity. However, the increasing heavy metal (HM) pollution in the soil presents a significant challenge to morels cultivation. Given the susceptibility of morels to HM accumulation, the quality and output of morels are at risk, posing a serious food safety concern that hinders the development of the morel industry. Nonetheless, research on the mechanism of HM enrichment and mitigation strategies in morel remains scarce. The morel, being cultivated in soil, shows a positive correlation between HM content in its fruiting body and the HM content in the soil. Therefore, soil remediation emerges as the most practical and effective approach to tackle HM pollution. Compared to physical and chemical remediation, bioremediation is a low-cost and eco-friendly approach that poses minimal threats to soil composition and structure. HMs easily enriched during morels cultivation were examined, including Cd, Cu, Hg, and Pb, and we assessed soil passivation technology, microbial remediation, strain screening and cultivation, and agronomic measures as potential approaches for HM pollution prevention. The current review underscores the importance of establishing a comprehensive system for preventing HM pollution in morels.

Phytoremediation as a way to clean technogenically polluted areas of Kazakhstan

One of the most serious problems worldwide is heavy metal (HM) pollution. HMs can have a toxic effect on human health and thus cause serious diseases. To date, several methods have been used to clean environments contaminated by HMs, but most of them are expensive, and it is difficult to achieve the desired result. Phytoremediation is currently an effective and affordable processing solution used to clean and remove HMs from the environment. This review article discusses in detail the technology of phytoremediation and mechanisms of HM absorption. In addition, methods are described using genetic engineering of various plants to enhance the resistance and accumulation of HMs. Thus, phytoremediation technology can become an additional aid to traditional methods of purification.

Mercury remediation potential of mercury-resistant strain Rheinheimera metallidurans sp. nov. isolated from a municipal waste dumping site

A novel mercury-resistant bacterium, designated strain DCL_24^T, was isolated from the legacy waste at the Daddu Majra dumping site in Chandigarh, India. It showed resistance up to 300 µM of inorganic mercury (mercuric chloride). The isolate was found to be a Gram-negative, facultative anaerobic, motile, and rod-shaped bacterium that can grow at 4 - 30 °C (optimum 25 °C), pH 6.0 - 12.0 (optimum 7.0), and 0 - 4.0 % (w/v) NaCl (optimum 0.5 - 2.0 %). The 16 S rRNA gene-based phylogenetic analysis showed that DCL_ 24 ^T shared a 97.53 % similarity with itsºlosest type strain Rheinheimera muenzenbergensis E-49^T. Insilico DNA-DNA hybridization and average nucleotide identity values were found to be 18.60 % and 73.77 %, respectively, between the genomes of DCL_24^T and R. muenzenbergensis E-49^T. The strain DCL_24^T has 44.33 DNA G+C content (mol %). Based on the phenotypic, chemotaxonomic, and genotypic data, the strain DCL_24^T represents a novel species within the genus Rheinheimera, for which the name Rheinheimera metallidurans sp. nov is proposed. The type strain is DCL_24^T (MTCC13203^T = NBRC115780^T = JCM 35551 ^T). The isolate was found to volatilize and remove mercury efficiently, as demonstrated by X-ray film and dithizone-based colorimetric methods. Around 92 % of mercury removal was observed within 48 h. The mercury-resistant determinant mer operon consisting of merA, encoding the mercuric reductase enzyme, and transport and regulatory genes (merT, merP, merD, and merR) were found in the isolate. Relative expression analysis of merA at increasing concentrations of HgCl₂ was confirmed by quantitative real-time PCR. These data indicate the merA-mediated reduction of toxic Hg²⁺ into a non-toxic volatile Hg⁰. The phytotoxicity assay performed using Arabidopsis thaliana seeds further demonstrated the mercury toxicity reduction potential of DCL_24^T. The study shows that this novel isolate, DCL_24^T, is an interesting candidate for mercury bioremediation. However, further studies are required to assess the bioremediation efficacy of the strain under the harsh environmental conditions prevailing in polluted sites.

Effects of metal contamination with physicochemical properties on the sediment microbial communities in a tropical eutrophic-hypereutrophic urban reservoir in Brazil

We investigated the effects of metals and physicochemical variables on the microbes and their metabolisms in the sediments of Guarapiranga reservoir, a tropical eutrophic-hypereutrophic freshwater reservoir located in a highly urbanized and industrialized area in Brazil. The metals cadmium, copper, and chromium showed minor contribution to changes in the structure, composition, and richness of sediment microbial communities and functions. However, the effects of metals on the microbiota are increased when taken together with physicochemical properties, including the sediment carbon and sulfur, the bottom water electrical conductivity, and the depth of the water column. Clearly, diverse anthropic activities, such as sewage discharge, copper sulfate application to control algal growth, water transfer, urbanization, and industrialization, contribute to increase these parameters and the metals spatially in the reservoir. Microbes found especially in metal-contaminated sites encompassed Bathyarchaeia, MBG-D and DHVEG-1, Halosiccatus, Candidatus Methanoperedens, Anaeromyxobacter, Sva0485, Thermodesulfovibrionia, Acidobacteria, and SJA-15, possibly showing metal resistance or acting in metal bioremediation. Knallgas bacteria, nitrate ammonification, sulfate respiration, and methanotrophy were inferred to occur in metal-contaminated sites and may also contribute to metal removal. This knowledge about the sediment microbiota and metabolisms in a freshwater reservoir impacted by anthropic activities allows new insights about their potential for metal bioremediation in these environments.

