Mechanism Of Microbial Degradation Research Articles

Characterization of a New Cyclohexylamine Oxidase From Acinetobacter sp. YT-02.

Cyclohexylamine (CHAM) is widely used in various industries, but it is harmful to human beings and the environment. Acinetobacter sp. YT-02 can degrade CHAM via cyclohexanone as an intermediate. In this study, the cyclohexylamine oxidase (CHAO) gene from Acinetobacter sp. YT-02 was cloned. Amino acid sequence alignment indicated that the cyclohexylamine oxidase (CHAOYT–02) was 48% identical to its homolog from Brevibacterium oxydans IH-35A (CHAOIH–35). The enzyme was expressed in Escherichia coli BL21 (DE3), and purified to apparent homogeneity by Ni-affinity chromatography. The purified enzyme was proposed to be a dimer of molecular mass of approximately 91 kDa. The enzyme exhibited its maximum activity at 50°C and at pH 7.0. The enzyme was thermolabile as demonstrated by loss of important percentage of its maximal activity after 30 min incubation at 50°C. Metal ions Mg2+, Co2+, and K+ had certain inhibitory effect on the enzyme activity. The kinetic parameters Km and Vmax were 0.25 ± 0.02 mM and 4.3 ± 0.083 μM min−1, respectively. The biochemical properties, substrate specificities, and three-dimensional structures of CHAOYT–02 and CHAOIH–35 were compared. Our results are helpful to elucidate the mechanism of microbial degradation of CHAM in the strain YT-02. In addition, CHAOYT–02, as a potential biocatalyst, is promising in controlling CHAM pollution and deracemization of chiral amines.

Impact of additives of commercial rubber compounds on the microbial and enzymatic degradation of poly(cis-1,4-isoprene).

Much fundamental research has already been performed to understand the mechanism of microbial rubber degradation. Due to the increasing amount of rubber waste, biotechnical methods to degrade that particular waste are strongly needed. The present study evaluates whether a microbial or an enzymatic process is more suitable for efficient biodegradation, due to less sensitivity towards rubber additives. Therefore we investigated the impact of 15 different frequently used rubber additives on cells of the potent rubber degrader Gordonia polyisoprenivorans VH2 and the enzyme Lcp1VH2. For this, cells were grown on poly(cis-1,4-isoprene) in presence of these rubber additives. Furthermore, the effect of those additives on the enzymatic cleavage of poly(cis-1,4-isoprene) by Lcp1VH2 was determined by in vitro studies. It was observed that additives, used to accelerate the vulcanization process, like N-cyclohexyl-2-benzothiazolesulfenamide and zinc-bis(N,N-dibenzyl-dithiocarbamate), are diminishing the growth of the microorganism depending on their concentration-higher toxicity with increasing concentration. In contrast, sulfur prevents cell growth, but does not affect Lcp1VH2. Stearic acid and paraffin wax were found to be consumed by G. polyisoprenivorans VH2. Plasticizers mainly prevent growth, but do not interfere with the enzyme activity. This study identified antioxidants as the most interfering group of additives for microbial and enzymatic rubber degradation. It was found that the in vitro degradation by Lcp1VH2 is much more resistant and less sensitive towards the investigated rubber additives, when compared to the in vivo approach. Therefore, an enzymatic process might be a promising method to enhance rubber degradation.

Multiple models and experiments underscore large uncertainty in soil carbon dynamics

Soils contain more carbon than plants or the atmosphere, and sensitivities of soil organic carbon (SOC) stocks to changing climate and plant productivity are a major uncertainty in global carbon cycle projections. Despite a consensus that microbial degradation and mineral stabilization processes control SOC cycling, no systematic synthesis of long-term warming and litter addition experiments has been used to test process-based microbe-mineral SOC models. We explored SOC responses to warming and increased carbon inputs using a synthesis of 147 field manipulation experiments and five SOC models with different representations of microbial and mineral processes. Model projections diverged but encompassed a similar range of variability as the experimental results. Experimental measurements were insufficient to eliminate or validate individual model outcomes. While all models projected that CO2 efflux would increase and SOC stocks would decline under warming, nearly one-third of experiments observed decreases in CO2 flux and nearly half of experiments observed increases in SOC stocks under warming. Long-term measurements of C inputs to soil and their changes under warming are needed to reconcile modeled and observed patterns. Measurements separating the responses of mineral-protected and unprotected SOC fractions in manipulation experiments are needed to address key uncertainties in microbial degradation and mineral stabilization mechanisms. Integrating models with experimental design will allow targeting of these uncertainties and help to reconcile divergence among models to produce more confident projections of SOC responses to global changes.

