Anaerobic degradation of 2,4-dichlorophenoxyacetic acid by Thauera sp. DKT

Niche-specification of aerobic 2,4-dichlorophenoxyacetic acid biodegradation by tfd-carrying bacteria in the rice paddy ecosystem

This study aimed for a better understanding of the niche specification of bacteria carrying the tfd-genes for aerobic 2,4-dichlorphenoxyacetic acid (2,4-D) degradation in the rice paddy ecosystem. To achieve this, a dedicated microcosm experiment was set up to mimic the rice paddy system, with and without 2,4-D addition, allowing spatial sampling of the different rice paddy compartments and niches, i.e., the main anaerobic bulk soil and the aerobic surface water, surface soil, root surface and rhizosphere compartments. No effect of 2,4-D on the growth and morphology of the rice plant was noted. 2,4-D removal was faster in the upper soil layers compared to the deeper layers and was more rapid after the second 2,4-D addition compared to the first. Moreover, higher relative abundances of the 2,4-D catabolic gene tfdA and of the mobile genetic elements IncP-1 and IS1071 reported to carry the tfd-genes, were observed in surface water and surface soil when 2,4-D was added. tfdA was also detected in the root surface and rhizosphere compartment but without response to 2,4-D addition. While analysis of the bacterial community composition using high-throughput 16S rRNA gene amplicon sequencing did not reveal expected tfd-carrying taxa, subtle community changes linked with 2,4-D treatment and the presence of the plant were observed. These findings suggest (i) that the surface soil and surface water are the primary and most favorable compartements/niches for tfd-mediated aerobic 2,4-D biodegradation and (ii) that the community structure in the 2,4-D treated rice paddy ecosystem is determined by a niche-dependent complex interplay between the effects of the plant and of 2,4-D.

Bioaugmentation has temporary effect on anaerobic pesticide biodegradation in simulated groundwater systems

Groundwater is the most important source for drinking water in The Netherlands. Groundwater quality is threatened by the presence of pesticides, and biodegradation is a natural process that can contribute to pesticide removal. Groundwater conditions are oligotrophic and thus biodegradation can be limited by the presence and development of microbial communities capable of biodegrading pesticides. For that reason, bioremediation technologies such as bioaugmentation (BA) can help to enhance pesticide biodegradation. We studied the effect of BA using enriched mixed inocula in two column bioreactors that simulate groundwater systems at naturally occurring redox conditions (iron and sulfate-reducing conditions). Columns were operated for around 800 days, and two BA inoculations (BA1 and BA2) were conducted in each column. Inocula were enriched from different wastewater treatment plants (WWTPs) under different redox-conditions. We observed a temporary effect of BA1, reaching 100% removal efficiency of the pesticide 2,4-D after 100 days in both columns. In the iron-reducing column, 2,4-D removal was in general higher than under sulfate-reducing conditions demonstrating the influence of redox conditions on overall biodegradation. We observed a temporary shift in microbial communities after BA1 that is relatable to the increase in 2,4-D removal efficiency. After BA2 under sulfate-reducing conditions, 2,4-D removal efficiency decreased, but no change in the column microbial communities was observed. The present study demonstrates that BA with a mixed inoculum can be a valuable technique for improving biodegradation in anoxic groundwater systems at different redox-conditions.

