Effect and mechanism of simultaneous cadmium-tetracycline removal by a self-assembled microbial-photocatalytic coupling system

Remediation of wastewater by using CdS-based biohybrids: Challenges and enhancement strategies

Co-existence of pollutants, specifically heavy metals and organic compounds, as well as multi-heavy metals, in wastewater presents a significant global environmental and public health concern. The combined presence of these pollutants can result in a synergistic increase in toxicity, making the simultaneous removal of heavy metals and organic contaminants a complex challenge. Cadmium sulfide-based photocatalyst-microbe biohybrids, which integrate the advantages of whole-cell biological catalysts and semiconducting nanomaterials, have garnered considerable interest. These biohybrids offer benefits such as the capacity for heavy metal ion recycling, enhanced remediation efficiency, and the simultaneous removal of combined pollutants. This review begins by outlining the strategy for developing CdS-based biohybrid systems. Subsequently, it explores the application and mechanisms of remediation facilitated by these systems. The current challenges and future perspectives for biohybrid systems are also discussed. Finally, the review highlights the potential of synthetic biology strategies for optimizing and constructing biohybrid systems.

A microbial-driven persulfate activating-cycling system for in-depth oxytetracycline degradation and bacterial antibiotic resistance control

Insufficient biodegradability of antibiotics (e.g., oxytetracycline, OTC) and the accompanying antibiotic resistance gene (ARG) spreading risk have been a serious concern in wastewater treatment plants. This study developed a microbial-driven persulfate activating-cycling system (MPCS) relying on the iron-reducing capacity of Shewanella oneidensis to sustainably degrade OTC and prevent ARG elevation. In MPCS, a nanosized bio-magnet shell (20-60 nm) was bio-generated and incorporated with S. oneidensis to activate peroxydisulfate and produce free radicals to attack OTC, removed by 98.78 % in 120 min. S. oneidensis metabolism re-generated the bio-magnet and cleared the toxic intermediates. Despite the stress of OTC and free radicals, S. oneidensis sustained (live/death ratio of 74.50 %: 25.50 %) under bio-magnet shell protection, showing a strong energy metabolism and iron-reducing strength. The tight coupling of biodegradation and advanced oxidation process (AOP) greatly improved degrading efficiency (132.65 %-2369.44 % higher than single biodegradation or AOP). MPCS continuously operated 5 cycles efficiently, exhibiting a diverse degrading pathway with less toxic intermediates than the single treatment. Notably, MPCS functioned well without peroxydisulfate, as the S. oneidensis produces low-level hydrogen peroxide as the AOP substrate, achieving favorable OTC elimination. Especially, the expression of sixteen tetracycline-related ARGs dropped by 62.94 %-100 % in MPCS than biodegradation, indicating resistance control advantage under bio-magnet shell protection and the synergism effect of AOP and biodegradation. This study spontaneously recyclably combined biodegradation and AOP to simultaneously eliminate antibiotics and ARGs, which provided a potential approach to control the drug resistance risk.

Enhancing degradation of antibiotic-combined pollutants by a hybrid system containing advanced oxidation and microbial treatment, a review

Antibiotics often co-exist with other pollutants, posing a significant threat to ecosystems. This review first examines the applications and limitations of microbial treatments for various types of antibiotic-combined pollutants. Then, it explores the mechanisms and application of hybrid systems that integrate advanced oxidation with microbial treatment, categorized into two-stage and intimately hybrid systems. Finally, the review highlights key knowledge gaps in hybrid systems and provides new insight into the removal of combined pollutants.

Light-driven biodegradation of chloramphenicol by photosensitized Shewanella oneidensis MR-1

Efficient and sustainable degradation of chloramphenicol has piqued the interest of the scientific community. This study constructed a photosensitized biohybrid system using Shewanella oneidensis MR-1 and cadmium sulfide (CdS). This system could efficiently degrade chloramphenicol with robust stability. Inhibitor experiments and transcriptome analysis revealed that reduced nicotinamide adenine dinucleotide dehydrogenase, iron-sulfur cluster, menaquinone, cytochrome b561, cytochrome c, cytochrome P450, and formate dehydrogenase/hydrogenase are involved in direct electron transfer from S. oneidensis MR-1 to photogenerated holes of CdS. The S. oneidensis MR-1/CdS biohybrid alleviated chloramphenicol-induced physiological impairments, which can be attributed to the decreased levels of extracellular polymeric substances, malondialdehyde, and extracellular membrane permeability and the increased levels of superoxide dismutase and catalase activities. The GCN5-related N-acetyltransferase, alkene reductase, and carboxymuconolactone decarboxylase promoted the inactivation and further degradation of chloramphenicol. In summary, this study demonstrated the potential applications of the S. oneidensis MR-1/CdS biohybrid in the remediation of chloramphenicol contamination.