Atomic-scale investigation of the interaction between coniferyl alcohol and laccase for lignin degradation using molecular dynamics simulations and spectroscopy

The interaction between coniferyl alcohol (CA) and laccase (LAC) was investigated using molecular dynamics (MD) simulations and spectral experiments. The mode of interaction between CA and LAC was established by MD simulations. The micro-environmental changes, stability and rigidity of the LAC-CA system were assessed by relevant parameters. These parameters include root mean square deviation (RMSD), root mean square fluctuation (RMSF) and radius of gyration (Rg). The calculated binding free energy (ΔGbinding= −19.99 kcal·mol.−1), the van der waals (VDW) contribution (ΔGvdw=−23.99 kcal·mol−1) and the electrostatic energy (ΔGele=−23.09 kcal·mol−1) of LAC-CA system demonstrated that the interaction of LAC-CA was a spontaneous process and the main interaction forces were van der Waal's and electrostatic forces. The values of ΔGvdw and ΔGele were negative, which demonstrated that VDW interactions and electrostatic interactions were favorable for the binding of CA and LAC. The binding constants, thermodynamic parameters, molecular force types and binding distances confirmed the interaction between CA and LAC and further verified the rationality of the theoretical model by spectral experiments. The MD simulations and experimental approaches provide clues for the discovery of new mediators and useful references for the mechanism of microbial degradation of lignin and industrialization of lignocellulose.

Key Bacteria for the Microbial Degradation of Pollutants in Cellar Water

The study aimed to identify the key bacteria and the potential interactions among these bacteria during the degradation of pollutants in cellar water, The main pollution characteristics were nitrogen, phosphorus and organic pollution. The structure and function of the bacterial community and its correlation with water quality variables were analyzed. A network of seven associations of microbial co-occurrence was set up, based on 16S rRNA and the model for inferring co-occurrence or interspecific interactions of microbial species. This showed that there were a large number of microorganisms with relatively specific ecological functions in the cellar water, and that many metabolic activities were involved. The ecological relationships of most bacteria in the association network were a form of mutualism. The most prominent genera included Lacibacter, Arthrobacter, Candidatus Protochlamydia, Methylocaldum, Sulfuritalea, Mycobacterium, Aquirestis, Rhodobacter, and, Methylotenera. The strong associations were observed between following bacteria:Sulfuritalea-Rhodobacter, Azospirillum-Rhodobacter, Methylocaldum-Rhodobacter, Arthrobacter-Rhodobacter, Rhodoplanes-Rhodobacter, Candidatus Protochlamydia-Rhodobacter, Methylotenera-Rhodobacter, Rhodobacter-Aquirestis, Mycobacterium-Rhodobacter, Planctomyces-Candidatus Solibacter, Planctomyces-Legionella, Hymenobacter-Adhaeribacter, and Luteolibacter-Crenothrix. It was considered that Rhodobacter, Methylocaldum, Methylotenera, Acinetobacter, Novosphingobium, Planctomyces, Hymenobacter, and Luteolibacter were the key bacteria involved in microbial degradation of cellar water pollutants, and Rhodobacter was the representative genus of the key bacteria. The authors concluded that the research results improved understanding of the microbial degradation mechanism of pollutants in cellar water.

An Amidase Gene, ipaH, Is Responsible for the Initial Step in the Iprodione Degradation Pathway of Paenarthrobacter sp. Strain YJN-5.

