Enriched Consortium Research Articles

Insight into furfural-tolerant and hydrogen-producing microbial consortia: Mechanism of furfural tolerance and hydrogen production

Furfural-tolerant and hydrogen-producing microbial consortia were enriched from soil, with hydrogen production of 259.84 mL/g-xylose under 1 g/L furfural stress. The consortia could degrade 2.5 g/L furfural within 24 h in the xylose system, more efficient than in the sugar-free system. Despite degradation of furfural to furfuryl alcohol, the release of reactive oxygen species and lactate dehydrogenase was also detected, suggesting that furfuryl alcohol is also a potential inhibitor of hydrogen production. The butyrate/acetate ratio was observed to decrease with increasing furfural concentration, leading to decreased hydrogen production. Furthermore, microbial community analysis suggested that dominated Clostridium butyricum was responsible for furfural degradation, while Clostridium beijerinckii reduction led to hydrogen production decrease. Overall, the enriched consortia in this study could efficiently degrade furfural and produce hydrogen, providing new insights into hydrogen-producing microbial consortia with furfural tolerance.

Degradation of Atrazine by an Anaerobic Microbial Consortium Enriched from Soil of an Herbicide-Manufacturing Plant.

Atrazine is an important herbicide that has been widely used for weed control in recent decades. However, with the extensive use of atrazine, its residue seriously pollutes the environment. Therefore, the microbial degradation and detoxification of atrazine have received extensive attention. To date, the aerobic degradation pathway of atrazine has been well studied; however, little is known about its anaerobic degradation in the environment. In this study, an anaerobic microbial consortium capable of efficiently degrading atrazine was enriched from soil collected from an herbicide-manufacturing plant. Six metabolites including hydroxyatrazine, deethylatrazine, N-isopropylammelide, deisopropylatrazine, cyanuric acid, and the novel metabolite 4-ethylamino-6-isopropylamino-1,3,5-triazine (EIPAT) were identified, and two putative anaerobic degradation pathways of atrazine were proposed: a hydrolytic dechlorination pathway is similar to that seen in aerobic degradation, and a novel pathway initiated by reductive dechlorination. During enrichment, Denitratisoma, Thiobacillus, Rhodocyclaceae_unclassified, Azospirillum, and Anaerolinea abundances significantly increased, dominating the enriched consortium, indicating that they may be involved in atrazine degradation. These findings provide valuable evidence for elucidating the anaerobic catabolism of atrazine and facilitating anaerobic remediation of residual atrazine pollution.

Biodegradation of chloroxylenol by an aerobic enrichment consortium and a newly identified Rhodococcus strain.

Chloroxylenol is a commonly used antimicrobial agent in antibacterial and disinfection products, which has been detected in various environments, such as wastewater treatment plants, rivers, seawater, and even drinking water, with concentrations ranging from ng/L to mg/L. However, the biodegradation of chloroxylenol received limited attention with only sporadic reports available so far. In this study, an efficient chloroxylenol-degrading consortium, which could degrade 20 mg/L chloroxylenol within two days, was obtained after five months of enrichment. Amplicon sequencing analysis revealed a decrease in the α-diversity (e.g., Shannon index and Inv_Simpson index) of the community during the domestication process. Microbial community dynamics were uncovered, with sequences affiliated to Achromobacter, Pseudomonas, and Rhodococcus identified as the most abundant taxonomic groups. From the consortium, five pure isolates were obtained; however, it was found that only one strain of Rhodococcus could degradechloroxylenol. Strain Rhodococcus sp. DMU2021 could degrade chloroxylenol efficiently under the conditions of temperature 30-40 °C, and neutral/alkaline conditions. Chloroxylenol was toxic to strain DMU2021 and triggered both enzymatic and non-enzymatic antioxidant systems in response. This study provides novel insights into the biodegradation process of chloroxylenol, as well as valuable bioresources for bioremediation.

