Role of extracellular polymeric substance (EPS) in toxicity response of soil bacteria Bacillus sp. S3 to multiple heavy metals

Mechanisms of adaptive resistance in Phytobacter sp. X4 to antimony stress under anaerobic conditions

Sb(III) oxidation by microorganisms plays a key role in the geochemical cycling of antimony and is effective for bioremediation. A previously discovered novel Sb(III)-oxidizing bacteria, Phytobacter sp. X4, was used to elucidate the response patterns of extracellular polypeptides (EPS), antioxidant system, electron transfer and functional genes to Sb(III) under anaerobic conditions. The toxicity of Sb(III) was mitigated by increasing Sb(III) oxidation capacity, and the EPS regulated the content of each component by sensing the concentration of Sb(III). High Sb(III) concentrations induced significant secretion of proteins and polysaccharides of EPS, and polysaccharides were more important. Functional groups including hydroxyl, carboxyl and amino groups on the cell surface adsorbed Sb(III) to block its entry. Hydroxyl radicals and hydrogen peroxide were involved in anaerobic Sb(III) oxidation, as revealed by changes in the antioxidant system and electron spin resonance (EPR) techniques. qPCR confirmed that proteins concerning nitrate and antimony transfer, antimony resistance and antioxidant system were regulated by Sb(III) concentration, and the synergistic cooperation of multiple proteins conferred high antimony resistance to X4. The adaptive antimony resistance mechanism of Phytobacter sp. X4 under anaerobic conditions was revealed, which also provides a reference value for bioremediation method of antimony contamination in anaerobic environment.

High cadmium-accumulating Salix ecotype shapes rhizosphere microbiome to facilitate cadmium extraction

Cadmium (Cd) contamination poses a significant threat to agricultural soils and food safety, necessitating effective remediation strategies. Salix species, with their high coverage and Cd accumulating capacity, hold promise for remediation efforts. The rhizosphere microbiome is crucial for enhancing Cd accumulating capacity for Salix. However, the mechanisms by how Salix interacts with its rhizosphere microbiome to enhance Cd extraction remains poorly understood. In this study, we compared the remediation performance of two Salix ecotypes: 51-3 (High Cd-accumulating Ecotype, HAE) and P646 (Low Cd-accumulating Ecotype, LAE). HAE exhibited notable advantages over LAE, with 10.80 % higher plant height, 43.80 % higher biomass, 20.26 % higher Cd accumulation in aboveground tissues (93.09 μg on average), and a superior Cd translocation factor (1.97 on average). Analysis of the rhizosphere bacterial community via 16S rRNA amplicon sequencing revealed that HAE harbored a more diverse bacterial community with a distinct composition compared to LAE. Indicator analysis identified 84 genera specifically enriched in HAE, predominantly belonging to Proteobacteria, Actinobacteria, and Firmicutes, including beneficial microbes such as Streptomyces, Bacillus, and Pseudomonas. Network analysis further elucidated three taxa groups specifically recruited by HAE, which were highly correlated with functional genes that associated with biosynthesis of secondary metabolites, glycan biosynthesis and metabolism, and metabolism of cofactors and vitamins. These functions contribute to enhancing plant growth, Cd uptake, and resistance to Cd in Salix. Overall, our findings highlight the importance of the rhizosphere microbiome in facilitating Cd extraction and provide insights into microbiome-based strategies for sustainable agricultural practices.

Microbially induced carbonate precipitation with Arthrobacter creatinolyticus: An eco-friendly strategy for mitigation of chromium contamination

Chromium contamination from abandoned industrial sites and inadequately managed waste disposal areas poses substantial environmental threat. Microbially induced carbonate precipitation (MICP) has shown promising, eco-friendly solution to remediate Cr(VI) and divalent heavy metals. In this study, MICP was carried out for chromium immobilization by an ureolytic bacterium Arthrobacter creatinolyticus which is capable of reducing Cr(VI) to less toxic Cr(III) via extracellular polymeric substances (EPS) production. The efficacy of EPS driven reduction was confirmed by cellular fraction analysis. MICP carried out in aqueous solution with 100 ppm of Cr(VI) co-precipitated 82.21% of chromium with CaCO3 and the co-precipitation is positively correlated with reduction of Cr(VI). The organism was utilized to remediate chromium spiked sand and found that MICP treatment decreased the exchangeable fraction of chromium to 0.54 ± 0.11% and increased the carbonate bound fraction to 26.1 ± 1.15% compared to control. XRD and SEM analysis revealed that Cr(III) produced during reduction, influenced the polymorph selection of vaterite during precipitation. Evaluation of MICP to remediate Cr polluted soil sample collected from Ranipet, Tamil Nadu also showed effective immobilization of chromium. Thus, A. creatinolyticus proves to be viable option for encapsulating chromium contaminated soil via MICP process, and effectively mitigating the infiltration of Cr(VI) into groundwater and adjacent water bodies.

The dominant role of extracellular polymeric substances produced by Achromobacter xylosoxidans BP1 in Cr(VI) microbial reduction

Extracellular polymeric substances (EPS) have demonstrated significant benefits for reducing multivalent metal contamination. Using Achromobacter xylosoxidans BP1 isolated from a coal chemical site in China, this study elucidated the contribution of EPS production to Cr (VI) reduction and revealed its biological removal mechanism. BP1 grew at an optimum pH of 8 and the lowest inhibitory concentration of Cr(VI) was 300 mg/L. The spent medium completely removed Cr(VI), whereas resting cells were only able to remove 10.47 % and inactivated cells were nearly incapable of Cr(VI) removal. S-EPS and B-EPS reduced Cr(VI) by 98.59 % and 11.64 %, respectively. SEM-EDS analysis showed that the BP1 cells were stimulated to produce EPS under Cr stress. The XPS results showed that 29.63 % of Cr(VI) was enriched by intracellular bioaccumulation or biosorption and 70.37 % of Cr(VI) was reduced by extracellular enzymes to produce Cr(OH)3 and organic Cr(III) complexes. According to FTIR, EPS with -OH, COO-, and amide groups supplied binding sites and electrons for the reductive adsorption of Cr(VI). Genomic studies showed that BP1 primarily produces extracellular polysaccharides, metabolises sulphur and nitrogen, and reduces reactive oxygen species damage as a result of DNA repair proteases.

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.

EPS Production by Lacticaseibacillus casei Using Glycerol, Glucose, and Molasses as Carbon Sources

This study demonstrates that Lactobacillus can produce exopolysaccharides (EPSs) using alternative carbon sources, such as sugarcane molasses and glycerol. After screening 22 strains of Lactobacillus to determine which achieved the highest production of EPS based on dry weight at 37 °C, the strain Ke8 (L. casei) was selected for new experiments. The EPS obtained using glycerol and glucose as carbon sources was classified as a heteropolysaccharide composed of glucose and mannose, containing 1730 g.mol-1, consisting of 39.4% carbohydrates and 18% proteins. The EPS obtained using molasses as the carbon source was characterized as a heteropolysaccharide composed of glucose, galactose, and arabinose, containing 1182 g.mol-1, consisting of 52.9% carbohydrates and 11.69% proteins. This molecule was characterized using Size Exclusion Chromatography (HPLC), Gas chromatography-mass spectrometry (GC-MS), Fourier-transform infrared spectroscopy (FTIR), and proton nuclear magnetic resonance spectroscopy (1H-NMR). The existence of polysaccharides was confirmed via FT-IR and NMR analyses. The results obtained suggest that Lacticaseibacillus casei can grow in media that use alternative carbon sources such as glycerol and molasses. These agro-industry residues are inexpensive, and their use contributes to sustainability. The lack of studies regarding the use of Lacticaseibacillus casei for the production of EPS using renewable carbon sources from agroindustry should be noted.

Efficient removal of hexavalent chromium from water by Bacillus sp. Y2-7 with production of extracellular polymeric substances

Bioremediation is an environmentally friendly technology for the treatment of chromium-contaminated sites. Here, a hexavalent chromium [Cr(VI)]-resistant strain was isolated from oil-contaminated soil and designated as Bacillus sp. Y2-7 based on 16S rDNA sequence characterization. The effects of various factors including inoculation dose, pH value, glucose concentration, and temperature on Cr(VI) removal rates were then evaluated. Based on the response surface methodology, optimal Cr(VI) removal efficiency (above 90%) could be achieved at an initial Cr(VI) concentration of 155.0 mg·L-1, glucose concentration of 11.479 g·L-1, and pH of 7.1. The potential removal mechanisms of Cr(VI) by strain Y2-7 were also supposed. The contents of polysaccharide and protein in extracellular polymer (EPS) of strain Y2-7 decreased slowly after cultured with Cr(VI) of 15 mg·L-1 from 1 to 7 days. We thus inferred that EPS bonded with Cr(VI) and underwent morphological changes in water. Molecular operating environment (MOE) analysis suggested that macromolecular protein complexes in Bacillus sp. Y2-7 and hexavalent chromium could establish hydrogen bonds. Collectively, our findings indicate that Bacillus sp. Y2-7 is an excellent bacterial candidate for chromium bioremediation.

