Co-metabolic degradation of tetrabromobisphenol A by novel strains of Pseudomonas sp. and Streptococcus sp

Fabrication of black phosphorus/CdS heterostructure with enhancement photocatalytic degradation activity for tetrabromobisphenol A and toxicity prediction of intermediates

Black phosphorus nanosheets (BPNs)/CdS heterostructure was successfully synthesized via hydrothermal method. The experimental results indicated that BPNs modified the surface of CdS nanoparticles uniformly. Meanwhile, the BPNs/CdS heterostructure exhibited a distinguished high rate of photocatalytic activity for Tetrabromobisphenol A (TBBPA) degradation under visible light irradiation (λ > 420 nm), the kinetic constant of TBBPA degradation reached 0.0261 min-1 was approximately 5.68 and 9.67 times higher than that of CdS and P25, respectively. Moreover, superoxide radical (•O2-) is the main active component in the degradation process of TBBPA (the relative contribution is 91.57%). The photocatalytic mechanism and intermediates of the TBBPA was clarified, and a suitable model and pathway for the degradation of TBBPA were proposed. The results indicated that the toxicities of some intermediates were higher than the parent pollutant. This research provided an efficient approach by a novel photocatalyst for the removal of TBBPA from wastewater, and the appraisal methods for the latent risks from the intermediates were reported in this paper.

Biological effects of culture medium on Tetraselmis chuii and Dunaliella tertiolecta: Implications for emerging pollutants degradation

In this study, laboratory-scale cultivation of T. chuii and D. tertiolecta was conducted using Conway, F/2, and TMRL media to evaluate their biochemical composition and economic costs. The highest cell density (30.36 × 106 cells/mL) and dry weight (0.65 g/L) for T. chuii were achieved with Conway medium. This medium also produced biomass with maximum lipid content (25.65%), proteins (27.84%), and total carbohydrates (8.45%) compared with F/2 and TMRL media. D. tertiolecta reached a maximum cell density of 17.50 × 106 cells/mL in F/2 medium, which was notably lower than that of T. chuii. Furthermore, the media cost varied from US$0.23 to US$0.74 for each 1 L of media, primarily due to the addition of Na3PO4, KNO3, and cyanocobalamin. Thus, biomass production rates varied between US$38.81 and US$128.80 per kg on a dry weight basis. These findings comprehensively compare laboratory conditions and the costs associated with biomass production in different media. Additionally, this study explored the potential of T. chuii and D. tertiolecta strains, as well as their consortia with bacteria, for the degradation of various emerging pollutants (EPs), including caffeine, salicylic acid, DEET, imidacloprid, MBT, cimetidine, venlafaxine, methylparaben, thiabendazole, and paracetamol. Both microalgal strains demonstrated effective degradation of EPs, with enhanced degradation observed in microalgae-bacterial consortia. These results suggest that the symbiotic relationship between microalgae and bacteria can be harnessed for the bioremediation of EPs, thereby offering valuable insights into the environmental applications of microalgal cultivation.

Biodegradation of emerging organic pollutant gemfibrozil: Mechanism, kinetics and pathway modelling

The increasing population has raised the demand for pharmaceutical and personal care products to maintain a good health. Gemfibrozil (GEM), is extensively used as a lipid regulator and is frequently detected in wastewater treatment systems and poses deleterious health and ecological effects. Hence, the current study employing Bacillus sp. N2 reports the degradation of gemfibrozil via co-metabolism in 15 days. The study reported 86 % degradation with GEM (20 mgL^-1) using sucrose (150 mgL^-1) as a co-substrate; as compared to 42 % without a co-substrate. Further, time-profiling studies of metabolites revealed significant demethylation and decarboxylation reactions during degradation that leads to formation of six (M1, M2, M3, M4, M5, M6) metabolites as by-products. Based on the LC-MS analysis a potential degradation pathway for GEM by Bacillus sp. N2 was proposed. The degradation of GEM has not been reported so far and the study envisages eco-friendly approach to tackle pharmaceutical- active- compounds.

Biodegradation of cefalexin by two bacteria strains from sewage sludge

Bioremediation has been used as an environmentally-friendly, energy-saving and efficient method for removing pollutants. However, there have been very few studies focusing on the specific antibiotic-degrading microorganisms in the activated sludge and their degradation mechanism. Two strains of cefalexin-degrading bacteria (Rhizobium sp. (CLX-2) and Klebsiella sp. (CLX-3)) were isolated from the activated sludge in this study. They were capable of rapidly eliminating over 99% of cefalexin at an initial concentration of 10 mg l^-1 within 12 h. The exponential phase of cefalexin degradation happened a little earlier than that of bacterial growth. The first-order kinetic model could elucidate the biodegradation process of cefalexin. The optimized environmental temperature and pH values for rapid biodegradation by these two strains were found to be 30°C and 6.5-7, respectively. Furthermore, two major biodegradation metabolites of CLX-3, 7-amino-3-cephem-4-carboxylic acid and 2-hydroxy-3-phenyl pyrazine were identified using UHPLC-MS and the biodegradation pathway of cefalexin was proposed. Overall, the results showed that Rhizobium sp. (CLX-2) and Klebsiella sp. (CLX-3) could possibly be useful resources for antibiotic pollution remediation.

