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

A holistic perspective on the efficiency of microbial enzymes in bioremediation process: Mechanism and challenges: A review

Industrial activities, pharmaceutical contaminants, excessive agricultural inputs, and improper waste disposal have contributed to the widespread pollution of soil and water. Traditional remediation techniques, while effective, often generate secondary waste and are economically unfeasible. In contrast, microbial bioremediation offers a sustainable and cost-effective alternative by utilizing microorganisms and their enzymatic systems to degrade and detoxify pollutants. This review investigates the potential of microbial enzymes in remediation strategies for removing heavy metals and pharmaceutical contaminants from polluted environments. It analyzes the fundamental mechanisms by which microorganisms sequester and degrade these pollutants, emphasizing the enzymatic processes that facilitate their breakdown. Furthermore, it explores key microbial factors influencing bioremediation efficiency, including microbial diversity and environmental conditions. Additionally, it examines the challenges associated with scaling these bioremediation strategies for global environmental applications and provides insights for future research and implementation.

Biogenic iron mineral formation and the fate of arsenic driven by its coupling with ferrous iron in acid mine drainage environment

Acid mine drainage (AMD) containing arsenic produced during coal mining is a global environmental problem. However, the coupled driving process of the key element Fe and the associated element As in the AMD environment has received little attention. Therefore, in this study, we investigated the A. ferrooxidans-mediated ferrous iron-arsenic interaction in a simulated AMD system. We reveal that in As-rich AMD the co-existing element As can regulate the metabolic activity of A. ferrooxidans to accelerate the oxidation of Fe2 + and the subsequent formation of Fe3+ minerals, thereby altering the pH and ORP of the system. XRD, SEM, and XPS analyses showed that the synthesized Fe mineral mainly consisted of As-containing schwertmannite (Sch). As in an AMD system could be efficiently removed (98.7 % after 72 h) through the formation of Fe minerals, thereby reducing its own environmental risk. SO42- plays an important role in As precipitation on the surface and in crystal tunnels of Sch. As-containing Sch is not only beneficial for the precipitation of As, but also for long-term reduction in As toxicity in AMD systems. Our results provide new insight for evaluating the fates of Fe and As, and the environmental and ecological risks of As in AMD produced from natural coal mines.

The legacy of endophytes for the formation of bioactive agents, pigments, biofertilizers, nanoparticles and bioremediation of environment

Endophytes have significant prospects for applications beyond their existing utilization in agriculture and the natural sciences. They form an endosymbiotic relationship with plants by colonizing the root tissues without detrimental effects. These endophytes comprise several microorganisms, including bacteria and fungi. They act as repositories of compounds of medicinal importance. They are considered sources of pigments besides synthetic dyes and assist with soil fertility and plant growth as bio-fertilizers. They also have immense potential for advanced technology using endophyte-synthesized nanoparticles. In assisting bioremediation, they facilitate detoxification of pollutants in all spheres of the environment. Studies on the potential of endophytic microbes in drug discovery and biotic stress management are underway. In this review, published databases on endophytes and their diverse roles and applications in various fields, such as bio-fertilizers and nanoparticles, as well as bioremediation, are critically discussed while exploring unanswered questions. In addition, future perspectives on endosymbiotic microorganisms and their prospective use in plants, environmental management, and medicine are discussed in this review.

Cyperus esculentus var. sativus Adapts to Multiple Heavy Metal Stresses Through the Assembly of Endophytic Microbial Communities

Interactions between plants and their endophytes alter their metabolic functions and ability to cope with abiotic stresses. In this study, high-throughput sequencing was used to analyze the species diversity and functions of endophytes in Cyperus esculentus var. sativus (CES) tubers under different heavy metal stress conditions. The results indicated that the number of observed endophytic species in the tubers increased under heavy metal stress (p < 0.05), leading to changes in species diversity and composition. The response of tuber endophytes to different metal concentrations varied, with certain endophytic bacteria and fungi, such as Pseudomonas, Novosphingobium, and Fusarium, showing increased abundance and becoming the dominant species in the tubers. Additionally, new endophytic genera, Actinophytocola and Monosporascus, emerged at specific metal concentrations (p < 0.05). Fatty acid salvage was enriched in the endophytes of CES, which may play an important role in assisting CES in responding to multiple heavy metal stresses. These findings showed that CES tuber endophytes undergo adaptive changes to support the ability of plants to cope with heavy metal stress.

Root-associated functional microbiome endemism facilitates heavy metal resilience and nutrient poor adaptation in native plants under serpentine driven edaphic challenges

Serpentine soils are characterized by high concentrations of heavy metals (HMs) and limited essential nutrients with remarkable endemic plant diversity, yet the mechanisms enabling plant adaptation to thrive in such harsh environments remain largely unknown. Full-length 16S rRNA amplicon sequencing, coupled with physiological and functional assays, was used to explore root-associated bacterial community composition and their metabolic and ecological functions. The results revealed that serpentine plant species exhibited significantly higher metal transfer factor values compared to non-serpentine plant species, particularly evident in Bidens pilosa, Miscanthus floridulus, and Leucaena leucocephala. The serpentine root-associated microbes showed a higher utilization of carboxylic acid, whereas carbohydrate utilization was higher in the non-serpentine site. Zymomonas mobilis and Flavabacterium sp. exhibited high resistance to heavy metal concentrations, showing greater adaptability, while, Staphylococcus carnosus showed sensitivity to HMs, showing limited adaptability. Moreover, Ni, Cr, and Co resistance genes were found, while nitrogen and phosphorous metabolism genes were less abundant in the serpentine site compared to the non-serpentine site. Furthermore, Flavobacterium sp. had a strong positive relationship with Cd and Cu, Zymomonas mobilis with Ni, and Cr, Streptomyces sp. with Co, and Staphylococcus carnosus with N and P cycling. These findings underscore critical role of root-associated bacterial communities and distinctive soil conditions of serpentine habitats in fostering ecological adaptation of native plant species to the challenges posed by HMs and nutrient deficiencies.

Investigating the genomic and metabolic abilities of PGPR Pseudomonas fluorescens in promoting plant growth and fire blight management

Pseudomonas fluorescens is commonly found in diverse environments and is well known for its metabolic and antagonistic properties. Despite its remarkable attributes, its potential role in promoting plant growth remains unexplored. This study examines these traits across 14 strains residing in diverse rhizosphere environments through pangenome and comparative genome analysis, alongside molecular docking studies against Erwinia amylovora to combat fire blight. Whole genome analysis revealed circular chromosome (6.01-7.07 Mb) with GC content averaging 59.95-63.39%. Predicted genes included 16S rRNA and protein-coding genes ranging from 4435 to 6393 bp and 1527 to 1541 bp, respectively. Pangenome analysis unveiled an open pangenome, shedding light on genetic factors influencing plant growth promotion and biocontrol, including nitrogen fixation, phosphorus solubilization, siderophore production, stress tolerance, flagella biosynthesis, and induced systemic resistance. Furthermore, pyrrolnitrin, phenazine-1-carboxylic acid, pyoluteorin, lokisin, 2,4-diacetylpholoroglucinol and pseudomonic acid were identified. Molecular docking against key proteins of E. amylovora highlighted the high binding affinities of 2,4-diacetylphloroglucinol, pseudomonic acid, and lokisin. These findings underscore the multifaceted role of P. fluorescens in plant growth promotion and biocontrol, with key biomolecules showing promising applications in plant growth and defense against pathogens.

Stable and antibacterial tannic acid-based covalent polymeric hydrogel for highly selective Pb2+ recovery from lead-acid battery industrial wastewater

The resource of trace lead (Pb2+) from wastewater bearing intricate components is imperative for sustainable progression of the lead-acid battery industry. Herein, we fabricated a tannic acid-based covalent polymeric hydrogel (TA@PMAM) with antimicrobial properties and stability via facile Michael addition reaction. The incorporation of tannic acid (TA) through robust covalent bond leads to a stable porous 3D covalent polymer network with almost no loss of mechanical properties even after 20 compression cycles. Batch adsorption experiments of TA@PMAM revealed an extraordinary adsorption capacity of Pb2+(Qe =196.6 mg/g), achieving 87.2 % of Pb2+ adsorption within the first 5 min owing to porous structure, numerous adsorption sites and good hydrophilicity. Moreover, TA@PMAM demonstrated a strong affinity for Pb2+ in the presence of the interfere metal ions (Cu2+, Co2+, Mn2+etc.) due to the carbonyl and phenolic hydroxyl that can specifically pair with Pb2+. Stable adsorption properties of TA@PMAM were confirmed in fixed bed column adsorption experiment using lead-acid batteries wastewater, retaining 79.56 % of initial adsorption capacity even after 10 times' reuse. Besides, TA@PMAM possesses a broad spectrum of antimicrobial properties. This study sheds novel light on the design and fabrication of adsorbent, which holds great potential for commercialization in recovering lead from battery industrial wastewater.

