Bacterial Exopolysaccharide mediated heavy metal removal: A Review on biosynthesis, mechanism and remediation strategies

Sulfate-reducing consortium HQ23 stabilizes metal(loid)s and activates biological N-fixation in mixed heavy metal-contaminated soil

Sulfate-reducing bacteria (SRB) are used in the remediation of mine pollution; however, the mechanism of stabilizing multiple heavy metal(loid)s by the SRB consortium under low oxygen conditions needs further study. Indigenous microflora were extracted from non-ferrous metal-contaminated soil co-inoculated with enriched SRB consortium and assembled as the HQ23 consortium. The presence of Desulfovibrio (SRB) in HQ23 was confirmed by 16S rRNA sequencing and qPCR. The effects of culture media, dissolved oxygen (DO), SO42¯, and pH on the HQ23 growth rate, and the SO42¯-reducing activity were examined. Data indicates that the HQ23 sustained SRB function under low DO conditions (3.67 ± 0.1 mg/L), but the SRB activity was inhibited at high DO content (5.75 ± 0.39 mg/L). The HQ23 can grow from pH 5 to pH 9 and can decrease mobile or bioavailable Cr, Cu, and Zn concentrations in contaminated soil samples. FTIR revealed that Cu and Cr adsorbed to similar binding sites on bacteria, likely decreasing bacterial Cu toxicity. Increased abundances of DSV (marker for Desulfovibrio) and nifH (N-fixation) genes were observed, as well as an accumulation of nitrate-N content in soils suggesting that HQ23 stimulates the biological N-fixation in soils. This study strongly supports the future application of SRB for the bioremediation of heavy metal-polluted sites.

Mechanism and application of bacterial exopolysaccharides: An advanced approach for sustainable heavy metal abolition from soil

The escalation of heavy metal pollutants in soils and effluents, driven by industrialization and human activities, poses significant environmental and health risks. Conventional remediation methods are often costly and ineffective, prompting a shift towards sustainable alternatives such as biological treatments. Natural biosorbents, including microbial cells and their byproducts, have emerged as promising solutions. One such approach involves leveraging exopolysaccharides (EPS), complex high-molecular-weight biopolymers synthesized by microbes under environmental stress conditions. EPS are intricate organic macromolecules comprising proteins, polysaccharides, uronic acids, humic compounds, and lipids, either located within microbial cells or secreted into their surroundings. Their anionic functional groups enable efficient electrostatic binding of cationic heavy metals, making EPS effective biosorbents for soil remediation. This review thoroughly explores the pivotal role of bacterial EPS in the removal of heavy metals, focusing on EPS biosynthesis mechanisms, the dynamics of interaction with heavy metals, and case studies that illustrate their effectiveness in practical remediation strategies. By highlighting these aspects, the review underscores the innovation and practical implications of EPS-based bioremediation technologies, demonstrating their potential to address critical environmental challenges effectively while paving the way for sustainable environmental management practices. Key findings reveal that EPS exhibit robust metal-binding capacities, facilitated by their anionic functional groups, thereby offering a promising solution for mitigating metal pollution in diverse environmental matrices.

Molecular and eco-physiological responses of soil-borne lead (Pb2+)-resistant bacteria for bioremediation and plant growth promotion under lead stress

Lead (Pb) is the 2nd known portentous hazardous substance after arsenic (As). Being highly noxious, widespread, non-biodegradable, prolonged environmental presence, and increasing accumulation, particularly in arable land, Pb pollution has become a serious global health concern requiring urgent remediation. Soil-borne, indigenous microbes from Pb-polluted sites have evolved diverse resistance strategies, involving biosorption, bioprecipitation, biomineralization, biotransformation, and efflux mechanisms, under continuous exposure to Pb in human-impacted surroundings. These strategies employ a wide range of functional bioligands to capture Pb and render it inaccessible for leaching. Recent breakthroughs in molecular technology and understanding of lead resistance mechanisms offer the potential for utilizing microbes as biological tools in environmental risk assessment. Leveraging the specific affinity and sensitivity of bacterial regulators to Pb2+ ions, numerous lead biosensors have been designed and deployed worldwide to monitor Pb bioavailability in contaminated sites, even at trace levels. Besides, the ongoing degradation of croplands due to Pb pollution poses a significant challenge to meet the escalating global food demands. The accumulation of Pb in plant tissues jeopardizes both food safety and security while severely impacting plant growth. Exploring Pb-resistant plant growth-promoting rhizobacteria (PGPR) presents a promising sustainable approach to agricultural practices. The active associations of PGPR with host plants have shown enhancements in plant biomass and stress alleviation under Pb influence. They thus serve a dual purpose for plants grown in Pb-contaminated areas. This review aims to offer a comprehensive understanding of the role played by Pb-resistant soil-borne indigenous bacteria in expediting bioremediation and improving the growth of Pb-challenged plants essential for potential field application, thus broadening prospects for future research and development.

Biochemical transformation and bioremediation of thallium in the environment

Thallium (Tl) is a toxic element associated with minerals, and its redistribution is facilitated by both geological and anthropogenic activities. In the natural environment, the transformation and migration of Tl mediated by (micro)organisms have attracted increasing attention. This review presents an overview of the biochemical transformation of Tl and the bioremediation strategies for Tl contamination. In the environment, Tl exists in various forms and originates from diverse sources. The global distribution characteristics of Tl in various media are summarized here, while its speciation and toxicity mechanism to organisms are elucidated. Interactions between (micro)organisms and Tl are commonly observed in the environment. Microbial response mechanisms to typical Tl exposure are analyzed at both species and gene levels, and the possibility of microorganisms as bio-indicators for monitoring Tl contamination is also highlighted. The processes and mechanisms involved in the microbial and benthic mediated transformation of Tl, as well as its enrichment by plants, are discussed. Additionally, in situ bioremediation strategies for Tl contamination and bio-treatment techniques for Tl-containing wastewater are summarized. Finally, the existing knowledge gaps and future research challenges are emphasized, including Tl distribution characteristics in the atmosphere and ocean, the key molecular mechanisms underlying Tl transformation by organisms, the screening of potential Tl oxidizing microorganisms and hyperaccumulators, as well as the revelation of global biogeochemical cycling pathways of Tl.

Plant growth-promoting rhizobacterial secondary metabolites in augmenting heavy metal(loid) phytoremediation: An integrated green in situ ecorestorative technology

In recent times, increased geogenic and human-centric activities have caused significant heavy metal(loid) (HM) contamination of soil, adversely impacting environmental, plant, and human health. Phytoremediation is an evolving, cost-effective, environment-friendly, in situ technology that employs indigenous/exotic plant species as natural purifiers to remove toxic HM(s) from deteriorated ambient soil. Interestingly, the plant's rhizomicrobiome is pivotal in promoting overall plant nutrition, health, and phytoremediation. Certain secondary metabolites produced by plant growth-promoting rhizobacteria (PGPR) directly participate in HM bioremediation through chelation/mobilization/sequestration/bioadsorption/bioaccumulation, thus altering metal(loid) bioavailability for their uptake, accumulation, and translocation by plants. Moreover, the metallotolerance of the PGPR and the host plant is another critical factor for the successful phytoremediation of metal(loid)-polluted soil. Among the phytotechniques available for HM remediation, phytoextraction/phytoaccumulation (HM mobilization, uptake, and accumulation within the different plant tissues) and phytosequestration/phytostabilization (HM immobilization within the soil) have gained momentum in recent years. Natural metal(loid)-hyperaccumulating plants have the potential to assimilate increased levels of metal(loid)s, and several such species have already been identified as potential candidates for HM phytoremediation. Furthermore, the development of transgenic rhizobacterial and/or plant strains with enhanced environmental adaptability and metal(loid) uptake ability using genetic engineering might open new avenues in PGPR-assisted phytoremediation technologies. With the use of the Geographic Information System (GIS) for identifying metal(loid)-impacted lands and an appropriate combination of normal/transgenic (hyper)accumulator plant(s) and rhizobacterial inoculant(s), it is possible to develop efficient integrated phytobial remediation strategies in boosting the clean-up process over vast regions of HM-contaminated sites and eventually restore ecosystem health.

Simultaneous removal of malachite green and lead from water by consortium dry-biomasses of Bacillus licheniformis AG3 and Bacillus cereus M116

Synthetic textile dye malachite green (MG) and heavy metals present in industrial wastewater are hazardous to the ecosystem. Bioremediation of dyes and heavy metals using dry-biomasses has advantages over chemical methods. This study screened an acclimatized, heavy metal-resistant, and dye-degrading Gram positive Bacillus licheniformis AG3 strain from the textile wastewater near Kolkata, West Bengal. The EDXRF analysis of this colored wastewater effluent showed 36.33 mg/L lead, significantly higher than the WHO recommendation. Previously, Bag et al. showed bioremediation of synthetic dyes using dry-biomass of Bacillus cereus M116 from an aqueous solution (Bag et al. Arch Microbiol 203(7):3811-3823, 2021). Here, a consortium of dry-biomasses of B. licheniformis AG3 and B. cereus M116 strains (1:1 w/w ratio) was prepared for the simultaneous removal of lead and MG from wastewater. Statistical optimization determines that the pH, initial concentration of contaminants, and dry-biomass concentrations are critical for bioremediation under batch procedures. Further, optimization using the response surface methodology showed that 0.01% consortium dry-biomasses eliminated a maximum of 99.35% MG and 96.01% lead (II) within 6 h. SEM-EDS and FTIR confirmed a strong surface biosorption. Furthermore, a fixed-bed biofilter column of the consortium dry-biomasses was prepared, which was able to remove 98.1% MG and 98.5% lead at the 0.5-1 mL/min flow rate. Together, this study developed a biofilter with a consortium dry biomasses of B. licheniformis AG3 and B. cereus M116 for the simultaneous removal of MG and lead from wastewater.