Efficient biodegradation of tetrabromobisphenol A by the novel strain Enterobacter sp. T2 with good environmental adaptation: Kinetics, pathways and genomic characteristics

T2, a gram-positive bacterium capable of rapidly degrading tetrabromobisphenol A (TBBPA), and affiliated with the genus Enterobacter, was isolated for the first time from sludge that had been contaminated for several years. The TBBPA degradation data fitted the first-order model well. Under optimal conditions (pH of 7, temperature of 31 °C, TBBPA concentration of 5 mg L^-1, and inoculum size of 5%), 99.4% of the initially added TBBPA was degraded after 48 h. TBBPA degradation fitted the first-order model with the half-life of 3.3 h. These results illustrated that the TBBPA degradation capability of strain T2 was significantly better than that of previously reported bacteria. A total of 17 intermediates were detected, among which five were reported for the first time. Whole-genome sequencing revealed that strain T2 had a chromosome with the total length of 4 854 376 bp and a plasmid with the total length of 21 444 bp. It harbored essential genes responsible for debromination, such as cyp450, gstB, gstA, and HADH, and genes responsible for subsequent complete mineralization, such as bioC, yrrM, Tam, and Ubil. A key protein of haloacid dehalogenases responsible for the biodegradation of TBBPA may also be involved in the regulation of TBBPA degradation in natural environment. In soil bioremediation experiments, strain T2 showed excellent environmental adaptation. It was able to biodegrade TBBPA and its typical intermediate bisphenol A efficiently. Therefore, it could potentially be applied to treat TBBPA-contaminated sites.

A comprehensive review on the use of algal-bacterial systems for wastewater treatment with emphasis on nutrient and micropollutant removal

The scarcity of water resources and environmental pollution have highlighted the need for sustainable wastewater treatment. Existing conventional treatment systems are energy-intensive and not always able to meet stringent disposal standards. Recently, algal-bacterial systems have emerged as environmentally friendly sustainable processes for wastewater treatment and resource recovery. The algal-bacterial systems work on the principle of the symbiotic relationship between algae and bacteria. This paper comprehensively discusses the most recent studies on algal-bacterial systems for wastewater treatment, factors affecting the treatment, and aspects of resource recovery from the biomass. The algal-bacterial interaction includes cell-to-cell communication, substrate exchange, and horizontal gene transfer. The quorum sensing (QS) molecules and their effects on algal-bacterial interactions are briefly discussed. The effect of the factors such as pH, temperature, C/N/P ratio, light intensity, and external aeration on the algal-bacterial systems have been discussed. An overview of the modeling aspects of algal-bacterial systems has been provided. The algal-bacterial systems have the potential for removing micropollutants because of the diverse possible interactions between algae-bacteria. The removal mechanisms of micropollutants - sorption, biodegradation, and photodegradation, have been reviewed. The harvesting methods and resource recovery aspects have been presented. The major challenges associated with algal-bacterial systems for real scale implementation and future perspectives have been discussed. Integrating wastewater treatment with the algal biorefinery concept reduces the overall waste component in a wastewater treatment system by converting the biomass into a useful product, resulting in a sustainable system that contributes to the circular bioeconomy.

Tetrabromobisphenol A (TBBPA) anaerobic biodegradation occurs during acidogenesis

This is the first study to bring evidence on the anaerobic biodegradation of TBBPA occurring during acidogenesis in domestic sewage at environmentally relevant concentrations by complex microbial communities. This was accomplished by continuously operating two anaerobic structured bed reactors (ASTBR) for over 100 days under acidogenic (Acidogenic Reactor, AR) and multistep methanogenic (Methanogenic Reactor, MR) conditions. In the AR, the temporal carbohydrates consumption and the acetic acid production were strongly correlated with TBBPA removal by the Pearson's test. The spatial concentration of TBBPA and carbohydrates along the MR and the kinetic degradation profiles corroborate the AR results. It is hypothesized that TBBPA biodegradation in the studied conditions occurs during acidogenesis via the cometabolism supported by non-specific enzymes and the metabolism (dehalorespiration) established by electrons donors such as H₂, which are both produced during the macrocomponents breakdown in the early stages of the anaerobic digestion. The TBBPA mass balance showed that approximately 86.8 ± 0.05% and 97 ± 0.01% of the removed TBBPA was biodegraded in the AR and MR, respectively. Furthermore, TBBPA biodegradation went further than reductive debromination as total phenols were detected in the reactors' effluent.

Biodegradation and metabolism of tetrabromobisphenol A in microbial fuel cell: Behaviors, dynamic pathway and the molecular ecological mechanism

Tetrabromobisphenol A (TBBPA) has aroused widespread pollution in industrial wastewater. Microbial fuel cell (MFC) was proved powerful in organics degradation and simultaneous resource recovery during wastewater treatment. However, the TBBPA biotransformation potential, pathway and the related molecular mechanism remain poorly understood. In this study, the enhanced degradation and detoxification performance of TBBPA in MFC anode was confirmed, evidenced by the shorter degradation period (2.3 times shorter) and less generation of bisphenol A. UPLC-QTOF-MS analysis verified TBBPA metabolism went through reductive debromination, hydrolytic debromination, oxidative ring cleavage and o-methylation. Accompanied with those biochemical processes, the metabolites underwent dynamic changes. The distinctly decreased abundance and fewer interactions with other functional genera for the potential reductive dehalogenators (Pseudomonas, etc.) possibly led to the suppressed reductive debromination (5.1%) in the closed bioanode. Otherwise, the more abundant potential function bacteria with more collaborated interrelations, including hydrolytic dehalogenators (Acinetobacter, etc.), aromatics degrading bacteria (Geobacter, Holophaga, etc.) and electroactive bacteria (Geobacter, Desulfovibrio, etc.) made great sense to the enhanced hydrolytic debromination and detoxification of TBBPA. This study revealed that MFC anode was beneficial to TBBPA degradation and provided theoretical support for the decomposition and transformation of micro-pollutants in the municipal sewage treatment coupled with MFC process.