Recent and sustainable advances in phytoremediation of heavy metals from wastewater using aquatic plant species: Green approach

A key component in a nation's economic progress is industrialization, however, hazardous heavy metals that are detrimental to living things are typically present in the wastewater produced from various industries. Therefore, before wastewater is released into the environment, it must be treated to reduce the concentrations of the various heavy metals to maximum acceptable levels. Even though several biological, physical, and chemical remediation techniques are found to be efficient for the removal of heavy metals from wastewater, these techniques are costly and create more toxic secondary pollutants. However, phytoremediation is inexpensive, environmentally friendly, and simple to be applied as a green technology for heavy metal detoxification in wastewater. The present study provides a thorough comprehensive review of the mechanisms of phytoremediation, with an emphasis on the possible utilization of plant species for the treatment of wastewater containing heavy metals. We have discussed the concept, its applications, advantages, challenges, and independent variables that determine how successful and efficient phytoremediation could be in the decontamination of heavy metals from wastewater. Additionally, we argue that the standards for choosing aquatic plant species for target heavy metal removal ought to be taken into account, as they influence various aspects of phytoremediation efficiency. Following the comprehensive and critical analysis of relevant literature, aquatic plant species are promising for sustainable remediation of heavy metals. However, several knowledge gaps identified from the review need to be taken into consideration and possibly addressed. Therefore, the review provides perspectives that indicate research needs and future directions on the application of plant species in heavy metal remediation.

Bacillus altitudinis Mediated Lead Bioremediation for Enhanced Growth of Rice Seedlings

Lead (Pb) is a hazardous environmental pollutant that threatens soil health, water quality, and agricultural productivity. Plant growth-promoting rhizobacteria (PGPRs) mediated bioremediation is considered as an eco-friendly approach for agro-environmental sustainability. This study investigated the Pb bioremediation potential of Bacillus altitudinis (IHBT-705). The results revealed that IHBT-705 strain tolerated upto 15 mM of Pb, possessed 96% Pb bioaccumulation efficiency, and also maintained its plant growth-promoting (PGP) traits under Pb stress. Furthermore, IHBT-705 strain treated with 15 mM Pb solution (IHBT-W) and soil containing 15 mM Pb treated with IHBT-705 inoculum (IHBT-S) ameliorated the detrimental effects of Pb stress. Both IHBT-W and IHBT-S treatment significantly improved the shoot length, root length, total roots, chlorophyll content, and antioxidants enzyme activity of the rice seedlings as compared to the seedlings treated with 15 mM Pb solution (Pb-W) and soil containing 15 mM Pb (Pb-S). Also, IHBT-W and IHBT-S treatment decreased the Pb content in the rice plant by 97 and 96% over their respective Pb-W and Pb-S plants. Overall, our research underscores the remarkable Pb bioremediation potential of IHBT-705, offering a promising avenue for dual function, i.e. improving soil health and promoting plant growth under Pb contamination.

Exploring the Potential of Bacterial Endophytes in Plant Disease Management

Endophytic bacteria live in the internal tissues of plants, forming symbiotic, mutualistic, commensalistic and trophobiotic relationships. Some are spread via seeds after sprouting from the rhizosphere or phyllosphere. These bacteria capable of promoting plant growth and impart biotic stress by synthesing plant growth hormones, ACC deaminase, organic acids and siderophore. Endophytes aid in phytoremediation by removing soil contaminants and boosting soil fertility via phosphate solubilization and nitrogen fixation. The endophytic microbes are becoming increasingly popular in biotechnological applications which supports sustainable growth of non-food crops for biomass and biofuel. They offer valuable natural materials which is used in medicine, agriculture and industry. Bacterial endophytes are endowed with the enormous potential in the biological treatment of plant pathogens and considered as the superior alternative to synthetic fungicides. The review emphasizes benefits of bacterial endophytes in promoting plant growth and prospects of agricultural applications viz., increasing crop yield under biotic stress condition and their mode of action towards plant diseases. It also summarises the diverse and vital role of endophytes in agroecosystems as well as insights for sustainable agriculture and crop resilience.

Protective effects of the exogenous application of salicylic acid and chitosan on chromium-induced photosynthetic capacity and osmotic adjustment in Aconitum napellus

Chitosan (CTS) is recognized for enhancing a plant's resilience to various environmental stresses, such as salinity and drought. Moreover, salicylic acid (SA) is acknowledged as a growth regulator involved in addressing metal toxicity. However, the effectiveness of both compounds in mitigating Cr-induced stress has remained relatively unexplored, especially in the case of Aconitum napellus, a medicinally and floricultural important plant. Therefore, the primary objective of this study was to investigate the potential of CTS and SA in alleviating chromium (Cr)-induced stress in A. napellus. To address these research questions, we conducted a controlled experiment using potted plants to evaluate the individual and combined impacts of CTS and SA on plants exposed to Cr stress. Foliar application of CTS (0.4 g/L) or SA (0.25 mmol/L) led to significant improvements in the growth, chlorophyll content, fluorescence, and photosynthetic traits of A. napellus plants under Cr stress. The most notable effects were observed with the combined application of CTS and SA, resulting in increases in various morphological parameters, such as shoot length (2.89% and 7.02%) and root length (27.75% and 3.36%) under the Cr 1 and Cr 2 treatments, respectively. Additionally, several physiological parameters, such as chlorophyll a (762.5% and 145.56%), chlorophyll b (762.5% and 145.56%), carotenoid (17.03% and 28.57%), and anthocyanin (112.01% and 47.96%) contents, were notably improved under the Cr 1 and Cr 2 treatments, respectively. Moreover, the combined treatment of CTS and SA improved the fluorescence parameters while decreasing the levels of enzymatic antioxidants such as catalase (27.59% and 43.79%, respectively). The application also notably increased osmoprotectant parameters, such as the total protein content (54.11% and 20.07%) and the total soluble sugar content (78.17% and 49.82%) in the leaves of A. napellus in the Cr 1 and 2 treatments, respectively. In summary, these results strongly suggest that the simultaneous use of exogenous CTS and SA is an effective strategy for alleviating the detrimental effects of Cr stress on A. napellus. This integrated approach opens promising avenues for further exploration and potential implementation within agricultural production systems.

Exploring microbial diversity in the rhizosphere: a comprehensive review of metagenomic approaches and their applications

The rhizosphere, the soil region influenced by plant roots, represents a dynamic microenvironment where intricate interactions between plants and microorganisms shape soil health, nutrient cycling, and plant growth. Soil microorganisms are integral players in the transformation of materials, the dynamics of energy flows, and the intricate cycles of biogeochemistry. Considerable research has been dedicated to investigating the abundance, diversity, and intricacies of interactions among different microbes, as well as the relationships between plants and microbes present in the rhizosphere. Metagenomics, a powerful suite of techniques, has emerged as a transformative tool for dissecting the genetic repertoire of complex microbial communities inhabiting the rhizosphere. The review systematically navigates through various metagenomic approaches, ranging from shotgun metagenomics, enabling unbiased analysis of entire microbial genomes, to targeted sequencing of the 16S rRNA gene for taxonomic profiling. Each approach's strengths and limitations are critically evaluated, providing researchers with a nuanced understanding of their applicability in different research contexts. A central focus of the review lies in the practical applications of rhizosphere metagenomics in various fields including agriculture. By decoding the genomic content of rhizospheric microbes, researchers gain insights into their functional roles in nutrient acquisition, disease suppression, and overall plant health. The review also addresses the broader implications of metagenomic studies in advancing our understanding of microbial diversity and community dynamics in the rhizosphere. It serves as a comprehensive guide for researchers, agronomists, and policymakers, offering a roadmap for harnessing metagenomic approaches to unlock the full potential of the rhizosphere microbiome in promoting sustainable agriculture.