The role of an Sb-oxidizing bacterium in modulating antimony speciation and iron plaque formation to reduce the accumulation and toxicity of Sb in rice (Oryza sativa L.)

Microbial antimony (Sb) oxidation in the root rhizosphere and the formation of iron plaque (IP) on the root surface are considered as two separate strategies to mitigate Sb(III) phytotoxicity. Here, the effect of an Sb-oxidizing bacterium Bacillus sp. S3 on IP characteristics of rice exposed to Sb(III) and its alleviating effects on plant growth were investigated. The results revealed that Fe(II) supply promoted IP formation under Sb(III) stress. However, the formed IP facilitated rather than hindered the uptake of Sb by rice roots. In contrast, the combined application of Fe(II) and Bacillus sp. S3 effectively alleviated Sb(III) toxicity in rice, resulting in improved rice growth and photosynthesis, reduced oxidative stress levels, enhanced antioxidant systems, and restricted Sb uptake and translocation. Despite the ability of Bacillus sp. S3 to oxidize Fe(II), bacterial inoculation inhibited the formation of IP, resulting in a reduction in Sb absorption on IP and uptake into the roots. Additionally, the bacterial inoculum enhanced the transformation of Sb(III) to less toxic Sb(V) in the culture solution, further influencing the adsorption of Sb onto IP. These findings highlight the potential of combining microbial Sb oxidation and IP as an effective strategy for minimizing Sb toxicity in sustainable rice production systems.

Antimony precipitation and removal by antimony hyper resistant strain Achromobacter sp. 25-M

Microbes have been confirmed to play key role in biogeochemistry of antimony. However, the impact of indigenous bacteria (from active mines) on the behavior of dissolved antimony remained poorly understood. In current study, the hyper antimony-resistant strain, Achromobacter sp. 25-M, isolated from the world largest antimony deposit, Xikuangshan antimony deposit, was evaluated for its role in dissolved Sb(V) and Sb(III) precipitation and removal. Despite of the high resistance to Sb(III) (up to 50 mM), the facultative alkaliphile, 25-M was not capable of Sb(III) oxidation. Meanwhile 25-M can produce high amount of exopolymeric substance (EPS) with the presence of Sb, which prompted us to investigate the potential role of EPS in the precipitation and removal of Sb. To this end, 2 mM of Sb(III) and Sb(V) were added into the experimental systems with and without 25-M to discern the interaction mechanism between microbe and antimony. After 96 hrs' incubation, 88% [1.73 mM (210 mg/L)] of dissolved Sb(V) and 80% [1.57 mM (190 mg/L)] of dissolved Sb(III) were removed. X-ray diffraction and energy dispersive spectroscopy analysis confirmed the formation of valentinite (Sb2O3) in Sb(III) amended system and a solitary Sb(V) mineral mopungite [NaSb(OH)6] in Sb(V) amended group with microbes. Conversely, no precipitate was detected in abiotic systems. Morphologically valentinite was bowtie and mopungite was pseudo-cubic as indicated by scanning electronic microscopy. EPS was subjected to fourier transform infrared (FT-IR) analysis. FT-IR analysis suggested that -OH and -COO groups were responsible for the complexation and ligand exchange with Sb(III) and Sb(V), respectively. Additionally, the C-H group and N-H group could be involved in π-π interaction and chelation with Sb species. All these interactions between Sb and functional groups in EPS may subsequently favore the formation of valentinite and mopungite. Collectively, current results suggested that EPS play fundamental role in bioprecipitation of Sb, which offered a new strategy in Sb bioremediation.

Spectra metrology for interaction of heavy metals with extracellular polymeric substances (EPS) of Pseudomonas aeruginosa OMCS-1 reveals static quenching and complexation dynamics of EPS with heavy metals

The adsorption behavior and interaction mechanisms of extracellular polymeric substances (EPS) of Pseudomonas aeruginosa OMCS-1 towards chromium (Cr), lead (Pb), and cadmium (Cd) were investigated. EPS-covered (EPS-C) cells exhibited significantly higher (p < 0.0001; two-way ANOVA) removal of Cr (85.58 ± 0.39%), Pb (81.98 ± 1.02%), and Cd (73.88 ± 1%) than EPS-removed (EPS-R) cells. Interactions between EPS-heavy metals were spontaneous (ΔG<0). EPS-Cr(VI) and EPS-Pb(II) binding were exothermic (ΔH<0), while EPS-Cd(II) binding was endothermic (ΔH>0) process. EPS bonded to Pb(II) via inner-sphere complexation by displacement of surrounding water molecules, while EPS-Cr(VI) and EPS-Cd(II) binding occurred through outer-sphere complexation via electrostatic interactions. Increased zeta potential of Cr (29.75%), Pb (41.46%), and Cd (46.83%) treated EPS and unchanged crystallinity (CIXRD=0.13), inferred EPS-metal binding via both electrostatic interactions and complexation mechanism. EPS-metal interaction was predominantly promoted through hydroxyl, amide, carboxyl, and phosphate groups. Metal adsorption deviated EPS protein secondary structures. Strong static quenching mechanism between tryptophan protein-like substances in EPS and heavy metals was evidenced. EPS sequestered heavy metals via complexation with C-O, C-OH, CO/O-C-O, and NH/NH2 groups and ion exchange with -COOH group. This study unveils the fate of Cr, Pb, and Cd on EPS surface and provides insight into the interactions among EPS and metal ions for metal sequestration.

Study of mercury resistance and Fourier transform infrared spectroscopy-based metabolic profiling of a potent Bacillus tropicus strain from forest soil

Mercury (Hg) is a highly toxic heavy metal and Hg-resistant indigenous bacterial isolates may offer a green and cost-effective bioremediation strategy to counter Hg contamination. In this study, a potent Hg-resistant bacterium was isolated from the forest soil of a bird sanctuary. Identification using matrix-assisted laser desorption ionization-time of flight mass spectrometry depicted the isolate as a strain of Bacillus tropicus, validated by morphological, biochemical, and molecular studies. The isolate demonstrated biological Hg removal efficiency and capacity of 50.67% and 19.76 mg g-1 , respectively. The plasmid borne resistance determinant, merA, encoding mercuric reductase, was detected in the bacterium endowing it with effective Hg volatilization and resistance capability. A Fourier-transform infrared spectroscopic comparative metabolic profiling revealed the involvement of various functional groups like -COOH, -CH2 , -OH, PO4 - and so on, resulting in differential spectral patterns of the bacterium both in control and Hg-exposed situations. A temporal variance in metabolic signature was also observed during the early and mid-log phase of growth in the presence of Hg. The bacterium described in this study is the first indigenous Hg-resistant strain isolated from the Uttar Dinajpur region, which could be further explored and exploited as a potent bioresource for Hg remediation.

A sustainable solution for alleviating hexavalent chromium from water streams using Lactococcus lactis AM99 as a novel Cr(VI)-reducing bacterium

Chromium, extensively used in various industries, poses significant challenges due to its environmental impact. The threat of Cr(VI) causes critical concerns in aquatic ecosystems as a consequence of the fluidity of water. The conventional approach for the treatment of effluents containing Cr(VI) is reducing Cr(VI) to low-noxious Cr(III). This research is related to a Gram positive bacterium newly isolated from tannery effluent under aerobic conditions. To characterize functional groups on the isolate, Fourier transform infrared spectroscopy was utilized. The effect of different factors on Cr(VI) bioreduction was investigated, including temperature, initial Cr(VI) concentration, acetate concentration, and Tween 80 surfactant. Under optimal conditions (37 °C and 0.90 g/L sodium acetate), the bioreduction rate of the isolate, identified as Lactococcus lactis AM99, achieved 88.0 % at 300 mg/L Cr(VI) during 72 h (p < 0.05). It was observed that Cr(VI) bioreduction was enhanced by the acetate in both the quantity and intensity, while Tween 80 had no impact on the reaction. The strain AM99 exhibited remarkable characteristics, notably a marginal decrease in growth at elevated concentrations of hexavalent chromium and an exceptional potential to reduce Cr(VI) even at very low biomass levels, surpassing any prior findings in the associated research. Furthermore, The isolate could tolerate 1400 mg/L Cr(VI) in a solid medium. These distinctive features make the isolate a promising and well-suited candidate for remediating Cr(VI)-polluted environments. Additionally, the impact of biogenic extracellular polymer produced by the strain AM99 on reduction was examined at different temperatures.