Genome and pan-genome analysis of a new exopolysaccharide-producing bacterium Pyschrobacillus sp. isolated from iron ores deposit and insights into iron uptake

Bacterial exopolysaccharides (EPS) have emerged as one of the key players in the field of heavy metal-contaminated environmental bioremediation. This study aimed to characterize and evaluate the metal biosorption potential of EPS produced by a novel Psychrobacillus strain, NEAU-3TGS, isolated from an iron ore deposit at Tamra iron mine, northern Tunisia. Genomic and pan-genomic analysis of NEAU-3TGS bacterium with nine validated published Psychrobacillus species was also performed. The results showed that the NEAU-3TGS genome (4.48 Mb) had a mean GC content of 36%, 4,243 coding sequences and 14 RNA genes. Phylogenomic analysis and calculation of nucleotide identity (ANI) values (less than 95% for new species with all strains) confirmed that NEAU-3TGS represents a potential new species. Pangenomic analysis revealed that Psychrobacillus genomic diversity represents an "open" pangenome model with 33,091 homologous genes, including 65 core, 3,738 shell, and 29,288 cloud genes. Structural EPS characterization by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy showed uronic acid and α-1,4-glycosidic bonds as dominant components of the EPS. X-ray diffraction (XRD) analysis revealed the presence of chitin, chitosan, and calcite CaCO3 and confirmed the amorphous nature of the EPS. Heavy metal bioabsorption assessment showed that iron and lead were more adsorbed than copper and cadmium. Notably, the optimum activity was observed at 37°C, pH=7 and after 3 h contact of EPS with each metal. Genomic insights on iron acquisition and metabolism in Psychrobacillus sp. NEAU-3TGS suggested that no genes involved in siderophore biosynthesis were found, and only the gene cluster FeuABCD and trilactone hydrolase genes involved in the uptake of siderophores, iron transporter and exporter are present. Molecular modelling and docking of FeuA (protein peptidoglycan siderophore-binding protein) and siderophores ferrienterobactine [Fe+3 (ENT)]-3 and ferribacillibactine [Fe+3 (BB)]-3 ligand revealed that [Fe+3 (ENT)]-3 binds to Phe122, Lys127, Ile100, Gln314, Arg215, Arg217, and Gln252. Almost the same for [Fe+3 (ENT)]-3 in addition to Cys222 and Tyr229, but not Ile100.To the best of our knowledge, this is the first report on the characterization of EPS and the adsorption of heavy metals by Psychrobacillus species. The heavy metal removal capabilities may be advantageous for using these organisms in metal remediation.

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

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

PGPR-Enabled bioremediation of pesticide and heavy metal-contaminated soil: A review of recent advances and emerging challenges

The excessive usage of agrochemicals, including pesticides, along with various reckless human actions, has ensued discriminating prevalence of pesticides and heavy metals (HMs) in crop plants and the environment. The enhanced exposure to these chemicals is a menace to living organisms. The pesticides may get bioaccumulated in the food chain, thereby leading to several deteriorative changes in the ecosystem health and a rise in the cases of some serious human ailments including cancer. Further, both HMs and pesticides cause some major metabolic disturbances in plants, which include oxidative burst, osmotic alterations and reduced levels of photosynthesis, leading to a decline in plant productivity. Moreover, the synergistic interaction between pesticides and HMs has a more serious impact on human and ecosystem health. Various attempts have been made to explore eco-friendly and environmentally sustainable methods of improving plant health under HMs and/or pesticide stress. Among these methods, the employment of PGPR can be a suitable and effective strategy for managing these contaminants and providing a long-term remedy. Although, the application of PGPR alone can alleviate HM-induced phytotoxicities; however, several recent reports advocate using PGPR with other micro- and macro-organisms, biochar, chelating agents, organic acids, plant growth regulators, etc., to further improve their stress ameliorative potential. Further, some PGPR are also capable of assisting in the degradation of pesticides or their sequestration, reducing their harmful effects on plants and the environment. This present review attempts to present the current status of our understanding of PGPR's potential in the remediation of pesticides and HMs-contaminated soil for the researchers working in the area.

Nano-Bioremediation of Arsenic and Its Effect on the Biological Activity and Growth of Maize Plants Grown in Highly Arsenic-Contaminated Soil

Arsenic (As)-contaminated soil reduces soil quality and leads to soil degradation, and traditional remediation strategies are expensive or typically produce hazardous by-products that have negative impacts on ecosystems. Therefore, this investigation attempts to assess the impact of As-tolerant bacterial isolates via a bacterial Rhizobim nepotum strain (B1), a bacterial Glutamicibacter halophytocola strain (B2), and MgO-NPs (N) and their combinations on the arsenic content, biological activity, and growth characteristics of maize plants cultivated in highly As-contaminated soil (300 mg As Kg-1). The results indicated that the spectroscopic characterization of MgO-NPs contained functional groups (e.g., Mg-O, OH, and Si-O-Si) and possessed a large surface area. Under As stress, its addition boosted the growth of plants, biomass, and chlorophyll levels while decreasing As uptake. Co-inoculation of R. nepotum and G. halophytocola had the highest significant values for chlorophyll content, soil organic matter (SOM), microbial biomass (MBC), dehydrogenase activity (DHA), and total number of bacteria compared to other treatments, which played an essential role in increasing maize growth. The addition of R. nepotum and G. halophytocola alone or in combination with MgO-NPs significantly decreased As uptake and increased the biological activity and growth characteristics of maize plants cultivated in highly arsenic-contaminated soil. Considering the results of this investigation, the combination of G. halophytocola with MgO-NPs can be used as a nanobioremediation strategy for remediating severely arsenic-contaminated soil and also improving the biological activity and growth parameters of maize plants.

Optimization and Production of Exopolysaccharides (EPS) and Indole-3-Acetic Acid (IAA) Under Chromium by Halophilic Bacteria Oceanobacillus oncorhynchi W4

The current study assessed the levels of exopolysaccharides (EPS) and indole-3-acetic acid (IAA) and the impacts of halophilic bacteria Oceanobacillus oncorhynchi W4 under Cr (VI). The effects of W4 were tested for its ability to remove Cr (VI) at several concentrations, the removal rate was reached after 48 h at 58.4%, 53.3%, 49.2%, and 43.1%). After 12-48 h, the maximum removal rate of 29-58% was found at an initial concentration of 50 mg/L (Cr (VI)). The Box-Behnken design based on response surface methodology was utilized to optimize the EPS, including pH, sucrose concentration, and incubation period. The highest EPS yield (314.5 mg/L) was obtained under 96 h at pH 7.0, with 5% sucrose concentration. The strain Oceanobacillus oncorhynchi W4 was tested for its ability to create EPS at various concentrations of Cr (VI). After 96 h, it generated the maximum amount of EPS (216.3 mg/L) at a concentration of 50 mg/L. By using FT-IR spectrum measurements, it was confirmed that hexavalent chromium and EPS had surface chemical interactions. At various Cr (VI) concentrations, the isolate W4 was tested for its ability to secrete Indole-3 acetic acid. IAA secretion (control) without Cr (VI) achieved a maximum of 1.45 mg/ml at 120 h. At 200 mg/L Cr (VI) concentration, 1.65 mg/ml of IAA was also produced after 48 h. According to the findings, Oceanobacillus oncorhynchi W4 was a promising isolate in a stressful environment.

Nano-biogenic heavy metals adsorptive remediation for enhanced soil health and sustainable agricultural production

Hazardous heavy metal (HM) pollution constitutes a pervasive global challenge, posing substantial risks to ecosystems and human health. The exigency for expeditious detection, meticulous monitoring, and efficacious remediation of HM within ecosystems is indisputable. Soil contamination, stemming from a myriad of anthropogenic activities, emerges as a principal conduit for HM ingress into the food chain. Traditional soil remediation modalities for HM elimination, while effective are labor-intensive, susceptible to secondary contamination, and exhibit limited efficacy in regions characterized by low metal toxicity. In response to these exigencies, the eco-friendly paradigm of bioremediation has garnered prominence as a financially judicious and sustainable remedial strategy. This approach entails the utilization of hyperaccumulators, Genetically Modified Microorganisms (GMM), and advantageous microbes. The current review offers a comprehensive elucidation of cutting-edge phyto/microbe-based bioremediation techniques, with a specific emphasis on their amalgamation with nanotechnology. Accentuating their pivotal role in advancing sustainable agricultural practices, the review meticulously dissects the synergistic interplay between plants and microbes, underscoring their adeptness in HM remediation sans secondary contamination. Moreover, the review scrutinizes the challenges intrinsic to implementing bioremediation-nanotechnology interface techniques and propounds innovative resolutions. These discernments proffer auspicious trajectories for the future of agriculture. Through the environmentally conscientious marvels of phyto/microbe bioremediation, an optimistic outlook emerges for environmental preservation and the cultivation of a sustainable, salubrious planet via the conduit of cleaner agricultural production.