Halotolerant Endophytic Bacteria Priestia flexa 7BS3110 with Hg2+ Tolerance Isolated from Avicennia germinans in a Caribbean Mangrove from Colombia

The mangrove ecosystems of the Department of Atlántico (Colombian Caribbean) are seriously threatened by problems of hypersalinization and contamination, especially by heavy metals from the Magdalena River. The mangrove plants have developed various mechanisms to adapt to these stressful conditions, as well as the associated microbial populations that favor their growth. In the present work, the tolerance and detoxification capacity to heavy metals, especially to mercury, of a halotolerant endophytic bacterium isolated from the species Avicennia germinans located in the Balboa Swamp in the Department of Atlántico was characterized. Diverse microorganisms were isolated from superficially sterilized A. germinans leaves. Tolerance to NaCl was evaluated for each of the obtained isolates, and the most resistant was selected to assess its tolerance to Pb2+, Cu2+, Hg2+, Cr3+, Co2+, Ni2+, Zn2+, and Cd2+, many of which have been detected in high concentrations in the area of study. According to the ANI and AAI percentages, the most halotolerant strain was identified as Priestia flexa, named P. flexa 7BS3110, which was able to tolerate up to 12.5% (w/v) NaCl and presented a minimum inhibitory concentrations (MICs) of 0.25 mM for Hg, 10 mM for Pb, and 15 mM for Cr3+. The annotation of the P. flexa 7BS3110 genome revealed the presence of protein sequences associated with exopolysaccharide (EPS) production, thiol biosynthesis, specific proteins for chrome efflux, non-specific proteins for lead efflux, and processes associated with sulfur and iron homeostasis. Scanning electron microscopy (SEM) analysis showed morphological cellular changes and the transmission electron microscopy (TEM) showed an electrodense extracellular layer when exposed to 0.25 mM Hg2+. Due to the high tolerance of P. flexa 7BS3110 to Hg2+ and NaCl, its ability to grow when exposed to both stressors was tested, and it was able to thrive in the presence of 5% (w/v) NaCl and 0.25 mM of Hg2+. In addition, it was able to remove 98% of Hg2+ from the medium when exposed to a concentration of 14 mg/L of this metalloid. P. flexa 7BS3110 has the potential to bioremediate Hg2+ halophilic contaminated ecosystems.

Harnessing bacterial endophytes for environmental resilience and agricultural sustainability

In the current era of environmental disasters and the necessity of sustainable development, bacterial endophytes have gotten attention for their role in improving agricultural productivity and ecological sustainability. This review explores the multifaceted contributions of bacterial endophytes to plant health and ecosystem sustainability. Bacterial endophytes are invaluable sources of bioactive compounds, promising breakthroughs in medicine and biotechnology. They also serve as natural biocontrol agents, reducing the need for synthetic fertilizers and fostering environmentally friendly agricultural practices. It provides eco-friendly solutions that align with the necessity of sustainability since they can improve pest management, increase crop resilience, and facilitate agricultural production. This review also underscores bacterial endophytes' contribution to promoting sustainable and green industrial productions. It also presented how incorporating these microorganisms into diverse industrial sectors can harmonize humankind with ecological stability. The potential of bacterial endophytes has been largely untapped, presenting an opportunity for pioneering advancements in sustainable industrial applications. Their importance caught attention as they provided innovative solutions to the challenging problems of the new era. This review sheds light on the remarkable potential of bacterial endophytes in various industrial sectors. Further research is imperative to discover their multifaceted potential. It will be essential to delve deeper into their mechanisms, broaden their uses, and examine their long-term impacts.

Recent trends in the phytoremediation of radionuclide contamination of soil by cesium and strontium: Sources, mechanisms and methods: A comprehensive review

This comprehensive review examines recent trends in phytoremediation strategies to address soil radionuclide contamination by cesium (Cs) and strontium (Sr). Radionuclide contamination, resulting from natural processes and nuclear-related activities such as accidents and the operation of nuclear facilities, poses significant risks to the environment and human health. Cs and Sr, prominent radionuclides involved in nuclear accidents, exhibit chemical properties that contribute to their toxicity, including easy uptake, high solubility, and long half-lives. Phytoremediation is emerging as a promising and environmentally friendly approach to mitigate radionuclide contamination by exploiting the ability of plants to extract toxic elements from soil and water. This review focuses specifically on the removal of 90Sr and 137Cs, addressing their health risks and environmental implications. Understanding the mechanisms governing plant uptake of radionuclides is critical and is influenced by factors such as plant species, soil texture, and physicochemical properties. Phytoremediation not only addresses immediate contamination challenges but also provides long-term benefits for ecosystem restoration and sustainable development. By improving soil health, biodiversity, and ecosystem resilience, phytoremediation is in line with global sustainability goals and environmental protection initiatives. This review aims to provide insights into effective strategies for mitigating environmental hazards associated with radionuclide contamination and to highlight the importance of phytoremediation in environmental remediation efforts.

Exploring the Potential of Endophytic Microorganisms and Nanoparticles for Enhanced Water Remediation

Endophytic microorganisms contribute significantly to water bioremediation by enhancing pollutant degradation and supporting aquatic plant health and resilience by releasing bioactive compounds and enzymes. These microorganisms inhabit plant tissues without causing disease or any noticeable symptoms. Endophytes effectively aid in eliminating contaminants from water systems. Nanoparticles serve as potent enhancers in bioremediation processes, augmenting the efficiency of pollutant degradation by increasing surface area and bioavailability, thereby improving the efficacy and rate of remediation. Their controlled nutrient release and ability to stabilize endophytic colonization further contribute to the enhanced and sustainable elimination of contaminated environments. The synergistic effect of endophytes and nanoparticles in water remediation has been widely explored in recent studies, revealing compelling outcomes. Water pollution poses significant threats to human health, ecosystems, and economies; hence, the sixth global goal of the Sustainable Development Agenda 2030 of the United Nations aims to ensure the availability and sustainable management of water resources, recognizing their crucial importance for current and future generations. Conventional methods for addressing water pollution exhibit several limitations, including high costs, energy-intensive processes, the production of hazardous by-products, and insufficient effectiveness in mitigating emerging pollutants such as pharmaceuticals and microplastics. Noticeably, there is an inability to effectively remove various types of pollutants, thus resulting in incomplete purification cycles. Nanoparticle-enhanced water bioremediation offers an innovative, eco-friendly alternative for degrading contaminants. A growing body of research has shown that integrating endophytic microorganisms with nanoparticles for water bioremediation is a potent and viable alternative. This review examines the potential of using endophytic microorganisms and nanoparticles to enhance water remediation, exploring their combined effects and applications in water purification. The paper also provides an overview of synthetic methods for producing endophyte-nanoparticle composites to optimize their remediation capabilities in aqueous environments. The final section of the review highlights the constraints related to integrating endophytes with nanoparticles.

Impact of Vanadium-Titanium-Magnetite Mining Activities on Endophytic Bacterial Communities and Functions in the Root Systems of Local Plants

This study utilized 16S rRNA high-throughput sequencing technology to analyze the community structure and function of endophytic bacteria within the roots of three plant species in the vanadium-titanium-magnetite (VTM) mining area. The findings indicated that mining activities of VTM led to a notable decrease in both the biodiversity and abundance of endophytic bacteria within the root systems of Eleusine indica and Carex (p < 0.05). Significant reductions were observed in the populations of Nocardioides, concurrently with substantial increments in the populations of Pseudomonas (p < 0.05), indicating that Pseudomonas has a strong adaptability to this environmental stress. In addition, β diversity analysis revealed divergence in the endophytic bacterial communities within the roots of E. indica and Carex from the VTM mining area, which had diverged to adapt to the environmental stress caused by mining activity. Functional enrichment analysis revealed that VTM mining led to an increase in polymyxin resistance, nicotinate degradation I, and glucose degradation (oxidative) (p < 0.05). Interestingly, we found that VTM mining did not notably alter the endophytic bacterial communities or functions in the root systems of Dodonaea viscosa, indicating that this plant can adapt well to environmental stress. This study represents the primary investigation into the influence of VTM mining activities on endophytic bacterial communities and the functions of nearby plant roots, providing further insight into the impact of VTM mining activities on the ecological environment.

Draft Genome Sequence of Pantoea sp. Strain MHSD4, a Bacterial Endophyte With Bioremediation Potential

Pantoea sp. strain MHSD4 is a bacterial endophyte isolated from the leaves of the medicinal plant Pellaea calomelanos. Here, we report on strain MHSD4 draft whole genome sequence and annotation. The draft genome size of Pantoea sp. strain MHSD4 is 4 647 677 bp with a G+C content of 54.2% and 41 contigs. The National Center for Biotechnology Information Prokaryotic Genome Annotation Pipeline tool predicted a total of 4395 genes inclusive of 4235 protein-coding genes, 87 total RNA genes, 14 non-coding (nc) RNAs and 70 tRNAs, and 73 pseudogenes. Biosynthesis pathways for naphthalene and anthracene degradation were identified. Putative genes involved in bioremediation such as copA, copD, cueO, cueR, glnGm, and trxC were identified. Putative genes involved in copper homeostasis and tolerance were identified which may suggest that Pantoea sp. strain MHSD4 has biotechnological potential for bioremediation of heavy metals.