Filamentous fungi for sustainable remediation of pharmaceutical compounds, heavy metal and oil hydrocarbons

This review presents a comprehensive summary of the latest research in the field of bioremediation with filamentous fungi. The main focus is on the issue of recent progress in remediation of pharmaceutical compounds, heavy metal treatment and oil hydrocarbons mycoremediation that are usually insufficiently represented in other reviews. It encompasses a variety of cellular mechanisms involved in bioremediation used by filamentous fungi, including bio-adsorption, bio-surfactant production, bio-mineralization, bio-precipitation, as well as extracellular and intracellular enzymatic processes. Processes for wastewater treatment accomplished through physical, biological, and chemical processes are briefly described. The species diversity of filamentous fungi used in pollutant removal, including widely studied species of Aspergillus, Penicillium, Fusarium, Verticillium, Phanerochaete and other species of Basidiomycota and Zygomycota are summarized. The removal efficiency of filamentous fungi and time of elimination of a wide variety of pollutant compounds and their easy handling make them excellent tools for the bioremediation of emerging contaminants. Various types of beneficial byproducts made by filamentous fungi, such as raw material for feed and food production, chitosan, ethanol, lignocellulolytic enzymes, organic acids, as well as nanoparticles, are discussed. Finally, challenges faced, future prospects, and how innovative technologies can be used to further exploit and enhance the abilities of fungi in wastewater remediation, are mentioned.

Microbial assemblage for solid waste bioremediation and valorization with an essence of bioengineering

Environmental solid waste bioremediation is a method of treating contaminated solid waste that involves changing ecological conditions to foster the growth of a broad spectrum of microorganisms and the destruction of the target contaminants. A wide range of microorganisms creates metabolites that may break down and change solid waste-based pollution to various value-added molecules. Diverse bioremediation technologies, their limitations, and the procedure involve recycling solid waste materials from the environment. The existing environmental solid waste disposal services are insufficient and must be upgraded with more lucrative recovery, recycling, and reuse technologies to decrease the enormous expenditures in treatment procedures. Bioremediation of solid waste eliminates the toxic components. It restores the site with the advent of potential microbial communities towards solid waste valorization utilizing agriculture solid waste, organic food waste, plastic solid waste, and multiple industrial solid wastes.Bioengineering on diverse ranges of microbial regimes has accelerated to provide extra momentum toward solid waste recycling and valorization. This approach increases the activity of bioremediating microbes in the commercial development of waste treatment techniques and increases the cost-effective valuable product generation. This framework facilitates collaboration between solid waste and utilities. It can aid in establishing a long-term management strategy for recycling development with the advent of a broad spectrum of potential microbial assemblages, increasing solid waste contamination tolerance efficiency and solid waste degradability. The current literature survey extensively summarises solid waste remediation valorization using a broad spectrum of microbial assemblages with special emphasis on bioengineering-based acceleration. This approach is to attain sustainable environmental management and value-added biomolecule generation.

Evaluation of the Hybrid Membrane of ZnO Particles Supported in Cellulose Acetate for the Removal of Lead

Water polluted by discarded heavy metals such as lead is creating a global pollution problem. In this work, adsorption of Pb(II) was realized in batch studies by a hybrid membrane of cellulose acetate with ZnO particles. First, ZnO particles were prepared by precipitation and immobilized on the membrane. The hybrid membrane was elaborated by interfacial polymerization. The structure and surface were characterized based on Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Batch experiments were carried out under different conditions where the number of particles of ZnO present in the membrane and the pH of the aqueous solution were varied. The Langmuir and Freundlich isotherm models were evaluated in the best adsorption conditions. Data fitted well with a Langmuir model with a maximum adsorption capacity of 15.55 mg·g^-1, which was similar for this type of materials. Thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy showed that the process was spontaneous and favorable. The hybrid membrane was evaluated in simulated wastewater of the battery industry with a superior efficiency of up to 97%; without the medium, it did not generate interference. These results suggest that Pb(II) removal by hybrid membrane is possible.

Microbial community and predictive functionalities associated with the marine sediment of Coastal Gujarat

Marine sediments are complex ecosystems where structures and functions constantly change due to natural and anthropogenic influences. In this investigation, a comprehensive and comparative analysis of the bacterial communities and their functional potential of the pristine and polluted marine sediments were carried out using MiSeq. The phylum Proteobacteria was dominant in all study sites. Other phyla were Actinobacteria, Bacteroidetes, Planctomycetes, Acidobacteria, Chloroflexi, Nitrospirae, Cyanobacteria, Verrucomicrobia, Tenericutes, and Chlorobi. Interestingly, about 50% of genera belong to the unclassified categories. The key genera were identified as Acinetobacter, Bacillus, Pseudomona, Idiomarina, Thalassospira, and Marinobacter, Halomonas, Planctomyces, Psychrobacter, and Vogesella. PICRUSt analysis revealed that major functions are associated with the metabolism category. Additionally, metabolism related to amino acids, carbohydrates, energy generation, xenobiotics degradation, nitrogen, sulfate, and methane were prominent. Similarly, the predicted metabolisms by COG and KEGG were observed in the microbial communities of the marine sediments. To date, a comprehensive description of the microbial life with metabolic potential in these study sites has not been investigated. This study therefore significantly adds to our understanding of the microbiome and its functional attributes of marine sediments.