More than a contaminant: How zinc promotes carbonate-mineralizing bacteria metabolism and adaptation by reshaping precipitation conditions

Although microbial-induced carbonate precipitation (MICP) technology is both environmentally friendly and cost-effective, its efficiency is constrained by challenges such as low bacterial activity and heavy metal stress. This study explored the enhancement of mineralization efficiency by incorporating zinc (Zn) into the cultivation system of carbonate-mineralized bacteria. All Zn salts at a concentration of 30 μmol/L significantly enhanced the density and heavy metal resistance of bacterial cells, while also promoting CO2 hydration efficiency. The activities of urease and carbonic anhydrase (CA) were significantly elevated after treatment with 30 μmol/L ZnCl2 and Zn(C3H5O3)2 (ZnL) compared to the control. The results from qRT-PCR and ELISA confirmed that ZnL exhibited a stable biological effect on CA gene expression. Through the analysis of surface chemistry of cells and the subcellular distribution pattern of cadmium (Cd), it was observed that Zn supplementation maintained the cell surface stability and strengthened the cellular barrier against Cd uptake. SEM, FTIR and XRD results further confirmed that Zn supplementation significantly increased the complexity of the mineral morphology, resulting in a more stable crystal structure of CdCO3. This study offers additional theoretical and technical backing, opening a new avenue for the practical application of MICP technology in heavy metal remediation.

Study on Plant-blanket to reduce heavy metal migration caused by precipitation and to improve the soil environment of pyritic tailings

The increasing demand for mineral resources due to industrial development has led to significant tailings pollution during the mineral extraction process. In the southwestern region of China, a large amount of pyritic tailings containing pyrite cinder easily leaches heavy metals and other pollutants when exposed to precipitation, resulting in widespread soil contamination. Effective remediation methods are urgently needed to address this issue. This study utilized naturally occurring Plant-blanket formed by the symbiosis of moss and herbaceous plants on pyritic tailings as restoration material. Through leaching experiments and staining tracer techniques, the study investigated the ability of Plant-blanket to reduce the migration of heavy metals from pyrite cinder to soil under the influence of precipitation and its role in improving the soil environment. The results showed that within 12 h, the Plant-blanket could absorb water equivalent to 206.9 % of its own weight and had good water retention ability. It reduced the stained area ratio of soil horizontal and vertical profiles after precipitation leaching by a maximum of 76.08 % and 46.41 %, respectively, and improved the pH, cation exchange capacity (CEC), bulk density, and water content of soil at different depths. In addition, after being covered by Plant-blanket, the migration of Cd and Cu was reduced by a maximum of 44.35 % and 55.77 % respectively, and it increased the diversity and abundance of bacterial communities, promoting the recovery of soil microbial ecological functions. These findings indicate that Plant-blanket can regulate water and improve soil environment, and has certain control ability on the migration of Cd and Cu produced by pyritic tailings. Meanwhile, Plant-blanket plays an important role in improving the soil environment in mining areas and promoting ecosystem restoration, providing valuable reference for further exploration of ecological restoration of tailings.

Crystalline CdS/Amorphous Cd(OH)2 Composite for Electrochemical CO2 Reduction to CO in a Wide Potential Window

Electrochemical CO2 reduction is a promising method for converting atmospheric CO2 into valuable low-carbon chemicals. In this study, a crystalline cadmium sulfide/amorphous cadmium hydroxide composite was successfully deposited on the carbon paper substrate surface by in-situ chemical bath deposition (named as c-CdS/a-Cd(OH)2/CP electrodes) for the efficient electrochemical CO2 reduction to produce CO. The c-CdS/a-Cd(OH)2/CP electrode exhibited high CO Faradaic efficiencies (>90 %) under a wide potential window of 1.0 V, with the highest value reaching ~100 % at the applied potential ranging from -2.16 V to -2.46 V vs. ferrocene/ferrocenium (Fc/Fc+), superior to the crystalline counterpart c-CdS/CP and c-CdS/c-Cd(OH)2@CP electrodes. Meanwhile, the CO partial current density reached up to 154.7 mA cm-2 at -2.76 V vs. Fc/Fc+ on the c-CdS/a-Cd(OH)2/CP electrode. The excellent performance of this electrode was mainly ascribed to its special three-dimensional structure and the introduction of a-Cd(OH)2. These structures could provide more active sites, accelerate the charge transfer, and enhance adsorption of *COOH intermediates, thereby improving the CO selectivity. Moreover, the electrolytes consisting of 1-butyl-3-methylimidazolium tetrafluoroborate and acetonitrile also enhanced the reaction kinetics of electrochemical CO2 reduction to CO.