Iprodione [3-(3,5-dichlorophenyl) N-isopropyl-2,4-dioxoimidazolidine-1-carboxamide] is a highly effective broad-spectrum dicarboxamide fungicide. Several bacteria with iprodione-degrading capabilities have been reported; however, the enzymes and genes involved in this process have not been characterized. In this study, an iprodione-degrading strain, Paenarthrobacter sp. strain YJN-5, was isolated and characterized. Strain YJN-5 degraded iprodione through the typical pathway, with hydrolysis of its N-1 amide bond to N-(3,5-dichlorophenyl)-2,4-dioxoimidazolidine as the initial step. The ipaH gene, encoding a novel amidase responsible for this step, was cloned from strain YJN-5 by the shotgun method. IpaH shares the highest similarity (40%) with an indoleacetamide hydrolase (IAHH) from Bradyrhizobium diazoefficiens USDA 110. IpaH displayed maximal enzymatic activity at 35°C and pH 7.5, and it was not a metalloamidase. The kcat and Km of IpaH against iprodione were 22.42 s-1 and 7.33 μM, respectively, and the catalytic efficiency value (kcat/Km ) was 3.09 μM-1 s-1 IpaH has a Ser-Ser-Lys motif, which is conserved among members of the amidase signature family. The replacement of Lys82, Ser157, and Ser181 with alanine in IpaH led to the complete loss of enzymatic activity. Furthermore, strain YJN-5M lost the ability to degrade iprodione, suggesting that ipaH is the only gene responsible for the initial iprodione degradation step. The ipaH gene could also be amplified from another previously reported iprodione-degrading strain, Microbacterium sp. strain YJN-G. The sequence similarity between the two IpaHs at the amino acid level was 98%, indicating that conservation of IpaH exists in different strains.IMPORTANCE Iprodione is a widely used dicarboxamide fungicide, and its residue has been frequently detected in the environment. The U.S. Environmental Protection Agency has classified iprodione as moderately toxic to small animals and a probable carcinogen to humans. Bacterial degradation of iprodione has been widely investigated. Previous studies demonstrate that hydrolysis of its N-1 amide bond is the initial step in the typical bacterial degradation pathway of iprodione; however, enzymes or genes involved in iprodione degradation have yet to be reported. In this study, a novel ipaH gene encoding an amidase responsible for the initial degradation step of iprodione in Paenarthrobacter sp. strain YJN-5 was cloned. In addition, the characteristics and key amino acid sites of IpaH were investigated. These findings enhance our understanding of the microbial degradation mechanism of iprodione.

Biodegradation of 2,6-dibromo-4-nitrophenol by Cupriavidus sp. strain CNP-8: Kinetics, pathway, genetic and biochemical characterization.

Compound 2,6-dibromo-4-nitrophenol (2,6-DBNP) with high cytotoxicity and genotoxicity has been recently identified as an emerging brominated disinfection by-product during chloramination and chlorination of water, and its environmental fate is of great concern. To date, the biodegradation process of 2,6-DBNP is unknown. Herein, Cupriavidus sp. strain CNP-8 was reported to be able to utilize 2,6-DBNP as a sole source of carbon, nitrogen and energy. It degraded 2,6-DBNP in concentrations up to 0.7 mM, and the degradation of 2,6-DBNP conformed to Haldane inhibition model with μmax of 0.096 h-1, Ks of 0.05 mM and Ki of 0.31 mM. Comparative transcriptome and real-time quantitative PCR analyses suggested that the hnp gene cluster was likely responsible for 2,6-DBNP catabolism. Three Hnp proteins were purified and functionally verified. HnpA, a FADH2-dependent monooxygenase, was found to catalyze the sequential denitration and debromination of 2,6-DBNP to 6-bromohydroxyquinol (6-BHQ) in the presence of the flavin reductase HnpB. Gene knockout and complementation revealed that hnpA is essential for strain CNP-8 to utiluze 2,6-DBNP. HnpC, a 6-BHQ 1,2-dioxygenase was proposed to catalyze the ring-cleavage of 6-BHQ during 2,6-DBNP catabolism. These results fill a gap in the understanding of the microbial degradation process and mechanism of 2,6-DBNP.

Hydrolase CehA and Monooxygenase CfdC Are Responsible for Carbofuran Degradation in Sphingomonas sp. Strain CDS-1.