Challenges and opportunities in bringing nonbiological atoms to life with synthetic metabolism

The relatively narrow spectrum of chemical elements within the microbial 'biochemical palate' limits the reach of biotechnology, because several added-value compounds can only be produced with traditional organic chemistry. Synthetic biology offers enabling tools to tackle this issue by facilitating 'biologization' of non-canonical chemical atoms. The interplay between xenobiology and synthetic metabolism multiplies routes for incorporating nonbiological atoms into engineered microbes. In this review, we survey natural assimilation routes for elements beyond the essential biology atoms [i.e., carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S)], discussing how these mechanisms could be repurposed for biotechnology. Furthermore, we propose a computational framework to identify chemical elements amenable to biologization, ranking reactions suitable to build synthetic metabolism. When combined and deployed in robust microbial hosts, these approaches will offer sustainable alternatives for smart chemical production.

Bacteria isolated from e-waste soil enhance plant growth and mobilize trace metals in e-waste-amended soils

Worldwide accumulation of e-waste poses a major threat to environmental health. However, printed circuit boards contain precious metals, such as gold, and silver, and also contain micronutrient metal elements, such as Fe, Cu, Zn, etc. Therefore, the present study investigated the effects of e-waste-tolerant bacteria (ETB) on promoting plant growth in e-waste-amended soils and mobilizing trace metals into the plants. For this, a total of 18 bacteria were isolated and screened for e-waste tolerance. Screening for plant growth-promoting properties revealed the production of indole-3-acetic acid-like compounds, siderophore production, and phosphate solubilization. Identification based on 16S rRNA gene sequencing revealed that all isolates belonged to the genus Bacillus. Pot experiment revealed that the treated seeds showed the enhancement of chili plants root growth ranging from 106.55 to 208.07% compared to control plants (e-waste) and 0.0 to 47.90% (without e-waste). A similar enhancement was also observed in the shoot length, and size of the leaf compared to e-waste amended control plants. Inoculation of ETB significantly (p < 0.05) mobilized Fe, Zn, Cu, and Ni into chili plants. The identified ETB could be used to mitigate the toxicity posed by the e-waste, enhancing plant growth and mobilization of micronutrients into plants from e-waste.

Fungal assisted bio-treatment of environmental pollutants with comprehensive emphasis on noxious heavy metals: Recent updates

In the present time of speedy developments and industrialization, heavy metals are being uncovered in aquatic environment and soil via refining, electroplating, processing, mining, metallurgical activities, dyeing and other several metallic and metal based industrial and synthetic activities. Heavy metals like lead (Pb), mercury (Hg), cadmium (Cd), arsenic (As), Zinc (Zn), Cobalt (Co), Iron (Fe), and many other are considered as seriously noxious and toxic for the aquatic environment, human, and other aquatic lives and have damaging influences. Such heavy metals, which are very tough to be degraded, can be managed by reducing their potential through various processes like removal, precipitation, oxidation-reduction, bio-sorption, recovery, bioaccumulation, bio-mineralization etc. Microbes are known as talented bio-agents for the heavy metals detoxification process and fungi are one of the cherished bio-sources that show noteworthy aptitude of heavy metal sorption and metal tolerance. Thus, the main objective of the authors was to come with a comprehensive review having methodological insights on the novel and recent results in the field of mycoremediation of heavy metals. This review significantly assesses the potential talent of fungi in heavy metal detoxification and thus, in environmental restoration. Many reported works, methodologies and mechanistic sights have been evaluated to explore the fungal-assisted heavy metal remediation. Herein, a compact and effectual discussion on the recent mycoremediation studies of organic pollutants like dyes, petroleum, pesticides, insecticides, herbicides, and pharmaceutical wastes have also been presented.

The Therapeutic Potential of Algal Nanoparticles: A Brief Review

Recently, the green synthesis of metallic nanoparticles (NPs) has received tremendous attention as a simple approach. The green pathway of biogenic synthesis of metallic NPs through microbes may provide a sustainable and environmentally friendly protocol. Green technology is the most innovative technology for various biological activities and lacks toxic effects. Reports have shown the algae-mediated synthesis of metal NPs. Algae are widely used for biosynthesis as they grow fast; they produce biomass on average ten times that of plants and are easily utilized experimentally. In the future, the production of metal NPs by different microalgae and their biological activity can be explored in diverse areas such as catalysis, medical diagnosis, and anti-biofilm applications.