A concerted enzymatic de-structuring of lignocellulosic materials using a compost-derived microbial consortia favoring the consolidated pretreatment and bio-saccharification

The robustness of microbial consortia isolated from compost habitat encompasses the complementary metabolism that aids in consolidated bioprocessing (CBP) of lignocellulosic biomass (LCB) by division of labor across the symbionts. Composting of organic waste is deemed to be an efficient way of carbon recycling, where the syntrophic microbial population exerts a concerted action of lignin and polysaccharide (hemicellulose and cellulose) component of plant biomass. The potential of this interrelated microorganism could be enhanced through adaptive laboratory evolution (ALE) with LCB for its desired functional capabilities. Therefore, in this study, microbial symbionts derived from organic compost was enriched on saw dust (SD) (woody biomass), aloe vera leaf rind (AVLR) (agro-industrial waste) and commercial filter paper (FP) (pure cellulose) through ALE under different conditions. Later, the efficacy of enriched consortium (EC) on consolidated pretreatment and bio-saccharification was determined based on substrate degradation, endo-enzymes profiling and fermentable sugar yield. Among the treatment sets, AVLR biomass treated with EC-5 has resulted in the higher degradation rate of lignin (47.01 ± 0.66%, w/w) and polysaccharides (45.87 ± 1.82%, w/w) with a total sugar yield of about 60.01 ± 4.24 mg/g. In addition, the extent of structural disintegration of substrate after EC-treatment was clearly deciphered by FTIR and XRD analysis. And the factors of Pearson correlation matrix reinforces the potency of EC-5 by exhibiting a strong positive correlation between AVLR degradation and the sugar release. Thus, a consortium based CBP could promote the feasibility of establishing a sustainable second generation biorefinery framework.

Self-assembling a 1,4-dioxane-degrading consortium and identifying the key role of Shinella sp. through dilution-to-extinction and reculturing.

Assembling a functional consortium and identifying novel degraders from contaminated environments are still challenging due to the large diversity of microorganisms and the difficulty in isolating pure cultures. Here, we constructed a relatively simple functional consortium by enriching 1,4-dioxane-degrading-consortia using a culture-dependent dilution-to-extinction (DTE) method and reported a new key dioxane-degrader Shinella sp. Our results showed that serial dilution and reculture led to a divergence in the degradation ability of each consortium. Next-generation sequencing data revealed that the divergence in degradation performance was due to the reassembly of microbiota in the DTE process, which occurred most notably in 10-8 and 10-9 dilutions. The shift in community structure at 10-9 prevented the recovery of 1,4-dioxane degradation capacity, and the newly dominant taxa, Xanthobacter and Acinetobacter, struggled to replace the original dominant genus Shinella for 1,4-dioxane biodegradation. Combining differential analysis of community structure and metabolic function, we confirmed that Shinella species have a stronger 1,4-dioxane degradation ability than Xanthobacter species in the enriched consortium. In addition, we verified our findings using our isolated dioxane-degrading bacteria, Shinella yambaruensis, resulting in the rapid recovery of degradation performance of a 10-9 dilution consortium with Xanthobacter and Acinetobacter as the dominant microbiota. Taken together, this study provides a strategy for self-assembling functional consortiums and identifying the key degraders to explore the underlying biological mechanisms of enriched contaminant-degrading consortia.IMPORTANCEAssembling a functional microbial consortium and identifying key degraders involved in the degradation of 1,4-dioxane are crucial for the design of synergistic consortia used in enhancing the bioremediation of 1,4-dioxane-contaminated sites. However, due to the vast diversity of microbes, assembling a functional consortium and identifying novel degraders through a simple method remain a challenge. In this study, we reassembled 1,4-dioxane-degrading microbial consortia using a simple and easy-to-operate method by combining dilution-to-extinction and reculture techniques. We combined differential analysis of community structure and metabolic function and confirmed that Shinella species have a stronger 1,4-dioxane degradation ability than Xanthobacter species in the enriched consortium. In addition, a new dioxane-degrading bacterium was isolated, Shinella yambaruensis, which verified our findings. These results demonstrate that DTE and reculture techniques can be used beyond diversity reduction to assemble functional microbial communities, particularly to identify key degraders in contaminant-degrading consortia.