Insights into the Occurrence, Fate, and Impacts of Halogenated Flame Retardants in Municipal Wastewater Treatment Plants

Halogenated flame retardants (HFRs) have been extensively used in various consumer products and many are classified as persistent organic pollutants due to their resistance to degradation, bioaccumulation potential and toxicity. HFRs have been widely detected in the municipal wastewater and wastewater treatment solids in wastewater treatment plants (WWTPs), the discharge and agricultural application of which represent a primary source of environmental HFRs contamination. This review seeks to provide a current overview on the occurrence, fate, and impacts of HFRs in WWTPs around the globe. We first summarize studies recording the occurrence of representative HFRs in wastewater and wastewater treatment solids, revealing temporal and geographical trends in HFRs distribution. Then, the efficiency and mechanism of HFRs removal by biosorption, which is known to be the primary process for HFRs removal from wastewater, during biological wastewater treatment processes, are discussed. Transformation of HFRs via abiotic and biotic processes in laboratory tests and full-scale WWTPs is reviewed with particular emphasis on the transformation pathways and functional microorganisms responsible for HFRs biotransformation. Finally, the potential impacts of HFRs on reactor performance (i.e., nitrogen removal and methanogenesis) and microbiome in bioreactors are discussed. This review aims to advance our understanding of the fate and impacts of HFRs in WWTPs and shed light on important questions warranting further investigation.

Characterization of Lactobacillus reuteri WQ-Y1 with the ciprofloxacin degradation ability

OBJECT

As a broad-spectrum fluoroquinolone antibiotic drug, ciprofloxacin (CIP) is frequently used in the treatment of a wide variety of infections. However, the residues of this antibiotic pose a big threat to the aquatic environment and human health. In this research, Lactobacillus reuteri WQ-Y1 with CIP degradation ability was screened and identified.

RESULTS

L. reuteri WQ-Y1 with a degradation rate of 65.1% for 4 µg mL^-1 CIP was screened from 17 lactic acid bacteria (LAB), and cytochrome P450 enzyme was confirmed to promote the degradation of CIP by L. reuteri WQ-Y1. Meanwhile, the CIP degradation rate were also higher in 48 h' culture time when co-cultured with 1 mg/mL of glucose in the culture media. Furthermore, result also proved that fluoroquinolone antibiotics with the similar piperazine ring structures could be degraded by L. reuteri WQ-Y1.

CONCLUSIONS

L. reuteri WQ-Y1 could degrade fluoroquinolone antibiotics with the similar piperazine ring structure. However, future work still needs to be done on the confirmation of the key enzymes in the cytochrome P450 enzymes family in the biodegradation. The isolated ciprofloxacin-degrading strain L. reuteri WQ-Y1 had a CIP degradation rate of 65.1% at 24 hours, and one biodegradation metabolite was identified and proved to be an important metabolite of CIP from cytochrome P450 enzymes family hydrolysis with UPLC-MS/MS spectrograms approach.

Biodegradation of Di (2-Ethylhexyl) Phthalate by a novel Enterobacter spp. Strain YC-IL1 Isolated from Polluted Soil, Mila, Algeria

Di-(2-ethylhexyl) phthalate (DEHP) is one of the phthalic acid ester representatives and is mainly used as a plasticizer to endow polyvinyl chloride plastics with desirable physical properties. It is synthesized in massive amounts worldwide. Many studies have proved the adverse effects of DEHP on human health and wildlife. DEHP is labeled as an endocrine disruptor which causes human reproductive problems. Enterobacter spp. YC-IL1, a novel isolated strain from contaminated soil, was identified by 16S rRNA gene analysis and electronic microscope. It is capable of efficiently degrading DEHP (100%) and a wide range of phthalic acid ester PAEs, particularly those containing side chains with branches, or ring structures such as dutylbenzyl phthalate and dicyclohexyl phthalate, which are hard to degrade, with, respectively, 81.15% and 50.69% degradation after 7 days incubation. YC-IL1 is an acido-tolerant strain which remained in pH values lower than pH 5.0 with the optimum pH 7.0 and temperature 30 °C. The DEHP metabolites were detected using HPLC-QQQ and then the degradation pathway was tentatively proposed. Strain YC-IL1 showed high DEHP degradation rate in artificially contaminated soil with 86% removed in 6 days. These results indicate the application potential of YC-IL1 in bioremediation of PAE-polluted sites, even the acidic ones.