Heavy metals and their sources, potential pollution situations and health risks for residents in Adıyaman province agricultural lands, Türkiye

In this study, the contents of heavy metals (HMs) such as Al, Cd, Co, Cr, Cu Fe, Mn, Ni, Pb and Zn in soil samples collected from 403 sampling locations of the agricultural lands of Adıyaman Province (Türkiye) were determined by Inductively Coupled Plasma‒Optical Emission Spectrometry (ICP‒OES). The mean concentrations of Al, Cd, Co Cr, Cu Fe, Mn, Ni, Pb and Zn HMs were detected 28,986, 3.60, 15, 127, 52.67, 45,830, 817, 62.40, 10.75 and 66.25 mg kg^-1, respectively. These results showed that the average concentrations of Cd, Cr, Cu, Fe, Mn and Ni exceeded the Upper continental crust average. To determine and to evaluate the contamination status and distribution of HMs in agricultural soils, metal pollution parameters such as enrichment factor (EF), geoaccumulation index (I_geo), contamination factor (Cf), pollution load index, potential ecological risk factor (Er), and potential ecological risk index (RI) were used. Factor analyses (FA) and principal component analyses (PCA) indicated that Cd, Cr and Ni levels were influenced by anthropogenic sources, Fe by both lithological and anthropogenic sources, and other HMs by lithogenic origins. For both children and adults, the hazard index (HI) and total hazard index (THI) values of HMs were < 1, suggesting that non-carcinogenic health risks to residents through ingestion, inhalation pathways, and dermal contact were currently absent. In addition, the cumulative carcinogenic risk (CCR) results were within the acceptable risk range (10^-4 to 10^-6). The results showed that children were more sensitive to the non-carcinogenic and carcinogenic effects of HMs.

Biosorption potential and molecular characterization of metal-resistant autochthonous microbes from tannery solid waste

This study encompasses isolation and screening of heavy metal-resistant fungal and bacterial strains from tannery solid waste (TSW). Twelve fungal strains and 25 bacterial strains were isolated from TSW. The growth of fungal strains was observed against different heavy metals ranging from 10 to 1050 mg L^-1 and the growth of bacteria was observed in metal concentrations ranging from 10 to 1200 mg L^-1. Five multi-metal-resistant fungal isolates belonging to the genus Trichoderma and ten bacterial isolates belonging to the genus Bacillus showed good metal resistance and biosorption potential. They were identified through molecular techniques, fungi based on ITS region ribotyping, and bacteria based on 16S rRNA ribotyping. The fungal strains were characterized as T. hamatum (TSWF-06), T. harzianum (TSWF-11), T. lixii (TSWF-02), and T. pseudokoningii (TSWF-03, TSWF-10). The bacterial strains were characterized as Bacillus xiamenensis (TSW-02), B. velezensis (TSW-05), B. piscis (TSW-06), B. safensis (TSW-10), B. subtilis (TSW-14, TSW-15, TSW-17) B. licheniformis (TSW-19), B. cereus (TSW-20), and B. thuringiensis (TSW-22). The fungal strains, namely, T. pseudokoningii (TSWF-03) and T. harzianum, proved to be two multi-metal-resistant strains with good biosorption efficiency. Unlike fungi, bacterial strains showed metal-specific resistance. The strains Bacillus xiamenensis, B. subtilis (TSW-14), and B. subtilis (TSW-15) showed good biosorption efficiency against Cr, B. safensis against Cu, B. piscis, and B. subtilis (TSW-17) against Pb and B. licheniformis and B. thuringiensis against Zn. The autochthonous fungal and bacterial strains can therefore be employed to clean metal-contaminated environments.

Investigating the role of bentonite clay with different soil amendments to minimize the bioaccumulation of heavy metals in Solanum melongena L. under the irrigation of tannery wastewater

Wastewater from tanneries is a major source of heavy metals in soil and plants when used for crop irrigation. The unavoidable toxicological effects of this contamination, however, can be minimized through two independent steps discussed in the present study. In the first step, a batch sorption experiment was conducted in which Cr was adsorbed through bentonite clay. For this purpose, DTPA extraction method was used to analyze Cr concentration in the soil after regular time intervals (0.5, 1, 2, 6, 8, 9, 10.5, 11.5, and 20.3 h) which reduced Cr concentration from 38.542 mgL^-1 for 30 min to 5.6597 mgL^-1 for 20.3 h, respectively, by applying 1% bentonite. An increase in the contact time efficiently allowed soil adsorbent to adsorb maximum Cr from soil samples. In the second step, a pot experiment was conducted with 10 different treatments to improve the physiological and biochemical parameters of the Solanum melongena L. irrigated under tanneries' wastewater stress. There were four replicates, and the crop was harvested after 30 days of germination. It was seen that the application of wastewater significantly (P < 0.01) reduced growth of Solanum melongena L. by reducing root (77%) and shoot (63%) fresh weight when compared with CFOP (Ce-doped Fe₂O₃ nanoparticles); chlorophyll a and b (fourfolds) were improved under CFOP application relative to control (CN). However, the deleterious effects of Cr (86%) and Pb (90%) were significantly decreased in shoot through CFOP application relative to CN. Moreover, oxidative damage induced by the tannery's wastewater stress (P < 0.01) was tolerated by applying different soil amendments. However, results were well pronounced with the application of CFOP which competitively decreased the concentrations of MDA (95%), H₂O₂ (89%), and CMP (85%) by efficiently triggering the activities of antioxidant defense mechanisms such as APX (threefold), CAT (twofold), and phenolics (75%) in stem relative to CN. Consequently, all the applied amendments (BN, BT, FOP, and CFOP) have shown the ability to efficiently tolerate the tannery's wastewater stress; results were more pronounced with the addition of CFOP and FOP+BT by improving physiological and biochemical parameters of Solanum melongena L. in an eco-friendly way.