Microbiology and Biochemistry of Pesticides Biodegradation

Pesticides are chemicals used in agriculture, forestry, and, to some extent, public health. As effective as they can be, due to the limited biodegradability and toxicity of some of them, they can also have negative environmental and health impacts. Pesticide biodegradation is important because it can help mitigate the negative effects of pesticides. Many types of microorganisms, including bacteria, fungi, and algae, can degrade pesticides; microorganisms are able to bioremediate pesticides using diverse metabolic pathways where enzymatic degradation plays a crucial role in achieving chemical transformation of the pesticides. The growing concern about the environmental and health impacts of pesticides is pushing the industry of these products to develop more sustainable alternatives, such as high biodegradable chemicals. The degradative properties of microorganisms could be fully exploited using the advances in genetic engineering and biotechnology, paving the way for more effective bioremediation strategies, new technologies, and novel applications. The purpose of the current review is to discuss the microorganisms that have demonstrated their capacity to degrade pesticides and those categorized by the World Health Organization as important for the impact they may have on human health. A comprehensive list of microorganisms is presented, and some metabolic pathways and enzymes for pesticide degradation and the genetics behind this process are discussed. Due to the high number of microorganisms known to be capable of degrading pesticides and the low number of metabolic pathways that are fully described for this purpose, more research must be conducted in this field, and more enzymes and genes are yet to be discovered with the possibility of finding more efficient metabolic pathways for pesticide biodegradation.

Residual chlorine persistently changes antibiotic resistance gene composition and increases the risk of antibiotic resistance in sewer systems

During the COVID-19 pandemic, excessive amounts of disinfectants and their transformation products entered sewer systems worldwide, which was an extremely rare occurrence before. The stress of residual chlorine and disinfection by-products is not only likely to promote the spread of antibiotic resistance genes (ARGs), but also leads to the enrichment of chlorine-resistant bacteria that may also be resistant to antibiotics. Therefore, the potential impact of such discharge on ARG composition should be studied and the health risks should be assessed. Thus, this study combined high-throughput 16S rRNA gene amplicon sequencing and metagenomic analysis with long-term batch tests that involved two stages of stress and recovery to comprehensively evaluate the impact of residual chlorine on the microbial community and ARG compositions in sewer systems. The tests demonstrated that the disturbance of the microbial community structure by residual chlorine was reversible, but the change in ARG composition was persistent. This study found that vertical propagation and horizontal gene transfer jointly drove ARG composition succession in the biofilm, while the driving force was mainly horizontal gene transfer in the sediment. In this process, the biocide resistance gene (BRG) subtype chtR played an important role in promoting co-selection with ARGs through plasmids and integrative and conjugative elements. Moreover, it was further shown that the addition of sodium hypochlorite increased the risk of ARGs to human health, even after discontinuation of dosing, signifying that the impact was persistent. In general, this study strengthens the co-selection theory of ARGs and BRGs, and calls for improved disinfection strategies and more environmentally friendly disinfectants.

Complete biodegradation of the oldest organic herbicide 2,4-Dichlorophenoxyacetic acid by engineering Escherichia coli

After nearly 80 years of extensive application, the oldest organic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has caused many problems of environmental pollution and ecological deterioration. Bioremediation is an ideal method for pollutant treatment. However, difficult screening and preparation of efficient degradation bacteria have largely hindered its application in 2,4-D remediation. We have created a novel engineering Escherichia coli with a reconstructed complete degradation pathway of 2,4-D to solve the problem of screening highly efficient degradation bacteria in this study. The results of fluorescence quantitative PCR demonstrated that all nine genes in the degradation pathway were successfully expressed in the engineered strain. The engineered strains can quickly and completely degrade 0.5 mM 2, 4-D within 6 h. Inspiring, the engineered strains grew with 2,4-D as the sole carbon source. By using the isotope tracing method, the metabolites of 2,4-D were found incorporated into the tricarboxylic acid cycle in the engineering strain. Scanning electron microscopy showed that 2,4-D had less damage on the engineered bacteria than the wild-type strain. Engineered strain can also rapidly and completely remedy 2,4-D pollution in natural water and soil. Assembling the metabolic pathways of pollutants through synthetic biology was an effective method to create pollutant-degrading bacteria for bioremediation.