Screening of cadmium-chromium-tolerant strains and synergistic remediation of heavy metal-contaminated soil using king grass combined with highly efficient microbial strains

The present study involved the isolation of two cadmium (Cd) and chromium (Cr) resistant strains, identified as Staphylococcus cohnii L1-N1 and Bacillus cereus CKN12, from heavy metal contaminated soils. S. cohnii L1-N1 exhibited a reduction of 24.4 % in Cr6+ and an adsorption rate of 6.43 % for Cd over a period of 5 days. These results were achieved under optimal conditions of pH (7.0), temperature (35 °C), shaking speed (200 rpm), and inoculum volume (8 %). B. cereus strain CKN12 exhibited complete reduction of Cr6+ within a span of 48 h, while it demonstrated a 57.3 % adsorption capacity for Cd over a period of 120 h. These results were achieved under conditions of optimal pH (8.0), temperature (40 °C), shaking speed (150 rpm), and inoculum volume (2-3 %). Additionally, microcharacterization and ICP-MS analysis revealed that Cr and Cd were accumulated on the cell surface, whereas Cr6+ was mainly reduced extracellularly. Subsequently, a series of pot experiments were conducted to provide evidence that the inclusion of S. cohnii L1-N1 or B. cereus CKN12 into the system resulted in a notable enhancement in both the plant height and biomass of king grass. In particular, it was observed that the presence of S. cohnii L1-N1 or B. cereus CKN12 in king grass led to a significant reduction in the levels of Cd and Cr in the soils (36.0 % and 27.8 %, or 72.9 % and 47.4 %, respectively). Thus, the results of this study indicate that the combined use of two bacterial strains can effectively aid in the remediation of tropical soils contaminated with moderate to light levels of Cd and Cr.

Wastewater Treatment Using Membrane Bioreactor Technologies: Removal of Phenolic Contaminants from Oil and Coal Refineries and Pharmaceutical Industries

Huge amounts of noxious chemicals from coal and petrochemical refineries and pharmaceutical industries are released into water bodies. These chemicals are highly toxic and cause adverse effects on both aquatic and terrestrial life. The removal of hazardous contaminants from industrial effluents is expensive and environmentally driven. The majority of the technologies applied nowadays for the removal of phenols and other contaminants are based on physio-chemical processes such as solvent extraction, chemical precipitation, and adsorption. The removal efficiency of toxic chemicals, especially phenols, is low with these technologies when the concentrations are very low. Furthermore, the major drawbacks of these technologies are the high operation costs and inadequate selectivity. To overcome these limitations, researchers are applying biological and membrane technologies together, which are gaining more attention because of their ease of use, high selectivity, and effectiveness. In the present review, the microbial degradation of phenolics in combination with intensified membrane bioreactors (MBRs) has been discussed. Important factors, including the origin and mode of phenols' biodegradation as well as the characteristics of the membrane bioreactors for the optimal removal of phenolic contaminants from industrial effluents are considered. The modifications of MBRs for the removal of phenols from various wastewater sources have also been addressed in this review article. The economic analysis on the cost and benefits of MBR technology compared with conventional wastewater treatments is discussed extensively.

Selenium bio-nanocomposite based on extracellular polymeric substances (EPS): Synthesis, characterization and application in alleviating cadmium toxicity in rice (Oryza sativa L.)

Selenium nanoparticles (SeNPs) have gained significant attention owing to their favorable bioavailability and low toxicity, making them widely applications in the fields of medicine, food and agriculture. In this study, bacterial extracellular polymeric substances (EPS) were used as a novel stabilizer and capping agent to prepare dispersed SeNPs. Results show that EPS-SeNPs presented negative potential (-38 mV), spherical morphologies with average particle size about 100-200 nm and kept stable at room temperature for a long time. X-ray diffraction (XRD) analysis demonstrated that the synthesized nanoparticles were pure amorphous nanoparticles, and X-ray photoelectron spectroscopy (XPS) spectrum showed a spike at 55.6 eV, indicating the presence of zero-valent nano‑selenium. Fourier-transform infrared spectroscopy (FTIR) and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy analysis confirmed proteins and polysaccharides in EPS played a crucial role in the synthesis of EPS-SeNPs. Compared to EPS or sodium selenite (Na2SeO3), EPS-SeNPs showed a relatively moderate result in terms of scavenging free radicals in vitro. In contrast, EPS-SeNPs demonstrated lower toxicity to rice seeds than Na2SeO3. Notably, the exogenous application of EPS-SeNPs effectively alleviated the growth inhibition and oxidative damaged caused by cadmium (Cd), and significantly reduced Cd accumulation in rice plants.

Soil moisture dynamics regulates the release rates and lability of copper in contaminated paddy soils

The climate changes have caused more extreme precipitation and drought events in the field and have exacerbated the severity of wet-dry events in soils, which will inevitably lead to severe fluctuations in soil moisture content. Soil moisture content has been recognized to influence the distribution of heavy metals, but how temporal changes of soil moisture dynamics affect the release rates and lability of heavy metals is still poorly understood, which precludes accurate prediction of environmental behavior and environmental risk of heavy metals in the field. In this study, we combined experimental and modeling approaches to quantify copper release rates and labile copper fractions in two paddy soils from southern China under different moisture conditions. Our kinetic data and models showed that the release rates and lability of copper were highly associated with the soil moisture contents, in which, surprisingly, high soil moisture contents effectively reduced the release rates of copper even with little changes in the reactive portions of copper in soils. A suite of comprehensive characterization on soil solid and solution components along the incubation suggested that soil microbes may regulate soil copper lability through forming microbially derived organic matter that sequestered copper and by increasing soil particle aggregation for protecting copper from release. This study highlights the importance of incorporating soil moisture dynamics into future environmental models. The experimental and modeling approaches in this study have provided basis for further developing predictive models applicable to paddy soils with varying soil moisture under the impact of climate change.

Fate of iron nanoparticles in anammox system: Dissolution, migration and transformation

Iron nanoparticles (FeNPs) are commonly used in various industrial processes, leading to their release into the environment and eventual entrance into wastewater treatment plants (WWTPs). FeNPs undergo dissolution, migration, and transformation in WWTPs, which can potentially affect the stable operation of anaerobic ammonia oxidation (anammox) systems and may be discharged with wastewater or biomass. To better understand the fate of FeNPs in anammox systems, exposure experiments were conducted using anammox granular sludges (AnGS) and FeNPs. Results demonstrated that FeNPs released Fe2+ upon contact with water, with a portion being bound to functional groups in extracellular polymeric substances (EPS) and the rest entering the bacteria to form highly absorbable substances. A significant amount of FeNPs was observed to cover the surface of AnGS or aggregate and deposit at the bottom of the reactor, eventually converting into Fe3O4 and stably existing within the anammox system. The findings of this study clarify the fate of FeNPs in anammox systems and provide important insights into the stable operation of anammox systems under FeNPs exposure.

Dissolved organic matter evolution and straw decomposition rate characterization under different water and fertilizer conditions based on three-dimensional fluorescence spectrum and deep learning

Straw returning is a sustainable way to utilize agricultural solid waste resources. However, incomplete decomposition of straw will cause harm to crop growth and soil quality. Currently, there is a lack of technology to timely monitor the rate of straw decomposition. Dissolved organic matter (DOM) is the most active organic matter in soil and straw is mainly immersed in the soil in the form of DOM. In order to formulate reasonable straw returning management measures , a timely monitoring method of straw decomposition rate was developed in the study. Three water treatment (60%-65%, 70%-75% and 80%-85% maximum field capacity) and two fertilizer (organic fertilizer and chemical fertilizer) were set up in the management of straw returning to the field. Litterbag method was used to monitor the weight loss rate of straw decomposition under different water and fertilizer conditions in strawberry growth stage. The changes of DOM components were determined by three-dimensional fluorescence spectroscopy (3D-EEM). From the faster decomposition period to the slower decomposition period, the main components of DOM changed from protein-like components to humus-like components. At the end of the experiment, the relative content of humus-like components under the treatment of organic fertilizer and moderate water was the highest. Convolutional neural network (CNN) combined with 3D-EEM was used to identify the decomposition speed of straw. The classification precision of neural network validation set and test are 85.7% and 81.2%, respectively. In order to predict the decomposition rate of straw under different water and fertilizer conditions, 3D-EEM data of DOM were used as the input of CNN, parallel factor analysis (PARAFAC) and fluorescence region integral (FRI), and dissolved organic carbon data were used as the input of dissolved organic carbon linear prediction. The prediction model based on CNN had the best effect (R2 = 0.987). The results show that this method can effectively identify the spectral characteristics and predict the decomposition rate of straw under different conditions of water and fertilizer, which is helpful to promote the efficient decomposition of straw.

Enhanced cadmium phytoextraction efficiency of ryegrass (Lolium perenne L.) by porous media immobilized Enterobacter sp. TY-1

Although studies on immobilized microorganisms have been conducted, their performance remains unclear for enhancing plants to remediate cadmium (Cd)-contaminated soil. In this study, a Cd-resistant strain TY-1 with good plant growth promotion traits was immobilized by biochar (BC) or oyster shell (OS) power to strengthen ryegrass to remediate Cd-contaminated soil. SEM-EDS combined with FTIR showed that TY-1 could tolerate Cd toxicity by surface precipitation, and functional groups such as hydroxyl and carbonyl groups might be involved. In the biocomposite treatments, soil pH increased, and the activity of fertility-related enzymes such as dehydrogenase increased by 109.01%-128.01%. The relative abundance of genus Saccharimonadales decreased from 7.97% to 3.35% in BS-TY and 2.61% in OS-TY, respectively. Thus, a suitable environment for ryegrass growth was created. The fresh weight, dry weight, plant height and Cd accumulation of ryegrass in TY treatment increased by 122.92%, 114.81%, 42.08% and 8.05%, respectively, compared to the control. Cd concentration in ryegrass was further increased in BC-TY and OS-TY by 24.14% and 40.23%, respectively. The improvement in soil microcosm and plant biomass forms an ongoing virtuous cycle, demonstrating that using carrier materials to improve the efficiency of microbial-assisted phytoremediation is realistic and feasible.