Evaluating the potential of pectin de-esterifying bacterial cultures for the production of methanol from fruit waste: Optimization of critical operational parameters

Fruit wastes are a good source of pectin, which can be de-esterified into pectate and methanol by microbial pectinesterases. Methanol is an important fuel substance and thus, this study aimed at developing a scalable process for efficient biological conversion of fruit wastes into methanol. Pectin digesting bacteria were enriched, identified and the consortium was used for methanol production. Experiments were conducted in two phases, where, feasibility of methanol production using the enriched consortium was investigated in phase I and in phase II, the critical operational parameters such as substrate/inoculum (S/I) ratio, fraction of fruit waste, temperature and rpm were optimized. Initial reactor experimental study resulted in the production of 44.13 g/L methanol which was further optimized with respect to substrate fractionation, S/I ratio, temperature and rpm. Maximum methanol was obtained with whole blend fruit wastes as substrate with S/I ratio of 3 at 40 °C and 150 rpm. By further studying the pectin conversion efficiency of the microbe and efforts towards increasing it for higher methanol production this process can be scaled up or integrated into other biomass conversion processes for methanol as another product.

Selective enrichment of homoacetogens and optimization of the operational conditions for effective acetate production in hydrogen-mediated microbial electrosynthesis reactors

Microbial electrosynthesis (MES) can use microorganisms and power to convert CO2 reduction into valuable chemicals. The non-biofilm-driven and H2-mediated MES could dramatically enhance the current density of MES reactors. However, thus far there is no enriched microbial community dedicated to H2-mediated MES for acetate production. Here, we enriched a highly efficient hydrogenotrophic acetate-producing microbial consortium (Acetobacterium abundance 85%) from anaerobic granular sludge in an H2-mediated MES reactor. Then, orthogonal experiments were used to optimize the operational conditions for this enriched consortium. The optimal operational conditions were 37 °C, pH 7.5, and 400 rpm. The maximum acetate production rate (1.77 g/L/d) and acetate titer (24.6 g/L) obtained under the optimal conditions were higher than most reported MES reactors. This study demonstrated that selective enrichment of the hydrogenotrophic acetate-producing microbial community and optimization of the operational conditions could effectively enhance the performance of H2-mediated MES reactors.

Microbial reduction of tellurate by an enriched consortium performing anaerobic oxidation of methane in a sequencing batch reactor

Anaerobic oxidation of methane (AOM) is capable of coupling the reduction of various substrates, which plays a crucial role in accelerating the abatement of pollution. In this study, we employed a sequencing batch reactor (SBR) to enrich a mixed consortium that included AOM microbes and examined the ensuing microbial reduction of tellurate. To obtain the mixed consortium, we enriched AOM microbes in anaerobic conditions utilizing methane as the only electron donor, with nitrate serving as the electron acceptor. We evaluated the abundance of typical methane-oxidizing microbes and associated genes in the reactor using quantitative PCR. Notably, the enriched microbes were able to achieve microbial tellurate reduction and produce elemental tellurium. An analysis of community structure further indicated the vital roles of methanotrophs, denitrifiers, and other heterotrophs in the reactor, although their molecular mechanisms require further investigation. These findings underscore the role of enriched microbial communities in tellurate reduction using a lab-scale SBR, laying the groundwork for future studies into the mechanism of this process, which utilizes methane as an electron donor.

Pharmaceutical active compounds in sewage sludge: Degradation improvement and conversion into an organic amendment by bioaugmentation-composting processes

Around 143,000 chemicals find their fate in wastewater treatment plants in the European Union. Low efficiency on their removal at lab-based studies and even poorer performance at large scale experiments have been reported. Here, a coupled biological technology (bioaugmentation and composting) is proposed and proved for pharmaceutical active compounds degradation and toxicity reduction. The optimization was conducted through in situ inoculation of Penicillium oxalicum XD 3.1 and an enriched consortium (obtained from non-digested sewage sludge), into pilot scale piles of sewage sludge under real conditions. This bioaugmentation-composting system allowed a better performance of micropollutants degradation (21 % from the total pharmaceuticals detected at the beginning of the experiment) than a traditional composting process. Particularly, inoculation with P. oxalicum allowed the degradation of some recalcitrant compounds like carbamazepine, cotinine and methadone, and also produced better stabilization features in the mature compost (significant passivation of copper and zinc, higher macronutrients value, adequate physicochemical conditions for soil direct application and less toxic effect on germination) compared to the control and the enriched culture. These findings provide a feasible, alternative strategy to obtain a safer mature compost and a better removal of micropollutants performance at large scale.