Co-metabolic degradation of tetrabromobisphenol A by Pseudomonas aeruginosa and its auto-poisoning effect caused during degradation process

In this study, Pseudomonas aeruginosa was applied to degrade tetrabromobisphenol A (TBBPA) with glucose as a co-metabolic substrate. Influencing factors of co-metabolic degradation such as pH, TBBPA and glucose concentration were examined and the degradation efficiency under optimal condition reached about 50% on the 7th day. The study also proved that the extracellular action, rather than intracellular one, played a leading role in TBBPA degradation. Five metabolites including debromination and beta-scission products were identified in this study. The extracellular active substance pyocyanin was considered as the origin of H₂O₂ and OH·. The variation of concentrations of H₂O₂ and OH· shared the same trend, they increased in the early days and then declined gradually. On the 1st day, the OD600 of P.aeruginosa in the co-metabolic group was 6.0 times higher than the initial value while total organic carbon (TOC) decreased about 78%, which might lead to the occurrence of pyocyanin auto-poisoning. Flow cytometry was applied to detect the cellular state of P.aeruginosa during degradation. The increasing intracellular ROS showed that cells were suffering from oxidative stress and the change of membrane potential revealed that cellular dysfunction had occurred since the 1st day. This research indicated that the toxic effect on P.aeruginosa was probably not directly correlated with TBBPA, but was caused by pyocyanin auto-poisoning.

Carbamazepine toxicity and its co-metabolic removal by the cyanobacteria Spirulina platensis

Bioremediation of pharmaceutical-contaminated wastewater using microalgae has attracted increasing attention. Cyanobacteria, which are important prokaryotic microalgae, are widely distributed in different water environments, and have the advantages of simple culture and a fast growth rate. However, studies on either the toxicity of pharmaceutical contaminants (PhCs) to cyanobacteria or the removal of PhCs by cyanobacteria are scarce. In this study, carbamazepine (CBZ) and Spirulina platensis were selected as model PhCs and cyanobacteria, respectively. CBZ (>1 mg/L) had toxicity effects on S. platensis, showing maximal growth inhibition (34.0%) at 100 mg/L after 10 days of cultivation. At CBZ < 25 mg/L, S. platensis showed a trend similar to that of eukaryotic microalgae in increasing superoxide dismutase and catalase activities and content of chlorophylls, carotenoids, carbohydrates, and lipids. These results indicated that S. platensis had a similar protective mechanism to CBZ toxicity as that of the eukaryotic microalgae. Increasing CBZ concentration (50-100 mg/L) significantly decreased these biochemical characteristics and photosynthetic activity owing to the serious damage of the structure and function of S. platensis. However, with increasing cultivation time, the growth and photosynthetic activity of S. platensis recovered from the toxicity of CBZ. S. platensis showed a maximum of 30.97 ± 1.30% removal of CBZ (1 mg/L), mainly through biodegradation. Addition of 0.3 mg/L glucose enhanced this removal efficiency to 50.13 ± 2.51% via co-metabolism. These findings indicated that S. platensis can be used for the removal of CBZ or other PhCs from wastewater.

Effective removal of polymer quaternary ammonium salt by biodegradation and a subsequent Fenton oxidation process

In this paper, a process combining biodegradation and Fenton oxidation was proposed for the removal of polydiallyldimethylammonium chloride-acrylic-acrylamide-hydroxyethyl acrylate (PDM) in aqueous phase. Biodegradation of PDM was investigated in activated sludge systems, and the effects of the solution pH, mixed liquid suspended solids (MLSS), salinity, co-substrate, and initial substrate concentration, were studied. The biodegradation process was well-described with the Monod model and the values of the kinetics parameters v_max, k_s were 0.05 h^-1 and 333 mg/L. The optimal biodegradation conditions in the experimental range were determined to be: pH = 7.0, 0%-0.01% (w/v) NaCl, 4000 mg/L of MLSS, and 500 mg/L of glucose as co-substrate. FT-IR analysis indicated that PDM molecules biodegradation partly. The microbial community structures and dehydrogenase activity analysis revealed that PDM showed some toxicity to microorganisms in activated sludge. The effects of several parameters, including the pH and chemical doses, were investigated for removing PDM in Fenton oxidation process. The optimal Fenton oxidation process conditions in the experimental range were pH = 2.0, Fe²⁺ concentration of 40 mg/L, and H₂O₂ dosage of 23 mL/L. PDM was treated by biodegradation and subsequent Fenton oxidation under the optimal operating conditions. The removal efficiency was 44.5% after the biodegradation process and further increased to 85.5% after Fenton oxidation. The combined process was revealed to be a promising solution for achieving effective and economical removal of PDM.

Biodegradation of endocrine disruptor Bisphenol A by Pseudomonas putida strain YC-AE1 isolated from polluted soil, Guangdong, China

Background

Bisphenol A is an important organic chemical as an intermediate, final and inert ingredient in manufacturing of many important products like polycarbonate plastics, epoxy resins, flame retardants, food–drink packaging coating, and other. BPA is an endocrine disruptor compound that mimics the function of estrogen causing damage to reproductive organs. Bacterial degradation has been consider as a cost effective and eco-friendly method for BPA degradation compared with physical and chemical methods. This study aimed to isolate and identify bacterial strain capable to degrade and tolerate high concentrations of this pollutant, studying the factors affecting the degradation process and study the degradation mechanism of this strain.