Unravelling the molecular and biochemical responses in cotton plants to biochar and biofertilizer amendments for Pb toxicity mitigation

Over the past few years, there has been a rising interest in employing biochar (BC) and biofertilizers (BF) as a means of restoring soils that have been polluted by heavy metals. The primary objective of this study was to examine how the application of BC and BF affects the ability of cotton plants to withstand Pb toxicity at varying concentrations (0, 500, and 1000 mg/kg soil). The findings revealed that exposure to Pb stress, particularly at the 1000 mg/kg level, led to a decline in the growth and biomass of cotton plants. Pb toxicity triggered oxidative damage, impaired the photosynthetic apparatus, and diminished the levels of photosynthetic pigments. By increasing the expression of Rubisco-S, Rubisco-L, P5CR, and PRP5 genes and regulating proline metabolism, BC and BF increased the levels of proline and photosynthetic pigments and protected the photosynthetic apparatus. The application of BC and BF resulted in an upregulation of genes such as CuZnSOD, FeSOD, and APX1, as well as an increase in the activity of the glyoxalase system and antioxidant enzymes. These changes enhanced the antioxidant capacity of the plants and provided protection to membrane lipids from oxidative stress caused by Pb. The inclusion of BC and BF offered protection to photosynthesis and other essential intracellular processes in leaves by minimizing the transfer of Pb to leaves and promoting the accumulation of thiol compounds. This protective effect helped mitigate the negative impact of the toxic metal Pb on leaf function. By improving plant tolerance, reducing metal transfer, strengthening the antioxidant defense system, and enhancing the level of protective substances, these amendments show promise as valuable tools in tackling heavy metal pollution.

Exopolymeric substances production by Bacillus cereus KMS3-1 enhanced its biosorption efficiency in removing Cd2+ and Pb2+ in single and binary metal mixtures

The present study investigated the growth, exopolymeric substance (EPS) production, and biosorption efficiency of strain Bacillus cereus KMS3-1 in the Cd²⁺ and Pb²⁺ ions containing single and binary metal-treated broth (50 mg/L). In addition, the interaction of the KMS3-1 strain with Cd²⁺ and Pb²⁺ ions in single and binary metal-treated broths was investigated using SEM-EDS, FTIR, and XRD analyses. The results showed that the biosorption efficiency (%) and EPS production of KMS3-1 biomass in both single and binary metal-treated broths had increased with increasing incubation time and were higher for Pb²⁺ ions than for Cd²⁺ ions. In the single and binary metal-treated broths, the maximum biosorption efficiency of KMS3-1 for Pb²⁺ ions were 70.8% and 46.3%, respectively, while for Cd²⁺ ions, they were 29.3% and 16.8%, respectively, after 72 h. Moreover, the biosorption efficiency of strain KMS3-1 for both metal ions was dependent on its EPS production and peaked at the maximum EPS production. The copious EPS production by KMS3-1 was observed in metal-treated media (50 mg/L), in the following order: Pb²⁺ ions (1925.7 μg/mL) > binary metal mixtures (1286.8 μg/mL) > Cd²⁺ ions (1185.5 μg/mL), > control (1099 μg/mL) after 72 h of incubation. This result indicates that the metal biosorption efficiency of the KMS3-1 strain was enhanced by the increased EPS production in the surrounding metal-treated broth. SEM-EDS and FTIR characterization studies revealed that the KMS3-1 biomass effectively adsorbed Cd²⁺ and Pb²⁺ ions from the medium by interacting with their surface functional groups (hydroxyl, carbonyl, carboxyl, amide, and phosphate). Moreover, the biosorbed Cd²⁺ and Pb²⁺ ions were transformed into CdS and PbS, respectively, by the KMS3-1 biomass. This study suggests that the Bacillus cereus KMS3-1 strain may be a promising candidate for the treatment of metal contamination.

Exopolysaccharides of Serratia fonticola CPSE11 can alleviate the toxic effect of Cd2+ on Codonopsis pilosula

In order to study the detoxification effect of microbial exopolysaccharides (EPS) on the heavy metal cadmium (Cd2+), this study took an EPS-producing Serratia fonticola CPSE11 (NZ_CP050171.1) isolated from Codonopsis pilosula root as the research object. The whole genome and EPS synthesis gene clusters of this strain were predicted and analyzed, the adsorption kinetics of EPS on Cd2+ were studied by using pseudo-first-order and second-order kinetic equations, the isothermal adsorption curves were simulated and analyzed by using the Langmuir isothermal adsorption equation, and the effects of Cd2+ and EPS on the growth of C. pilosula were explored by seed germination experiment and hydroponic experiment. The analysis revealed that this strain contained three gene clusters related to EPS synthesis, and the metabolic pathway for EPS synthesis was obtained on the basis of the whole genome analysis and microbial physiological metabolism. The molecular weight and monosaccharide composition of EPS were determined by HPLC analysis, which showed that EPS consisted of mannose, glucosamine, rhamnose, galactosamine, glucose, and galactose with a molar ratio of 1:1.74:4.57:3.96:14.04:10.28, with the molecular weight of 366,316.09 kDa. The adsorption process of EPS on Cd2+ was in accordance with the second-order kinetic model, and the results of seed germination experiments showed that EPS could promote seed germination and improve seed activity. In the hydroponic experiment, high concentration of Cd2+ (15 mg/L) caused toxic symptoms in C. pilosula, while the addition of EPS reduced the toxic effect of Cd2+ on C. pilosula, and the plant growth was significantly improved.

Characterization of a cadmium-resistant functional bacteria (Burkholderia sp. SRB-1) and mechanism analysis at physiochemical and genetic level

In this study, the capacity of cadmium (Cd)-resistant plant growth-promoting bacteria (PGPB) Burkholderia sp. SRB-1 (SRB-1) and its mechanisms were explored through morphological characterizations, biochemical response, plant growth-promoting traits, and functional gene expression patterns. The results showed that SRB-1 was an excellent Cd-resistant bacteria (MIC was 420 mg L^-1), and its maximum Cd removal rate reached 72.25%. Biosorption was the main removal method of Cd for SRB-1, preventing intracellular Cd accumulation and maintaining cellular metabolism. Various functional groups on the cell wall were involved in Cd binding, which deposited as CdS and CdCO₃ on the cell surface according to XPS analysis and might be critical for reducing Cd physiochemical toxicity. Furthermore, metals exporting (zntA, czcA, czcB, czcC), detoxification (dsbA, cysM), and antioxidation (katE, katG, SOD1) related genes were annotated in the SRB-1 genome. The results of Cd distribution and antioxidative enzyme activity in SRB-1 also illustrated that Cd²⁺ efflux and antioxidative response were the main intracellular Cd-resistant mechanisms. These conclusions were further verified by qRT-PCR analysis. Overall, the strategies of extracellular biosorption, cation efflux, and intracellular detoxification jointly build the Cd-resistant system, which invested Burkholderia sp. SRB-1 with potential for bioremediation in heavily Cd-contaminated environmental sites.

A critical review on adsorptive removal of antimony from waters: Adsorbent species, interface behavior and interaction mechanism

Antimony (Sb) has raised widespread concern because of its negative effects on ecology and human health. The extensive use of antimony-containing products and corresponding Sb mining activities have discharged considerable amounts of anthropogenic Sb into the environment, especially the water environment. Adsorption has been employed as the most effective strategy for Sb sequestration from water; thus, a comprehensive understanding of the adsorption performance, behavior and mechanisms of adsorbents benefits to develop the optimal adsorbent to remove Sb and even drive its practical application. This review presents a holistic analysis of adsorbent species with the ability to remove Sb from water, with a special emphasis on the Sb adsorption behavior of various adsorption materials and their Sb-adsorbent interaction mechanisms. Herein, we summarize research results based on the characteristic properties and Sb affinities of reported adsorbents. Various interactions, including electrostatic interactions, ion exchange, complexation and redox reactions, are fully reviewed. Relevant environmental factors and adsorption models are also discussed to clarify the relevant adsorption processes. Overall, iron-based adsorbents and corresponding composite adsorbents show relatively excellent Sb adsorption performance and have received widespread attention. Sb removal mainly depends on chemical properties of the adsorbent and Sb itself, and complexation is the main driving force for Sb removal, assisted by electrostatic attraction. The future directions of Sb removal by adsorption focus on the shortcomings of current adsorbents; more attention should be given to the practicability of adsorbents and their disposal after use. This review contributes to the development of effective adsorbents for removing Sb and provides an understanding of Sb interfacial processes during Sb transport and the fate of Sb in the water environment.