Anaerobic degradation of thiobencarb by mixed culture of isolated bacteria

Thiobencarb is a highly effective thiocarbamate herbicide frequently used in rice fields globally. In this study, three bacterial strains (Dechloromonas sp. Th1, Thauera sp. Th2, and Azoarcus sp. Th3) isolated from immobilized biomass were analyzed for thiobencarb degradation under anaerobic conditions, with nitrate serving as an electron acceptor. The experimental results showed that thiobencarb was transformed by Dechloromonas sp. Th1 and Thauera sp. Th2 to produce high concentrations of metabolites in a mineral medium. Dechloromonas sp. Th1 dechlorinated the herbicide to benzyl mercaptan, which was then degraded by Thauera sp. Th2 and Azoarcus sp. Th3. Azoarcus sp. Th3 effectively degraded intermediates, i.e. 4-chlorobenzyl alcohol, 4-chlorobenzoic acid, and benzoic acid, produced from the degradation by Dechloromonas sp. Th1 and Thauera sp. Th2. The cross-feeding, nutrient sharing, and cooperation of all isolates in the degradation process decreased the concentrations of intermediate products. The determination of the degradation kinetics showed that the utilization in the exponential phase of the mixed bacteria was consistent with the Michaelis-Menten model, with a maximum degradation rate of 1.56 ± 0.16 µM day-1. This study showed the degradation mechanisms in bacteria and the synergistic process in the degradation of thiobencarb and its metabolites.

Different acesulfame potassium fate and antibiotic resistance propagation pattern in nitrifying and denitrifying sludge systems

Acesulfame potassium (ACE-K) is a widely utilized sugar substitute with increasing demand, which is frequently detected in various environmental matrix due to recalcitrance. However, a general consensus on the contribution of nitrifying and denitrifying process to ACE-K removal is lacking. Therefore, ACE-K removal, its effects on antibiotic resistant genes (ARGs) propagation and microbial community in nitrifying sequencing batch reactor (N-SBR) and denitrifying sequencing batch reactor (D-SBR) inoculated with the identical activated sludge were investigated. In this study, ACE-K can be eliminated in N-SBR with satisfying removal efficiency (96.76 ± 8.33 %) after 13 d acclimation, while it remained persistent (average ACE-K removal efficiency of 2.24 ± 1.86 %) in D-SBR during 84 d exposure. Moreover, ACE-K hardly affected the performances of these two types of reactors and had little impact on nitrifying and denitrifying functional genes. However, initial contact with ACE-K would increase ARGs abundance, network analysis showed functional bacteria in each reactor were possible ARGs hosts. Potential ACE-K degrading genera Chelatococcus, Bosea and Aquamicrobium were found in both reactors. LefSe analysis showed that Phyllobacteriaceae containing Aquamicrobium genus was a differentially enriched family in N-SBR. This research might provide a perspective for better understanding factor affecting ACE-K fate in wastewater treatment process and its ecological risks.

Magnetic activated charcoal/Fe2O3 nanocomposite for the adsorptive removal of 2,4-Dichlorophenoxyacetic acid (2,4-D) from aqueous solutions: Synthesis, characterization, optimization, kinetic and isotherm studies

Magnetic activated charcoal/Fe₂O₃ nanocomposite (AC/Fe₂O₃NC) was fabricated using Spondias dulcis leaf extract by a facile method and used for the adsorptive removal of 2,4-Dichlorophenoxyacetic acid (2,4-D) from aqueous solutions for the first time. The nanocomposite was characterized by methods such as FE-SEM, EDS, XRD, FTIR, TGA, VSM, and BET to identify and confirm the surface morphology, elemental composition, crystalline nature, functional groups, thermal stability, magnetic behavior, and surface area respectively. Box-Behnken Design (BBD) - an optimization method, which belongs to the Response surface methodology (RSM) and a modeling tool - Artificial Neural Network (ANN) were employed to design, optimize and predict the relationship between the input parameters (pH, initial concentration of 2,4-D, time and agitation speed) versus the output parameter (adsorption efficiency of 2,4-D). Adsorption efficiency of 98.12% was obtained at optimum conditions (pH: 2.05, initial concentration: 32 ppm, contact time: 100 min, agitation speed: 130 rpm, temperature: 30 °C, and dosage: 0.2 g/L). The predictive ability of the ANN was superior (R² = 0.99) than the quadratic model, given by the RSM (R² = 0.93). The equilibrium data were best-fitted to Langmuir isotherm (R² = 0.9944) and the kinetics obeyed pseudo-second-order model (R² = 0.9993) satisfactorily. Thermodynamic studies revealed the spontaneity and exothermic nature of adsorption. The maximum adsorption capacity, q_m was found to be 255.10 mg/g, substantially larger than the reported values for 2,4-D adsorption by other magnetic nanoadsorbents. Therefore, this nanoadsorbent may be utilized as an excellent alternative for the elimination of 2,4-D from the waterbodies.