Results

YC-AE1 is a Gram negative bacterial strain isolated from soil and identified as Pseudomonas putida by 16S rRNA gene sequence and BIOLOG identification system. This strain found to have a high capacity to degrade the endocrine disruptor Bisphenol A (BPA). Response surface methodology using central composite design was used to statistically optimize the environmental factors during BPA degradation and the results obtained by significant model were 7.2, 30 °C and 2.5% for optimum initial pH, temperature and inoculum size, respectively. Prolonged incubation period with low NaCl concentration improve the biodegradation of BPA. Analysis of variance (ANOVA) showed high coefficient of determination, R² and Adj-R² which were 0.9979 and 0.9935, respectively. Substrate analysis found that, strain YC-AE1 could degrade a wide variety of bisphenol A-related pollutants such as bisphenol B, bisphenol F, bisphenol S, Dibutyl phthalate, Diethylhexyl phthalate and Diethyl phthalate in varying proportion. Pseudomonas putida YC-AE1 showed high ability to degrade a wide range of BPA concentrations (0.5–1000 mg l^− 1) with completely degradation for 500 mg l^− 1 within 72 h. Metabolic intermediates detected in this study by HPLC-MS were identified as 4,4-dihydroxy-alpha-methylstilbene, p-hydroxybenzaldeyde, p-hydroxyacetophenone, 4-hydroxyphenylacetate, 4-hydroxyphenacyl alcohol, 2,2-bis(4-hydroxyphenyl)-1-propanol, 1,2-bis(4-hydroxyphenyl)-2-propanol and 2,2-bis(4-hydroxyphenyl) propanoate.

Conclusions

This study reports Pseudomonas putida YC-AE1 as BPA biodegrader with high performance in degradation and tolerance to high BPA concentration. It exhibited strong degradation capacity and prominent adaptability towards a wide range of environmental conditions. Moreover, it degrades BPA in a short time via two different degradation pathways.

Purification, molecular characterization and metabolic mechanism of an aerobic tetrabromobisphenol A dehalogenase, a key enzyme of halorespiration in Ochrobactrum sp. T

Due to the detoxification of tetrabromobisphenol A (TBBPA) varies from different bacterial strains and depends on their specific enzymatic machinery, it is necessary to understand them for potential in situ bioremediation application. The special ability of our previously isolated Ochrobactrum sp. T to simultaneously debrominate and aerobic mineralize TBBPA urgent us to continuously study its degradation molecular mechanism. Herein, the purification and characterization of the dehalogenase which can debrominate TBBPA was investigated based on its corresponding encoding gene tbbpaA. Results showed that an enzyme with molecular mass of 117 kDa, K_m of 26.6 μM and V_max of 0.133 μM min^-1 mg^-1 was purified and designated as bromophenol dehalogenase. It was the only detected dehalogenase which exhibited TBBPA degradation ability (78%). Moreover, its activity was significantly enhanced by adding NADPH or methyl viologen to the reaction solution. The high similarity of substrate spectrum between the dehalogenase from the recombinant strain and the wild strain further indicated that it was the main dehalogenase responsible for the debromination in wild strain. Based on three identified metabolites, a metabolic pathway of TBBPA by purified enzyme under oxic condition was proposed. This study provides an excellent dehalogenase candidate for mechanistic study of aerobic dehalogenation of brominated aromatic compound.

The stimulatory effect of humic acid on the co-metabolic biodegradation of tetrabromobisphenol A in bioelectrochemical system

In this paper, the typical organic component of humic acid (HA) was studied to explore its effect on the co-metabolic biodegradation of Tetrabromobisphenol A (TBBPA) in bioelectrochemical systems (BES). The degradation efficiency, intermediate metabolites and microbial diversity were investigated to demonstrate the impact of HA on the biodegradation of TBBPA in BES-HA-T (Bioelectrochemical system with TBBPA as substrate and HA as a stimulating factor). The highest biodegradation rate (93.2%) for TBBPA were obtained, which illustrated that HA played a positive role in the biodegradation of TBBPA. According to the analysis of the intermediate metabolites, it can be concluded that HA has changed the biodegradation pathway of TBBPA. The analysis of microbial diversity showed that the interaction of microorganisms had great effects on the anaerobic biodegradation of TBBPA, especially Trichococcus and Anaerolineaceae. Meanwhile, the abundance of Desulfobulbus in the BES-HA (Bioelectrochemical system with HA as a stimulating factor) had a positive effect on the improvement of electrochemical system performance.

Acetate promotes microbial reductive debromination of tetrabromobisphenol A during the startup phase of anaerobic wastewater sludge bioreactors

The detection of increasing concentrations of tetrabromobisphenol A (TBBPA) in wastewater treatment plants is raising concerns as TBBPA has been identified as a potentially toxic flame retardant. The objectives of this study were to evaluate the effect of acetate biostimulation on TBBPA microbial reductive debromination, and the response of anaerobic sludge associated microbial communities repeatedly exposed to TBBPA. Results indicate that the bulk of the microbial community did not experience significant shifts as a result of TBBPA exposure, and that only a small fraction of the community responded to the presence of TBBPA. Taxa most likely responsible for TBBPA transformation affiliated to Clostridiales and the wastewater sludge group Blvii28. The biostimulating effect of acetate was only observed during reactor startup, when acetogenesis was likely not yet occurring. However, when acetate likely started to be microbially generated in the reactor, acetate addition resulted in a slight but significant inhibiting effect on TBBPA transformation. A significant increase of hydrogenotrophic methanogens in the TBBPA-spiked reactor overtime implies that TBBPA degraders were not in direct competition with methanogens for H₂. These results strongly suggest that TBBPA degrading taxa might have been primarily using acetate as an electron donor for the reductive debromination of TBBPA.