Different survival strategies of the phosphate-mineralizing bacterium Enterobacter sp. PMB-5 in response to cadmium stress: Biomineralization, biosorption, and bioaccumulation

The phosphate-mineralizing bacteria (PMBs) has shown great potential as a sustainable solution to support pollution remediation through its induced mineralization capacity. However, few studies have been conducted on the mechanism of cadmium (Cd) tolerance in PMBs. In this study, a PMB strain, Enterobacter sp. PMB-5, screened from Cd-contaminated rhizosphere soil, has high resistance to Cd (540 - 1220 mg/L) and solubilized phosphate (232.08 mg/L). The removal experiments showed that the strain PMB-5 removed 71.69-98.24% and 34.83-76.36% of Cd with and without biomineralization, respectively. The characterization result of SEM, EDS, TEM, XPS and XRD revealed that PMB-5 induced Cd to form amorphous phosphate precipitation through biomineralization and adopted different survival strategies, including biomineralization, bioaccumulation, and biosorption to resistance Cd in the microbial induced phosphate precipitation (MIPP) system and the non-MIPP system, respectively. Moreover, the results of whole genome sequencing and qRT-PCR indicated that phosphorus metabolism genes such as pst, pit, phn, ugp, ppk, etc. and heavy metal tolerance genes (including ion transport, ion efflux, redox, antioxidant stress), such as czcD, zntA, mgtA, mgtC, katE, SOD2, dsbA, cysM, etc. were molecular for the PMB-5 mineralization and Cd tolerance of PMB-5. Together, our findings suggested Enterobacter sp. PMB-5 is a potential target for developing more effective bioinoculants for Cd contamination remediation.

In situ mycoremediation of acid rain and heavy metals co-contaminated soil through microbial inoculation with Pleurotus ostreatus

The combined pollution of acid rain and heavy metals in soil is a pressing environmental problem, especially in the regions with large-scale heavy industrial production activities. Low remediation efficiency and weak long-lasting stability are major challenges when disposing the heavy metals contaminated soil in acid rain polluted sites. Herein, a specific microbe, strain CT13 was isolated and domesticated to exhibit high tolerance to both acid rain and cadmium (Cd). Then, an in situ mycoremediation method by adopting a bioaugmentation technology of strain CT13 inoculation with Pleurotus ostreatus was developed. The remediation performance was investigated in acidic conditions with Cd concentrations in soil ranging from 0 to 15 mg/kg. While most of the bacteria strains (e.g. strain CT6/13) significantly improved the dry weight of mushroom and Cd accumulation in neutral environment, the performance of strain CT6 was remarkably deteriorated in acid rain environment. In contrast, strain CT13 maintained its behavior in acidic conditions, displaying ∼30 % and 150 % enhancements (vs the neutral environment) in the dry weight of mushroom and Cd accumulation, respectively. In addition, inoculation of strain CT13 led to significant reductions in the content of superoxide dismutase, peroxidase and lipid peroxidation in the fruiting body of P. ostreatus, indicating an improvement in the mushroom's tolerance to both acid rain and heavy metals. The synergistic effect of strain CT13 and P. ostreatus realized the significant improvement in soil remediation efficiency and long-lasting stability in acidic conditions, providing valuable insights into the remediation of heavy metal contaminated soil in the regions affected by acid rain.

A comprehensive study on the co-removal of Cr (VI) and ciprofloxacin via microbial-photocatalytic coupling: Mechanistic insights and performance evaluation

The increasing contamination of water systems by antibiotics and heavy metals has become a growing concern. The intimately coupled photocatalysis and biodegradation (ICPB) approach offers a promising strategy for the effective removal of mixed pollutants. Despite some prior research on ICPB applications, the mechanism by which ICPB eliminates mixed pollutants remains unclear. In our current study, the ICPB approach achieved approximately 1.53 times the degradation rate of ciprofloxacin (CIP) and roughly 1.82 times the reduction rate of Cr (VI) compared to photocatalysis. Remarkably, after 30 days, the ICPB achieved a 96.1% CIP removal rate, and a 97.8% reduction in Cr (VI). Our investigation utilized three-dimensional fluorescence analysis and photo-electrochemical characterization to unveil the synergistic effects of photocatalysis and biodegradation in removal of CIP and Cr (VI). Incorporation of B-Bi3O4Cl (B-BOC) photocatalyst facilitated electron-hole separation, leading to production of ·O2-, ·OH, and h+ species which interacted with CIP, while electrons reduced Cr (VI). Subsequently, the photocatalytic products were biodegraded by a protective biofilm. Furthermore, we observed that CIP, acting as an electron donor, promoted the reduction of Cr (VI). The microbial communities revealed that the number of bacteria favoring pollutant removal increased during ICPB operation, leading to a significant enhancement in performance.