Microbial community response of the full-scale MBR system for mixed leachates treatment

In practice, mature landfill leachate and incineration (young) leachate are mixed to improve the biodegradability and enhance biological treatment performance. However, the ratio of mature-to-young leachates greatly influences MBR treatment efficiency and microbial community structure. This study investigated the treatment efficiency and microbial community structure of full-scale MBR systems operated under two mix ratios, mature leachate: young leachate = 7:3 (v/v, denoted as LL) and 3:7 (v/v, denoted as IL). LL group showed lower Cl- and COD concentrations but a higher aromatic organic content comparing to IL group, and the COD and UV254 removals for LL were significantly lower than those for IL by MBR treatment. Microbial community structures were similar in both groups at phylum level, with dominant phyla being Proteobacteria (23.8%-32.3%), Bacteroidetes (15.25%-20.7%), Chloroflexi (10.5%-23.1%), and Patescibacteria (9.9%-13.2%). However, the richness and diversity of LL group were lower, and differences were observed at lower taxonomy levels. Results indicated that salinity mainly changed the structure of microbial community, resulting in greater abundance of salt-tolerant microbials, while refractory organics affected microbial community structure, and also led to decreased diversity and metabolic activity. Therefore, in mixed leachates biological treatment, a higher young leachate ratio is recommended for better organics removal performance. PRACTITIONER POINTS: The trade-off between refractory organics and salinity in mixed leachate treatment should be paid attention. Refractory organics reduced alpha and functional diversities of microorganisms. Mixed leachate with a higher young leachate ratio reached a better organic removal.

Microbial approaches for remediation of pollutants: Innovations, future outlook, and challenges

Environmental contamination with persistent organic pollutants has emerged as a serious threat of pollution. Bioremediation is a key to eliminate these harmful pollutants from the environment and has gained the interest of researchers during the past few decades. Scientific knowledge upon microbial interactions with individual pollutants over the past decades has helped to abate environmental pollution. Traditional bioremediation approaches have limitations for their applications; hence, it is essential to discover new bioremediation approaches with biotechnological interventions for best results. The developments in various methodologies are expected to increase the efficiency of bioremediation techniques and provide environmentally sound strategies. This paper deals with the profiling of microorganisms present in polluted sites using various techniques such as culture-based approaches and omics-based approaches. Besides this, it also provides up-to-date scientific literature on the microbial electrochemical technologies which are nowadays considered as the best approach for remediation of pollutants. Detailed information about future outlook and challenges to evaluate the effect of various treatment technologies for remediation of pollutants has been discussed.

2,4-Dichlorophenoxyacetic acid degradation in methanogenic mixed cultures obtained from Brazilian Amazonian soil samples

2,4-Dichlorophenoxyacetic acid (2,4-D) is the third most applied pesticide in Brazil to control broadleaf weeds in crop cultivation and pastures. Due to 2,4-D's high mobility and long half-life under anoxic conditions, this herbicide has high probability for groundwater contamination. Bioremediation is an attractive solution for 2,4-D contaminated anoxic environments, but there is limited understanding of anaerobic 2,4-D biodegradation. In this study, methanogenic enrichment cultures were obtained from Amazonian top soil (0-40 cm) and deep soil (50 -80 cm below ground) that biotransform 2,4-D (5 µM) to 4-chlorophenol and phenol. When these cultures were transferred (10% v/v) to fresh medium containing 40 µM or 160 µM 2,4-D, the rate of 2,4-D degradation decreased, and biotransformation did not proceed beyond 4-chlorophenol and 2,4-dichlorophenol in the top and deep soil cultures, respectively. 16S rRNA gene sequencing and qPCR of a selection of microbes revealed no significant enrichment of known organohalide-respiring bacteria. Furthermore, a member of the genus Cryptanaerobacter was identified as possibly responsible for phenol conversion to benzoate in the top soil inoculated culture. Overall, these results demonstrate the effect of 2,4-D concentration on biodegradation and microbial community composition, which are both important factors when developing pesticide bioremediation technologies.