Isolation of endophytes from Dioscorea nipponica Makino for stimulating diosgenin production and plant growth

KEY MESSAGE

Both bacterial and fungal endophytes exhibited one or more plant growth-promoting (PGP) traits. Among these strains, the Paenibacillus peoriae SYbr421 strain demonstrated the greatest activity in the direct biotransformation of tuber powder from D. nipponica into diosgenin. Endophytes play crucial roles in shaping active metabolites within plants, significantly influencing both the quality and yield of host plants. Dioscorea nipponica Makino accumulates abundant steroidal saponins, which can be hydrolyzed to produce diosgenin. However, our understanding of the associated endophytes and their contributions to plant growth and diosgenin production is limited. The present study aimed to assess the PGP ability and potential of diosgenin biotransformation by endophytes isolates associated with D. nipponica for the efficient improvement of plant growth and development of a clean and effective approach for producing the valuable drug diosgenin. Eighteen bacterial endophytes were classified into six genera through sequencing and phylogenetic analysis of the 16S rDNA gene. Similarly, 12 fungal endophytes were categorized into 5 genera based on sequencing and phylogenetic analysis of the ITS rDNA gene. Pure culture experiments revealed that 30 isolated endophytic strains exhibited one or more PGP traits, such as nitrogen fixation, phosphate solubilization, siderophore synthesis, and IAA production. One strain of endophytic bacteria, P. peoriae SYbr421, effectively directly biotransformed the saponin components in D. nipponica. Moreover, a high yield of diosgenin (3.50%) was obtained at an inoculum size of 4% after 6 days of fermentation. Thus, SYbr421 could be used for a cleaner and more eco-friendly diosgenin production process. In addition, based on the assessment of growth-promoting isolates and seed germination results, the strains SYbr421, SYfr1321, and SYfl221 were selected for greenhouse experiments. The results revealed that the inoculation of these promising isolates significantly increased the plant height and fresh weight of the leaves and roots compared to the control plants. These findings underscore the importance of preparing PGP bioinoculants from selected isolates as an additional option for sustainable diosgenin production.

Fungal Endophytes as Mitigators against Biotic and Abiotic Stresses in Crop Plants

The escalating global food demand driven by a gradually expanding human population necessitates strategies to improve agricultural productivity favorably and mitigate crop yield loss caused by various stressors (biotic and abiotic). Biotic stresses are caused by phytopathogens, pests, and nematodes, along with abiotic stresses like salt, heat, drought, and heavy metals, which pose serious risks to food security and agricultural productivity. Presently, the traditional methods relying on synthetic chemicals have led to ecological damage through unintended impacts on non-target organisms and the emergence of microbes that are resistant to them. Therefore, addressing these challenges is essential for economic, environmental, and public health concerns. The present review supports sustainable alternatives, emphasizing the possible application of fungal endophytes as innovative and eco-friendly tools in plant stress management. Fungal endophytes demonstrate capabilities for managing plants against biotic and abiotic stresses via the direct or indirect enhancement of plants' innate immunity. Moreover, they contribute to elevated photosynthesis rates, stimulate plant growth, facilitate nutrient mineralization, and produce bioactive compounds, hormones, and enzymes, ultimately improving overall productivity and plant stress resistance. In conclusion, harnessing the potentiality of fungal endophytes represents a promising approach toward the sustainability of agricultural practices, offering effective alternative solutions to reduce reliance on chemical treatments and address the challenges posed by biotic and abiotic stresses. This approach ensures long-term food security and promotes environmental health and economic viability in agriculture.

Physiological characteristics, rhizosphere soil properties, and root-related microbial communities of Trifolium repens L. in response to Pb toxicity

Trifolium repens L. (T. repens) is considered a potential phytoremediation species due to its large biomass and ability to accumulate and tolerate heavy metals. Lead (Pb) is an important heavy metal pollutant that can affect plant growth, photosynthesis, and enzyme activity. However, response mechanism of microorganisms in three root niches of metal tolerant plants to Pb is not completely understood. Therefore, in this study, a Pb poisoning model of T. repens was established with a Pb gradient (0, 1000 mg/kg, 2000 mg/kg, and 3000 mg/kg), and was used to evaluate growth and physiological responses, as well as enrichment and transport coefficients in T. repens, and explore the characteristics of rhizosphere soil and microbial composition of three root niches. We found that Pb stress caused oxidative injury, and inhibited photosynthesis in T. repens. 16S rDNA sequencing analysis showed that the richness of microbial communities in bulk soil was higher than that in rhizosphere soil both under Pb stress and Pb nonstress conditions. Moreover, Proteobacteria was dominant phylum in bulk and rhizosphere soils, and Proteobacteria and Cyanobacteria were dominant phylum in endophytic bacteria. For the first time, we systematically investigated the response of Pb from bulk soil to plant leaves. The results showed that microbial interaction existed between bulk and rhizosphere soil. Rhizosphere bacterium Haliangium was positively correlated with urease activity and soil nutrients. Endophytic bacterium Pseudomonas was positively correlated with plant biomass and played an important role in Pb tolerance of T. repens. In addition, endophytic bacteria formed complex correlation networks with growth and physiological indexes of both root and shoot, moreover the network in root was more complicated. Taken together, Pb stress dose-dependently inhibited the growth of plants. This study provided a theoretical basis for the further development of microbial cooperation with plant remediation of heavy metal contaminated soil.

Uptake of toxic and nutrient elements by foraged edible and medicinal mushrooms (sporocarps) throughout Connecticut River Valley, New England, USA

Foraging for edible and medicinal mushrooms is a cultural and social practice both globally and in the United States. Determining the toxic and nutrient element concentrations of edible and medicinal mushrooms is needed to ensure the safe consumption of this food source. Our research examined wild, foraged mushrooms in New England, USA to assess nutrient (Ca, K, Mg, P) and toxic (As, Hg, Pb, Cd) element relationships between mushrooms, substrates, and soils. We examined a gradient in nutrient and toxic elements from more rural Mountain and Hill Zones in Massachusetts, Vermont, and New Hampshire to more developed and urban Valley and Coastal Zones in Connecticut. Substrates and mineral soils were moderate to weak predictors of mushroom tissue concentrations. We found significant differences in nutrient and toxic element concentration among the five common genera: Ganoderma, Megacollybia, Pluteus, Pleurotus, and Russula. In particular, Pluteus had consistently higher toxic element concentrations while Pleurotus and Russula had the highest Bioaccumulation Factors (BAFs). We found that the urban areas of the Valley and Coastal zones of Connecticut had Cd Target Hazard Quotient (THQ) values and ΣTHQ values > 1.0, indicating potential non-carcinogenic health hazard. However, the trend was largely driven by the > 2.0 Cd THQ for Pluteus. Our results suggest that foraging in more urban areas can still yield mushrooms with safe concentrations of toxic elements and abundant nutrients. Further research of this kind needs to be conducted within this region and globally to ensure humans are consuming safe, foraged mushrooms.

Bioremediation of Cr(VI) using indigenous bacterial strains isolated from a common industrial effluent treatment plant in Vishakhapatnam

The present study focuses on removing hexavalent chromium (Cr(VI)) using indigenous metal-resistant bacterial strains isolated from a common industrial effluent treatment plant, a contaminated site in Vishakhapatnam. Three high metal-resistant isolates were screened by growing them in nutrient agar media containing different Cr(VI) concentrations for 24 h at 35 ± 2 °C. The three strains' minimum inhibitory concentrations of Cr(VI) were examined at neutral pH and 35 ± 2 °C temperature. Morphological, biochemical, and molecular characterizations were carried out, and the strains were identified as Bacillus subtilis NITSP1, Rhizobium pusense NITSP2, and Pseudomonas aeruginosa NITSP3. Elemental composition and functional group analysis of the native and metal-loaded cells were done using energy-dispersive spectroscopy and Fourier-transform infrared spectroscopy, respectively. The operating conditions were optimized using a one-factor-at-a-time analysis. When compared with three bacterial isolates, maximum Cr(VI) removal (80.194 ± 4.0%) was observed with Bacillus subtilis NITSP1 with an initial Cr(VI) concentration of 60 mg/L, pH 7.0, an inoculum size of 2% (v/v), and an incubation period of 24 h. The logistic model was used to predict the variation of biomass growth with time. The present study can be extended to remove heavy metals from industrial wastewater in an environmental-friendly manner.