Potential of the plant growth-promoting rhizobacterium Rhodococcus qingshengii LMR356 in mitigating lead stress impact on Sulla spinosissima L

Mining-related lead (Pb) pollution of the soil poses serious hazards to ecosystems and living organisms, including humans. Improved heavy metal phytoremediation efficacy, achieved by using phytostabilizing plants assisted by plant-growth-promoting (PGP) microorganisms, has been presented as an effective strategy for remediating polluted soils. The objective of this research was to examine the response and potential of the plant-growth-promoting bacterium LMR356, a Rhodococcus qingshengii strain isolated from an abandoned mining soil, under lead stress conditions. Compared to non-contaminated culture media, the presence of lead induced a significant decrease in auxin production (from 21.17 to 2.65 μg mL-1) and phosphate solubilization (from 33.60 to 8.22 mg L-1), whereas other PGP traits increased drastically, such as 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity (from 38.17 to 71.37 nmol mg-1 h-1 α-ketobutyrate), siderophore production (from 69 to 83%), exopolysaccharide production (from 1952.28 to 3637.72 mg mL-1), biofilm formation, and motility. We, therefore, investigated the behavior of Sulla spinosissima L. in the presence or absence of this strain under a variety of experimental conditions. Under hydroponic conditions, Sulla plants showed endurance to varying lead concentrations (500-1000 μM). Inoculation of plants with Rhodococcus qingshengii strain LMR356 enhanced plant tolerance, as demonstrated by the increase in plant biomass (ranging from 14.41 to 79.12%) compared to non-inoculated Pb-stressed and non-stressed control plants. Antioxidant enzyme activities (increasing by -42.71 to 126.8%) and chlorophyll (383.33%) and carotenoid (613.04%) content were also augmented. In addition to its impact on plant lead tolerance, strain LMR356 showed a growth-promoting effect on Sulla plants when cultivated in sterilized non-contaminated sand. Parameters such as plant biomass (16.57%), chlorophyll (24.14%), and carotenoid (30%) contents, as well as ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT) activities, were all elevated compared to non-inoculated plants. Furthermore, when the same plant species was cultivated in highly polluted soil, inoculation increased plant biomass and improved its physiological properties. These findings demonstrate that LMR356 is a phytobeneficial bacterial strain capable of enhancing Sulla growth under normal conditions and improving its heavy metal tolerance in multi-polluted soils. Thus, it can be considered a promising biofertilizer candidate for growing Sulla spinosissima L. or other selected plants intended for application in restoration and stabilization initiatives aimed at reviving and safeguarding environmentally compromised and polluted soils after mining activities.

Production of Exopolysaccharides and İndole Acetic Acid (IAA) by Rhizobacteria and Their Potential against Drought Stress in Upland Rice

Peatlands are marginal agricultural lands due to highly acidic soil conditions and poor drainage systems. Drought stress is a big problem in peatlands as it can affect plants through poor root development, so technological innovations are needed to increase the productivity and sustainability of upland rice on peatlands. Rhizobacteria can overcome the effects of drought stress by altering root morphology, regulating stress-responsive genes, and producing exopolysaccharides and indole acetic acid (IAA). This study aimed to determine the ability of rhizobacteria in upland rice to produce exopolysaccharides and IAA, identify potential isolates using molecular markers, and prove the effect of rhizobacteria on viability and vigor index in upland rice. Rhizobacterial isolates were grown on yeast extract mannitol broth (YEMB) medium for exopolysaccharides production testing and Nutrient Broth (NB)+L-tryptophan medium for IAA production testing. The selected isolates identify using sequence 16S rRNA. The variables observed in testing the effect of rhizobacteria were germination ability, vigour index, and growth uniformity. EPS-1 isolate is the best production of exopolysaccharides (41.6 mg/ml) and IAA (60.83 ppm). The isolate EPS-1 was identified as Klebsiella variicola using 16S rRNA sequencing and phylogenetic analysis. The isolate EPS-1 can increase the viability and vigor of upland rice seeds. K. variicola is more adaptive and has several functional properties that can be developed as a potential bioagent or biofertilizer to improve soil nutrition, moisture and enhance plant growth. The use of rhizobacteria can reduce dependence on the use of synthetic materials with sustainable agriculture.

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

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

The Cd resistant mechanism of Proteus mirabilis Ch8 through immobilizing and detoxifying

Cadmium (Cd) pollution is a serious global environmental problem, which requires a global concern and practical solutions. Microbial remediation has received widespread attention owing to advantages, such as environmental friendliness and soil amelioration. However, Cd toxicity also severely deteriorates the remediation performance of functional microorganisms. Analyzing the mechanism of bacterial resistance to Cd stress will be beneficial for the application of Cd remediation. In this study, the bacteria strain, up to 1400 mg/L Cd resistance, was employed and identified as Proteus mirabilis Ch8 (Ch8) through whole genome sequence analyses. The results indicated that the multiple pathways of immobilizing and detoxifying Cd maintained the growth of Ch8 under Cd stress, which also possessed high Cd extracellular adsorption. Firstly, the changes in surface morphology and functional groups of Ch8 cells were observed under different Cd conditions through SEM-EDS and FTIR analyses. Under 100 mg/L Cd, Ch8 cells exhibited aggregation and less flagella; the Cd biosorption of Ch8 was predominately by secreting exopolysaccharides (EPS) and no significant change of functional groups. Under 500 mg/L Cd, Ch8 were present irregular polymers on the cell surface, some cells with wrapping around; the Cd biosorption capacity exhibited outstanding effects (38.80 mg/g), which was mainly immobilizing Cd by secreting and interacting with EPS. Then, Ch8 also significantly enhanced the antioxidant enzyme activity and the antioxidant substance content under different Cd conditions. The activities of SOD and CAT, GSH content of Ch8 under 500 mg/L Cd were significantly increased by 245.47%, 179.52%, and 241.81%, compared to normal condition. Additionally, Ch8 significantly induced the expression of Acr A and Tol C (the resistance-nodulation-division (RND) efflux pump), and some antioxidant genes (SodB, SodC, and Tpx) to reduce Cd damage. In particular, the markedly higher expression levels of SodB under Cd stress. The mechanism of Ch8 lays a foundation for its application in solving soil remediation.

An assessment of metal absorption competence of indigenous metal tolerant bacterial species- an in-vitro study

Heavy metals pose a serious global threat to the environment. Hence, removing hazardous metals from soil samples has become complicated over the past few years. The current work looked into the remediation of heavy metals from aqueous solutions using a bacterial community and a unique bacterium obtained from metal-contaminated soil. In this investigation, the isolates of Bacillus anthracis A1-7, Bacillus. thuringiensis A1-3, Bacillus. cereus A1-5, and Pseudomonas aeruginosa A-33 actively demonstrated metal tolerances to various tested metals. Furthermore, an in-vitro biosorption study was performed under ideal concentration. The bacterial consortia achieved the highest biosorption effectiveness for Cu & Zn, 92.7% and 90.3%, respectively. When compared with a single bacterium, the group exhibited inferior Pb biosorption (86%). Since then, P. aeruginosa A33 has had the highest Pb biosorption. Finally, a bacterial consortium has devised an intriguing strategy for eliminating Cu and Pb from the polluted medium. P. aeruginosa A33 was found to be a mighty microbe that extracts Zn from polluted water. This metal-tolerant bacterium also exhibited specific proportions of selective commercially available antibiotics, which were analyzed using the Multiple Antibiotic Resistance (MAR) Index. In conclusion, these findings indicated that bacterial consortia composed of four bacterial isolates can remove metals from a metal-polluted medium.

Understanding the role of biofilms and estimation of life-span of a tire derived aggregates-based underground stormwater treatment system

The importance of biofilm in tire derived aggregates (TDA) based underground systems has been investigated in this paper, to assess the utilization of tire waste as a cost-effective and sustainable resource for stormwater treatment. The primary objective of this study is to look into the role of biofilms in preventing metal leaching from a TDA based stormwater treatment system and to estimate the life span of a TDA based stormwater treatment system. TDA subjected to different influents to promote or limit the growth of biofilms were analyzed for their leaching and adsorption potential for fifteen different metals through 72 flushes, which is representative of roughly 9 years of TDA exposure to storm events in the upper Midwest USA. Biofilm growth on a manufacturing byproduct (wire exposed-TDA) was higher than on the traditional TDA. The presence of biofilm on TDA had a minor impact on orthophosphate adsorption as observed in a previous study conducted by the authors. However, metals such as iron, zinc and copper, which were previously a concern, had substantially lower leaching into the stored runoff. In addition, the orthophosphate removal from runoff by TDA with a biofilm through 72 flushes indicates that TDA based underground systems can have orthophosphate removal life span beyond 8-9 years. Thus, TDA with biofilms in an underground storage/infiltration chamber has the potential to establish itself as a sustainable, cost-effective, and long life-span alternative for stormwater remediation of orthophosphate pollution without leaching of metals.