Sustained anaerobic degradation of 4-chloro-2-methylphenoxyacetic acid by acclimated sludge in a continuous-flow reactor

4-Chloro-2-methylphenoxyacetic acid (MCPA) is a widely used herbicide across the world. MCPA is persistent and easily transports into anoxic environment, such as groundwater, sediments and deep soils. However, little research on anaerobic microbial degradation of MCPA was carried out. The functional microorganisms as well as the catabolic pathway are still unknown. In this research, an anaerobic MCPA-degrading bacterial consortium was enriched from the river sediment near a pesticide-manufacturing plant. After about 6 months’ acclimation, the MCPA transformation rate of the consortium reached 4.32 μmol g−1 day−1, 25 times faster than that of the original sludge. 96% of added MCPA (2.5 mM) was degraded within 9 d of incubation. Three metabolites including 4-chloro-2-methylphenol (MCP), 2-methylphenol (2-MP) and phenol were identified during the anaerobic degradation of MCPA. An anaerobic catabolic pathway was firstly proposed: firstly, MCPA was transformed to MCP via the cleavage of the aryl ether, then MCP was reductively dechlorinated to 2-MP which was further demethylated to phenol. The 16S rRNA gene amplicon sequencing revealed a substantial shift in the bacterial community composition after the acclimation. SBR1031, Acidaminococcaceae, Aminicenantales, Syntrophorhabdus, Acidaminobacter, Bacteroidetes_vadinHA17, Methanosaeta, Bathyarchaeia, KD4-96, Anaeromyxobacter, and Dehalobacter were significantly increased in the enriched consortium after acclimation, and positively correlated with the anaerobic degradation of MCPA as suggested by heat map correlation analysis. This study provides a basis for further elucidation of the anaerobic catabolism of MCPA, and contributes to developing efficient and low-cost anaerobic treatment technologies for MCPA pollution.

Methanotroph detection and bioconversion of methane to methanol by enriched microbial consortium from rice field soil

Fast depletion of fossil fuels has triggered research in gas to liquid (GTL) technologies for synthesis of green transportation fuels. Utilization of natural gas pockets located in remote areas for methanol synthesis is a viable GTL process. This study has examined potential of microbial consortium enriched from rice field soil for bioconversion of methane to methanol. The presence of Type I methanotrophs was confirmed through PCR amplification of genomic DNA from soil using mmoY1-mmoY2 primer set which is specific to Methylococcus capsulatus. Further, the methanol production profiling (without MDH inhibitors) revealed ~130 mM (4.16 g/L) methanol production from enriched consortium, which was close to 132.5 mM (4.24 g/L) methanol production by pure strain of Methylococcus capsulatus. The yield of methanol for enriched consortium was 78.31 % and M. capsulatus was 79.81 %. These results show that enriched consortium holds high potential for BioGTL process for methanol synthesis.

Polyethylene Valorization by Combined Chemical Catalysis with Bioconversion by Plastic-Enriched Microbial Consortia

There are few reports of microbial deconstruction or functionalization of the recalcitrant backbone of polyolefins. However, microbes can utilize polyolefin deconstruction products, including n-alkanes. Here, we combined chemical catalysis with bioconversion to valorize polyethylene (PE) deconstruction products. High-density PE (HDPE) was deconstructed via hydrogenolysis over a ruthenium on carbon catalyst. The resulting n-alkane mixture (C4–C35) was utilized as a feedstock for microbial consortia derived from soil from local recycling plants. We found two consortia that utilized the PE-deconstruction product mix as a sole carbon source. We adapted the consortia on a commercially available n-alkane mix to reduce the number of species present and enrich for enhanced alkane utilization. Both resulting enriched consortia utilized the PE-deconstruction product mix more effectively than the original (parent) consortia. The predominant metabolite produced from a model alkane hexadecane by both enriched consortia was a C16–C16 wax ester. Wax esters have considerable industrial value, with longer chain lengths (C32–C36) having the highest value. We identified two Rhodococcus aetherivorans strains that grow well on C24, indicating that this species is important for the functionalization of long-chain alkanes. This work demonstrates that enriched consortia from plastic-enriched environments can be combined with chemical catalysis to valorize PE.