Co-over expression of Ascorbate Glutathione pathway enzymes improve mercury tolerance in tomato

The genetic modification of plants for the removal of inorganic pollutants from contaminated soil and water bodies is an emerging area for addressing environmental concerns. This approach is based on the ability of plants to take up and accumulate heavy metals, with efficiency being dependent on the underlying mechanisms of heavy metal accumulation and tolerance. A robust antioxidant pathway is determinantal for heavy metal uptake and accumulation and, therefore, in this study, we evaluated the transgenic tomato plants installed with Ascorbate Glutathione (ASA-GSH) pathway genes for uptake, accumulation, and response to mercury (Hg). We observed that ASA-GSH overexpressing lines were resilient to Hg stress as they displayed higher photosynthetic activity and increased photosynthetic gas exchange parameters with a concomitant decrease in ion leakage under Hg stress. Additionally, transgenic lines accumulated high osmolytes and showed enhanced activity of antioxidant enzymes. Moreover, the results of SEM and confocal microscopy confirmed least damage to plant tissue in ASA-GSH overexpressing lines compared to wild-type under Hg-stress which was further supported by Atomic absorption study that revealed a significant decline in Hg accumulation in the leaves of transgenic lines compared to wild-type under stress conditions. In conclusion, pyramiding of ASA-GSH pathway genes in tomato plants is an efficient approach for the development of Hg-resistant tomato plants and the reclamation of Hg-contaminated sites.

Immobilization of heavy metals by microbially induced carbonate precipitation using hydrocarbon-degrading ureolytic bacteria

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Heavy metal toxicity to hydrocarbon-degrading ureolytic bacteria is Cd > Ni > Cr > Cu > Zn.

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The ureolytic bacteria can tolerate heavy metals and co-precipitate heavy metals.

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The precipitated minerals shifted between calcite and brushite depending on the heavy metal.

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The immobilization of heavy metals resulted in removal efficiency reaching 100%.

Crude oil contamination introduces multiple threats to human health and the environment, most of which are from toxic heavy metals. Heavy metals cause significant threats because of their persistence, toxicity, and bio-accumulation. Biomineralization, performed through many microbial processes, can lead to the immobilization of heavy metals in formed minerals. The potential of the microbially carbonate-induced precipitation (MICP) in removal by biomineralization of several heavy metals was investigated. A collection of diverse 11 bacterial strains exhibited ureolytic activity and tolerance to heavy metals when growing in Luria-Bertani (LB) and urea medium. Determination of the minimum inhibitory concentrations (MIC) revealed that heavy metal toxicity was arranged as Cd > Ni > Cr > Cu > Zn. Three hydrocarbon-degrading bacterial strains (two of Pseudomonas aeruginosa and one of Providencia rettgeri) exhibited the highest tolerance (MIC > 5 mM) to Cu, Cr, Zn, and Ni, whereas Cd exerted significantly higher toxicity with MIC <1 mM. At all MICP conditions, different proportions of calcium carbonate (calcite) and calcium phosphate (brushite) were formed. Pseudomonas aeruginosa strains (QZ5 and QZ9) exhibited the highest removal efficiency of Cr (100%), whereas Providencia rettgeri strain (QZ2) showed 100% removal of Zn. Heavy metal complexes were found as well. Cd removal was evidenced by the formation of cadmium phosphate induced by Providencia rettgeri bacterial activity. Our study confirmed that hydrocarbon-degrading ureolytic bacteria not only can tolerate heavy metal toxicity but also have the capability to co-precipitate heavy metals. These findings indicate an effective and novel biological approach to bioremediate petroleum hydrocarbons and immobilize multiple heavy metals with mineral formation. This is of high importance for ecological restoration via stabilization of soil and alleviation of heavy metal toxicity.

Phylogenetic Illustration of Eisenia fetida Associated Vermi-bacteria Involved in Heavy Metals Remediation and Retaining Plant Growth Promoting Traits

Heavy metals contamination in the soil is a major threat to wildlife, the environment, and human health. Microbial remediation is an emerging and promising technology to reduce heavy metals toxicity. Therefore, the present research aimed to isolate and to identify the heavy metals tolerated bacteria from the Eisenia fetida for the first time, and to screen the bacto-remediation capabilities and plant growth promoting traits of vermi-bacterial isolates. Vermi-bacteria was isolated from the gut of E. fetida, identified through staining, culturing, biochemical tests, and ribotyping. Plant growth-promoting traits were also evaluated. Phylogenetic results revealed that isolated Vermi-bacterial strains showed resemblance with Bacillus thuringiensis, Bacillus aryabhattai, Staphylococcus hominis, Bacillus toyonensis, Bacillus cabrialesii, Bacillus tequilensis, Bacillus mojavensis, Bacillus amyloliquefaciens, Bacillus toyonensis, Bacillus anthracis, and Bacillus paranthracis. All identified Vermi-bacterial species are Gram-positive (rod and cocci) in nature, not only indicated the efficient biosorption of lead, cadmium, and chromium but also produce all plant growth stimulating traits such as indole acetic acid (IAA), amylase, protease, lipase, hydrogen cyanide, ammonia, and siderophore production, and also act as a phosphate solubilizers. Bacillus anthracis showed significant production of siderophore (33.0±0.0 mm), phosphate solubilizing (33.0±0.0 mm), proteolytic (15.0±0.0 mm), and lipolytic activities (20.0±0.0 mm) compared to other vermi-bacterial isolates. Bioaccumulation factor results revealed that Bacillus anthracis showed more accumulation of Cd (12.00±0.01 ppm), Cr (5.38±0.01 ppm), and Pb (4.38±0.01 ppm). Therefore, the current findings showed that all identified vermi-bacteria could be used as potential bactoremediation agents in heavy metals polluted environments and could be used as microbial biofertilizers to enhance crop production in a polluted area.