Brucella pituitosa strain BU72, a new hydrocarbonoclastic bacterium through exopolysaccharide-based surfactant production

Hydrocarbon and heavy metal pollution are amongst the most severe and prevalent environmental problems due to their toxicity and persistence. Bioremediation using microorganisms is considered one of the most effective ways to treat polluted sites. In the present study, we unveil the bioremediation potential of Brucella pituitosa strain BU72. Besides its ability to grow on multiple hydrocarbons as the sole carbon source and highly tolerant to several heavy metals, BU72 produces different exopolysaccharide-based surfactants (EBS) when grown with glucose or with crude oil as sole carbon source. These EBS demonstrated particular and specific functional groups as determined by Fourier transform infrared (FTIR) spectral analysis that showed a strong absorption peak at 3250 cm-1 generated by the -OH group for both EBS. The FTIR spectra of the produced EBS revealed major differences in functional groups and protein content. To better understand the EBS production coupled with the degradation of hydrocarbons and heavy metal resistance, the genome of strain BU72 was sequenced. Annotation of the genome revealed multiple genes putatively involved in EBS production pathways coupled with resistance to heavy metals genes such as arsenic tolerance and cobalt-zinc-cadmium resistance. The genome sequence analysis showed the potential of BU72 to synthesise secondary metabolites and the presence of genes involved in plant growth promotion. Here, we describe the physiological, metabolic, and genomic characteristics of Brucella pituitosa strain BU72, indicating its potential as a bioremediation agent.

The cepacian-like exopolysaccharide of Paraburkholderia ultramafica STM10279T enhances growth and metal adaptation of Tetraria comosa on New Caledonian ultramafic soil

Paraburkholderia ultramafica STM10279T is a metal-tolerant rhizobacterium that promotes plant growth. It was isolated from the roots of Tetraria arundinaceae, a pioneer endemic tropical herb growing on ultramafic soils in New Caledonia. We have recently shown that the main mechanism of metal tolerance of P. ultramafica is related to the production of an acidic exopolysaccharide (EPS). To explore the potential role of this EPS in the plant's environmental adaptation, we first elucidated its structure by employing a combination of chromatography and mass spectrometry techniques. These analyses revealed that the EPS is highly branched and composed of galactosyl (35.8%), glucosyl (33.2%), rhamnosyl (19.5%), mannosyl (7.2%), and glucuronosyl residues (4.4%), similar to the EPS of the Burkholderia cepacia complex known as cepacian. We subsequently conducted greenhouse experiments on Tetraria comosa plantlets inoculated with P. ultramafica or a solution of its EPS during transplanting onto ultramafic substrate. The data showed that the dry weight of T. comosa shoots was 2.5 times higher in the plants treated with the EPS compared to the unexposed plants. In addition, inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis revealed that exposure to the EPS significantly increased Ca, Mg, K, and P uptake as well as K content in roots. In vitro experiments using the Pikovskaya method showed that the EPS was able to solubilize phosphorus. Consistent with the retention of metals in roots and a reduction in shoots, our data revealed a significant decrease in metal translocation factors (TFs) in the plants inoculated with the EPS. These results suggest a beneficial effect of the rhizobacterial EPS on plant growth and abiotic stress mitigation. In addition, the data suggest that the reduced levels of trace metals in plants exposed to P. ultramafica STM10279T are due to metal chelation by the EPS. Further investigations are needed to firmly demonstrate whether this EPS could be used as a biostimulant for plant growth and adaptation to ultramafic soils.

Mechanistic and future prospects in rhizospheric engineering for agricultural contaminants removal, soil health restoration, and management of climate change stress

Climate change, food insecurity, and agricultural pollution are all serious challenges in the twenty-first century, impacting plant growth, soil quality, and food security. Innovative techniques are required to mitigate these negative outcomes. Toxic heavy metals (THMs), organic pollutants (OPs), and emerging contaminants (ECs), as well as other biotic and abiotic stressors, can all affect nutrient availability, plant metabolic pathways, agricultural productivity, and soil-fertility. Comprehending the interactions between root exudates, microorganisms, and modified biochar can aid in the fight against environmental problems such as the accumulation of pollutants and the stressful effects of climate change. Microbes can inhibit THMs uptake, degrade organic pollutants, releases biomolecules that regulate crop development under drought, salinity, pathogenic attack and other stresses. However, these microbial abilities are primarily demonstrated in research facilities rather than in contaminated or stressed habitats. Despite not being a perfect solution, biochar can remove THMs, OPs, and ECs from contaminated areas and reduce the impact of climate change on plants. We hypothesized that combining microorganisms with biochar to address the problems of contaminated soil and climate change stress would be effective in the field. Despite the fact that root exudates have the potential to attract selected microorganisms and biochar, there has been little attention paid to these areas, considering that this work addresses a critical knowledge gap of rhizospheric engineering mediated root exudates to foster microbial and biochar adaptation. Reducing the detrimental impacts of THMs, OPs, ECs, as well as abiotic and biotic stress, requires identifying the best root-associated microbes and biochar adaptation mechanisms.

Deciphering the mechanistic role of Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52) in bio-sorption and phyto-assimilation of Cadmium via Linum usitatissimum L. Seedlings

Three Cd2+ resistant bacterium's minimal inhibition concentrations were assessed and their percentages of Cd2+ accumulation were determined by measurements using an atomic absorption spectrophotometer (AAS). The results revealed that two isolates Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52), identified by 16S rDNA gene sequencing, showed a higher percentage of Cd2+ accumulation i.e., 83.78% and 81.79%, respectively. Moreover, both novel strains can tolerate Cd2+ levels up to 2000 mg/L isolated from district Chakwal. Amplification of the czcD, nifH, and acdS genes was also performed. Batch bio-sorption studies revealed that at pH 7.0, 1 g/L of biomass, and an initial 150 mg/L Cd2+ concentration were the ideal bio-sorption conditions for Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52). The experimental data were fit to Langmuir isotherm measurements and Freundlich isotherm model R2 values of 0.999 for each of these strains. Bio sorption processes showed pseudo-second-order kinetics. The intra-diffusion model showed Xi values for Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52) of 2.26 and 2.23, respectively. Different surface ligands, was investigated through Fourier-transformation infrared spectroscopy (FTIR). The scanning electron microscope SEM images revealed that after Cd2+ adsorption, the cells of both strains became thick, adherent, and deformed. Additionally, both enhanced Linum usitatissimum plant seed germination under varied concentrations of Cd2+ (0 mg/L, 250 mg/L,350 mg/L, and 500 mg/L). Current findings suggest that the selected strains can be used as a sustainable part of bioremediation techniques.

The quorum sensing SinI/R system contributes to cadmium immobilization in Ensifer adhaerens NER9 in the cadmium-contaminated solution

In this study, the cadmium (Cd)-tolerant Ensifer adhaerens strain NER9 with quorum sensing (QS) systems (responsible for N-acyl homoserine lactone (AHL) production) was characterized for QS system-mediated Cd immobilization and the underlying mechanisms involved. Whole-genome sequence analysis revealed that strain NER9 contains the QS SinI/R and TraI/R systems. Strains NER9 and the NER9∆sinI/R, NER9∆traI/R, and NER9∆sinI/R-traI/R mutants were constructed and compared for QS SinI/R and TraI/R system-mediated Cd immobilization in the solution and the mechanisms involved. After 24 h of incubation, strain NER9 significantly decreased the Cd concentration in the Cd-contaminated solution compared with the NER9∆sinI/R, NER9∆traI/R, and NER9∆sinI/R-traI/R mutants. The NER9∆sinI/R mutant had a greater impact on Cd immobilization and a lower impact on the activities of AHLs than did the NER9∆traI/R mutant. The NER9∆sinI/R mutant had significantly greater Cd concentrations and lower cell wall- and exopolysaccharide (EPS)-adsorbed Cd contents than did strain NER9. Furthermore, the NER9∆sinI/R mutant presented a decrease in the number of functional groups interacting with Cd, compared with strain NER9. These results suggested that the SinI/R system in strain NER9 contributed to Cd immobilization by mediating cell wall- and EPS-adsorption in Cd-containing solution.

Guardians of the Gut: Harnessing the Power of Probiotic Microbiota and Their Exopolysaccharides to Mitigate Heavy Metal Toxicity in Human for Better Health

Heavy metal pollution is a significant global health concern, posing risks to both the environment and human health. Exposure to heavy metals happens through various channels like contaminated water, food, air, and workplaces, resulting in severe health implications. Heavy metals also disrupt the gut's microbial balance, leading to dysbiosis characterized by a decrease in beneficial microorganisms and proliferation in harmful ones, ultimately exacerbating health problems. Probiotic microorganisms have demonstrated their ability to adsorb and sequester heavy metals, while their exopolysaccharides (EPS) exhibit chelating properties, aiding in mitigating heavy metal toxicity. These beneficial microorganisms aid in restoring gut integrity through processes like biosorption, bioaccumulation, and biotransformation of heavy metals. Incorporating probiotic strains with high affinity for heavy metals into functional foods and supplements presents a practical approach to mitigating heavy metal toxicity while enhancing gut health. Utilizing probiotic microbiota and their exopolysaccharides to address heavy metal toxicity offers a novel method for improving human health through modulation of the gut microbiome. By combining probiotics and exopolysaccharides, a distinctive strategy emerges for mitigating heavy metal toxicity, highlighting promising avenues for therapeutic interventions and health improvements. Further exploration in this domain could lead to groundbreaking therapies and preventive measures, underscoring probiotic microbiota and exopolysaccharides as natural and environmentally friendly solutions to heavy metal toxicity. This, in turn, could enhance public health by safeguarding the gut from environmental contaminants.