Microbial extracellular polymeric substances alleviate cadmium toxicity in rice (Oryza sativa L.) by regulating cadmium uptake, subcellular distribution and triggering the expression of stress-related genes

Cadmium (Cd) accumulation in crops causes potential risks to human health. Microbial extracellular polymeric substances (EPS) are a complex mixture of biopolymers that can bind various heavy metals. The present work examined the alleviating effects of EPS on Cd toxicity in rice and its detoxification mechanism. The 100 μM Cd stress hampered the overall plant growth and development, damaged the ultrastructures of both leaf and root cells, and caused severe lipid peroxidation in rice plants. However, applying EPS at a concentration of 100 mg/L during Cd stress resulted in increased biomass, reduced Cd accumulation and transport, and minimized the oxidative damage. EPS application also enhanced Cd retention in the shoot cell walls and root vacuoles, and actively altered the expression of genes involved in cell wall formation, antioxidant defense systems, transcription factors, and hormone metabolism. These findings provide new insights into EPS-mediated mitigation of Cd stress in plants and help us to develop strategies to improve crop yield in Cd-contaminated soils in the future.

Insight into the roles of soluble, loosely bound and tightly bound extracellular polymeric substances produced by Enterobacter sp. in the Cd2+ and Pb2+ biosorption process: Characterization and mechanism

Extracellular polymeric substances (EPSs) are macromolecular polymers formed by metabolic secretion, and they have great potential for removing heavy metal (HM) ions from the aquatic phase. In this study, the contributions of soluble EPSs (S-EPSs), loosely bound EPSs (LB-EPSs) and tightly bound EPSs (TB-EPSs) secreted by Enterobacter sp. to Cd²⁺ and Pb²⁺ adsorption were analyzed. The results indicated that in a solution containing both Cd²⁺ and Pb²⁺, pH= 6.0 was best suited for the adsorption process, and adsorption equilibrium was reached in approximately 120 min. Moreover, the mechanism for adsorption of Cd²⁺ and Pb²⁺ by the different layers of EPSs involved spontaneous chemical processes. However, Cd²⁺ adsorption by the three layers of the EPSs was an exothermic process (∆H⁰ <0), but Pb²⁺ adsorption by the three layers of the EPSs was an endothermic process (∆H⁰ >0). The variations in zeta potentials indicated that ion exchange occurred during Cd²⁺ and Pb²⁺ adsorption. FT-IR, XPS and 3D-EEM analyses indicated that the functional groups of the EPSs involved in adsorption were mainly the CO, C-O and C-O-C groups of the polysaccharides; furthermore, fulvic acid-like substances, humic-like substances and tyrosine-like proteins played important roles in the adsorption of Cd²⁺ and Pb²⁺ by the different EPS layers.

Bacterial extracellular polymeric substances: Biosynthesis and interaction with environmental pollutants

Extracellular polymeric substances (EPS) are highly hydrated matrices produced by bacteria, containing various polymers such as polysaccharides, proteins, lipids, and DNA. Extracellular polymer concentrations, ions, and functional groups provide physical stability to the EPS. Constituents of EPS form the three-dimensional architecture and help acquire nutrition for the bacteria. Structural and functional diversity of the extracellular polymer depends on the specific glycosyltransferases, polymerase and transporter proteins. These enzymes are encoded by specific genes present in operons such as crd, alg, wca, and gum reported in Agrobacterium, Pseudomonas, Enterobacteriaceae, and Xanthomonas. The operons regulate the biosynthesis of extracellular polymers such as curdlan, alginate, colonic acid, and xanthan, respectively. Various functional groups in the EPS, such as carbonyl, hydroxyl, phosphoryl, and amide, provide the sorption site for interaction with environmental pollutants. Hydrophobic interactions and coordinate bonds mainly dominate the binding of EPS with environmental pollutants. EPS binds, emulsifies, and solubilizes the organic compounds, enhancing the degradation process. EPS binds with heavy metals through complexation, surface adsorption, precipitation, and ion exchange mechanisms. The biodegradability efficiency and nontoxicity properties of EPS make it an excellent biopolymer for decontaminating environmental pollutants. This review summarizes an overview of the biosynthetic mechanisms and interaction of the bacterial extracellular polymer with environmental pollutants. Interaction mechanisms of pollutants with EPS and EPS-mediated bioremediation will help develop removal applications. Moreover, understanding the genes responsible for EPS production, and implementation of new genetic methodology can be helpful for the enhanced biosynthesis of EPS to control pollution by sequestrating more environmental pollutants.

Impacts of metal stress on extracellular microbial products, and potential for selective metal recovery

Harnessing microbial capabilities for metal recovery from secondary waste sources is an eco-friendly and sustainable approach for the management of metal-containing wastes. Soluble microbial products (SMP) and extracellular polymeric substances (EPS) are the two main groups of extracellular compounds produced by microorganisms in response to metal stress that are of great importance for remediation and recovery of metals. These include various high-, and low, molecular weight components, which serve various functional and structural roles. These compounds often contain functional groups with metal binding potential that can attenuate metal stress by sequestering metal ions, making them less bioavailable. Microorganisms can regulate the content and composition of EPS and SMP in response to metal stress in order to increase the compounds specificity and capacity for metal binding. Thus, EPS and SMP represent ideal candidates for developing technologies for selective metal recovery from complex wastes. To discover highly metal-sorptive compounds with specific metal binding affinity for metal recovery applications, it is necessary to investigate the metal binding affinity of these compounds, especially under metal stressed conditions. In this review we critically reviewed microbial EPS and SMP production as a response to metal stress with a particular emphasis on the metal binding properties of these compounds and their role in altering metal bioavailability. Furthermore, for the first time, we compiled the available data on potential application of these compounds for selective metal recovery from waste streams.

Study of Cadmium Metal Resistance in Stenotrophomonas maltophilia

Metal-resistant bacteria are recommended for metal removal applications due to their rapid multiplication and growth rates. To ensure safety replenishment in contaminated areas frequently hampered by heavy metal toxicity, it is crucial to comprehend their coping mechanisms under heavy metal stress. This study primarily examines the role of EPS (exopolysaccharide) in Stenotrophomonas maltophilia, a Gram-negative, aerobic, and rod-shaped bacteria, in response to Cd, as well as the binding behavior and biosorption mechanism between EPS and Cd, using SEM and FTIR. The studies showed that Stenotrophomonas maltophilia, can resist up to 150 μM of Cd due to the binding of Cd to EPS. SEM analysis showed significant morphological changes and FTIR was to identify main structural groups like carboxyl and hydroxyl which confirms the presence of EPS. The study will also describe the mechanism of cross-reactivity between exopolysaccharide and siderophore production in metal-tolerant Stenotrophomonas maltophilia. This study proved that siderophore-mediated metal detoxification and effective absorption have been linked to metal chelation.

Sporadic Pb accumulation by plants: Influence of soil biogeochemistry, microbial community and physiological mechanisms

Recent results revealed that considerable Pb accumulation in plants is possible under specific soil conditions that make Pb phytoavailable. In this review, the sources and transformations of Pb in soils, the interaction of Pb with bacteria and specifically the microbiota in the soil, factors and mechanisms of Pb uptake, translocation and accumulation in plants and Pb toxicity in living organisms are comprehensively elaborated. Specific adsorption and post-adsorption transformations of Pb in soil are the main mechanisms affecting the mobility, bioavailability, and toxicity of Pb. The adsorption ability of Pb largely depends on the composition and properties of soils and environmental conditions. Microbial impact on Pb mobility in soil and bioavailability as well as bacterial resistance to Pb are considered. Specific mechanisms conferring Pb-resistance, including Pb-efflux, siderophores, and EPS, have been identified. Pathways of Pb entry into plants as well as mechanisms of in planta Pb transport are poorly understood. Available evidence suggests the involvement of Ca transporters, organic acids and the phytochelatin pathway in Pb transport, mobility and detoxification, respectively.

Chromate Removal by Enterobacter cloacae Strain UT25 from Tannery Effluent and Its Potential Role in Cr (VI) Remediation

An indigenous chromate-resistant bacterial strain isolated from tannery effluent was identified based on morphological, biochemical, and 16S rRNA gene sequencing, as Enterobacter cloacae UT25. It was found to resist heavy metal ions such as Cr (VI), Pb (II), Cu (II), Co (II), Ni (II), Hg (II), and Zn (II) and antibiotics. The strain was able to remove 89 and 86% chromate, after 24 h of incubation in a Luria-Bertani (LB) medium at an initial Cr (VI) concentration of 1000 and 1500 µg/ml, respectively. Minimum inhibitory concentration (MIC) was observed for chromate to be 80,000 and 1850 µg/ml, after 48 h of incubation in LB and acetate minimal media (AMM), respectively. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analysis showed discrete cells with intact and smooth cell walls and homogenous cytoplasm in the absence of metal stress, whereas chromate stress caused cell lysis and reduction in size, which was a characteristic response to Cr (VI) toxicity. Energy Dispersive X-Ray Spectroscopy (EDX) confirmed the adsorption of oxyanions to the cell wall which was one of the Cr (VI) removal mechanisms by the bacterium. Atomic Force Microscopy (AFM) micrographs of chromate-untreated and treated cells revealed Root Mean Square roughness (Rq) values of 16.25 and 11.26 nm, respectively, indicating less roughness in the presence of stress. The partial gene sequence of class 1 integrons (intI1) of strain UT25 showed 94% homology with intI1 gene of strain Enterobacter hormaechei strain ECC59 plasmid pECC59-1. The present analysis highlighted the potential of E. cloacae UT25 as a promissory bacterium that could be applied in removing chromate from polluted environments.