Influences of Dimethyl Phthalate on Bacterial Community and Enzyme Activity in Vertical Flow Constructed Wetland

Dimethyl phthalate (DMP), belonging to the family of Phthalate esters (PAEs), is a plasticizer and has been widely used in the world for many years. Nowadays, it has become a ubiquitous environmental pollutant and is listed as an environmental priority pollutant by China’s Environmental Monitoring Center. The purpose of this study is to estimate the responses of the bacterial community and enzyme activity to DMP contamination in three vertical flow constructed wetlands (VFCW), namely the constructed wetland A (planted with Pennisetum sinese Roxb), constructed wetland B (planted with Pennisetum purpureum Schum.), and constructed wetland C (unplanted), respectively. The results showed that the relative percentages of some genera associated with nitrogen metabolism and the function of degrading aromatic hydrocarbons were increased by DMP contamination, such as Dechloromonas agitata, Pleomorphomonas sp., Denitratisoma oestradiolicum, Plasticicumulans lactativorans, Novosphingobium sp., Alicycliphilus denitrificans, and Thauera sp. Meanwhile, principal coordinate analysis (PCA) analysis showed that the addition of DMP divided 12 samples into two groups as followed: one was the DMP group containing a-1, a-2, b-1, b-2, c-1 and c-2 while the other was no DMP group including A-1, A-2, B-1, B-2, C-1 and C-2. It indicated that DMP was the main reason for this change. In addition, by monitoring the activity of substrate enzymes, the activity of urease, phosphatase, catalase, and invertase in the wetlands before and after the experiment, these were significantly higher in the upper layer than in the lower layer and maintained high activity. Ultimately, the average influent concentration of DMP in three VFCWs was 8.12 mg/L and the average removal efficiency of the effluent was over 90%. Our results suggested that DMP was an important factor affecting the microbial community structure of wetland and the upper layer of the VFCW was the main site for the degradation of DMP. VFCW has great potential for the removal of the high concentration of DMP and it can be a good choice for the treatment of PAEs.

Environmental chemical exposures in the urine of dogs and people sharing the same households

Introduction:

Urothelial carcinoma (UCC) develops in both humans and dogs and tracks to regions of high industrial activity. We hypothesize that dogs with UCC may act as sentinels for human urothelial carcinogen exposures. The aim of this pilot study was to determine whether healthy people and dogs in the same households share urinary exposures to potentially mutagenic chemical carcinogens.

Methods:

We measured urinary concentrations of acrolein (as its metabolite 3-HPMA), arsenic species, 4-aminobiphenyl, and 4-chlorophenol (a metabolite of the phenoxyherbicide 2,4-D) in healthy dogs and their owners. We assessed possible chemical sources through questionnaires and screened for urothelial DNA damage using the micronucleus assay.

Results:

Biomarkers of urinary exposure to acrolein, arsenic, and 4-chlorophenol were found in the urine of 42 pet dogs and 42 owners, with 4-aminobiphenyl detected sporadically. Creatinine-adjusted urinary chemical concentrations were significantly higher, by 2.8- to 6.2-fold, in dogs compared to humans. Correlations were found for 3-HPMA (r = 0.32, P = 0.04) and monomethylarsonic acid (r = 0.37, P = 0.02) between people and their dogs. Voided urothelial cell yields were inadequate to quantify DNA damage, and questionnaires did not reveal significant associations with urinary chemical concentrations.