Detoxification of copper and zinc from anaerobic digestate effluent by indigenous bacteria: Mechanisms, pathways and metagenomic analysis

The presence of organic-complexed copper and zinc in anaerobic digestate effluent (ADE) poses persistent ecological toxicity. This study investigated the detoxification performance and biotic responses of indigenous bacteria against ethylene diamine tetraacetic acid (EDTA)-complexed Cu(II) and Zn(II). Heavy metals (HMs) stress induced reactive oxygen species (ROS) generation and enhanced extracellular polymeric substances (EPS) secretion. At a Cu(II) influent concentration of 20.0 mg·L-1, indigenous bacteria removed 88.2% of Cu(II) within nine days. The majority of copper and zinc sequestered by bacteria were stored in the cell envelope, with over 50% of copper and 60% of zinc being immobilized. Transmission electron microscopy mapping (TEM-mapping) revealed significant mineralization of copper and zinc on the cell wall. Proteins abundant in EPS, alongside humic acid-like substances, effectively adsorbed HMs. Indigenous bacteria exhibited the capacity to reduce cupric to the cuprous state and cupric is preferentially reduced to cuprous before reaching reducing capacity saturation. Sulfur precipitation emerges as a crucial pathway for Zn(II) removal. Metagenomic analysis indicated that indigenous bacteria upregulated genes related to HMs homeostasis, efflux, and DNA repair, enhancing its resistance to high concentrations HMs. This study provided theoretical guidance for employing bacterial consortia to eliminate HMs in complex aquatic environments.

Enhancing soil health to minimize cadmium accumulation in agro-products: the role of microorganisms, organic matter, and nutrients

Agro-products accumulate Cd from the soil and are the main source of Cd in humans. Their use must therefore be minimized using effective strategies. Large soil beds containing low-to-moderate Cd-contamination are used to produce agro-products in many developing countries to keep up with the demand of their large populations. Improving the health of Cd-contaminated soils could be a cost-effective method for minimizing Cd accumulation in crops. In this review, the latest knowledge on the physiological and molecular mechanisms of Cd uptake and translocation in crops is presented, providing a basis for developing advanced technologies for producing Cd-safe agro-products. Inoculation of plant growth-promoting rhizobacteria and arbuscular mycorrhizal fungi, application of organic matter, essential nutrients, beneficial elements, regulation of soil pH, and water management are efficient techniques used to decrease soil Cd bioavailability and inhibiting the uptake and accumulation of Cd in crops. In combination, these strategies for improving soil health are environmentally friendly and practical for reducing Cd accumulation in crops grown in lightly to moderately Cd-contaminated soil.

Cadmium/zinc stresses and plant cultivation influenced soil microflora: a pot experiment conducted in field

It's of great challenge to address for heavy metal-contaminated soil. Once the farmland is contaminated with heavy metals, the microbial ecology of the plant rhizosphere will change, which in turn impacts crop productivity and quality. However, few studies have explored the effects of heavy metals on plant rhizosphere microbes in farmland and the role that plant cultivation plays in such a phytoremediation practice. In this study, the impacts of comfrey (Symphytum officinale L.) cultivation and the stresses of cadmium/zinc (Cd/Zn) on rhizosphere soil microflora were examined. Microbial DNA was collected from soils to evaluate the prevalence of bacteria and fungi communities in rhizosphere soils. High-throughput 16 S rRNA sequencing was used to determine the diversity of the bacterial and fungal communities. The results showed that growing comfrey on polluted soils reduced the levels of Cd and Zn from the vertical profile. Both the comfrey growth and Cd/Zn stresses affected the community of rhizosphere microorganisms (bacteria or fungi). Additionally, the analysis of PCoA and NMDS indicated that the cultivation of comfrey significantly changed the bacterial composition and structure of unpolluted soil. Comfrey cultivation in polluted and unpolluted soils did not result in much variance in the fungi's species composition, but the fungal compositions of the two-type soils were noticeably different. This work provided a better understanding of the impacts of Cd/Zn stresses and comfrey cultivation on rhizosphere microbial community, as well as new insight into phytoremediation of heavy metal-contaminated soils.

Mixed Consortium of Salt-Tolerant Phosphate Solubilizing Bacteria Improves Maize (Zea mays) Plant Growth and Soil Health Under Saline Conditions

The rhizobacterial isolate SP-167 exhibited considerable phosphate solubilization, IAA production, exo-polysaccharides, proline, APX, and CAT at a concentration of 6% NaCl (w/v). 16S rDNA sequencing and BLAST analysis showed that isolate SP-167 was Klebsiella sp. In this study, T2 and T8 consortium was developed on the basis of the compatibility of isolate SP-167 with Kluyvera sp. and Enterobacter sp. At 6% NaCl (w/v) concentration, T2 and T8 showed increased PGP properties such as phosphate solubilization, IAA, Proline activity, CAT, POD, and EPS than isolate SP-167. The maximum increase in shoot length was recorded in T2-treated maize plants as compared to the control after 60 days in 1% NaCl stress. The N, P, and K content of leaves were significantly increased in maize plants with the inoculation of both the T2 and T8 consortium. The electrical conductivity of soil was decreased significantly in the T2 inoculated 1% NaCl (w/v) treated pot after 30, 60, and 90 days. In this study, soil enzymes DHA and PPO were significantly increased in both T2 and T8 treated combinations. The Na concentration in root and shoot were significantly decreased in T8 inoculated plant than in T2, as confirmed by the translocation factor study.

Exopolysaccharides from agriculturally important microorganisms: Conferring soil nutrient status and plant health

A wide variety of microorganisms secretes extracellular polymeric substances or commonly known as exopolysaccharides (EPS), which have been studied to influence plant growth via various mechanisms. EPS-producing microorganisms have been found to have positive effects on plant health such as by facilitating nutrient entrapment in the soil, or by improving soil quality, especially by helping in mitigating various abiotic stress conditions. The various types of microbial polysaccharides allow for the compartmentalization of the microbial community enabling them to endure undressing stress conditions. With the growing population, there is a constant need for developing sustainable agriculture where we could use various PGPR to help the plant cope with various stress conditions and simultaneously enhance the crop yield. These polysaccharides have also found application in various sectors, especially in the biomedical fields, manifesting their potential to act as antitumor drugs, play a significant role in immune evasion, and reveal various therapeutic potentials. These constitute high levels of bioactive polysaccharides which possess a wide range of implementation starting from industrial applications to novel food applications. In this current review, we aim at presenting a comprehensive study of how these microbial extracellular polymeric substances influence agricultural productivity along with their other commercial applications.

Metal sequestration by Microcystis extracellular polymers: a promising path to greener water treatment

The problem of heavy metal pollution in water bodies poses a significant threat to both the environment and human health, as these toxic substances can persist in aquatic ecosystems and accumulate in the food chain. This study investigates the promising potential of using Microcystis aeruginosa extracellular polymeric substances (EPS) as an environmentally friendly, highly efficient solution for capturing copper (Cu2+) and nickel (Ni2+) ions in water treatment, emphasizing their exceptional ability to promote green technology in heavy metal sequestration. We quantified saccharides, proteins, and amino acids in M. aeruginosa biomass and isolated EPS, highlighting their metal-chelating capabilities. Saccharide content was 36.5 mg g-1 in biomass and 21.4 mg g-1 in EPS, emphasizing their metal-binding ability. Proteins and amino acids were also prevalent, particularly in EPS. Scanning electron microscopy (SEM) revealed intricate 3D EPS structures, with pronounced porosity and branching configurations enhancing metal sorption. Elemental composition via energy dispersive X-ray analysis (EDAX) identified essential elements in both biomass and EPS. Fourier transform infrared (FTIR) spectroscopy unveiled molecular changes after metal treatment, indicating various binding mechanisms, including oxygen atom coordination, π-electron interactions, and electrostatic forces. Kinetic studies showed EPS expedited and enhanced Cu2+ and Ni2+ sorption compared to biomass. Thermodynamic analysis confirmed exothermic, spontaneous sorption. Equilibrium biosorption studies displayed strong binding and competitive interactions in binary metal systems. Importantly, EPS exhibited impressive maximum sorption capacities of 44.81 mg g-1 for Ni2+ and 37.06 mg g-1 for Cu2+. These findings underscore the potential of Microcystis EPS as a highly efficient sorbent for heavy metal removal in water treatment, with significant implications for environmental remediation and sustainable water purification.