Carbofuran, a broad-spectrum systemic insecticide, has been extensively used for approximately 50 years. Diverse carbofuran-degrading bacteria have been described, among which sphingomonads have exhibited an extraordinary ability to catabolize carbofuran; other bacteria can only convert carbofuran to carbofuran phenol, while all carbofuran-degrading sphingomonads can degrade both carbofuran and carbofuran phenol. However, the genetic basis of carbofuran catabolism in sphingomonads has not been well elucidated. In this work, we sequenced the draft genome of Sphingomonas sp. strain CDS-1 that can transform both carbofuran and carbofuran phenol but fails to grow on them. On the basis of the hypothesis that the genes involved in carbofuran catabolism are highly conserved among carbofuran-degrading sphingomonads, two such genes, cehACDS-1 and cfdCCDS-1, were predicted from the 84 open reading frames (ORFs) that share ≥95% nucleic acid similarities between strain CDS-1 and another sphingomonad Novosphingobium sp. strain KN65.2 that is able to mineralize the benzene ring of carbofuran. The results of the gene knockout, genetic complementation, heterologous expression, and enzymatic experiments reveal that cehACDS-1 and cfdCCDS-1 are responsible for the conversion of carbofuran and carbofuran phenol, respectively, in strain CDS-1. CehACDS-1 hydrolyzes carbofuran to carbofuran phenol. CfdCCDS-1, a reduced flavin mononucleotide (FMNH2)- or reduced flavin adenine dinucleotide (FADH2)-dependent monooxygenase, hydroxylates carbofuran phenol at the benzene ring in the presence of NADH, FMN/FAD, and the reductase CfdX. It is worth noting that we found that carbaryl hydrolase CehAAC100, which was previously demonstrated to have no activity toward carbofuran, can actually convert carbofuran to carbofuran phenol, albeit with very low activity.IMPORTANCE Due to the extensive use of carbofuran over the past 50 years, bacteria have evolved catabolic pathways to mineralize this insecticide, which plays an important role in eliminating carbofuran residue in the environment. This study revealed the genetic determinants of carbofuran degradation in Sphingomonas sp. strain CDS-1. We speculate that the close homologues cehA and cfdC are highly conserved among other carbofuran-degrading sphingomonads and play the same roles as those described here. These findings deepen our understanding of the microbial degradation mechanism of carbofuran and lay a foundation for the better use of microbes to remediate carbofuran contamination.

Biodegradation of diethyl terephthalate and polyethylene terephthalate by a novel identified degrader Delftia sp. WL-3 and its proposed metabolic pathway.

This study demonstrates that Delftia sp. WL-3 can mineralize completely diethyl terephthalate by biochemical processes. The study reveals the metabolic mechanism of diethyl terephthalate biodegradation. Furthermore, the cracks on the surface of Polyethylene terephthalate film that form upon inoculation with strain WL-3 were observed using SEM. These results highlight the potential of the strain WL-3 in the bioremediation of environments contaminated with Polyethylene terephthalate or diethyl terephthalate.

Soil Microorganisms and Their Potential in Pesticide Biodegradation; A Review Article

Pesticides play an important role in preventing insect pests and weeds in crops. However, excessive use of pesticides has been known to be unsafe, due to their toxicity to non-target organisms and the ecosystem. Biodegradation is an innovative approach for decontaminating pesticide pollution. However, compared with the list of extensively used pesticides there are few well-characterized strains of microbes that transform pesticides into less-toxic or more labile products at environmentally useful rates. Fortunately, the technology required to isolate and characterize such microbial strains has improved immensely in the recent years. Furthermore, recent experimental developments have made practical the modification of potentially beneficial biodegradation genes so that they may be optimally expressed in a wide range of microbial species. This reviews article explore the recent studies that have focused on biodegradation of pesticide residues, the mechanism of microbial degradation of pesticides, the factors that affect the degradation of pesticides and the new application of microbial degradation of pesticides.