Manganese Removal from Acid Mine Drainage by a Consortium of Mn-Oxidizing Bacteria in Continuous Stirred Tank Bioreactor: Long-Term Treatment and Reactive Mixture Characterization

Biological treatments based on Mn-oxidizing bacteria can effectively remove Mn from contaminated water. However, the mechanisms and key organisms of biological low-pH Mn(II) removal are largely unexplored. In this study, bioremediation based on an enriched consortium of acid-resistant Mn-oxidizing bacteria for Mn-rich acid mine drainage (AMD) was evaluated in a continuous stirred tank bioreactor (CSTB), and the removal mechanism of Mn(II) was further studied. The highest removal rate of 33.2 ± 1.8 mg/L/d and maximum removal efficiency of 82.4 ± 1.8% were achieved with a pH of 5.5, hydraulic retention time (HRT) of 48 h, chemical oxygen demand (COD) concentration of 2000.0 mg/L, and Mn concentration of 80.0 mg/L, respectively. The Mn oxidation rate was ∼4.1 μM/h in the continuous stirred tank bioreactor (CSTB) under stable conditions. Acinetobacter and Azospirillum were the main contributors for Mn oxidation in the bioreactor. X-ray diffraction (XRD) analysis suggested that Mn removal proceeds via the formation of biogenic precipitates consisting of MnO2, MnOOH, and MnCO3. The performance of the CSTB was further evaluated by actual Mn-rich acid mine drainage, and Mn, Cu, Zn, and Cd removal efficiencies were 86.5 ± 2.4%, 98.8 ± 2.2%, and 96.9 ± 1.0%, and 97.0 ± 1.7%, respectively. Results from this work have demonstrated that Mn-oxidizing bacteria can be effective at processing complex Mn-rich acid mine drainage.

Functional Microbial Communities in Hybrid Linear Flow Channel Reactors for Desulfurization of Tannery Effluent.

Recent research has demonstrated that hybrid linear flow channel reactors (HLFCRs) can desulfurize tannery effluent via sulfate reduction and concurrent oxidation of sulfide to elemental sulfur. The reactors can be used to pre-treat tannery effluent to improve the efficiency of downstream anaerobic digestion and recover sulfur. This study was conducted to gain insight into the bacterial communities in HLFCRs operated in series and identify structure-function relationships. This was accomplished by interpreting the results obtained from amplicon sequencing of the 16S rRNA gene and quantification of the dissimilatory sulfite reducing (dsrB) gene. In an effort to provide a suitable inoculum, microbial consortia were harvested from saline estuaries and enriched. However, it was found that bioaugmentation was not necessary because native communities from tannery wastewater were selected over exogenous communities from the enriched consortia. Overall, Dethiosulfovibrio sp. and Petrimonas sp. were strongly selected (maximum relative abundances of 29% and 26%, respectively), while Desulfobacterium autotrophicum (57%), and Desulfobacter halotolerans (27%) dominated the sulfate reducing bacteria. The presence of elemental sulfur reducing genera such as Dethiosulfovibrio and Petrimonas is not desirable in HLFCRs, and strategies to counter their selection need to be considered to ensure efficiency of these systems for pre-treatment of tannery effluent.

Perchlorate reduction kinetics and genome-resolved metagenomics identify metabolic interactions in acclimated saline lake perchlorate-reducing consortia

Perchlorate is a widely detected environmental contaminant in surface and underground water, that seriously impacts human health by inhibiting the uptake of thyroidal radioiodine. Perchlorate reduction due to saline lake microorganisms is not as well understood as that in marine environments. In this study, we enriched a perchlorate-reducing microbial consortium collected from saline lake sediments and found that the perchlorate reduction kinetics of the enriched consortium fit the Michaelis–Menten kinetics well, with a maximum specific substrate reduction rate (qmax) of 0.596 ± 0.001 mg ClO4−/mg DW/h and half-saturation constant (Ks) of 16.549 ± 0.488 mg ClO4−/L. Furthermore, we used improved metagenome binning to reconstruct high-quality metagenome-assembled genomes from the metagenomes of the microbial consortia, including the perchlorate-reducing bacteria (PRB) Dechloromonas agitata and Wolinella succinogenes, with the genome of W. succinogenes harboring complete functional genes for perchlorate reduction being the first recovered. Given that the electrons were directly transferred to the electronic carrier cytochrome c-553 from the quinone pool, the electron transfer pathway of W. succinogenes was shorter and more efficient than the canonical pattern. This finding provides a theoretical basis for microbial remediation of sites contaminated by high concentrations of perchlorate. Metagenomic binning and metatranscriptomic analyses revealed the gene transcription variation of perchlorate reductase pcr and chlorite dismutase cld by PRB and the synergistic metabolic mechanism.