Advances, challenges, and prospects in microalgal-bacterial symbiosis system treating heavy metal wastewater

Heavy metal (HM) pollution, particularly in its ionic form in water bodies, is a chronic issue threatening environmental security and human health. The microalgal-bacterial symbiosis (MABS) system, as the basis of water ecosystems, has the potential to treat HM wastewater in a sustainable manner, with the advantages of environmental friendliness and carbon sequestration. However, the differences between laboratory studies and engineering practices, including the complexity of pollutant compositions and extreme environmental conditions, limit the applications of the MABS system. Additionally, the biomass from the MABS system containing HMs requires further disposal or recycling. This review summarized the recent advances of the MABS system treating HM wastewater, including key mechanisms, influence factors related to HM removal, and the tolerance threshold values of the MABS system to HM toxicity. Furthermore, the challenges and prospects of the MABS system in treating actual HM wastewater are analyzed and discussed, and suggestions for biochar preparation from the MABS biomass containing HMs are provided. This review provides a reference point for the MABS system treating HM wastewater and the corresponding challenges faced by future engineering practices.

Effects of blister blight disease on endophytic microbial diversity and community structure in tea (Camellia sinensis) leaves

In this study, metagenomic sequencing technology was employed to analyze the ITS1 region sequence of the ITS rDNA gene of endophytic fungi and 16S sequence of endophytic bacteria in tea leaves with varying degrees of infection by tea blister blight disease as well as healthy tea leaves. Subsequently, a comparative analysis was conducted on the endophytic microbial diversity and the community structure in tea leaves. The findings of this investigation reveal a shift in the dominant endophytic fungal genera from Ascomycota to Basidiomycota as the disease progressed. Furthermore, a negative correlation was observed between Exobasidium and Talaromyce, with Talaromyce exhibiting potential as an antagonist against the disease. Meanwhile, our findings reveal that Proteobacteria, Firmicutes, and Actinobacteria were the three most abundant bacteria phyla in tea leaves. As the disease progressed, there was an increase in the relative abundance of Actinobacteria, while Variovorax, Sphingomonas, and Pseudomonas were found to have higher abundance in later stages. The diversity analysis results indicated that the endophytic microbial diversity and the community structure in tea leaves in the diseased group were lower than those in the healthy control group. In general, blister blight disease altered the community structure of endophytic microorganisms in tea leaves, resulting in a few species with high abundance. The study lays a foundation for investigating the pathogenic mechanism of tea blister disease and establishing a theoretical basis for controlling diseases in tea trees.

Strategic use of crop residue biochars for removal of hazardous compounds in wastewater

Crop residues are affordable lignocellulosic waste in the world, and a large portion of the waste has been burned, releasing toxic pollutants into the environment. Since the crop residue is a carbon and ingredient rich material, it can be strategically used as a sorptive material for (in)organic pollutants in the wastewater after thermo-chemical valorization (i.e., biochar production). In this review, applications of crop residue biochars to adsorption of non-degradable synthetic dyes, antibiotics, herbicides, and inorganic heavy metals in wastewater were discussed. Properties (porosity, functional groups, heteroatom, and metal(oxide)s, etc.) and adsorption capacity relationships were comprehensively reviewed. The current challenges of crop residue biochars and guidelines for development of efficient adsorbents were also provided. In the last part, the future research directions for practical applications of the crop residue biochars in wastewater treatment plants have been suggested.

Contribution of endophytes towards improving plant bioactive metabolites: a rescue option against red-taping of medicinal plants

Medicinal plants remain a valuable source for natural drug bioprospecting owing to their multi-target spectrum. However, their use as raw materials for novel drug synthesis has been greatly limited by unsustainable harvesting leading to decimation of their wild populations coupled with inherent low concentrations of constituent secondary metabolites per unit mass. Thus, adding value to the medicinal plants research dynamics calls for adequate attention. In light of this, medicinal plants harbour endophytes which are believed to be contributing towards the host plant survival and bioactive metabolites through series of physiological interference. Stimulating secondary metabolite production in medicinal plants by using endophytes as plant growth regulators has been demonstrated to be one of the most effective methods for increasing metabolite syntheses. Use of endophytes as plant growth promotors could help to ensure continuous supply of medicinal plants, and mitigate issues with fear of extinction. Endophytes minimize heavy metal toxicity in medicinal plants. It has been hypothesized that when medicinal plants are exposed to harsh conditions, associated endophytes are the primary signalling channels that induce defensive reactions. Endophytes go through different biochemical processes which lead to activation of defence mechanisms in the host plants. Thus, through signal transduction pathways, endophytic microorganisms influence genes involved in the generation of secondary metabolites by plant cells. Additionally, elucidating the role of gene clusters in production of secondary metabolites could expose factors associated with low secondary metabolites by medicinal plants. Promising endophyte strains can be manipulated for enhanced production of metabolites, hence, better probability of novel bioactive metabolites through strain improvement, mutagenesis, co-cultivation, and media adjustment.

Endophytic bacteria isolated from Urtica dioica L.- preliminary screening for enzyme and polyphenols production

Endophytes, especially those isolated from herbal plants, may act as a reservoir of a variety of secondary metabolites exhibiting biological activity. Some endophytes express the ability to produce the same bioactive compounds as their plant hosts, making them a more sustainable industrial supply of these substances. Urtica dioica L. (common stinging nettle) is a synanthropic plant that is widely used in herbal medicine due to the diversity of bioactive chemicals it contains, e.g., polyphenols, which demonstrate anti-inflammatory, antioxidant, and anti-cancerous capabilities. This study aimed at isolating endophytic bacteria from stinging nettles for their bioactive compounds. The endophytic isolates were identified by both biochemical and molecular methods (16S rRNA) and investigated for enzymes, biosurfactants, and polyphenols production. Each of the isolated bacterial strains was capable of producing biosurfactants and polyphenols. However, three of the isolated endophytes, identified as two strains of Bacillus cereus and one strain of Bacillus mycoides, possessed the greatest capacity to produce biosurfactants and polyphenols. The derivatized extracts from culture liquid showed the 1.633 mol l-1 (9.691 mg l-1) concentration of polyphenol compounds. Therefore, the present study signifies that endophytic B. cereus and B. mycoides isolated from Urtica dioica L. could be a potential source of biosurfactants and polyphenols. However, further study is required to understand the mechanism of the process and achieve efficient polyphenol production by endophytic bacteria.

Bacterial assemblages imply methylmercury production at the rice-soil system

The plant microbiota can affect plant health and fitness by promoting methylmercury (MeHg) production in paddy soil. Although most well-known mercury (Hg) methylators are observed in the soil, it remains unclear how rice rhizosphere assemblages alter MeHg production. Here, we used network analyses of microbial diversity to identify bulk soil (BS), rhizosphere (RS) and root bacterial networks during rice development at Hg gradients. Hg gradients greatly impacted the niche-sharing of taxa significantly relating to MeHg/THg, while plant development had little effect. In RS networks, Hg gradients increased the proportion of MeHg-related nodes in total nodes from 37.88% to 45.76%, but plant development enhanced from 48.59% to 50.41%. The module hub and connector in RS networks included taxa positively (Nitrososphaeracea, Vicinamibacteraceae and Oxalobacteraceae) and negatively (Gracilibacteraceae) correlating with MeHg/THg at the blooming stage. In BS networks, Deinococcaceae and Paludibacteraceae were positively related to MeHg/THg, and constituted the connector at the reviving stage and the module hub at the blooming stage. Soil with an Hg concentration of 30 mg kg-1 increased the complexity and connectivity of root microbial networks, although microbial community structure in roots was less affected by Hg gradients and plant development. As most frequent connector in root microbial networks, Desulfovibrionaceae did not significantly correlate with MeHg/THg, but was likely to play an important role in the response to Hg stress.

Endophytic Plant Growth-Promoting Bacterium Bacillus subtilis Reduces the Toxic Effect of Cadmium on Wheat Plants

Heavy metal ions, in particular cadmium (Cd), have a negative impact on the growth and productivity of major crops, including wheat. The use of environmentally friendly approaches, in particular, bacteria that have a growth-stimulating and protective effect, can increase the resistance of plants. The effects of the pre-sowing seed treatment with the plant growth-promoting endophyte Bacillus subtilis 10-4 (BS) on cadmium acetate (Cd)-stressed Triticum aestivum L. (wheat) growth, photosynthetic pigments, oxidative stress parameters, roots' lignin content, and Cd ions accumulation in plants were analyzed. The results showed that the tested Cd-tolerant BS improved the ability of wheat seeds to germinate in the presence of different Cd concentrations (0, 0.1, 0.5, and 1 mM). In addition, the bacterial treatment significantly decreased the damaging effects of Cd stress (1 mM) on seedlings' linear dimensions (lengths of roots and shoots), biomass, as well as on the integrity and permeability of the cell walls (i.e., lipid peroxidation and electrolyte leakage) and resulted in reduced H₂O₂ generation. The pretreatment with BS prevented the Cd-induced degradation of the leaf photosynthetic pigments chlorophyll (Chl) a, Chl b, and carotenoids. Moreover, the bacterial treatment intensified the lignin deposition in the roots under normal and, especially, Cd stress conditions, thereby enhancing the barrier properties of the cell wall. This manifested in a reduced Cd ions accumulation in the roots and in the restriction of its translocation to the aboveground parts (shoots) of the bacterized plants under Cd stress in comparison with non-bacterized controls. Thus, the pre-sowing seed treatment with the endophyte BS may serve as an eco-friendly approach to improve wheat production in Cd-contaminated areas.