Microbial degradation mechanism of pyridine by Paracoccus sp. NJUST30 newly isolated from aerobic granules

In this study, a pyridine-degrading strain namely NJUST30 was isolated from aerobic granules capable of degrading pyridine and was identified as Paracoccus sp. At incubation temperature of 30 °C, initial pH of 7.0 and initial pyridine concentration of 500 mg L−1, complete pyridine removal could be achieved within incubation period as short as 54 h. Pyridine biodegradation profile by NJUST30 could be well fitted by the first-order decay kinetic model, suggesting the recalcitrant nature of pyridine and the inhibitory effect of pyridine towards NJUST30. Major intermediates during pyridine biodegradation by NJUST30, including 2,4-dihydroxy-2H-pyridine-3-one, 2-carbonyl-succinic acid, 1,2-dihydro-pyridin-2-ol, piperidin-2-ol and 4-formylamino-butyric acid were identified through HPLC/MS. Based on these intermediates, a distinct pyridine biodegradation pathway via hydroxylation, pyridine ring cleavage, carbonylation and carboxylation was revealed for the first time.

Identification and characterization of a new three-component nicotinic acid hydroxylase NahAB1 B2 from Pusillimonas sp. strain T2.

Nicotinic acid (NA) serves as a model system for the degradation of N-heterocyclic aromatic compounds and the microbial degradation mechanisms are diverse. This is the first time that a three-component hydroxylase has been identified. This study provides a novel insight into the NA degradation by bacteria.

Microbial Resources and Ecology - Microbial Degradation of Pesticides

ABSTRACT Pesticides play an important role in preventing insect pests and weeds in crops. However, due to the serious threat of pesticide residues to environmental and human health, this paper reviews the hazards of pesticide residues, the mechanism of microbial degradation of pesticides, the factors that affect the degradation of pesticides and the new application of microbial degradation of pesticides.

Surfing and dining on the “plastisphere”: Microbial life on plastic marine debris

Plastic marine debris represents a global threat for the marine environment, having serious consequences for the ocean, the wildlife and the human health. While the plastics distribution, fate, persistence and toxicity mechanisms for the marine fauna have been more studied in the last decade, small efforts have been devoted to identify and characterize marine microbes that colonize plastic and microplastic debris in the ocean, and their potential to degrade plastics. Here we review the knowledge on the microbial biodiversity and degradation mechanisms of marine plastic debris, and present data, based on metagenomic analyses, on the distribution patterns of genes potentially involved in microbially-mediated plastic degradation in coastal locations across the global ocean. Most studies on plastic-colonizing microbes have focused on seawater rather than sediment, with most studies underlining striking differences in composition between assemblages attached to plastic particles and those in the surrounding environment. The diversity of microbes attached to plastic is high, and the core epiplastic microbial assemblages include often hydrocarbon-degrading bacteria, as well as prokaryotic and eukaryotic phototrophs. Several marine microbes have shown to be able to degrade or deteriorate plastic in the laboratory, or to grow on plastic as the only source of carbon, while indirect evidences suggest that microbially-mediated degradation of recalcitrant plastics also occur in the ocean, though at very low rates. Metagenomic analyses show that plastic degradation-related genes are present in microbial assemblages in several coastal ocean sites, with relative abundance related to the magnitude of plastic pollution at each site. Further research is required to study microbial plastic-degraders in the marine ecosystem, to decipher and exploit the potential of microbial consortia to degrade or mineralize plastic compounds, and to better understand the fate and residence times of plastic waste in the ocean.

PH Stress-Induced Cooperation between Rhodococcus ruber YYL and Bacillus cereus MLY1 in Biodegradation of Tetrahydrofuran.

Microbial consortia consisting of cooperational strains exhibit biodegradation performance superior to that of single microbial strains and improved remediation efficiency by relieving the environmental stress. Tetrahydrofuran (THF), a universal solvent widely used in chemical and pharmaceutical synthesis, significantly affects the environment. As a refractory pollutant, THF can be degraded by some microbial strains under suitable conditions. There are often a variety of stresses, especially pH stress, that inhibit the THF-degradation efficiency of microbial consortia. Therefore, it is necessary to study the molecular mechanisms of microbial cooperational degradation of THF. In this study, under conditions of low pH (initial pH = 7.0) stress, a synergistic promotion of the THF degradation capability of the strain Rhodococcus ruber YYL was found in the presence of a non-THF degrading strain Bacillus cereus MLY1. Metatranscriptome analysis revealed that the low pH stress induced the strain YYL to up-regulate the genes involved in anti-oxidation, mutation, steroid and bile acid metabolism, and translation, while simultaneously down-regulating the genes involved in ATP production. In the co-culture system, strain MLY1 provides fatty acids, ATP, and amino acids for strain YYL in response to low pH stress during THF degradation. In return, YYL shares the metabolic intermediates of THF with MLY1 as carbon sources. This study provides the preliminary mechanism to understand how microbial consortia improve the degradation efficiency of refractory furan pollutants under environmental stress conditions.