Investigating the effects of biodegradable microplastics and copper ions on probiotic (Bacillus amyloliquefaciens): Toxicity and application

Currently, microplastic pollution is more serious and complicates the toxic effects of other co-existing pollutants in the environment. However, the effect and mechanism of biodegradable plastics on the growth and metabolism of probiotic remain unclear. This work selected Bacillus amyloliquefaciens as model bacterium for a three-day exposure experiment to probe the issues. The results showed that 100 mg/L polylactic acid microplastics (PLA MPs) (3-4 mm, flake shape) caused oxidative damage to cell membranes, disrupted cell wall composition and inhibited cell growth by 21.2-27.5 %. The toxicity was not simply additive or synergistic effects when PLA MPs (100 mg/L) and copper ions (10 mg/L) coexisted. PLA MPs did not significantly increase the toxicity of copper to bacteria, instead triggered some mechanisms to resist the toxicity of copper. The bacteria formed spores to resist PLA MPs, while the copper ions toxicity was weaken by chelation and efflux. It is worth noting that copper ions instead increased the expression of genes related fengycin and iturin then improving the bacteriostatic activity of the probiotic. This paper deeply analyzes the toxicity mechanism of combined pollution on Bacillus amyloliquefacien, and also provides new perspective for helping to inhibit pathogenic bacteria under biodegradable microplastics and metal stress.

Bioleaching and immobilizing of copper and zinc using endophytes coupled with biochar-hydroxyapatite: Bipolar remediation for heavy metals contaminated mining soils

Copper and zinc are toxic heavy metals in soils that require development of feasible strategies for remediation of contaminated soils around the mine areas. In this study, the processing conditions and mechanisms of immobilization and bioleaching for remediation of highly contaminated soils with heavy metals are investigated. Soil remediation is carried out using a bioleaching-immobilization bipolar method. The results show that LSE03 bacteria provide efficient leaching result and immobilization on Cu²⁺ and Zn²⁺. Among the bacterial metabolites, cis, cis-muconic acid and isovaleric acid play major roles in the bioleaching process. The bacterial extracellular polymeric substances are rich in a variety of organic acids that show a significant decrease in content after the adsorption process, indicating that all of these substances are involved in the binding of heavy metals. Characterization of the endophytes and immobilizing agents with FTIR, TEM-mapping, and XPS techniques reveal the ability of both bacteria and composites to adsorb Cu-Zn as well as the main functional groups of -OH, -COOH, -PO₄^3-, and -NH. According to the heavy metals species analyses, competitive adsorption experiments, and bioleaching desorption experiments, it is planned to carry out the bipolar remediation of contaminated soil through immobilization followed by bioleaching process. After bipolar remediation processing, 97.923% and 96.387% of available Cu and Zn are respectively removed. Soils fertility significantly increases in all cases. Our study provides a green, practical, and environmentally friendly treatment method for soils contaminated with high concentrations of heavy metals.

Reduction mechanisms of V5+ by vanadium-reducing bacteria in aqueous environments: Role of different molecular weight fractionated extracellular polymeric substances

Extracellular polymeric substances (EPS) are high-molecular polymers secreted by microbes and play essential roles in metallic biogeochemical cycling. Previous studies demonstrated the reducing capacity of the functional groups on EPS for metal reduction. However, the roles of different EPS components in vanadium speciation and their responsible reducing substances for vanadium reduction are still unknown. In this study, the EPS of Bacillus sp. PFYN01 was fractionated via ultrafiltration into six components with different kDa (EPS_>100, EPS_100-50, EPS_50-30, EPS_30-10, EPS_10-3, and EPS_<3). Batch reduction experiments of the intact cells, EPS-free cells, the pristine and fractionated EPS with V⁵⁺ were conducted and characterized. The results demonstrated that the extracellular reduction of V⁵⁺ into V⁴⁺ by EPS was the major reduction process. Among the functional groups in EPS, C=O/C-N of amide in protein/polypeptide and CO of carboxyl in fulvic acid-like substances might act as the reductants for V⁵⁺, while CO in polysaccharide molecules and PO in phosphodiester played a key role in the adsorption process. The intracellular reduction was via translocating V⁵⁺ into the cells and releasing V⁴⁺ by the intracellular reductases. The reducing capacity of the fractionated EPS followed a sequence of EPS_<3 > EPS_10-3 > EPS_50-30 > EPS_100-50 > EPS_30-10 > EPS_>100. The small molecules of fulvic acid-like substances and amino acids were responsible for the high reducing capacity of EPS_<3. EPS_>100 had the lowest reducing capacity due to its macromolecular structure decreasing the exposure of the reactive sites. In addition to reduction, those intermediate EPS components may also have supporting functions, such as connecting protein skeletons and increasing the specific surface area of EPS. Therefore, the diverse effects of the EPS components cannot be neglected in vanadium biogeochemical cycling.

Response mechanism of microbial community during anaerobic biotransformation of marine toxin domoic acid

Domoic acid (DA) is a potent neurotoxin produced by toxigenic Pseudo-nitzschia blooms and quickly transfers to the benthic anaerobic environment by marine snow particles. DA anaerobic biotransformation is driven by microbial interactions, in which trace amounts of DA can cause physiological stress in marine microorganisms. However, the underlying response mechanisms of microbial community to DA stress remain unclear. In this study, we utilized an anaerobic marine DA-degrading consortium GLY (using glycine as co-substrate) to systematically investigate the global response mechanisms of microbial community during DA anaerobic biotransformation.16S rRNA gene sequencing and metatranscriptomic analyses were applied to measure microbial community structure, function and metabolic responses. Results showed that DA stress markedly changed the composition of main species, with increased levels of Firmicutes and decreased levels of Proteobacteria, Cyanobacteria, Bacteroidetes and Actinobacteria. Several genera of tolerated bacteria (Bacillus and Solibacillus) were increased, while, Stenotrophomonas, Sphingomonas and Acinetobacter were decreased. Metatranscriptomic analyses indicated that DA stimulated the expression of quorum sensing, extracellular polymeric substance (EPS) production, sporulation, membrane transporters, bacterial chemotaxis, flagellar assembly and ribosome protection in community, promoting bacterial adaptation ability under DA stress. Moreover, amino acid metabolism, carbohydrate metabolism and lipid metabolism were modulated during DA anaerobic biotransformation to reduce metabolic burden, increase metabolic demands for EPS production and DA degradation. This study provides the new insights into response of microbial community to DA stress and its potential impact on benthic microorganisms in marine environments.

Simultaneous removal of ternary heavy metal ions by a newly isolated Microbacterium paraoxydans strain VSVM IIT(BHU) from coal washery effluent

In the present work, the removal of Cr (VI), Cd (II) and Pb (II) at 50 mg/L of each metal ion concentration was investigated by Microbacterium paraoxydans strain VSVM IIT(BHU). The heavy metal binding on the bacterial cell surface was confirmed through X-ray photoelectron spectroscopy and energy dispersive X-ray. X-ray photoelectron spectroscopy analysis also confirmed the reduction of Cr (VI) to Cr (III). Heavy metal removal dynamics was investigated by evaluating dimensionless, and the value of N_k (9.49 × 10^-3, 9.92 × 10^-3 and 1.23 × 10^-2 for Cr (VI), Cd (II) and Pb (II) ions) indicated that the removal of heavy metals by bacterial isolate was mixed diffusion and transfer controlled. It was found that both the experimental and predicted values for isolated bacterial strain coincided with each other with a good R² value in the L-M Algorithm range of 0.94-0.98 for the ternary metal ion system. The bacterial isolate presented a maximum heavy metal ion removal efficiency of 91.62% Cr (VI), 89.29% Pb (II), and 83.29% Cd (II) at 50 mg/L.

Pseudomonas stutzeri Immobilized Sawdust Biochar for Nickel Ion Removal

Nickel ions generated from the electroplating industry and stainless steel and battery manufacturing industries contribute to water pollution, harm human health, and pose environmental risks. A long-term, sustainable, and efficient treatment method should be developed to address this issue. Bioremediation in the presence of biochar and microorganisms is a potential approach for metal ion abatement. This study evaluates the feasibility of Pseudomonas stutzeri immobilized sawdust biochar (PSDB) for Ni2+ removal. Sawdust biochar was prepared by pyrolyzing in a muffle furnace and was characterized using SEM, FTIR, and BET. The influence of biochar preparation parameters such as pyrolysis temperature, time on biochar yield, and impact on cell immobilization was investigated. The effect of various parameters, such as incubation time, pH, temperature, and biocatalyst dosage, was studied. The total Ni2+ in solution was analyzed using inductively coupled plasma optical emission spectrometry. PSDB showed an 83% Ni2+ removal efficiency and reusability up to three cycles. FT-IR analysis revealed that the mechanism of Ni2+ removal by PSDB was the synergistic effect of adsorption by biochar and bioaccumulation by P. stutzeri. This study presents a novel approach for environmental application by utilizing waste biomass-derived biochar as a carrier support for bacteria and an adsorbent for pollutants.