Physico-chemical and biological remediation techniques for the elimination of endocrine-disrupting hazardous chemicals

Due to their widespread occurrence and detrimental effects on human health and the environment, endocrine-disrupting hazardous chemicals (EDHCs) have become a significant concern. Therefore, numerous physicochemical and biological remediation techniques have been developed to eliminate EDHCs from various environmental matrices. This review paper aims to provide a comprehensive overview of the state-of-the-art remediation techniques for eliminating EDHCs. The physicochemical methods include adsorption, membrane filtration, photocatalysis, and advanced oxidation processes. The biological methods include biodegradation, phytoremediation, and microbial fuel cells. Each technique's effectiveness, advantages, limitations, and factors affecting their performance are discussed. The review also highlights recent developments and future perspectives in EDHCs remediation. This review provides valuable insights into selecting and optimizing remediation techniques for EDHCs in different environmental matrices.

New insights into the bioremediation of petroleum contaminants: A systematic review

Petroleum product is an essential resource for energy, that has been exploited by wide range of industries and regular life. A carbonaceous contamination of marine and terrestrial environments caused by errant runoffs of consequential petroleum-derived contaminants. Additionally, petroleum hydrocarbons can have adverse effects on human health and global ecosystems and also have negative demographic consequences in petroleum industries. Key contaminants of petroleum products, primarily includes aliphatic hydrocarbons, benzene, toluene, ethylbenzene, and xylene (BTEX), polycyclic aromatic hydrocarbons (PAHs), resins, and asphaltenes. On environmental interaction, these pollutants result in ecotoxicity as well as human toxicity. Oxidative stress, mitochondrial damage, DNA mutations, and protein dysfunction are a few key causative mechanisms behind the toxic impacts. Henceforth, it becomes very evident to have certain remedial strategies which could help on eliminating these xenobiotics from the environment. This brings the efficacious application of bioremediation to remove or degrade pollutants from the ecosystems. In the recent scenario, extensive research and experimentation have been implemented towards bio-benign remediation of these petroleum-based pollutants, aiming to reduce the load of these toxic molecules in the environment. This review gives a detailed overview of petroleum pollutants, and their toxicity. Methods used for degrading them in the environment using microbes, periphytes, phyto-microbial interactions, genetically modified organisms, and nano-microbial remediation. All of these methods could have a significant impact on environmental management.

Ni, Cr and Co Phytoremediations by Alyssum murale Grown in the Serpentine Soils Around Guleman Cr Deposits, Elazig Turkey

Serpentine soils containing high levels of nickel and other metals are particularly preferred by some plants that accumulate nickel in their bodies. In this study, the Ni, Co, and Cr accumulation capacities of A. murale grown in Guleman's serpentine soils were measured. In this respect, 12 A. murale and their soils were collected from the mining site and surroundings. Afterwards, the collected samples were measured in order to evaluate the translocation and accumulation amounts of Ni, Cr, and Co. For that, soil and plant samples were analyzed using inductively coupled plasma mass spectroscopy (ICP-MS). The mean Ni concentrations in the soil, roots, and shoots of A. murale were measured as 2475, 7384, and 7694 mg/kg, respectively. The mean Cr concentrations in the soil, roots, and shoots of A. murale were measured as 742, 33, and 8.4 mg/kg while the mean Co concentrations of A. murale in the soil, roots, and shoots were 166, 10.2, and 23.5 mg/kg, respectively. Then, ECR and ECS values were calculated for Ni, Co, and Cr. The results indicated that A. murale grown in Guleman's serpentine soils may be helpful for the rehabilitation studies of mining soils contaminated by Ni and can be utilized for phytoextraction.

Current overview and future perspective in fungal biorecovery of metals from secondary sources

Microorganisms are intimately involved in many biogeochemical processes that underpin the transformation of metals and cycling of related substances, such as metalloids and radionuclides. Many processes determine the mobility and bioavailability of metals, thereby influencing their transfer to the environment and living organisms. These processes are closely related to global phenomena such as soil formation and bioweathering. In addition to environmental significance, microbial metal transformations play an essential role in both in situ and ex situ bioremediation processes for solid and liquid wastes. The solubilization of heavy metals from industrial waste and soil is commonly used in bioremediation. Moreover, immobilization processes are applicable to bioremediation of metals and radionuclides from aqueous solutions. This review provides an overview of critical metal extraction and recovery from secondary sources, applied microorganisms and methods, metal-microbe interactions, as well as a detailed description of known metal recovery mechanisms.

Trends in Harnessing Plant Endophytic Microbiome for Heavy Metal Mitigation in Plants: A Perspective

Plant microbiomes represent dynamic entities, influenced by the environmental stimuli and stresses in the surrounding conditions. Studies have suggested the benefits of commensal microbes in improving the overall fitness of plants, besides beneficial effects on plant adaptability and survival in challenging environmental conditions. The concept of 'Defense biome' has been proposed to include the plant-associated microbes that increase in response to plant stress and which need to be further explored for their role in plant fitness. Plant-associated endophytes are the emerging candidates, playing a pivotal role in plant growth, adaptability to challenging environmental conditions, and productivity, as well as showing tolerance to biotic and abiotic stresses. In this article, efforts have been made to discuss and understand the implications of stress-induced changes in plant endophytic microbiome, providing key insights into the effects of heavy metals on plant endophytic dynamics and how these beneficial microbes provide a prospective solution in the tolerance and mitigation of heavy metal in contaminated sites.

Chromium toxicity and tolerance mechanisms in plants through cross-talk of secondary messengers: An overview of pathways and mechanisms

Environmental sources of chromium (Cr) such as solid waste, battery chemicals, industrial /waste, automotive exhaust emissions, mineral mining, fertilizers, and pesticides, have detrimental effects on plants. An excessive amount of Cr exposure can lead to toxic accumulations in human, animal, and plant tissues. In plants, diverse signaling molecules like hydrogen sulfide (H₂S) and nitric oxide (NO) play multiple roles during Cr stress. Consequently, the molecular mechanisms of Cr toxicity in plants, such as metal binding, modifying enzyme activity, and damaging cells are examined by several studies. The reactive oxygen species (ROS) that are formed when Cr reacts with lipids, membranes, DNA, proteins, and carbohydrates are all responsible for damage caused by Cr. ROS regulate plant growth, programmed cell death (PCD), cell cycle, pathogen defense, systemic communication, abiotic stress responses, and growth. Plants accumulate Cr mostly through the root system, with very little movement to the shoots. The characterization of stress-inducible proteins and metabolites involved in Cr tolerance and cross-talk messengers has been made possible due to recent advances in metabolomics, transcriptomics, and proteomics. This review discusses Cr absorption, translocation, subcellular distribution, and cross-talk between secondary messengers as mechanisms responsible for Cr toxicity and tolerance in plants. To mitigate this problem, soil-plant systems need to be monitored for the biogeochemical behavior of Cr and the identification of secondary messengers in plants.

Astragalicola ephedrae sp. nov., isolated from the stem of Ephedra gerardiana in Ladakh, India

An endophytic fungus designated as EIT4^T (MCC 9756^T) was isolated from the asymptomatic stem tissue of Ephedra gerardiana collected from the Kargil district of Ladakh Union territory, India. Phylogenetic analysis based on concatenated nuclear ribosomal ITS (internal transcribed spacer) and LSU (large ribosomal subunit) sequence datasets revealed its placement within the genus Astragalicola. However, it formed a separate clade exhibiting strong bootstrap support value (80%). The highest nrITS sequence similarity between EIT4^T and species of Astragalicola was 95.19% (A. vasilyevae) and 94.26% (A. amorpha), while nrLSU sequence similarity was 99.27% (A. amorpha). Morphologically, EIT4^T differs from the other species of Astragalicola in having larger sub-globose to pyriform conidiomata, smaller and mostly unbranched conidiophores, and polymorphic translucent conidia with two terminal guttules. Based on combined cultural, micromorphological, molecular, and phylogenetic analyses, EIT4^T represents a novel species in the genus Astragalicola proposed here as Astragalicola ephedrae sp. nov. Detailed description and illustrations of the novel species are provided. The type strain is EIT4^T (= MCC 9756 ^T = MN29^T).