Conclusions:

Healthy humans and pet dogs have shared urinary exposures to known mutagenic chemicals, with significantly higher levels in dogs. Higher urinary exposures to acrolein and arsenic in dogs correlate to higher exposures in their owners. Follow-up studies will assess the mutagenic potential of these levels in vitro and measure these biomarkers in owners of dogs with UCC.

Aerobic biodegradation of p-nitrophenol in a nitrifying sludge bioreactor: System performance, sludge property and microbial community shift

The system performance, sludge property and microbial community shift were evaluated in a nitrifying sludge (NS) bioreactor for simultaneous treating p-Nitrophenol (PNP) and high ammonia wastewater. After long-term acclimation for 80 days, the removal efficiencies of PNP and NH₄⁺-N reached to 99.9% and 99.5%, respectively. Meanwhile, the effluent PNP gradually decreased from 7.9 to 0.1 mg/L by acclimation of sludge. The particle size of NS increased from 115.2 μm to 226.3 μm accompanied by the decreased zeta potential as a self-protection strategy. The presence of PNP exposure altered the effluent soluble microbial products (SMP) fluorescent components and molecular composition. The increase in the relative abundance of Thauera, Nitrospiraceae and Nitrosomonas indicated the nitrification and denitrification capacities of NS increased, which maybe the PNP cometabolic biodegradation effect. Moreover, Ignavibacteria and Aeromonas were responsible as the dominant bacteria for degrading PNP in the nitrifying system.

Ortho and para oxydehalogenation of dihalophenols catalyzed by the monooxygenase TcpA and NAD(P)H:FAD reductase Fre

Dihalophenols such as dichlorophenols (DCPs) are important industrial chemical intermediates, but also persistent pollutants in the environment. Oxidative dehalogenation by microbes is an efficient biological method to degrade halophenols, but the mechanism is unclear yet. Cupriavidus nantongensis X1^T was a type strain of genus Cupriavidus, and could degrade 2,4-dichlorophenol of 50 mg/L within 12 h. The degradation rate constant was approximately 84 fold greater than that by Bacillus endophyticus CP1R43, a well-studied 2,4-DCP-degrading bacterial strain. The genes encoding 2,4,6-trichlorophenol monooxygenase (TcpA) and NAD(P)H:FAD reductase (Fre) from strain X1^T were cloned and expressed. The expressed TcpA Fre were purified. The molecular docking of TcpA with DCPs and point mutation experiments showed that the degradation activity of TcpA was associated with the length of the hydrogen bond between the substrates and the amino acids in the active pocket. DCPs were degraded via a stepwise oxidative dechlorination in a positive relationship between the oxidation ability and the electron-withdrawing potential of the p-position group. In addition, TcpA has dual dehalogenation and denitration functions. The results demonstrate that either strain X1^T or TcpA and Fre can effectively dehalogenate dihalophenols, which can be useful for the treatment of dihalophenols in wastewaters and remediation of DCP-contaminated environments.

Degradation of p-chlorocresol by facultative Thauera sp. strain DO

In this work, Thauera sp. DO isolated from sludge and sediment utilized p-chlorocresol and some related compounds as the sole carbon and energy sources under both aerobic and anaerobic conditions. The pathways for p-chlorocresol in the isolate under each condition were different. Under the aerobic condition, p-chlorocresol was degraded via two separate pathways. The first was the reductive dehalogenation reaction, in which the substrate was transformed to m-cresol followed by the catechol degradation pathway, and the second aerobic pathway for p-chlorocresol was the methyl oxidation to 4-chlorobenzoate. Under the anaerobic conditions, p-chlorocresol was rapidly dechlorinated in the first step to m-cresol, followed by sevaral steps prior to the complete degradation. The determination of p-chlorocresol degradation in liquid media by whole cells showed that 100% and 85% of the substrate (0.3 mM) were transformed within 12 h under aerobic and anaerobic conditions, respectively, while nearly 100% of this compound was degraded within 6 h using the two-stage anaerobic-aerobic degradation process. These results show a novel method to increase the degradation rates of p-chlorocresol using the anaerobic process followed by the aerobic process.