Debromination of Hexabromocyclododecane by Anaerobic Consortium and Characterization of Functional Bacteria

A microbial consortium which can efficiently remove hexabromocyclododecane (HBCD) under anaerobic condition have been successfully enriched over 300 days. Under the optimal conditions, the degradation efficiency was 92.4% removal after treatment of 12 days with original addition of 500 μg/L HBCD, yielding 321.7 μg/L bromide in total as well. A typical debromination product, dibromocyclododecadiene (DBCD), was detected during the degradation process. The debromination profiles of three main HBCD diastereomers fitted well with first-order model (R²: 0.96–0.99), with the rate constants ranging from 1.3 × 10^-1 to 1.9 × 10^-1. The microbial community analysis by high throughput sequencing showed that the composition of the microbial communities varied dynamically with time and the population of functional bacteria increase sharply after enrichment. The population of Bacteroidetes increased from 5 to 47%. And some bacteria which are relatively minority in population at the beginning, such as Azospira oryzae (OTU2), Microbacterium (OTU13), and Achromobacter insolitus (OTU39) increased more than 22 times after enrichment (from 0.5 to 13%, 12%, and 11%, respectively). However, no reported dehalogenating bacteria were found after enrichment. And the contribution for debromination may come from new dehalogenating bacteria. All in all, the present study provided in-depth information on anaerobic microbial communities for HBCD removal by debromination.

Co-metabolic degradation of iomeprol by a Pseudomonas sp. and its application in biological aerated filter systems

The non-ionic water-soluble X-ray contrast agent iomeprol (IOM) enters the water supply through sewage treatment plants, which can cause considerable environmental harm. In this study, Pseudomonas sp. I-24 (I-24) was tested for its ability to remove IOM from water via co-metabolic pathways. The optimum removal rate of IOM by I-24 was 38.43% ± 3.70% when starch served as the source of external carbon, and its co-metabolism of IOM conformed to the first-order kinetics. The highest activity of intracellular enzyme (degrading enzyme) extracted from I-24 was 0.143 ± 0.005 mU in starch condition. The Michaelis constant of the degrading enzyme was found to be 91.08 μmol L^-1. However, glucose and maltose showed the best promotive effects on the growth and electron transport activity of I-24, indicating that overgrowth may result in competitive inhibition and a reduced degradation rate of IOM. Adding I-24 and degrading enzymes to biological aerated filters increased IOM removal rates without affecting COD_Mn removal.

Study of ciprofloxacin biodegradation by a Thermus sp. isolated from pharmaceutical sludge

Ciprofloxacin (CIP) is an antibiotic drug frequently detected in manure compost and is difficult to decompose at high temperatures, resulting in a potential threat to the environment. Microbial degradation is an effective and environmentally friendly method to degrade CIP. In this study, a thermophilic bacterium that can degrade CIP was isolated from sludge sampled from an antibiotics pharmaceutical factory. This strain is closely related to Thermus thermophilus based on 16S rRNA gene sequence analysis and is designated C419. The optimal temperature and pH values for CIP degradation are 70°C and 6.5, respectively, and an appropriate sodium acetate concentration promotes CIP degradation. Seven major biodegradation metabolites were identified by an ultra-performance liquid chromatography tandem mass spectrometry analysis. In addition, strain C419 degraded other fluoroquinolones, including ofloxacin, norfloxacin and enrofloxacin. The supernatant from the C419 culture grown in fluoroquinolone-containing media showed attenuated antibacterial activity. These results indicate that strain C419 might be a new auxiliary bacterial resource for the biodegradation of fluoroquinolone residue in thermal environments.

Synthesis of silver phosphate/graphene oxide composite and its enhanced visible light photocatalytic mechanism and degradation pathways of tetrabromobisphenol A

In the present study, silver phosphate/graphene oxide (Ag₃PO₄/GO) composite was synthesized by ultrasound-precipitation processes. Afterwards, physicochemical properties of the resulting samples were studied through scanning electron microscope, transmission electron microscope, X-ray diffraction, N₂ adsorption/desorption, UV-vis diffuse reflectance spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, surface photovoltage spectroscopy and photoelectrochemical measurements. Results indicated that spherical Ag₃PO₄ displayed an average diameter of 150 nm and body-centered cubic crystal phase, which was integrated with GO. In addition, the visible light absorbance, charge separation efficiency and lifetime of Ag₃PO₄ were significantly improved by integration with GO. In addition, Ag₃PO₄/GO composite was applied to decompose tetrabromosphenol A (TBBPA) in water body. It was found that TBBPA could be completely decomposed within 60 min illumination. Furthermore, several scavenger experiments were conducted to distinguish the contribution of reactive species to the photoctalytic efficiency. Moreover, the enhanced visible light mechanism of Ag₃PO₄/GO was proposed and discussed. Eventually, several PC decomposition pathways of TBBPA were identified including directly debromination and oxidation, and subsequently further oxidation and hydroxylation processes.

Biochar and activated carbon act as promising amendments for promoting the microbial debromination of tetrabromobisphenol A

The increasing occurrence of tetrabromobisphenol A (TBBPA) in the environment is raising questions about its potential environmental health impacts as it has been shown to cause various deleterious effects in humans. The fact that the highest concentrations of TBBPA have been reported in wastewater sludge is concerning as effluent discharge and biosolids land application are likely a route by which TBBPA can be further disbursed to the environment. Our objectives in this study were to evaluate the effect of biochar (BC) and activated carbon (AC) in promoting the biodegradation of TBBPA, and characterize the response of anaerobic sludge microbial communities following amendments. Both carbonaceous amendments were found to promote the reductive debromination of TBBPA. Nearly complete transformation of TBBPA to BPA was observed in the amended reactors ∼20 days earlier than in the control reactors. In particular, the transformation of diBBPA to monoBBPA, which appears to be the rate-limiting step, was accelerated in the presence of either amendment. Overall, microbial taxa responding to the amendments, i.e., 'sensitive responders', represented a small proportion of the community (i.e., 7.2%), and responded positively. However, although both amendments had a similar effect on TBBPA degradation, the taxonomic profile of the sensitive responders differed greatly from one amendment to the other. BC had a taxonomically broader and slightly more pronounced effect than AC. This work suggests that BC and AC show great potential to promote the biodegradation of TBBPA in anaerobic sludge, and their integration into wastewater treatment processes may be helpful for removing TBBPA and possibly other emerging hydrophobic contaminants.