Enhanced exopolysaccharide production in gamma irradiated Bacillus subtilis: A biofilm-mediated strategy for ZnO nanoparticles removal

Biofilm-mediated strategy was studied for ZnO nanoparticle removal from aqueous media. Bacillus subtilis isolated from the soil rhizosphere was selected based on its high viscosity (133 Pa/s) of the cultivated culture and biofilm formation. The bacterium was exposed to gamma-irradiation to enhance EPS production along with its cultivation in EPS-producing media. The results show an increase in viscosity that reached 160 Pa/s at 2 kGy. EPS production increased from 4.45 to 7.95 mg/mL and the protein/carbohydrate ratio increased from 3 to 4.4 which reflects the stickiness of EPS. Thermal Gravimetric Analysis (TGA) showed 2 phase weight loss for gamma irradiated EPS and defined protein peaks when characterized using Matrix Assisted Laser Desorption Ionization-Time of Flight (MALDI-TOF). Native and gamma-irradiated Bacillus subtilis cells with their enhanced EPS were grown as a biofilm on sterile waste gauze fabric, Scanning Electron Microscopy (SEM) showed an increased biofilm attachment in gamma-irradiated samples. The latter was used for the removal of ZnO NP from aqueous media. Energy dispersive X-ray (EDX) mapping confirms that ZnO NPs were entrapped within the carbon and oxygen elements forming the biofilm with net intensities of 14.04, 1713, and 1190, respectively. The results confirm that biofilm-mediated strategy is effective in nanoparticles removal.

Exopolysaccharides of lactic acid bacteria: Structure, biological activity, structure-activity relationship, and application in the food industry: A review

Over the past few decades, researchers have discovered that probiotics play an important role in our daily lives. With the further deepening of research, more and more evidence show that bacterial metabolites have an important role in food and human health, which opens up a new direction for the research of lactic acid bacteria (LAB) in the food and pharmaceutical industry. Many LAB have been widely studied because of the ability of exopolysaccharides (EPS). Lactic acid bacteria exopolysaccharides (LAB EPS) not only have great potential in the treatment of human diseases but also can become natural ingredients in the food industry to provide special qualitative structure and flavor. This paper has organized and summarized the biosynthesis, strain selection, production process parameters, structure, and biological activity of LAB EPS, filling in the monotony and incompleteness of previous articles' descriptions of LAB EPS. Therefore, this paper focuses on the general biosynthetic pathway, structural characterization, structure-activity relationship, biological activity of LAB EPS, and their application in the food industry, which will help to deepen people's understanding of LAB EPS and develop new active drugs from LAB EPS. Although the research results are relatively affluent, the low yield, complex structure, and few clinical trials of EPS are still the reasons that hinder its development. Therefore, future knowledge expansion should focus on the regulation of structure, physicochemical properties, function, higher production of EPS, and clinical trial applications, which can further increase the commercial significance and value of EPS. Furthermore, better understanding the structure-function relationship of EPS in food remains a challenge to date.

The Involvement of Lactic Acid Bacteria and Their Exopolysaccharides in the Biosorption and Detoxication of Heavy Metals in the Gut

Heavy metal pollution has become one of the most important global environmental issues. The human health risk posed by heavy metals encountered through the food chain and occupational and environmental exposure is increasing, resulting in a series of serious diseases. Ingested heavy metals might disturb the function of the gut barrier and cause toxicity to organs or tissues in other sites of the body. Probiotics, including some lactic acid bacteria (LAB), can be used as an alternative strategy to detoxify heavy metals in the host body due to their safety and effectiveness. Exopolysaccharides (EPS) produced by LAB possess varied chemical structures and functional properties and take part in the adsorption of heavy metals via keeping the producing cells vigorous. The main objective of this paper was to summarize the roles of LAB and their EPS in the adsorption and detoxification of heavy metals in the gut. Accumulated evidence has demonstrated that microbial EPS play a pivotal role in heavy metal biosorption. Specifically, EPS-producing LAB have been reported to show superior absorption, tolerance, and efficient abatement of the toxicity of heavy metals in vitro and/or in vivo to non-EPS-producing species. The mechanisms underlying EPS-metal binding are mainly related to the negatively charged acidic groups and unique steric structure on the surface of EPS. However, whether the enriched heavy metals on the bacterial cell surface increase toxicity to local mammal cells or tissues in the intestine and whether they are released during excretion remain to be elucidated.

Microbial and Monosaccharide Composition of Biofilms Developing on Sandy Loams from an Aquifer Contaminated with Liquid Radioactive Waste

The development of microbial biofilms increases the survival of microorganisms in the extreme conditions of ecosystems contaminated with components of liquid radioactive waste (LRW) and may contribute to the successful bioremediation of groundwater. The purpose of this work was to compare the composition of the microorganisms and the exopolysaccharide matrix of the biofilms formed on sandy loams collected at the aquifer from a clean zone and from a zone with nitrate and radionuclide contamination. The aquifer is polluted from the nearby surface repository for liquid radioactive waste (Russia). The phylogenetic diversity of prokaryotes forming biofilms on the sandy loams' surface was determined during 100 days using high-throughput sequencing of the V4 region of the 16S rRNA genes. Scanning electron microscopy was used to study the development of microbial biofilms on the sandy loams. The ratio of proteins and carbohydrates in the biofilms changed in the course of their development, and the diversity of monosaccharides decreased, depending on the contamination of the sites from which the rocks were selected. The presence of pollution affects biofilm formation and EPS composition along with the dominant taxa of microorganisms and their activity. Biofilms establish a concentration gradient of the pollutant and allow the microorganisms involved to effectively participate in the reduction of nitrate and sulfate; they decrease the risk of nitrite accumulation during denitrification and suppress the migration of radionuclides. These biofilms can serve as an important barrier in underground water sources, preventing the spread of pollution. Pure cultures of microorganisms capable of forming a polysaccharide matrix and reducing nitrate, chromate, uranyl, and pertechnetate ions were isolated from the biofilms, which confirmed the possibility of their participation in the bioremediation of the aquifer from nonradioactive waste components and the decrease in the radionuclides' migration.

Bacterial tolerance and detoxification of cyanide, arsenic and heavy metals: Holistic approaches applied to bioremediation of industrial complex wastes

Cyanide is a highly toxic compound that is found in wastewaters generated from different industrial activities, such as mining or jewellery. These residues usually contain high concentrations of other toxic pollutants like arsenic and heavy metals that may form different complexes with cyanide. To develop bioremediation strategies, it is necessary to know the metabolic processes involved in the tolerance and detoxification of these pollutants, but most of the current studies are focused on the characterization of the microbial responses to each one of these environmental hazards individually, and the effect of co-contaminated wastes on microbial metabolism has been hardly addressed. This work summarizes the main strategies developed by bacteria to alleviate the effects of cyanide, arsenic and heavy metals, analysing interactions among these toxic chemicals. Additionally, it is discussed the role of systems biology and synthetic biology as tools for the development of bioremediation strategies of complex industrial wastes and co-contaminated sites, emphasizing the importance and progress derived from meta-omic studies.

Reveal molecular mechanism on the effects of silver nanoparticles on nitrogen transformation and related functional microorganisms in an agricultural soil

Silver nanoparticles (AgNPs) are widely present in aquatic and soil environment, raising significant concerns about their impacts on creatures in ecosystem. While the toxicity of AgNPs on microorganisms has been reported, their effects on biogeochemical processes and specific functional microorganisms remain relatively unexplored. In this study, a 28-day microcosmic experiment was conducted to investigate the dose-dependent effects of AgNPs (10 mg and 100 mg Ag kg-1 soil) on nitrogen transformation and functional microorganisms in agricultural soils. The molecular mechanisms were uncovered by examining change in functional microorganisms and metabolic pathways. To enable comparison, the toxicity of positive control with an equivalent Ag+ dose from CH3COOAg was also included. The results indicated that both AgNPs and CH3COOAg enhanced nitrogen fixation and nitrification, corresponding to increased relative abundances of associated functional genes. However, they inhibited denitrification via downregulating nirS, nirK, and nosZ genes as well as reducing nitrate and nitrite reductase activities. In contrast to high dose of AgNPs, low levels increased bacterial diversity. AgNPs and CH3COOAg altered the activities of associated metabolic pathways, resulting in the enrichment of specific taxa that demonstrated tolerance to Ag. At genus level, AgNPs increased the relative abundances of nitrogen-fixing Microvirga and Bacillus by 0.02 %-629.39 % and 14.44 %-30.10 %, respectively, compared with control group (CK). The abundances of denitrifying bacteria, such as Rhodoplanes, Pseudomonas, and Micromonospora, decreased by 19.03 % to 32.55 %, 24.73 % to 50.05 %, and 15.66 % to 76.06 %, respectively, compared to CK. CH3COOAg reduced bacterial network complexity, diminished the symbiosis mode compared to AgNPs. The prediction of genes involved in metabolic pathways related to membrane transporter and cell motility showed sensitive to AgNPs exposure in the soil. Further studies involving metabolomics are necessary to reveal the essential effects of AgNPs and CH3COOAg on biogeochemical cycle of elements in agricultural soil.