Biodegradation of propanil by Acinetobacter baumannii DT in a biofilm-batch reactor and effects of butachlor on the degradation process

The herbicide, propanil, has been extensively applied in weed control, which causes serious environmental pollution. Acinetobacter baumannii DT isolated from soil has been used to determine the degradation rates of propanil and 3,4-dichloroaniline by freely suspended and biofilm cells. The results showed that the bacterial isolate could utilize both compounds as sole carbon and nitrogen sources. Edwards's model could be fitted well to the degradation kinetics of propanil, with the maximum degradation of 0.027 ± 0.003 mM h-1. The investigation of the degradation pathway showed that A. baumannii DT transformed propanil to 3,4-dichloroaniline before being completely degraded via the ortho-cleavage pathway. In addition, A. baumannii DT showed high tolerance to butachlor, a herbicide usually mixed with propanil to enhance weed control. The presence of propanil and butachlor in the liquid media increased the cell surface hydrophobicity and biofilm formation. Moreover, the biofilm reactor showed increased degradation rates of propanil and butachlor and high tolerance of bacteria to these chemicals. The obtained results showed that A. baumannii DT has a high potential in the degradation of propanil.

Anaerobic degradation of 2,4,5-trichlorophenoxyacetic acid by enrichment cultures from freshwater sediments

The anaerobic biodegradation of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) was investigated using enrichment cultures from freshwater sediments at two different sites in the region of Halle, central Germany. 2,4,5-T and different organic acids or hydrogen were added as possible electron acceptor and electron donors, respectively. The primary enrichment cultures from Saale river sediment completely degraded 2,4,5-T to 3-chlorophenol (3-CP) (major product) and 3,4-dichlorophenol (3,4-DCP) during a 28-day incubation period. Subcultures showed ether cleavage of 2,4,5-T to 2,4,5-trichlorophenol and its stoichiometric dechlorination to 3-CP only in the presence of butyrate. In contrast, the primary enrichment culture from sediment of Posthorn pond dechlorinated 2,4,5-T to 2,5-dichlorophenoxyacetic acid (2,5-D), which, in the presence of butyrate, was degraded further to products such as 3,4-DCP, 2,5-DCP, and 3CP, indicating ether cleaving activities and subsequent dechlorination steps. Experiments with pure cultures of Dehalococcoides mccartyi and Desulfitobacterium hafniense demonstrated their specific dechlorination steps within the overall 2,4,5-T degradation pathways. The results indicate that the route and efficiency of anaerobic 2,4,5-T degradation in the environment depend heavily on the microorganisms present and the availability of slowly fermentable organic compounds.

Anaerobic degradation of 2-chloro-4-nitroaniline by Geobacter sp. KT7 and Thauera aromatica KT9

2-chloro-4-nitroaniline is a nitroaromatic compound widely used in industrial and agricultural sectors, causing serious environmental problems. This compound and some of its analogs were utilized by two Fe3+-reducing microbial strains Geobacter sp. KT7 and Thauera aromatica KT9 isolated from contaminated sediment as sole carbon and nitrogen sources under anaerobic conditions. The anaerobic degradation of 2-chloro-4-nitroaniline by the mixed species was increased approximately by 45% compared to that of individual strains. The two isolates’ crossfeeding, nutrient sharing and cooperation in the mixed culture accounted for the increase in degradation rates. The determination of degradation pathways showed that Geobacter sp. KT7 transformed the nitro group in 2-chloro-4-nitroaniline to the amino group following by the dechlorination process, while T. aromatica KT9 dechlorinated the compound before removing the nitro group and further transformed it to aniline. This study provided an intricate network of 2-chloro-4-nitroaniline degradation in the bacterial mixture and revealed two parallel routes for the substrate catabolism.