Isolation and characterization of chromium (VI) tolerant bacteria from tannery effluents

BACKGROUND

The tannery industry is a potent environment polluting agent worldwide. Chromium (VI) is a major heavy metal in tannery effluents and their accumulation in soil and water is a serious environmental problem. This study investigates the capacity of indigenous bacteria isolated from tannery effluents for tolerance to chromium (VI).

METHODS

The chromium tolerance of isolates assessed through both agar dilution and broth microdilution methods. Isolates were identified by morphological and biochemical analysis. The tolerance of isolates to cadmium, nickel, lead, and vanadium and also their multidrug-resistant (MDR) profile were determined. Then the top isolate was characterized via 16S rRNA sequencing and its growth temperature and pH were optimized. Finally, the kinetic of chromium biosorption and chromium removal efficiency was determined using a Nutrient broth medium and wastewater containing 20 mg/L chromium, respectively.

RESULTS

Of 32 screened chromium tolerant isolates, 14 isolates with higher chromium tolerance were selected for further study. 78.57% of isolates represented simultaneous MDR and Multi Heavy Metal tolerance (MHMT) phenotypes and MDR indices of 0.2-1 indicating their source from niches with high antibiotic contamination. However, there was no significant correlation between MDR and MHMT phenotypes among isolates. The top isolate was identified as Lactococcus lactis and showed optimal growth at pH 6 and 25 °C. The maximum chromium biosorption occurred at the end of the exponential phase upon optimized conditions and the approximate chromium removal efficiency of 52.5% was obtained.

CONCLUSION

The isolated bacteria specifically L. lactis after more evaluations, may show the potential for bioremediation of chromium from tannery effluents.

Plants-Microorganisms-Based Bioremediation for Heavy Metal Cleanup: Recent Developments, Phytoremediation Techniques, Regulation Mechanisms, and Molecular Responses

Rapid industrialization, mine tailings runoff, and agricultural activities are often detrimental to soil health and can distribute hazardous metal(loid)s into the soil environment, with harmful effects on human and ecosystem health. Plants and their associated microbes can be deployed to clean up and prevent environmental pollution. This green technology has emerged as one of the most attractive and acceptable practices for using natural processes to break down organic contaminants or accumulate and stabilize metal pollutants by acting as filters or traps. This review explores the interactions between plants, their associated microbiomes, and the environment, and discusses how they shape the assembly of plant-associated microbial communities and modulate metal(loid)s remediation. Here, we also overview microbe-heavy-metal(loid)s interactions and discuss microbial bioremediation and plants with advanced phytoremediation properties approaches that have been successfully used, as well as their associated biological processes. We conclude by providing insights into the underlying remediation strategies' mechanisms, key challenges, and future directions for the remediation of metal(loid)s-polluted agricultural soils with environmentally friendly techniques.

Microbial bioremediation strategies with wastewater treatment potentialities - A review

The demand for innovative waste treatment techniques has arisen because of the establishment and operation of rigorous waste discharge guidelines into the environment. Due to the rapid increase in the human population, wastewater treatment is a procedure of increasing significance. As a result, wastewater treatment systems are intended to sustain high activities and densities of such microorganisms which meet the different purification requirements. The waste produced by the pharmaceutical industry, if not adequately treated, has harmful repercussions for the environment as well as public health. Bioremediation is an innovative and optimistic technology that can be used to remove and reduce heavy metals from polluted water and contaminated soil. Because of cost-effectiveness and environmental compatibility, bioremediation using microorganisms has an excellent potential for future development. A diverse range of microorganisms, including algae, fungi, yeasts, and bacteria, can function as biologically active methylators, capable of modifying toxic species. Microorganisms play a crucial role in heavy metal bioremediation. Nanotechnology may minimize industry expenses by producing environmentally friendly nanomaterials to alleviate these contaminants. The use of microorganisms in nanoparticle synthesis gives green biotechnology a positive impetus to cost reduction and sustainable production as a developing nanotechnology sector.

Practical limitations of bioaugmentation in treating heavy metal contaminated soil and role of plant growth promoting bacteria in phytoremediation as a promising alternative approach

Bioaugmentation, the addition of cultured microorganisms to enhance the currently existing microbial community, is an option to remediate contaminated areas. Several studies reported the success of the bioaugmentation method in treating heavy metal contaminated soil, but concerns related to the applicability of this method in real-scale application were raised. A comprehensive analysis of the mechanisms of heavy metal treatment by microbes (especially bacteria) and the concerns related to the possible application in the real scale were juxtaposed to show the weakness of the claim. This review proposes the use of bioaugmentation-assisted phytoremediation in treating heavy metal contaminated soil. The performance of bioaugmentation-assisted phytoremediation in treating heavy metal contaminated soil as well as the mechanisms of removal and interactions between plants and microbes are also discussed in detail. Bioaugmentation-assisted phytoremediation shows greater efficiencies and performs complete metal removal from soil compared with only bioaugmentation. Research related to selection of hyperaccumulator species, potential microbial species, analysis of interaction mechanisms, and potential usage of treating plant biomass after treatment are suggested as future research directions to enhance this currently proposed topic.