Genetic and Biochemical Characterization of 2-Chloro-5-Nitrophenol Degradation in a Newly Isolated Bacterium, Cupriavidus sp. Strain CNP-8.

Compound 2-chloro-5-nitrophenol (2C5NP) is a typical chlorinated nitroaromatic pollutant. To date, the bacteria with the ability to degrade 2C5NP are rare, and the molecular mechanism of 2C5NP degradation remains unknown. In this study, Cupriavidus sp. strain CNP-8 utilizing 2-chloro-5-nitrophenol (2C5NP) and meta-nitrophenol (MNP) via partial reductive pathways was isolated from pesticide-contaminated soil. Biodegradation kinetic analysis indicated that 2C5NP degradation by this strain was concentration dependent, with a maximum specific degradation rate of 21.2 ± 2.3 μM h−1. Transcriptional analysis showed that the mnp genes are up-regulated in both 2C5NP- and MNP-induced strain CNP-8. Two Mnp proteins were purified to homogeneity by Ni-NTA affinity chromatography. In addition to catalyzing the reduction of MNP, MnpA, a NADPH-dependent nitroreductase, also catalyzes the partial reduction of 2C5NP to 2-chloro-5-hydroxylaminophenol via 2-chloro-5-nitrosophenol, which was firstly identified as an intermediate of 2C5NP catabolism. MnpC, an aminohydroquinone dioxygenase, is likely responsible for the ring-cleavage reaction of 2C5NP degradation. Gene knockout and complementation indicated that mnpA is necessary for both 2C5NP and MNP catabolism. To our knowledge, strain CNP-8 is the second 2C5NP-utilizing bacterium, and this is the first report of the molecular mechanism of microbial 2C5NP degradation.

Molecular Mechanism and Genetic Determinants of Buprofezin Degradation.

Buprofezin is a widely used insect growth regulator whose residue has been frequently detected in the environment, posing a threat to aquatic organisms and nontarget insects. Microorganisms play an important role in the degradation of buprofezin in the natural environment. However, the relevant catabolic pathway has not been fully characterized, and the molecular mechanism of catabolism is still completely unknown. Rhodococcus qingshengii YL-1 can utilize buprofezin as a sole source of carbon and energy for growth. In this study, the upstream catabolic pathway in strain YL-1 was identified using tandem mass spectrometry. Buprofezin is composed of a benzene ring and a heterocyclic ring. The degradation is initiated by the dihydroxylation of the benzene ring and continues via dehydrogenation, aromatic ring cleavage, breaking of an amide bond, and the release of the heterocyclic ring 2-tert-butylimino-3-isopropyl-1,3,5-thiadiazinan-4-one (2-BI). A buprofezin degradation-deficient mutant strain YL-0 was isolated. A comparative genomic analysis combined with gene deletion and complementation experiments revealed that the gene cluster bfzBA3A4A1A2C is responsible for the upstream catabolic pathway of buprofezin. The bfzA3A4A1A2 cluster encodes a novel Rieske nonheme iron oxygenase (RHO) system that is responsible for the dihydroxylation of buprofezin at the benzene ring; bfzB is involved in dehydrogenation, and bfzC is in charge of benzene ring cleavage. Furthermore, the products of bfzBA3A4A1A2C can also catalyze dihydroxylation, dehydrogenation, and aromatic ring cleavage of biphenyl, flavanone, flavone, and bifenthrin. In addition, a transcriptional study revealed that bfzBA3A4A1A2C is organized in one transcriptional unit that is constitutively expressed in strain YL-1.IMPORTANCE There is an increasing concern about the residue and environmental fate of buprofezin. Microbial metabolism is an important mechanism responsible for the buprofezin degradation in the natural environment. However, the molecular mechanism and genetic determinants of microbial degradation of buprofezin have not been well identified. This work revealed that gene cluster bfzBA3A4A1A2C is responsible for the upstream catabolic pathway of buprofezin in Rhodococcus qingshengii YL-1. The products of bfzBA3A4A1A2C could also degrade bifenthrin, a widely used pyrethroid insecticide. These findings enhance our understanding of the microbial degradation mechanism of buprofezin and benefit the application of strain YL-1 and bfzBA3A4A1A2C in the bioremediation of buprofezin contamination.