Construction and carbon source optimization of a microbial-plant coupled reactor for treating acid mine drainage

Acid mine drainage (AMD) is recognized as one of the most serious contamination sources in the nonferrous metal mining industry. In this study, aerobic strains VCZ02 and VCZ09, which were identified as Leclercia adecarboxylata and Klebsiella aerogenes, were screened from 11 strains of copper-zinc-resistant bacteria in the soil of the Dexing copper mine with Cu²⁺/Zn²⁺ removal rates of 46.32%/41.03% and 57.96%/67.05%, respectively. The composition of extracellular polymers plays an important role in the removal of heavy metals by these two strains. A mixed community consisting of VCZ02 and VCZ09 was coupled with Sagittaria trifolia L.var.sinensis (Sims) Mak to construct a microbial-plant coupled reactor to remediate AMD. Under the optimal condition of sodium acetate as carbon source, the pH of AMD increased from less than 5 to above 6.5, showing Cu²⁺/Zn²⁺ removal rates of 70-80% and above 30%, respectively. SEM-EDS results showed that VZC02 and VZC09 in the coupled reactor also helped with resisting the toxicity of heavy metals to plants by forming biofilms on the root surface and increasing the content of heavy metals on the surface of roots, thus improving the treatment effect of plants. This study provides a theoretical basis for the bioremediation of AMD and its application.

Exopolysaccharides from marine microbes with prowess for environment cleanup

A variety of both small and large biologically intriguing compounds can be found abundantly in the marine environment. Researchers are particularly interested in marine bacteria because they can produce classes of bioactive secondary metabolites that are structurally diverse. The main secondary metabolites produced by marine bacteria are regarded as steroids, alkaloids, peptides, terpenoids, biopolymers, and polyketides. The global urbanization leads to the increased use of organic pollutants that are both persistent and toxic for humans, other life forms and tend to biomagnified in environment. The issue can be addressed, by using marine microbial biopolymers with ability for increased bioremediation. Amongst biopolymers, the exopolysaccharides (EPS) are the most prominent under adverse environmental stress conditions. The present review emphasizes the use of EPS as a bio-flocculent for wastewater treatment, as an adsorbent for the removal of textile dye and heavy metals from industrial effluents. The biofilm-forming ability of EPS helps with soil reclamation and reduces soil erosion. EPS are an obvious choice being environmentally friendly and cost-effective in processes for developing sustainable technology. However, a better understanding of EPS biosynthetic pathways and further developing novel sustainable technologies is desirable and certainly will pave the way for efficient usage of EPS for environment cleanup.

Bioremediation of metal(loid) cocktail, struvite biosynthesis and plant growth promotion by a versatile bacterial strain Serratia sp. KUJM3: Exploiting environmental co-benefits

In this study the multiple metal(loid) (As, Cd, Cu and Ni) resistant bacterium Serratia sp. KUJM3 was able to grow in both single and multiple metal(loid) contaminated wastewater and removed them by 34.93-48.80% and 22.93-32%, respectively. It reduced As(v) to As(III) by 68.44-85.06% in a concentration dependent manner. The strain's IAA production potential increased significantly under both metal(loid)s regime. The lentil (Lens culinaris) seed germination and seed production were enhanced with the exogenous bacterial inoculation by 20.39 and 16.43%, respectively. Under both multi-metal(loid) regimes the bacterial inoculation promoted shoot length (22.65-51.34%), shoot dry weight (33.89-66.11%) and seed production (13.46-35%). Under bacterial manipulation the metal(loid)s immobilization increased with concomitant curtailment of translocation in lentil plant by 61.89-75.14% and 59.19-71.14% in shoot and seed, respectively. The strain biomineralized struvite (MgNH₄ PO₄ ·6H₂O) from human urine @ 403 ± 6.24 mg L^-1. The fertilizer potential of struvite was confirmed with the promotion of cowpea (Vigna unguiculata) growth traits e.g. leaf number (37.04%), pod number (234%), plant wet weight (65.47%) and seed number (134.52%). Thus Serratia sp. KUJM3 offers multiple benefits of metal(loid)s bioremediation, As(V) reduction, plant growth promotion, and struvite biomineralization garnering a suite of appealing environmental applications.

Characteristics of EPS from Pseudomonas aeruginosa and Alcaligenes faecalis under Cd(II) stress: changes in chemical components and adsorption performance

EPS (extracellular polymeric substance) production is a self-protection mechanism by which microorganisms slow or eliminate adverse effects in unfavorable environments. In this study, Pseudomonas aeruginosa and Alcaligenes faecalis were selected to explore changes in EPS components, especially protein components, under stress caused by different concentrations of Cd(II). The results showed that the protein content in EPS was the highest. The two strains achieved maximum EPS production levels of 109.17 and 214.96 mg/g VSS at Cd(II) stress concentrations of 20 and 50 mg/L, which were increased by 52.07% and 409.69% compared with the levels exhibited before stress, respectively. The protein content correlated very well with data from adsorption experiments. Furthermore, FTIR, 3D-EEM, and XPS results illustrated that after Cd(II) stress, C-N, C=O/-COOH, and R-NO₂^- moieties were formed in substantial quantities, and the stress effects of Pseudomonas aeruginosa were significantly higher than those of Alcaligenes faecalis. The results of this study showed that addition of Cd(NO₃)₂ effectively regulated the components of EPS, especially the protein content, and improved the adsorption capacity, which has application prospects for prevention and control of heavy metals.

Impact of key parameters involved with plant-microbe interaction in context to global climate change

Anthropogenic activities have a critical influence on climate change that directly or indirectly impacts plant and microbial diversity on our planet. Due to climate change, there is an increase in the intensity and frequency of extreme environmental events such as temperature rise, drought, and precipitation. The increase in greenhouse gas emissions such as CO2, CH4, NOx, water vapor, increase in global temperature, and change in rainfall patterns have impacted soil–plant-microbe interactions, which poses a serious threat to food security. Microbes in the soil play an essential role in plants’ resilience to abiotic and biotic stressors. The soil microbial communities are sensitive and responsive to these stressors. Therefore, a systemic approach to climate adaptation will be needed which acknowledges the multidimensional nature of plant-microbe-environment interactions. In the last two scores of years, there has been an enhancement in the understanding of plant’s response to microbes at physiological, biochemical, and molecular levels due to the availability of techniques and tools. This review highlights some of the critical factors influencing plant-microbe interactions under stress. The association and response of microbe and plants as a result of several stresses such as temperature, salinity, metal toxicity, and greenhouse gases are also depicted. New tools to study the molecular complexity of these interactions, such as genomic and sequencing approaches, which provide researchers greater accuracy, reproducibility, and flexibility for exploring plant-microbe–environment interactions under a changing climate, are also discussed in the review, which will be helpful in the development of resistant crops/plants in present and future.

Bacterial extracellular polymeric substances: Impact on soil microbial community composition and their potential role in heavy metal-contaminated soil

In this study, six different treatments involving extracellular polymeric substances (EPS) from Enterobacter sp. FM-1 (FM-1) (no EPS (control), original bacterial cells (FM-1), FM-1 cells with EPS artificially removed (EPS-free cells, EPS-R), different forms of EPS (soluble EPS (S-EPS), loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS)) obtained from FM-1) and three types of soils (non-contaminated soil (NC soil), high-contamination soil (HC soil) and low-contamination soil (LC soil)) were used to investigate the impact of different EPS treatments on soil microbial community composition and their potential role in the remediation of heavy metal (HM)-contaminated soil. The results indicate that the EPS secreted by FM-1 played a vital role in changing soil pH and helped increase soil bio- HMs. In addition, EPS secretion by FM-1 helped increase the soil EPS-polysaccharide and EPS-nucleic acid contents; even in HC soil, where the HM content was relatively high, LB-EPS addition still increased the EPS-polysaccharide and EPS-nucleic acid contents in the soil by 1.18- and 15.54-fold, respectively. FM-1, LB-EPS and TB-EPS addition increased the soil invertase, urease and alkaline phosphatase activities and increased the soil organic matter (SOM), NH₄⁺-N and available phosphorus (AP) contents, which helped regulate soil nutrient reserves. Moreover, the addition of different EPS fractions modified the soil microbial community composition to help microbes adapt to an HM-contaminated environment. In the HC and LC soils, where the HM content was relatively high, the soil bacteria were dominated by Protobacteria, while fungi in the soil were dominated by Ascomycota. Among the soil physicochemical properties, the soil SOM and NH₄⁺-N contents and invertase activity significantly impacted the diversity and community composition of both bacteria and fungi in the soil.