Genomic and proteomic insights into the heavy metal bioremediation by cyanobacteria

Heavy metals (HMs) pose a global ecological threat due to their toxic effects on aquatic and terrestrial life. Effective remediation of HMs from the environment can help to restore soil's fertility and ecological vigor, one of the key Sustainable Development Goals (SDG) set by the United Nations. The cyanobacteria have emerged as a potential option for bioremediation of HMs due to their unique adaptations and robust metabolic machineries. Generally, cyanobacteria deploy multifarious mechanisms such as biosorption, bioaccumulation, activation of metal transporters, biotransformation and induction of detoxifying enzymes to sequester and minimize the toxic effects of heavy metals. Therefore, understanding the physiological responses and regulation of adaptation mechanisms at molecular level is necessary to unravel the candidate genes and proteins which can be manipulated to improve the bioremediation efficiency of cyanobacteria. Chaperons, cellular metabolites (extracellular polymers, biosurfactants), transcriptional regulators, metal transporters, phytochelatins and metallothioneins are some of the potential targets for strain engineering. In the present review, we have discussed the potential of cyanobacteria for HM bioremediation and provided a deeper insight into their genomic and proteomic regulation of various tolerance mechanisms. These approaches might pave new possibilities of implementing genetic engineering strategies for improving bioremediation efficiency with a future perspective.

Influence of cobalt chloride and ferric citrate on purple non-sulfur bacteria Rhodopseudomonas yavorovii

Heavy metals that enter the environment due to natural processes or industrial activities, when accumulated, have a negative impact on organisms, including microorganisms. Microorganisms have developed various adaptations to heavy metal compounds. The aim of our work was to investigate the influence of ferric citrate and cobalt (II) chloride on biomass accumulation, indicators of free radical damage and activity of enzymes of the antioxidant defense system of bacteria Rhodopseudomonas yavorovii IMV B-7620, that were isolated from the water of Yavorivske Lake (Ukraine, Lviv region), which was formed as a result of flooding of a sulfur quarry. We used cultural, photometric methods, and statistical processing of the results was performed using two-way ANOVA and factor analysis. It was found that ferric citrate at a concentration of 1–12 mM causes inhibition of the accumulation of biomass of bacteria Rh. yavorovii IMV B-7620 up to 44.7%, and cobalt (II) chloride at a concentration of 1–15 mM – up to 70.4%, compared with the control. The studied concentrations of ferric citrate and cobalt (II) chloride cause free radical damage to lipids and proteins of Rh. yavorovii IMV B-7620. As a result of two-way ANOVA we found that under the influence of ferric citrate statistically significant changes in biomass accumulation, lipid hydroperoxides and thiobarbiturate reactive species content, superoxide dismutase activity were predetermined by increasing the concentration of metal salts as well as increasing the duration of cultivation of bacteria, while the content of diene conjugates and catalase activity changed with increasing duration of cultivation. Under the influence of cobalt (II) chloride, statistically significant changes in all studied indicators were found both due to the increase in the concentration of metal salts and with increasing duration of bacterial cultivation. The studied parameters of Rh. yavorovii IMV B-7620 cells under the influence of ferric citrate and cobalt (II) chloride are combined into two factors, that explain 95.4% and 99.2% of the total data variance, respectively. Under the influence of ferric citrate, the first latent factor included diene conjugates, thiobarbiturate reactive species, carbonyl groups in proteins, which are closely linked by a direct bond and inversely related to the content of lipid hydroperoxides and catalase activity. The second latent factor included duration of cultivation of bacteria, biomass accumulation, and superoxide dismutase activity, which are inversely related to lipid hydroperoxide content and catalase activity. Under the influence of cobalt (II) chloride, the first latent factor included the content of lipid hydroperoxides, carbonyl groups in proteins, as well as catalase and superoxide dismutase activities, which are inversely related to bacterial biomass.

Bio- and phytoremediation: plants and microbes to the rescue of heavy metal polluted soils

Bio- and phytoremediation, being encouraging terms implying the use of biological systems for cleansing purposes, have risen a worthy venture toward environmental restoration in discouraging scenarios, such as the augmentation of indestructible heavy metals. Hyperaccumulating plants and heavy metal resistant microbes own mechanisms embedded in their metabolism, proteins, and genes that confer them with “super characteristics” allowing them to assimilate heavy metals in order to amend polluted soils, and when combined in a symbiotic system, these super features could complement each other and be enhanced to overpower the exposure to toxic environments. Though xenobiotic pollution has been an object of concern for decades and physicochemical procedures are commonly carried out to offset this purpose, a “live” remediation is rather chosen and looked upon for promising results. A variety of benefits have been registered from symbiotic relationships, including plants teaming up with microbes to cope down with non-biodegradable elements such as heavy metals; but a carefully maneuvered interaction might signify a greater insight toward the application of bioremediation systems. These manipulations could consist of genetic engineering and/or additional supplementation of molecules and microbes. In the present study, a contemporary connection between plants and microbes involving their controlled management is summarized in a visionary display.