Ciprofloxacin toxicity and its co-metabolic removal by a freshwater microalga Chlamydomonas mexicana

This study evaluated the toxicity and cellular stresses of ciprofloxacin (CIP) and its co-metabolic removal in a freshwater microalga Chlamydomonas mexicana. The toxicological effects of CIP on C. mexicana were assessed by studying the growth and biochemical characteristics of the microalga including total chlorophyll, carotenoid content, malondialdehyde (MDA) and superoxide dismutase (SOD) activity. The calculated effective concentration (EC₅₀) of CIP on C. mexicana was 65±4mgL^-1 at 96h. The growth of C. mexicana was significantly inhibited at increased concentrations of CIP, showing 36±1, 75±3. and 88±3% inhibition at 40, 60 and 100mgL^-1 CIP, respectively, compared to the control after 11days of cultivation. The total chlorophyll, carotenoid, MDA and SOD activity were significantly increased as a result of relatively high concentrations of CIP stress. C. mexicana showed 13±1% removal of CIP (2mgL^-1) after 11days of cultivation; however, the addition of an electron donor (sodium acetate, 4gL^-1) highly enhanced the removal of CIP (2mgL^-1) by>3-fold after 11days. Kinetic studies showed that removal of CIP followed a first-order model (R² 0.94-0.97) with the apparent rate constants (k) ranging from 0.0121 to 0.079 d^-1.

Anaerobic co-metabolic biodegradation of tetrabromobisphenol A using a bioelectrochemical system

Tetrabromobisphenol A(TBBPA), a pollutant in industrial wastewaters, needs to be removed due to its high toxicity and persistence. The main biodegradation pathway for TBBPA has been studied, and bisphenol A(BPA), which is toxic to the environment, is recognized as the general terminal product. In this study, we explored a new approach for the anaerobic biodegradation of TBBPA in a bioelectrochemical system (BES) through co-metabolic degradation of TBBPA with glucose. The half-life of TBBPA was significantly reduced to 13.5h^-1 at 25μg/l of TBBPA. With an increase in the concentration of TBBPA, the removal rates of TBBPA rose to more than eighty percent. Based on the analysis of the products, we found that the degradation products of TBBPA were 2,6-dibromo-4-(1-methyl-1-phenylethyl) phenol, (double-benzenes product) and 2,6-dibromo-4-(prop-1-en-2-yl) phenol (single-benzene product), rather than BPA. Simultaneously, we proposed two degradation pathways for TBBPA in a BES system. According to the microbial diversity analysis of the anode biofilm, we speculated that the microorganism responsible for the biodegradation of TBBPA was Azoarcus. Additionally, we briefly analyzed the effect of TBBPA on the performance of BES system to pave the way for the further analysis of the interaction between the TBBPA and the BES system.

Salinity and nutrient contents of tidal water affects soil respiration and carbon sequestration of high and low tidal flats of Jiuduansha wetlands in different ways

Soils were collected from low tidal flats and high tidal flats of Shang shoal located upstream and Xia shoal located downstream with different tidal water qualities, in the Jiuduansha wetland of the Yangtze River estuary. Soil respiration (SR) in situ and soil abiotic and microbial characteristics were studied to clarify the respective differences in the effects of tidal water salinity and nutrient levels on SR and soil carbon sequestration in low and high tidal flats. In low tidal flats, higher total nitrogen (TN) and lower salinity in the tidal water of Shang shoal resulted in higher TN and lower salinity in its soils compared with Xia shoal. These would benefit β-Proteobacteria and Anaerolineae in Shang shoal soil, which might have higher heterotrophic microbial activities and thus soil microbial respiration and SR. In low tidal flats, where soil moisture was high and the major carbon input was active organic carbon from tidal water, increasing TN was a more important factor than salinity and obviously enhanced soil microbial heterotrophic activities, soil microbial respiration and SR. While, in high tidal flats, higher salinity in Xia shoal due to higher salinity in tidal water compared with Shang shoal benefited γ-Proteobacteria which might enhance autotrophic microbial activity, and was detrimental to β-Proteobacteria in Xia shoal soil. These might have led to lower soil microbial respiration and thus SR in Xia shoal compared with Shang shoal. In high tidal flats, where soil moisture was relatively lower and the major carbon input was plant biomass that was difficult to degrade, soil salinity was the major factor restraining microbial activities, soil microbial respiration and SR.