Effect of humic substances on nitrogen cycling in soil-plant ecosystems: Advances, issues, and future perspectives

Nitrogen (N) cycle is one of the most significant biogeochemical cycles driven by soil microorganisms on the earth. Exogenous humic substances (HS), which include composted-HS and artificial-HS, as a new soil additive, can improve the water retention capacity, cation exchange capacity and soil nutrient utilization, compensating for the decrease of soil HS content caused by soil overutilization. This paper systematically reviewed the contribution of three different sources of HS in the soil-plant system and explained the mechanisms of N transformation through physiological and biochemical pathways. HS convert the living space and living environment of microorganisms by changing the structure and condition of soil. Generally, HS can fix atmospheric and soil N through biotic and abiotic mechanisms, which improved the availability of N. Besides, HS transform the root structure of plants through physiological and biochemical pathways to promote the absorption of inorganic N by plants. The redox properties of HS participate in soil N transformation by altering the electron gain and loss of microorganisms. Moreover, to alleviate the energy crisis and environmental problems caused by N pollution, we also illustrated the mechanisms reducing soil N2O emissions by HS and the application prospects of artificial-HS. Eventually, a combination of indoor simulation and field test, molecular biology and stable isotope techniques are needed to systematically analyze the potential mechanisms of soil N transformation, representing an important step forward for understanding the relevance between remediation of environmental pollution and improvement of the N utilization in soil-plant system.

Effects of polystyrene microplastics on the agronomic traits and rhizosphere soil microbial community of highland barley

This study investigated the influence of polystyrene microplastics (MPs) with two different particle sizes (<1 mm, 1-5 mm) and three concentrations (1 g/m2, 10 g/m2, 50 g/m2), as well as added degrading bacteria, on the agronomic traits of highland barley and the bacterial communities in the rhizosphere soil. Results revealed that the small particle size treatment had a significant effect on reducing the 1000-grain weight of highland barley, while the large particle size treatment had an effect on reducing the spike length, width, and awn length (P < 0.05). Additionally, the MP treatment was found to significantly reduce the rhizosphere soil bacterial diversity and richness, including the Shannon, Chao1, observed species, and dominance indices (P < 0.05). Interestingly, the inoculation treatment also reduced microbial diversity, though the microbial diversity after treatment was similar to that of the control community structure, indicating its regulating effect on the soil microbial community. The abundance of Domibacillus, Pedosphaeraceae, and Enterococcus decreased due to the MP treatment, whereas Achromobacter, Massilia, Ralstonia, and Nitrosospira increased (P < 0.05). Furthermore, functional prediction indicated that MP treatment resulted in the enrichment of microbial functions, such as an AraC-type DNA-binding domain, etc. The microbial communities exposed to different sizes and concentrations of MPs had their own unique functions in response to the effects of the MPs. This study provided novel insights into the effects of different particle sizes and concentrations of MPs on the rhizosphere microbial community and agronomic traits of highland barley. It could be used to improve the understanding of the impact of MPs on the rhizosphere soil microecology and enhance bioremediation of MPs.

Toxic effects of lead (Pb), cadmium (Cd) and tetracycline (TC) on the growth and development of Triticum aestivum: A meta-analysis

The environmental issue of lead (Pb), cadmium (Cd), and tetracycline (TC) contamination in cereal crops has become a growing concern worldwide. An in-depth understanding of this issue would be of importance to promote effective management strategies for heavy metals and antibiotics worldwide. The present study was conducted to assess the toxic effects of heavy metals (Cd, Pb) and antibiotics (TC) on Triticum aestivum (T. aestivum, common wheat) based on studies conducted in the past 22 years. Data pertaining to the growth and development of T. aestivum were extracted and analyzed from 89 publications spanning from 2000 to 2022. Our results showed that Pb, Cd and TC significantly reduced growth and development by 11 %, 9 %, and 5 %, respectively. Additionally, significant accumulation of Cd (42 %) and Pb (17 %) was observed in T. aestivum samples, although there was little change in TC accumulation, which showed limited absorption, accumulation, and translocation of TC in wheat plants. Pb had the greatest impact on the yield of T. aestivum, followed by Cd, while TC had no apparent effect. Furthermore, exposure to Cd, Pb and TC reduced the photosynthetic rate due to chlorophyll reduction, with Cd having the most pronounced effect (58 %), followed by Pb (37 %) and TC (8 %). Cd exposure also significantly enhanced gaseous exchange (37 %) compared to TC and Pb, which reduced gaseous exchange by 4 % and 10 %, respectively. However, the treatments with TC (>50-100 mgL-1), Pb (>1000-2000 mg L-1) and Cd (>500-1000 mg L-1) increased the defense system of T. aestivum samples by 38 %, 15 %, and 11 %, respectively. The obtained findings have significant implications for risk assessment, pollution prevention, and remediation strategies to address soil contamination from Pb, Cd and TC in farmland.