Promising strategies of circular bioeconomy using heavy metal phytoremediated plants - A critical review

Phytoremediation is an excellent method for removing harmful heavy metals from the environment since it is eco-friendly, uses little energy, and is inexpensive. However, as phytoremediated plants can turn into secondary sources for heavy metals, complete heavy metal removal from phytoremediated plants is necessary. Elimination of toxic heavy metals from phytoremediated plants should be considered with foremost care. This review highlights about important sources of heavy metal contamination, health effects caused by heavy metal contamination and technological breakthroughs of phytoremediation. This review critically emphasis about promising strategies to be engaged for absolute reutilization of heavy metals and spectacular approaches of production of commercially imperative products from phytoremediated plants through circular bioeconomy with key barriers. Thus, phytoremediation combined with circular bioeconomy can create a new platform for the eco-friendly life.

An exopolysaccharide-producing novel Agrobacterium pusense strain JAS1 isolated from snake plant enhances plant growth and soil water retention

A peculiar bacterial growth was very often noticed in leaf-initiated tissue cultures of Sansevieria trifasciata, a succulent belonging to the Asparagaceae family. The isolate left trails of some highly viscous material on the walls of the suspension vessels or developed a thick overlay on semisolid media without adversities in plant growth. FTIR identified this substance to be an extracellular polysaccharide. Various morphological, biochemical tests, and molecular analyses using 16S rRNA, atpD, and recA genes characterized this isolate JAS1 as a novel strain of Agrobacterium pusense. Its mucoidal growth over Murashige and Skoog media yielded enormous exopolysaccharide (7252 mg l^-1), while in nutrient agar it only developed fast-growing swarms. As a qualifying plant growth-promoting bacteria, it produces significant indole-3-acetic acid (86.95 mg l^-1), gibberellic acid (172.98 mg l^-1), ammonia (42.66 µmol ml^-1). Besides, it produces siderophores, 1-aminocyclopropane-1-carboxylic acid deaminase, fixes nitrogen, forms biofilms, and productively solubilizes soil inorganic phosphates, and zinc. Under various treatments with JAS1, wheat and chickpea resulted in significantly enhanced shoot and root growth parameters. PGP effects of JAS1 positively enhanced plants' physiological growth parameters reflecting significant increments in overall chlorophyll, carotenoids, proline, phenols, flavonoids, and sugar contents. In addition, the isolated strain maintained both plant and soil health under an intermittent soil drying regime, probably by both its PGP and EPS production attributes, respectively.

Lead Responses and Tolerance Mechanisms of Koelreuteria paniculata: A Newly Potential Plant for Sustainable Phytoremediation of Pb-Contaminated Soil

Phytoremediation could be an alternative strategy for lead (Pb) contamination. K. paniculata has been reported as a newly potential plant for sustainable phytoremediation of Pb-contaminated soil. Physiological indexes, enrichment accumulation characteristics, Pb subcellular distribution and microstructure of K. paniculata were carefully studied at different levels of Pb stress (0-1200 mg/L). The results showed that plant growth increased up to 123.8% and 112.7%, relative to the control group when Pb stress was 200 mg/L and 400 mg/L, respectively. However, the average height and biomass of K. paniculata decrease when the Pb stress continues to increase. In all treatment groups, the accumulation of Pb in plant organs showed a trend of root > stem > leaf, and Pb accumulation reached 81.31%~86.69% in the root. Chlorophyll content and chlorophyll a/b showed a rising trend and then fell with increasing Pb stress. Catalase (CAT) and peroxidase (POD) activity showed a positive trend followed by a negative decline, while superoxide dismutase (SOD) activity significantly increased with increasing levels of Pb exposure stress. Transmission electron microscopy (TEM) showed that Pb accumulates in the inactive metabolic regions (cell walls and vesicles) in roots and stems, which may be the main mechanism for plants to reduce Pb biotoxicity. Fourier transform infrared spectroscopy (FTIR) showed that Pb stress increased the content of intracellular -OH and -COOH functional groups. Through organic acids, polysaccharides, proteins and other compounds bound to Pb, the adaptation and tolerance of K. paniculata to Pb were enhanced. K. paniculata showed good phytoremediation potential and has broad application prospects for heavy metal-contaminated soil.

Engineered microbes as effective tools for the remediation of polyaromatic aromatic hydrocarbons and heavy metals

Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) have become a major concern to human health and the environment due to rapid industrialization and urbanization. Traditional treatment measures for removing toxic substances from the environment have largely failed, and thus development and advancement in newer remediation techniques are of utmost importance. Rising environmental pollution with HMs and PAHs prompted the research on microbes and the development of genetically engineered microbes (GEMs) for reducing pollution via the bioremediation process. The enzymes produced from a variety of microbes can effectively treat a range of pollutants, but evolutionary trends revealed that various emerging pollutants are resistant to microbial or enzymatic degradation. Naturally, existing microbes can be engineered using various techniques including, gene engineering, directed evolution, protein engineering, media engineering, strain engineering, cell wall modifications, rationale hybrid design, and encapsulation or immobilization process. The immobilization of microbes and enzymes using a variety of nanomaterials, membranes, and supports with high specificity toward the emerging pollutants is also an effective strategy to capture and treat the pollutants. The current review focuses on successful bioremediation techniques and approaches that make use of GEMs or engineered enzymes. Such engineered microbes are more potent than natural strains and have greater degradative capacities, as well as rapid adaptation to various pollutants as substrates or co-metabolizers. The future for the implementation of genetic engineering to produce such organisms for the benefit of the environment andpublic health is indeed long and valuable.

Augmented growth of Cd-stressed rice seedlings with the application of phytostimulating, root-colonizing, Cd-tolerant, leaf-endophytic fungi Colletotrichum spp. isolated from Eupatorium triplinerve

The potential of plant growth-promoting endophytic fungi (PGPEF) in mycoremediation has received notable attention in recent years. Unlike other root-colonizing microorganisms, PGPEF colonization under Cadmium (Cd) stress is a less-revealed phenomenon. Among eighteen fungal isolates from the leaves of Eupatorium triplinerve, twelve were found as the species of Colletotrichum and remaining six belong to Fusarium based on phenotypic characterization. However, only two PGPEF isolates (ALE15 and ALE18) were finally selected based on possession of ACCD activity (~0.84 and 0.47 nM/µg protein/h, respectively) and higher Cd tolerance (1000 and 750 µg/mL, respectively). Moreover, the said isolates showed IAA production (~248 and 289 µg/mL), GA production (~86 and 88 AUs), phosphate solubilization (~165 and 256 µg/mL, respectively) under Cd stress. ALE18 strain was found to produce siderophore too. Molecular identification through sequencing of ITS region of both isolates confirmed their identity as species of Colletotrichum. Furthermore, FESEM-EDAX and AAS analyses supported their Cd bioaccumulation ability in mycelial cells that directly impacted to assist rice seedlings' (IR-36 cultivar) growth under Cd stress. Successful root colonization was also observed through FESEM and fluorescence microscopic studies. Finally, the detached leaf experiment with six economically important crops assured their applicability on field-scale as non-pathogenic PGPEF candidates.

Advances in bioremediation of emerging contaminants from industrial wastewater by oxidoreductase enzymes

The bioremediation of emerging recalcitrant pollutants in wastewater via enzyme biotechnology has been evolving as cost-effective with an input of low-energy technological approach. However, the enzyme based bioremediation technology is still not fully developed at a commercial level. The oxidoreductases being the domineering biocatalysts are promising candidates for wastewater treatments. Henceforth, comprehending their global market and biotransformation efficacy is mandatory for establishing these techno-economic bio-enzymes in commercial scale. The biocatalytic strategy can be established as a combinatorial approach with existing treatment technology to achieve towering bioremediation and effective removal of emerging pollutants from wastewater. This review provides a novel insight on the toxicological xenobiotics released from industries such as paper and pulps, soap and detergents, pharmaceuticals, textiles, pesticides, explosives and aptitude of peroxidases, nitroreductase and cellobiose dehydrogenase in their bio-based treatment. Moreover, the review comprehensively covers environmental relevance of wastewater pollution and the critical challenges based on remediation achieved through biocatalysts for future prospectives.