Effect of H2O2 concentration as electron Acceptor on bioregeneration of activated carbon contaminated with a benzene-toluene mixture

Granular Activated carbon (AC) is commonly used for cleaning water contaminated with Benzene and toluene (BT). Regeneration is needed to extend the lifetime of GAC. This study examines the effect of H2O2 concentration as an electron acceptor for GAC bioregeneration by the consortium of Pseudomonas aeruginosa, Pseudomonas fluorescens, Aeromonas hydrophila, Bacillus coagulants, and Bacillus substilis in a fixed-bed bioreactor. Enrichment was carried out for adaptation to benzene and toluene. The enriched consortium was injected into a bioreactor column containing GAC saturated with benzene and toluene. The H2O2 concentration was varied 10 mg/l, 30 mg/l, 40 mg/l, and 50 mg/l. The contaminant mixture was continuously added with Lockhead and Chase (LC) and H2O2 at a flow rate of 18.2 ml/minute and 1 ml/minute, respectively. The outlet sample was analyzed using a Gas Chromatograph-Flame Ionization Detector (GC FID). The consortium regenerated the GAC by biodegradation of adsorbed benzene toluene. Initial inoculation of enrichment was 3.5 x 105 CFU/ml. The final stationary phase was at 120 hours with 1.37 x 1011 CFU/ml. The optimum biodegradation process was at a concentration of 30 mg/l H2O2 with a concentration of benzene and toluene outlet column II of 25 ppm and 40.5 ppm, respectively.

Bacterial community shifts in a di-(2-ethylhexyl) phthalate-degrading enriched consortium and the isolation and characterization of degraders predicted through network analyses

Di-(2-ethylhexyl) phthalate (DEHP) is an extensively used and toxic phthalate plasticizer that is widely reported in marine environments. Degradation of DEHP by bacteria from several environments have been studied, but little is known about marine sediment bacteria that can degrade DEHP and other phthalate plasticizers. Therefore, in this study, we enriched a bacterial consortium C10 that can degrade four phthalate plasticizers of varying alkyl chain lengths (DEHP, dibutyl phthalate, diethyl phthalate, and dimethyl phthalate) from marine sediment. The major bacterial genera in C10 during degradation of the phthalate plasticizers were Glutamicibacter, Ochrobactrum, Pseudomonas, Bacillus, Stenotrophomonas, and Methylophaga. Growth of C10 on DEHP intermediates (mono-ethylhexyl phthalate, 2-ethylhexanol, phthalic acid, and protocatechuic acid) was studied and these intermediates enhanced the Brevibacterium, Ochrobactrum, Achromobacter, Bacillus, Sporosarcina, and Microbacterium populations. Using a network-based approach, we predicted that Bacillus, Stenotrophomonas, and Microbacterium interacted cooperatively and were the main degraders of phthalate plasticizers. Through selective isolation techniques, we obtained twenty isolates belonging to Bacillus, Microbacterium, Sporosarcina, Micrococcus, Ochrobactrum, Stenotrophomonas, Alcaligenes, and Cytobacillus. The best DEHP-degraders were Stenotrophomonas acidaminiphila OR13, Microbacterium esteraromaticum OR16, Sporosarcina sp. OR19, and Cytobacillus firmus OR20 (83.68%, 59.1%, 43.4%, and 40.6% degradation of 100 mg/L DEHP in 8 d), which agrees with the prediction of key degraders. This is the first report of DEHP degradation by all four bacteria and, thus, our findings reveal as yet unknown PAE-degradation capabilities of marine sediment bacteria. This study provides insights into how bacterial communities adapt to degrade or resist the toxicities of different PAEs and demonstrates a simple approach for the prediction and isolation of potential pollutant degraders from complex and dynamic bacterial communities.