The extracellular polysaccharide determine the physico-chemical surface properties of Microcystis

Microcystis possesses the capacity to form colonies and blooms in lakes and reservoirs worldwide, causing significant ecological challenges in aquatic ecosystems. However, little is known about the determining factors of physico-chemical surface properties that govern the competitive advantage of Microcystis. Here, The physico-chemical surface properties of Microcystis wesenbergii and Microcystis aeruginosa, including specific surface area (SSA), hydrophobicity, zeta potential, and functional groups were investigated. Additionally, the extracellular polysaccharide (EPS) were analyzed. Laboratory-cultured Microcystis exhibited hydrophilic, a negative zeta potential and negatively charged. Furthermore, no significant relationship was shown between these properties and the cultivation stage. Microcystis wesenbergii exhibited low free energy of cohesion, high surface free energy, high growth rate, and high EPS content during the logarithmic phase. On the other hand, M. aeruginosa displayed lower free energy of cohesion, high surface free energy, high EPS content, and high growth rate during the stationary phase. These characteristics contribute to their respective competitive advantage. Furthermore, the relationship between EPS and surface properties was investigated. The polysaccharide component of EPS primarily influenced the SSA and total surface energy of Microcystis. Likewise, the protein component of EPS influenced hydrophobicity and surface tension. The polysaccharide composition, including glucuronic acid, xylose, and fructose, mainly influenced surface properties. Additionally, hydrophilic groups such as O-H and P-O-P played a crucial role in determining hydrophobicity in Microcystis. This study elucidates that EPS influenced the SSA, hydrophobicity, and surface free energy of Microcystis cells, which in turn impact the formation of Microcystis blooms and the collection.

A cohesive effort to assess the suitability and disparity of carbon nanotubes for water treatment

Population growth, industrialization, and the extensive use of chemicals in daily life have all contributed to an increase in waste generation and an intensified release of organic pollutants into the aquatic environment. To ensure the quality of water (including natural resources), the removal of these pollutants from wastewater has become a challenging task for scientific community. Conventional physical, chemical, and biological treatment methods are commonly used in combinations and are not very effective. Recently, carbon nanotubes (CNTs) emerged as the most reliable and adaptable choice for efficient water treatment due to their extraordinary material properties appearing as a single-step solution for water treatment. High surface area, exceptional porosities, hollow and layered structures, and ease of chemical activation and functionalization are some properties which makes it excellent adsorption material. Hence, this review paper discusses the recent advances in the synthesis, purification, and functionalization of CNTs for water and wastewater treatment. In addition, this study also also provides a quick overview of CNTs-based advance technologies employed in water treatment and carefully assesses the benefits versus risks during large-scale water treatment. Furthermore, it concludes that identified risks to the environment and human health cannot be easily ignored and strict regulatory requirements are a must for producing low-cost innoxious CNTs.

Biofilm formation in xenobiotic-degrading microorganisms

The increased presence of xenobiotics affects living organisms and the environment at large on a global scale. Microbial degradation is effective for the removal of xenobiotics from the ecosystem. In natural habitats, biofilms are formed by single or multiple populations attached to biotic/abiotic surfaces and interfaces. The attachment of microbial cells to these surfaces is possible via the matrix of extracellular polymeric substances (EPSs). However, the molecular machinery underlying the development of biofilms differs depending on the microbial species. Biofilms act as biocatalysts and degrade xenobiotic compounds, thereby removing them from the environment. Quorum sensing (QS) helps with biofilm formation and is linked to the development of biofilms in natural contaminated sites. To date, scant information is available about the biofilm-mediated degradation of toxic chemicals from the environment. Therefore, we review novel insights into the impact of microbial biofilms in xenobiotic contamination remediation, the regulation of biofilms in contaminated sites, and the implications for large-scale xenobiotic compound treatment.

Deciphering the key pathway for triterpenoid biosynthesis in Azadirachta indica A. Juss.: a comprehensive review of omics studies in nature's pharmacy

Since ancient times, Azadirachta indica, or Neem, has been a well-known species of plant that produces a broad range of bioactive terpenoid chemicals that are involved in a variety of biological functions. Understanding the molecular mechanisms that are responsible for the biosynthesis and control of terpenoid synthesis is majorly dependent on successfully identifying the genes that are involved in their production. This review provides an overview of the recent developments concerning the identification of genes in A. indica that are responsible for the production of terpenoids. Numerous candidate genes encoding enzymes that are involved in the terpenoid biosynthesis pathway have been found through the use of transcriptomic and genomic techniques. These candidate genes include those that are responsible for the precursor synthesis, cyclization, and modification of terpenoid molecules. In addition, cutting-edge omics technologies, such as metabolomics and proteomics, have helped to shed light on the intricate regulatory networks that govern terpenoid biosynthesis. These networks are responsible for the production of terpenoids. The identification and characterization of genes involved in terpenoid biosynthesis in A. indica presents potential opportunities for genetic engineering and metabolic engineering strategies targeted at boosting terpenoid production as well as discovering novel bioactive chemicals.

Heavy Metal Tolerance of Microorganisms Isolated from Coastal Marine Sediments and Their Lead Removal Potential

In this study, 338 microorganisms, comprising 271 bacteria and 67 fungi, were isolated from sediment samples collected from underexplored Pacific and Caribbean regions of Colombia. Screening trials were conducted on selected strains (n = 276) to assess their tolerance to cadmium (Cd2+), lead (Pb2+), and zinc (Zn2+), leading to the identification of six bacteria capable of withstanding 750 mg·L-1 of each heavy metal ion. Three promising microorganisms, identified as Enterobacter sp. INV PRT213, Pseudomonas sp. INV PRT215, and Stenotrophomonas sp. INV PRT216 were selected for lead removal experiments using LB broth medium supplemented with 400 mg·L-1 Pb2+. Among these, Pseudomonas sp. INV PRT215 exhibited significant potential, removing 49% of initial Pb2+ after 240 min of exposure (16.7 g wet biomass·L-1, pH 5, 30 °C). Infrared spectra of Pb-exposed biomass showed changes in functional groups, including carbonyl groups of amides, carboxylate, phosphate, hydroxyl, and amine groups, compared to the not-exposed control. These changes suggested interactions between the metal and functional groups in the biomass. The findings of this study highlight the potential of microorganisms derived from coastal marine environments as promising candidates for future applications in bioremediation of polluted environments contaminated with heavy metals.

Metal tolerance and biosorption capacities of bacterial strains isolated from an urban watershed

Rapid industrialization and urbanization have led to widespread metal contamination in aquatic ecosystems. This study explores the metal tolerance and biosorption characteristics of four bacterial strains (Serratia sp. L2, Raoultella sp. L30, Klebsiella sp. R3, and Klebsiella sp. R19) isolated from Saint Clair River sediments. These strains effectively removed various metal cations (As3+, Pb2+, Cu2+, Mn2+, Zn2+, Cd2+, Cr6+, and Ni2+) in single and multi-metal solutions. Minimum inhibitory concentration (MIC) assays revealed strain-specific variations in metal tolerance, with L2 and L30 exhibiting higher tolerance. Surprisingly, R3 and R19, despite lower tolerance, demonstrated superior metal removal efficiency, challenging the notion that tolerance dictates removal efficacy. In single-metal solutions, R3 and R19 excelled at extracting various metal ions, while competitive binding in multi-metal solutions hindered removal. However, R3 and R19 retained higher removal efficiencies, possibly due to enhanced flocculation activities facilitating metal-ion contact. Comprehensive Fourier-transform infrared (FTIR) analysis highlighted the strains' metal-binding capabilities, with novel peaks emerging after metal exposure, indicative of extracellular polymeric substance (EPS) production. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) confirmed metal accumulation on bacterial surfaces and within cytoplasmic regions and revealed morphological changes and metal adsorption patterns, emphasizing the strains' ability to adapt to metal stress. Scanning transmission microscopy (STEM) and EDX analysis uncovered metal accumulation within bacterial cells, underscoring the complexity of microbial-metal interactions. This study also confirms that the simultaneous presence of an aqueous solution may cause a mutual inhibition in the adsorption of each metal to the EPS resulting in reduced metal uptake, which emphasizes the need to select specific bacterial strains for a given metal-containing effluent. The differences in metal distribution patterns between Klebsiella sp. R19 and Raoultella sp. L30 suggest species-specific metal accumulation strategies driven by environmental conditions and metal availability. The heavy metal-removing capabilities and the ability to grow over a wide range of metal concentrations of the strains used in this study may offer an advantage to employ these organisms for metal remediation in bioreactors or in situ.

Lactic Acid Bacteria-Derived Exopolysaccharides Mitigate the Oxidative Response via the NRF2-KEAP1 Pathway in PC12 Cells

Parabiotics, including L-EPSs, have been administered to patients with neurodegenerative disorders. However, the antioxidant properties of L-EPSs against H2O2-induced oxidative stress in PC12 cells have not been studied. Herein, we aimed to investigate the antioxidant properties of the L-EPSs, their plausible targets, and their mechanism of action. We first determined the amount of L-EPSs in Lactobacillus delbrueckii ssp. bulgaricus B3 and Lactiplantibacillus plantarum GD2 using spectrophotometry. Afterwards, we studied their effects on TDH, TOS/TAS, antioxidant enzyme activities, and intracellular ROS level. Finally, we used qRT-PCR and ELISA to determine the effects of L-EPSs on the NRF2-KEAP1 pathway. According to our results, the L-EPS groups exhibited significantly higher total thiol activity, native thiol activity, disulfide activity, TAS levels, antioxidant enzyme levels, and gene expression levels (GCLC, HO-1, NRF2, and NQO1) than did the H2O2 group. Additionally, the L-EPS groups caused significant reductions in TOS levels and KEAP1 gene expression levels compared with those in the H2O2 group. Our results indicate that H2O2-induced oxidative stress was modified by L-EPSs. Thus, we revealed that L-EPSs, which regulate H2O2-induced oxidative stress, could have applications in the field of neurochemistry.