Characterization and Adaptation of Anaerobic Sludge Microbial Communities Exposed to Tetrabromobisphenol A

The increasing occurrence of tetrabromobisphenol A (TBBPA) in the environment is raising questions about its potential ecological and human health impacts. TBBPA is microbially transformed under anaerobic conditions to bisphenol A (BPA). However, little is known about which taxa degrade TBBPA and the adaptation of microbial communities exposed to TBBPA. The objectives of this study were to characterize the effect of TBBPA on microbial community structure during the start-up phase of a bench-scale anaerobic sludge reactor, and identify taxa that may be associated with TBBPA degradation. TBBPA degradation was monitored using LC/MS-MS, and the microbial community was characterized using Ion Torrent sequencing and qPCR. TBBPA was nearly completely transformed to BPA via reductive debromination in 55 days. Anaerobic reactor performance was not negatively affected by the presence of TBBPA and the bulk of the microbial community did not experience significant shifts. Several taxa showed a positive response to TBBPA, suggesting they may be associated with TBBPA degradation. Some of these taxa had been previously identified as dehalogenating bacteria including Dehalococcoides, Desulfovibrio, Propionibacterium, and Methylosinus species, but most had not previously been identified as having dehalogenating capacities. This study is the first to provide in-depth information on the microbial dynamics of anaerobic microbial communities exposed to TBBPA.

Novel Biochar-Plant Tandem Approach for Remediating Hexachlorobenzene Contaminated Soils: Proof-of-Concept and New Insight into the Rhizosphere

Volatilization of semi/volatile persistent organic pollutants (POPs) from soils is a major source of global POPs emission. This proof-of-concept study investigated a novel biochar-plant tandem approach to effectively immobilize and then degrade POPs in soils using hexachlorobenzene (HCB) as a model POP and ryegrass (Lolium perenne L.) as a model plant growing in soils amended with wheat straw biochar. HCB dissipation was significantly enhanced in the rhizosphere and near rhizosphere soils, with the greatest dissipation in the 2 mm near rhizosphere. This enhanced HCB dissipation likely resulted from (i) increased bioavailability of immobilized HCB and (ii) enhanced microbial activities, both of which were induced by ryegrass root exudates. As a major component of ryegrass root exudates, oxalic acid suppressed HCB sorption to biochar and stimulated HCB desorption from biochar and biochar-amended soils, thus increasing the bioavailability of HCB. High-throughput sequencing results revealed that the 2 mm near rhizosphere soil showed the lowest bacterial diversity due to the increased abundance of some genera (e.g., Azohydromonas, Pseudomonas, Fluviicola, and Sporocytophaga). These bacteria were likely responsible for the enhanced degradation of HCB as their abundance was exponentially correlated with HCB dissipation. The results from this study suggest that the biochar-plant tandem approach could be an effective strategy for remediating soils contaminated with semi/volatile organic contaminants.

The potential of using low cost naturally available biogenic substrates for biological removal of chlorophenol

This study details the application of naturally available biogenic substrates (NABS) in microbial degradation of 2-chlorophenol (CP). Jatropha deoiled cakes (JDC) and Karanja deoiled cakes (KDC) are used as NABS. The potential of NABS is compared with standard biogenic substrate, glucose. The study was carried out with both acclimatized mixed culture and pure culture, Pseudomonas putida. Microbial activity of the culture was monitored by measuring reduction in chlorophenol concentration, COD, toxicity and Cl(-) ions evolution. The study was carried out for a total of 42days. It was observed that culture having NABS has shown similar chlorophenol reduction but higher COD and toxicity reduction. Amongst NABS, Jatropha deoiled cake (JDC) has shown superior results of 71% COD reduction compared to glucose and KDC. This study is one of the first kind illustrating the potential of these substrates in removing toxic chemicals from wastewaters.

Biotransformations of bisphenols mediated by a novel Arthrobacter sp. strain YC-RL1

Arthrobacter sp. strain YC-RL1, capable of utilizing bisphenol A (BPA) as sole carbon source for growth, was isolated from petroleum contaminated soil. YC-RL1 could rapidly degrade BPA in a wide range of pH (5.0-9.0) and temperature (20-40 °C). Substrate analysis found that YC-RL1 could also degrade bisphenol F (BPF) and tetrabromobisphenol A (TBBPA). The maximum and minimum concentrations of BPA (0.2-600 mg/L), BPF (0.2-600 mg/L), and TBBPA (0.2-300 mg/L) for efficient biodegradation were detected. The released bromide ion and metabolic intermediates of BPF and BPA/TBBPA were detected, as well as the degradation pathways for BPF and BPA/TBBPA were deduced tentatively. The present study provides important information for the investigation of BPs degrading mechanism and the application of microbial remediation in BP-contaminated environment. This study is the first report about a genus Arthrobacter bacterium which could simultaneously degrade BPA, BPF, and TBBPA.

Study of novel pure culture HBCD-1, effectively degrading Hexabromocyclododecane, isolated from an anaerobic reactor

In this study, two pure strains, named HBCD-1 and HBCD-2, were isolated from a continuous anaerobic reactor over 300-days acclimation, which processed high capability of biodegrading Hexabromocyclododecane. Both of the two strains degraded HBCD diastereomers in different extents, especially strain HBCD-1, which interestingly degraded α-HBCD effectively. All of the degrading results were well fitted with the first-order kinetics model. By morphological observation and 16S rRNA gene sequence analysis, the strain HBCD-1 showed highest similarity with Achromobacter sp. Under the optimal culturing conditions of 30°C, pH 7 and the initial HBCD concentration of 500μg/L, the biodegradation rate of HBCD-1 reached 90% after 8days treatment. Moreover, during the biodegradation process by HBCD-1 strain, the concentration of bromide ion was lower than the theoretical value. Finally, 4 metabolites were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS), as well as a biodegradation pathway was proposed.