Acesulfame Anoxic Biodegradation Coupled to Nitrate Reduction by Enriched Consortia and Isolated Shinella spp.

Acesulfame (ACE) is considered to be an emerging pollutant associated with growing concerns. Although aerobic biodegradation of ACE has been observed in wastewater treatment plants worldwide and verified in pure cultures, limited information is available on ACE biodegradation under anoxic conditions, which are ubiquitous in natural environments. Here, we found that ACE could be mineralized completely via a process coupled with nitrate reduction by enriched consortia, with the highest degradation rate of 9.95 mg ACE/g VSS·h-1. Meanwhile, three novel ACE-degrading strains affiliated with Shinella were isolated, examined, and sequenced, revealing that the isolates could utilize ACE as the sole carbon source under both aerobic and anoxic conditions, with maximum degradation rates of 30.3 mg ACE/g VSS·h-1 and 8.92 mg ACE/g VSS·h-1, respectively. Additionally, the biodegradation of ACE was suspected to be a plasmid-mediated process based on comparative genomic analysis. In ACE-degrading consortia, 83 near-complete metagenome-assembled genomes (MAGs) were obtained via Illumina and Nanopore sequencing, showing that Proteobacteria and Bacteroidetes were the dominant phyla. Moreover, nine MAGs affiliated with Hyphomicrobiales were proposed to be the major ACE degraders in the enrichments. This study demonstrated that ACE could be degraded under anoxic conditions, providing novel insights into ACE biodegradation in the environment.

Cloning of a novel tetrahydrofolate-dependent dicamba demethylase gene from dicamba-degrading consortium and characterization of the gene product.

Dicamba, an important hormone-type systemic herbicide, is widely used to control more than 200 kinds of broadleaf weeds in agriculture. Due to its broad-spectrum, high efficiency and effectively killing glyphosate-resistant weeds, dicamba is considered as an excellent target herbicide for the engineering of herbicide-resistant crops. In this study, an efficient dicamba-degrading microbial consortium was enriched from soil collected from the outfall of a pesticide factory. The enriched consortium could almost completely degrade 500 mg/L of dicamba within 12 h of incubation. A novel tetrahydrofolate (THF)-dependent dicamba demethylase gene, named dmt06, was cloned from the total DNA of the enriched consortium. Dmt06 shared the highest identity (72.3%) with dicamba demethylase Dmt50 from Rhizorhabdus dicambivorans Ndbn-20. Dmt06 was expressed in Escherichia coli BL21 and purified to homogeneity using Co2+-charged nitrilotriacetic acid affinity chromatography. The purified Dmt06 catalyzed the transfer of methyl from dicamba to THF, generating the herbicidally inactive metabolite 3,6-dichlorosalicylate (3,6-DCSA) and 5-methyl-THF. The optimum pH and temperature for Dmt06 were detected to be 7.4 and 35°C, respectively. Under the optimal condition, the specific activity of Dmt06 reached 165 nmol/min/mg toward dicamba, which was much higher than that of Dmt and Dmt50. In conclusion, this study cloned a novel gene, dmt06, encoding an efficient THF-dependent dicamba demethylase, which was a good candidate for dicamba-resistant transgenic engineering.

Enhanced removal of dissolved S2− from a river by the pump-and-treat ex-situ process with enriched consortium

Abstract S2− is one of the common pollutants in heavily polluted rivers. A pump-and-treat ex-situ process with enriched consortium (PEPEC) was used to remove S2− in this study. The kinetic model of S2− removal was developed, and the inflow ratio of the PEPEC was analyzed according to the results of the kinetic models. The results showed that the S2− removal ratio could reach 97.5% ± 0.5%, when the inflow ratio was controlled at 2% for the PEPEC operation. Meanwhile, the removal efficiency and operation performance were assessed for both the simulating ex-situ and in-situ bench-scale tests. Compared with the in-situ processes, the PEPEC showed a stable operation performance during 120 h of bio-treatment, and the concentrations of S2−, COD, NH3-N and TP in the effluent reached approximately 0.5, 20, 0.5 and 0.5 mg/L, respectively. The time consumption (8 h for one batch) and consortium dosage (3 g for the whole operation) in the PEPEC were significantly less than those in the in-situ processes. The PEPEC presented some potential advantages for the bio-treatment of a heavily polluted river.