Stress-Tolerant Endophytic Isolate Priestia aryabhattai BPR-9 Modulates Physio-Biochemical Mechanisms in Wheat (Triticum aestivum L.) for Enhanced Salt Tolerance

In efforts to improve plant productivity and enhance defense mechanisms against biotic and abiotic stresses, endophytic bacteria have been used as an alternative to chemical fertilizers and pesticides. In the current study, 25 endophytic microbes recovered from plant organs of Triticum aestivum L. (wheat) were assessed for biotic (phyto-fungal pathogens) and abiotic (salinity, drought, and heavy metal) stress tolerance. Among the recovered isolates, BPR-9 tolerated maximum salinity (18% NaCl), drought (15% PEG-6000), and heavy metals (µg mL-1): Cd (1200), Cr (1000), Cu (1000), Pb (800), and Hg (30). Based on phenotypic and biochemical characteristics, as well as 16S rDNA gene sequencing, endophytic isolate BPR-9 was recognized as Priestia aryabhattai (accession no. OM743254.1). This isolate was revealed as a powerful multi-stress-tolerant crop growth promoter after extensive in-vitro testing for plant growth-promoting attributes, nutrient (phosphate, P; potassium, K; and zinc, Zn) solubilization efficiency, extracellular enzyme (protease, cellulase, amylase, lipase, and pectinase) synthesis, and potential for antagonistic activity against important fungal pathogens viz. Alternaria solani, Rhizoctonia solani, Fusarium oxysporum, and Ustilaginoidea virens. At elevated salt levels, increases were noted in indole-3-acetic acid; siderophores; P, K, and Zn-solubilization; ACC deaminase; and ammonia synthesized by Priestia aryabhattai. Additionally, under in-vitro plant bioassays, wheat seedlings inoculated with P. aryabhattai experienced superior growth compared to non-inoculated seedlings in high salinity (0-15% NaCl) environment. Under NaCl stress, germination rate, plant length, vigor indices, and leaf pigments of wheat seedlings significantly increased following P. aryabhattai inoculation. Furthermore, at 2%-NaCl, B. aryabhattai greatly and significantly (p ≤ 0.05) decreased relative leaf water content, membrane damage, and electrolyte leakage compared with the non-inoculated control. Catalase, superoxide dismutase, and peroxidase activity increased by 29, 32, and 21%, respectively, in wheat seedlings exposed to 2% NaCl and inoculated with the bacteria. The present findings demonstrate that endophytic P. aryabhattai strains might be used in the future as a multi-stress reducer and crop growth promoter in agronomically important crops including cereals.

Roles of plant-associated microorganisms in regulating the fate of Hg in croplands: A perspective on potential pathways in maintaining sustainable agriculture

In heavy metal-contaminated croplands, plant-associated microorganisms play important roles in the adaptation of crops to heavy metals. Plant-associated microbes can interact with Hg and stimulate plant resistance to Hg toxicity, which is crucial for impeding Hg accumulation along the food chain. The roles of rhizosphere microorganisms for the improvement of plant growth and Hg resistance have drawn great research attention. However, the interactions among plant-endophyte-Hg have been neglected although they might be important for in vivo Hg detoxification. In this study, we systematically summarized 1) the roles of plant-associated microorganisms in Hg detoxification and plant growth, 2) Hg methylation and demethylation driven by plant-associated microbes, 3) the relationships between plant-associated microbes and Hg biogeochemical cycling. The possible mechanisms underlying crop-endophyte-Hg interactions were discussed, although limited studies on this aspect are available to date. The challenges and perspectives of plant-endophytes in dampening Hg phytotoxicity and controlling Hg accumulation in croplands were proposed on the basis of the present knowledge. Taken together, this work provides evidence for further understanding the interactions between soil-plant-endophyte-Hg systems and as well as new interpretations and perspectives into regulating the fate of Hg in croplands.

Omics approaches in bioremediation of environmental contaminants: An integrated approach for environmental safety and sustainability

Non-degradable pollutants have emerged as a result of industrialization, population growth, and lifestyle changes, endangering human health and the environment. Bioremediation is the process of clearing hazardous contaminants with the help of microorganisms, and cost-effective approach. The low-cost and environmentally acceptable approach to removing environmental pollutants from ecosystems is microbial bioremediation. However, to execute these different bioremediation approaches successfully, this is imperative to have a complete understanding of the variables impacting the development, metabolism, dynamics, and native microbial communities' activity in polluted areas. The emergence of new technologies like next-generation sequencing, protein and metabolic profiling, and advanced bioinformatic tools have provided critical insights into microbial communities and underlying mechanisms in environmental contaminant bioremediation. These omics approaches are meta-genomics, meta-transcriptomics, meta-proteomics, and metabolomics. Moreover, the advancements in these technologies have greatly aided in determining the effectiveness and implementing microbiological bioremediation approaches. At Environmental Protection Agency (EPA)-The government placed special emphasis on exploring how molecular and "omic" technologies may be used to determine the nature, behavior, and functions of the intrinsic microbial communities present at pollution containment systems. Several omics techniques are unquestionably more informative and valuable in elucidating the mechanism of the process and identifying the essential player's involved enzymes and their regulatory elements. This review provides an overview and description of the omics platforms that have been described in recent reports on omics approaches in bioremediation and that demonstrate the effectiveness of integrated omics approaches and their novel future use.

Crosstalk and gene expression in microorganisms under metals stress

Contamination of the environment with heavy metals (HMs) has led to huge global environmental issues. Industrialization activities such as mining, manufacturing, and construction generate massive amounts of toxic waste, posing environmental risks. HMs soil pollution causes a variety of environmental issues and has a detrimental effect on both animals and plants. To remove HMs from the soil, traditional physico-chemical techniques such as immobilization, electro-remediation, stabilization, and chemical reduction are used. Moreover, the high energy, trained manpower, and hazardous chemicals required by these methods make them expensive and non-environmentally friendly. Bioremediation process, which involves microorganism-based and microorganism-associated-plant-based approaches, is an ecologically sound and cost-effective strategy for restoring HMs polluted soil. Microbes adjust their physiology to these conditions to live, which can involve significant variations in the expression of the genes. A set of genes are activated in response to toxic metals in microbes. They can also adapt by modifying their shape, fruiting bodies creating biofilms, filaments, or chemotactically migrating away from stress chemicals. Microbes including Bacillus sp., Pseudomonas sp., and Aspergillus sp. has been found to have high metals remediation and tolerance capacity of up to 98% whether isolated or in combination with plants like Helianthus annuus, Trifolium repens, and Vallisneria denseserrulata. Several of the regulatory systems that have been discovered are unique, but there is also a lot of "cross-talk" among networks. This review discusses the current state of knowledge regarding the microbial signaling responses, and the function of microbes in HMs stress resistance.

Identification of heavy metals tolerant Brevundimonas sp. from rhizospheric zone of Saccharum munja L. and their efficacy in in-situ phytoremediation

Heavy metals phytoremediation from pulp and paper industry (PPI) sludge was conducted by employing root-associated Brevundimonas sp (PS-4 MN238722.1) in rhizospheric zone of Saccharum munja L. for its detoxification. The study was aimed to investigate the efficiency of Saccharum munja L. for the removal of heavy metals along with physico-chemical parameters through bacterial interactions. Physico-chemical examination of PPI sludge showed biochemical oxygen demand (8357 ± 94 mg kg^-1), electrical conductivity (2264 ± 49 μmhoscm^-1), total phenol (521 ± 24 mg kg^-1), total dissolve solid (1547 ± 23 mg kg^-1), total nitrogen (264 ± 2.13 mg kg^-1), pH (8.2 ± 0.11), chemical oxygen demand (34756 ± 214 mg kg^-1), color (2434 ± 45 Co-Pt), total suspended solid (76 ± 0.67 mg kg^-1), sulphate (2462 ± 13 mg kg^-1), chlorolignin (597 ± 13.01 mg kg^-1), K⁺ (21.04 ± 0.26 mg kg^-1), total solid (1740 ± 54 mg kg^-1), phosphorous, Cl^-, and Na⁺. Heavy metals, such as Fe followed by Zn, Mn, Cd, Cu, Ni, Pb, As, Cr and Hg were above the permissible limit. Root and shoot of Saccharum munja L. revealed highest concentrations of Cd followed by Mn, Ni, Fe, Zn, Cu, As, Cr, Hg, and Pb. Tested metals (Fe, Mn, Pb, Cd, Cr, Cu, Zn, Ni, As, and Hg) bioaccumulation and translocation factors were also revealed to be < 1 and >1, respectively, demonstrating that these plants have considerable absorption and translocation abilities. Plant growth-promoting activity, such as ligninolytic enzymes, hydrolytic enzymes, indole acetic acid, and siderophore production activity of Brevundimonas sp. (PS-4 MN238722.1) were also noted to be higher. These findings support the use of Brevundimonas sp (PS-4 MN238722.1) in combination with Saccharum munja L. plant as interdisciplinary management of industrial sludge at polluted areas for the prevention of soils near the industrial site.