Biological remediation technologies for dyes and heavy metals in wastewater treatment: New insight

The pollution of the environment caused by dyes and heavy metals emitted by industries has become a worldwide problem. The development of efficient, environmentally acceptable, and cost-effective methods of wastewater treatment containing dyes and heavy metals is critical. Biologically based techniques for treating effluents are fascinating since they provide several benefits over standard treatment methods. This review assesses the most recent developments in the use of biological based techniques to remove dyes and heavy metals from wastewater. The remediation of dyes and heavy metals by diverse microorganisms such as algae, bacteria, fungi and enzymes are depicted in detail. Ongoing biological method's advances, scientific prospects, problems, and the future prognosis are all highlighted. This review is useful for gaining a better integrated view of biological based wastewater treatment and for speeding future research on the function of biological methods in water purification applications.

Insights into the response of mangrove sediment microbiomes to heavy metal pollution: Ecological risk assessment and metagenomics perspectives

Rapid urbanisation and ensuing anthropogenic pollution lead to an escalated occurrence of heavy metals and metal-resistant bacteria in the soil ecosystem. Mangrove ecosystems are particularly vulnerable to heavy metal bioaccumulation and often act as metal sinks of the coastal areas. As a consequence, the microbial population in mangrove sediments develop multifarious metal tolerance mechanisms to combat metal toxicity. In this context, metagenomic investigation of two mangroves, viz. Mangalavanam and Puthuvypin from the heavily populated metropolitan city, Cochin (Central Kerala, India) was undertaken to discern the metal resistance functions and taxonomic diversity of the microbial consortia. Estimation of heavy metal content using Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-MS) identified the abundance of zinc, chromium, nickel copper, lead, arsenic, and cadmium in the mangrove sediments. Ecological risk index values indicated high cadmium contamination of the two estuarine samples. Whole metagenome shotgun sequencing of the Central Kerala mangroves and comparative analysis with mangrove metal resistomes from other geographical regions revealed the prevalence of cobalt-zinc-cadmium resistance and preponderance of Proteobacteria in all the datasets. Cation efflux system protein CusA constituted the majority of the reads at the function level. Comparative analysis of taxonomy identified the dominance of Anaeromyxobacter, Geobacter, Pseudomonas, Candidatus Solibacter, and Pelobacter in the mangrove datasets. Non-metric multidimensional scaling analysis of the metal resistance genes depicted strong geographical clustering of the function and composition of metal resistant bacteria, suggesting a strong innate resilience of microbiome towards anthropogenic perturbations. More robust studies with intensive sampling will enhance our understanding of the occurrence, interactions, and functions of microbial heavy metal resistome in mangrove ecosystems.

Advances in Heavy Metal Bioremediation: An Overview

The pollution of toxic heavy metals is considered one of the most important environmental issues which has accelerated dramatically due to changing industrial activities. This review focuses on the most common methods, strategies, and biological approaches of heavy metal bioremediation. Also, it provides a general overview of the role of microorganisms in the bioremediation of heavy metals in polluted environments. Advanced methods of heavy metal remediation include physicochemical and biological methods; the latter can be further classified into in situ and ex situ bioremediation. The in situ process includes bioventing, biosparging, biostimulation, bioaugmentation, and phytoremediation. Ex situ bioremediation includes land farming, composting, biopiles, and bioreactors. Bioremediation uses naturally occurring microorganisms such as Pseudomonas, Sphingomonas, Rhodococcus, Alcaligenes, and Mycobacterium. Generally, bioremediation is of very less effort, less labor intensive, cheap, ecofriendly, sustainable, and relatively easy to implement. Most of the disadvantages of bioremediation relate to the slowness and time-consumption; furthermore, the products of biodegradation sometimes become more toxic than the original compound. The performance evaluation of bioremediation might be difficult as it has no acceptable endpoint. There is a need for further studies to develop bioremediation technologies in order to find more biological solutions for bioremediation of heavy metal contamination from different environmental systems.

Bioremediation of heavy metals from industrial effluents by endophytes and their metabolic activity: Recent advances

Worldwide, heavy metals pollution is mostly caused by rapid population growth and industrial development which is accumulated in food webs causing a serious public health risk. Endophytic microorganisms have a variety of mechanisms for metal sequestration having metal biosorption capacities.Endophytic organisms like bacteria and fungi provide beneficial qualities that help plants to improve their health, reduce stress, and detoxify metals. Endophytes have a higher proclivity for improving metal and mineral solubility by cells that secrete low-molecular-weight organic acids and metal-specific ligands like siderophores, which change the pH of the soil and improve binding activity. Protein-related approaches like chromatin immunoprecipitation sequencing (ChIP-Seq) and modified enzyme-linked immunosorbent assay (ELISA test) can represent endophytic bacterial community and DNA-protein interactions during metal reduction. This review explored the role of endophytes in bioremediation approaches that can help in analyzing the potential and prospects in response to industrial effluents' detoxification.