Gravity-driven membrane system treating heavy metals-containing secondary effluent: Improved removal of heavy metals and mechanism

This study aimed at investigating the removal performance of the gravity-driven membrane (GDM) system in treating the heavy metals-containing secondary effluent, as well as evaluating the respective roles of Fe and Mn addition on the removal of heavy metals. GDM process with the formation of biocake layer exerted effective removals of Cr, Pb and Cd, with an average removal efficiency of 98%, 95% and 40%, respectively, however, after removing the biocake layer, the removal efficiencies of Cr, Pb and Cd reduced to 59%, 85% and 19%, respectively, indicating that the biocake layer played a fundamental role in removing heavy metals. With the assistance of Fe, the removal efficiency of heavy metals increased, and exhibited a positive response to the Fe dosage, due to the adsorption by the freshly generated iron oxides. On the contrary, the Mn involvement would result in the reduction of Cd removal due to the competitive adsorption of residual dissolved Mn2+ and Cd. Furthermore, the addition of a high dosage of Fe increased the diversity of eukaryotic communities and facilitated the elimination of heavy metals, however, the involvement of Mn would lead to a reduction in microbial diversity, resulting in a decrease of heavy metal removal efficiency. These findings are expected to develop new tactics to enhance heavy metal removal and promote widespread application of GDM technology in the fields of deep treatment of heavy metals-containing wastewater and reclamation of secondary effluent.

A mini-review on indigenous microbial biofilm from various wastewater for heavy-metal removal - new trends

Biofilm, as a form of the microbial community in nature, represents an evolutionary adaptation to the influence of various environmental conditions. In nature, the largest number of microorganisms occur in the form of multispecies biofilms. The ability of microorganisms to form a biofilm is one of the reasons for antibiotic resistance. The creation of biofilms resistant to various contaminants, on the other hand, improves the biological treatment process in wastewater treatment plants. Heavy metals cannot be degraded, but they can be transformed into non-reactive and less toxic forms. In this process, microorganisms are irreplaceable as they interact with the metals in a variety of ways. The environment polluted by heavy metals, such as wastewater, is also a source of undiscovered microbial diversity and specific microbial strains. Numerous studies show that biofilm is an irreplaceable strategy for heavy metal removal. In this review, we systematize recent findings regarding the bioremediation potential of biofilm-forming microbial species isolated from diverse wastewaters for heavy metal removal. In addition, we include some mechanisms of action, application possibilities, practical issues, and future prospects.

Metal and metalloid bioaccumulation in dried red seaweed Hypnea musciformis and health risk assessment for consumers

This study measured 22 metal and metalloid concentrations in Hypnea musciformis from the Bakkhali River estuary and Saint Martin's Island, Bangladesh and determined their potential impact on consumption. Student t-tests showed a significant variation in metal concentrations between the two sampling sites (p < 0.05). Mean concentrations of Co (2.49 ± 0.05 mg/kg), Fe (793.29 ± 11.76 mg/kg), Mn (368.72 ± 4.87 mg/kg), Pb (3.82 ± 0.02 mg/kg), V (11.23 ± 0.20 mg/kg) and Zn (16.60 ± 0.28 mg/kg) were higher in samples collected from the Bakkhali River estuary compared to Saint Martin's Island, while mean concentrations of Ca (484.18 ± 4.68 mg/kg), Cd (2.44 ± 0.03 mg/kg), Mg (2112.70 ± 17.80 mg/kg), Mo (1.57 ± 0.06 mg/kg), Sr (2377.57 ± 29.98 mg/kg), and Ti (258.27 ± 4.62 mg/kg) were higher in samples collected from Saint Martin's Island. Eight heavy metals (Pb, Cd, Zn, Cu, Ni, Mn, Cr, Fe) were used to assess potential health risks for adults, but no potential health risk was detected (HQ value>1). This study reveals positive Se-HBV for H. musciformis collected from both sampling sites, indicating no potential risks involved with Hg toxicity.

Microbial Biofilms for Environmental Bioremediation of Heavy Metals: a Review

Heavy metal pollution caused due to various industrial and mining activities poses a serious threat to all forms of life in the environment because of the persistence and toxicity of metal ions. Microbial-mediated bioremediation including microbial biofilms has received significant attention as a sustainable tool for heavy metal removal as it is considered safe, effective, and feasible. The biofilm matrix is dynamic, having microbial cells as major components with constantly changing and evolving microenvironments. This review summarizes the bioremediation potential of bacterial biofilms for different metal ions. The composition and mechanism of biofilm formation along with interspecies communication among biofilm-forming bacteria have been discussed. The interaction of biofilm-associated microbes with heavy metals takes place through a variety of mechanisms. These include biosorption and bioaccumulation in which the microbes interact with the metal ions leading to their conversion from a highly toxic form to a less toxic form. Such interactions are facilitated via the negative charge of the extracellular polymeric substances on the surface of the biofilm with the positive charge of the metal ions and the high cell densities and high concentrations of cell-cell signaling molecules within the biofilm matrix. Furthermore, the impact of the anodic and cathodic redox potentials in a bioelectrochemical system (BES) for the reduction, removal, and recovery of numerous heavy metal species provides an interesting insight into the bacterial biofilm-mediated bioelectroremediation process. The review concludes that biofilm-linked bioremediation is a viable option for the mitigation of heavy metal pollution in water and ecosystem recovery.

Recent Advances in Microbial-Assisted Remediation of Cadmium-Contaminated Soil

Soil contamination with cadmium (Cd) is a severe concern for the developing world due to its non-biodegradability and significant potential to damage the ecosystem and associated services. Industries such as mining, manufacturing, building, etc., rapidly produce a substantial amount of Cd, posing environmental risks. Cd toxicity in crop plants decreases nutrient and water uptake and translocation, increases oxidative damage, interferes with plant metabolism and inhibits plant morphology and physiology. However, various conventional physicochemical approaches are available to remove Cd from the soil, including chemical reduction, immobilization, stabilization and electro-remediation. Nevertheless, these processes are costly and unfriendly to the environment because they require much energy, skilled labor and hazardous chemicals. In contrasting, contaminated soils can be restored by using bioremediation techniques, which use plants alone and in association with different beneficial microbes as cutting-edge approaches. This review covers the bioremediation of soils contaminated with Cd in various new ways. The bioremediation capability of bacteria and fungi alone and in combination with plants are studied and analyzed. Microbes, including bacteria, fungi and algae, are reported to have a high tolerance for metals, having a 98% bioremediation capability. The internal structure of microorganisms, their cell surface characteristics and the surrounding environmental circumstances are all discussed concerning how microbes detoxify metals. Moreover, issues affecting the effectiveness of bioremediation are explored, along with potential difficulties, solutions and prospects.

Synthesis and molecular characterization of levan produced by immobilized Microbacterium paraoxydans

In this study, we report high molecular weight (HMW) levan production by whole cells of Microbacterium paraoxydans, previously reported to be a good producer of fructooligosaccharides. Structural analysis of the extracellularly produced fructan indicated the glycosidic bonds between the adjacent fructose to be of β-(2, 6) linkage with over 90% of the fructan to have molecular weight around 2 × 108 Da and 10% with a molecular weight of ∼20 kDa. Immobilization of the cells in Ca-alginate led to the production of 44.6 g/L levan with a yield of 0.29 g/g sucrose consumed. Factors affecting the conversion rate were identified by One-Factor-At-a-Time (OFAT) analysis and the combination of these (initial sucrose concentration of 400 g/L, 100 mM buffer pH 7, the temperature of 37 °C and 20 mM CaCl2) led to the production of ∼129 g/L of levan with a yield of ∼0.41 g/g sucrose consumed and volumetric productivity of 1.8 g/L/h.

Pantoea conspicua promoted sunflower growth and engulfed rhizospheric arsenate by secreting exopolysaccharide

A rhizobacterium, Pantoea conspicua, was examined against sunflower seedlings' growth under arsenate stress. Sunflower upon exposure to arsenate resulted in compromised growth that might be due to the accumulation of higher concentrations of arsenate and reactive oxygen species (ROS) in seedlings' tissues. The deposited arsenate led to oxidative damage and electrolyte leakage, making the sunflower seedlings vulnerable to compromise its growth and development. However, inoculation of sunflower seedlings with P. conspicua alleviated arsenate stress in host by initiating a multilayered defence mechanism. In fact, P. conspicua filtered out 75.1% of the arsenate from growth medium that were available to the plant roots in the absence of the said strain. To accomplish such activity, P. conspicua secreted exopolysaccharides as well as altered lignification in host roots. The arsenate (24.9%) that made its way to plant tissues was countered by helping the host seedlings to produce higher levels of indole acetic acid, non enzymatic antioxidants (phenolics and flavonoids) and antioxidant enzymes (catalase, ascorbte peroxidase, peroxidase, superoxide dismutase). As a result, ROS accumulation and electrolyte leakage were brought back to normal levels as observed in control seedlings. Hence, the rhizobacterium associated host seedlings achieved higher net assimilation (127.7%) and relative growth rate (113.5%) under 100 ppm of arsenate stress. The work concluded that P. conspicua alleviated arsenate stress in the host plants by imposing physical barrier as well as improving host seedlings' physiology and biochemistry.