Adaptive Response of Thermophiles to Redox Stress and Their Role in the Process of dye Degradation From Textile Industry Wastewater

Release of dye-containing textile wastewater into the environment causes severe pollution with serious consequences on aquatic life. Bioremediation of dyes using thermophilic microorganisms has recently attracted attention over conventional treatment techniques. Thermophiles have the natural ability to survive under extreme environmental conditions, including high dye concentration, because they possess stress response adaptation and regulation mechanisms. Therefore, dye detoxification by thermophiles could offer enormous opportunities for bioremediation at elevated temperatures. In addition, the processes of degradation generate reactive oxygen species (ROS) and subject cells to oxidative stress. However, thermophiles exhibit better adaptation to resist the effects of oxidative stress. Some of the major adaptation mechanisms of thermophiles include macromolecule repair system; enzymes such as superoxide dismutase, catalase, and glutathione peroxidase; and non-enzymatic antioxidants like extracellular polymeric substance (EPSs), polyhydroxyalkanoates (PHAs), etc. In addition, different bacteria also possess enzymes that are directly involved in dye degradation such as azoreductase, laccase, and peroxidase. Therefore, through these processes, dyes are first degraded into smaller intermediate products finally releasing products that are non-toxic or of low toxicity. In this review, we discuss the sources of oxidative stress in thermophiles, the adaptive response of thermophiles to redox stress and their roles in dye removal, and the regulation and crosstalk between responses to oxidative stress.

Interrelating EPS, soluble microbial products and metal solubility in a methanogenic consortium stressed by nickel and cobalt

The relationships between extracellular polymeric substances (EPS), soluble microbial product production, metal solubility, and methanogenic activity were investigated. The individual, and joint, toxic effects of nickel and cobalt on methanogenic consortia fed with glucose as model substrate were studied using biomethane potential assays. Cobalt was found to be less toxic to methanogens than nickel at each concentration tested, and the combined effects of Ni and Co on methane production in the bimetal experiment was higher than the sum of the effects of each metal alone. The protein content of EPS, and extracellular soluble protein fractions, decreased with increasing concentrations of total metals. Meanwhile, no significant change in response to metal stress was apparent for carbohydrate content of EPS or extracellular soluble carbohydrate. Decreasing protein content of EPS was accompanied by reduced methanogenic activity and an increase in the soluble metal fraction. The strong associations observed between these variables could be due to the critical role of EPS in protecting microbial cells against nickel and cobalt stress, possibly by capturing metal cations through their functional groups, thus reducing metal availability to the microbial cells in the methanogenic consortia underpinning the anaerobic digestion process.

Integrating Broussonetia papyrifera and Two Bacillus Species to Repair Soil Antimony Pollutions

Heavy metal resistant bacteria play an important role in the metal biogeochemical cycle in soil, but the benefits of microbial oxidation for plants and soil have not been well-documented. The purpose of this study was to explore the contribution of two Bacillus spp. to alleviate the antimony (Sb) toxicity in plants, and, then, to propose a bioremediation method for Sb contaminated soil, which is characterized by environmental protection, high efficiency, and low cost. This study explored the effects of Bacillus cereus HM5 and Bacillus thuringiensis HM7 inoculation on Broussonetia papyrifera and soil were evaluated under controlled Sb stressed conditions (0 and 100 mmol/L, antimony slag) through a pot experiment. The results show that the total root length, root volume, tips, forks, crossings, and root activities of B. papyrifera with inoculation are higher than those of the control group, and the strains promote the plant absorption of Sb from the soil environment. Especially in the antimony slag treatment group, B. cereus HM5 had the most significant effect on root promotion and promoting the absorption of Sb by B. papyrifera. Compared with the control group, the total root length, root volume, tips, forks, crossings, and root activities increased by 64.54, 70.06, 70.04, 78.15, 97.73, and 12.95%, respectively. The absorption of Sb by root, stem, and leaf increased by 265.12, 250.00, and 211.54%, compared with the control group, respectively. Besides, both B. cereus HM5 and B. thuringiensis HM7 reduce the content of malondialdehyde, proline, and soluble sugars in plant leaves, keeping the antioxidant enzyme activity of B. papyrifera at a low level, and alleviating lipid peroxidation. Principal component analysis (PCA) shows that both B. cereus HM5 and B. thuringiensis HM7 are beneficial to the maintenance of plant root functions and the improvement of the soil environment, thereby alleviating the toxicity of Sb. Therefore, B. cereus HM5 and B. thuringiensis HM7 in phytoremediation with B. papyrifera is a promising inoculant used for bacteria-assisted phytoremediation on Sb contaminated sites.

Extrapolymeric substances (EPS) in Mucilaginibacter rubeus P2 displayed efficient metal(loid) bio-adsorption and production was induced by copper and zinc

Strains of the genus Mucilaginibacter, belonging to the phylum Bacteroidetes, have been noted for exhibiting high genome plasticity and for the vigorous production of extracellular polymeric substances (EPS). Here we analyzed the composition and properties of EPS generated by M. rubeus P2, isolated from a gold-copper mine and exhibiting extremely high resistance to multiple heavy metals. Production of EPS increased significantly upon exposure to elevated concentrations of Cu(II) and Zn(II), but not Au(III). In addition, the EPS produced by M. rubeus P2 displayed extremely high bio-adsorption of As(III), Cu(II) and Au(III), but not of Zn(II). Moreover, EPS production in Mucilaginibacter rubeus P2 exposed to 1 mM of Cu(II) was 8.5 times higher than EPS production in the same strain without metal (loid)-exposure. These findings constitute the basis for a future use of these EPS-overproducing bacteria in bioremediation of heavy metal contaminated environments. The functional groups, especially -SH, CO, and N-H/C-N in the fingerprint zone of glutathione (GSH) and polysaccharides-like components of EPS, were the main components of EPS involved in both Zn(II) and Cu(II) binding and removal. Around 31.22% and 5.74% of Cu(II)-treated EPS was shown to exist as (CO) structures and these structures were converted into C-OH and O-C-O upon exposure to Cu(II), respectively. In contrast, (C-OH/C-O-C/P-O-C) groups in EPS were observed to be positively correlated to increasing concentrations of Zn(II) in strain P2. Furthermore, the complete genome of M. rubeus P2 helped us to identify 350 genes involved in carbohydrate metabolism, some of which are predicted to be involved in EPS production and modification. This work describes the first detailed biochemical and biophysical analysis of EPS from any strain of Mucilaginibacter with unique heavy metal binding properties. The results will be useful for a better understanding of how microorganisms such as M. rubeus P2 adapt to heavy metal polluted environments and how this knowledge can potentially be harnessed in biotechnological applications such as industrial waste water purification, bioremediation of heavy metal contaminated soil and beneficial plant microbe interactions. The toolbox provided in this paper will provide a valuable basis for future studies.

Insights into the role of extracellular DNA in heavy metal adsorption

Extracellular polymeric substances (EPS) participate in heavy metal adsorption in the aquatic environments. Extracellular DNA (eDNA) is an essential component of EPS, but its involvement in metal binding remains ambiguous. Herein, the role of eDNA in Cd(II) and Ni(II) adsorption was described using a combination of semi-quantitative and qualitative approaches. EPS were extracted from Burkholderia sp. MBR-1 and eDNA accounted for 6.9% of the total mass of EPS. The eDNA in the extracted EPS was digested using the DNase II to prepare an eDNA-free EPS sample. Potentiometric titration unveiled that the number of total binding sites of the eDNA-free EPS was 19% lower than the untreated EPS. The Cd(II) and Ni(II) adsorption capacity of the eDNA-free EPS was lower than the untreated EPS at the pH range of 4-7. At pH 7, the results of batch adsorption experiments showed that removing eDNA from EPS resulted in declines of 12.6% and 15.7% in the adsorption capacities for Cd(II) and Ni(II), respectively. Furthermore, Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy unraveled that the phosphoryl groups and purines of eDNA are responsible for Cd(II) and Ni(II) complexation. The results demonstrated that eDNA plays an essential role in heavy metal adsorption.

Effects of different exogenous cadmium compounds on the chemical composition and adsorption properties of two gram-negative bacterial EPS

Three different Cd(II) compounds were used to regulate Pseudomonas aeruginosa and Alcaligenes faecalis EPS (extracellular polymeric substances). The purpose of this study was to improve the content of EPS protein and the adsorption capacity of Cd(II) by different Cd(II) compounds. The results showed that Cd(NO₃)₂ had the best stress/induction effect on the two strains. Under the best stress/induction, the protein in EPS of the two strains increased most obviously, and the adsorption capacity of Cd(II) was increased by more than 40%. Under these conditions, the kinetics of the adsorption process of Cd(II) by Cd(NO₃)₂-EPS_{A. F} (EPS produced by Alcaligenes faecalis under Cd(NO₃)₂ stress) could be well fitted by the Langmuir isotherm model, and the theoretical maximum adsorption amount of 1111.11 mg/g EPS could be obtained. The results of 3D-EEM, FTIR and XPS indicated that proteins, especially CO, CN and NH in proteins, played a major role in the removal of Cd(II) by Cd(NO₃)₂-EPS_{A. F}. The results of this study show that the addition of Cd(NO₃)₂ can effectively regulate the content of chemical components, especially the content of protein, and thus greatly improve the removal efficiency of heavy metals, which shows great application prospects in the prevention and control of heavy metal pollution.