The metabolic pathway of metamifop degradation by consortium ME-1 and its bacterial community structure.

Metamifop is universally used in agriculture as a post-emergence aryloxyphenoxy propionate herbicide (AOPP), however its microbial degradation mechanism remains unclear. Consortium ME-1 isolated from AOPP-contaminated soil can degrade metamifop completely after 6days and utilize it as the carbon source for bacterial growth. Meanwhile, consortium ME-1 possessed the ability to degrade metamifop stably under a wide range of pH (6.0-10.0) or temperature (20-42°C). HPLC-MS analysis shows that N-(2-fluorophenyl)-2-(4-hydroxyphenoxy)-N-methyl propionamide, 2-(4-hydroxyphenoxy)-propionic acid, 6-chloro-2-benzoxazolinone and N-methyl-2-fluoroaniline, were detected and identified as four intermediate metabolites. Based on the metabolites identified, a putative metabolic pathway of metamifop was proposed for the first time. In addition, the consortium ME-1 was also able to transform or degrade other AOPP such as fenoxaprop-p-ethyl, clodinafop-propargyl, quizalofop-p-ethyl and cyhalofop-butyl. Moreover, the community structure of ME-1 with lower microbial diversity compared with the initial soil sample was investigated by high throughput sequencing. β-Proteobacteria and Sphingobacteria were the largest class with sequence percentages of 46.6% and 27.55% at the class level. In addition, 50genera were classified in consortium ME-1, of which Methylobacillus, Sphingobacterium, Bordetella and Flavobacterium were the dominant genera with sequence percentages of 25.79, 25.61, 14.68 and 9.55%, respectively.

A model for the biochemical degradation of inosine monophosphate in hake (Merluccius merluccius)

ATP-derived products are typically used as early indicators of fish quality loss during storage. In this work, we explore different biochemical routes that are potentially relevant in contributing to nucleotide degradation in hake (Merluccius merluccius). A major motivation of this study is to get more insight on the biochemical degradation mechanisms of nucleotide catabolites in hake muscle at fish storage and transport conditions. This requires the identification of its relevant pathways.To that purpose, different degradation routes proposed in the literature are considered and a mathematical model for the degradation process is derived. First order kinetics are assumed for all the reactions and temperature dependence is taken into account through the Arrhenius equation. Unknown model parameters, namely activation energies and pre-exponential Arrhenius coefficients, are estimated via fitting to experimental data. From the estimation results, relevant routes are identified. The kinetic study is performed on sterile fish juice to avoid coupling with microbial degradation mechanisms or possible interferences of the food matrix that might hide biochemical interactions.The proposed scheme adequately describes biochemical changes in nucleotide catabolites under variable temperature profiles. It also reveals a pathway which at least seems relevant for nucleotide degradation in hake.

Identification and degradation characteristics of a napropamide-degrading bacterium strain

In order to investigate the microbial degradation mechanism of amide herbicide napropamide and its degradation bioaugmentation in soil, a bacterial strain LGY06 capable of utilizing napropamide as sole carbon and energy source was isolated from a tobacco-planted soil after successive application of napropamide. LGY06 was identified as Bacillus cereus based on morphological, physiological and biochemical characteristics, and the 16S rDNA homologue sequence analysis. The degradation of napropamide in pure cultures by LGY06 was fitted to the first-order function. The strain LGY06 could degrade more than 75.7% of 50 mg·L-1 napropamide within 7 d. The optimal temperature and pH for napropamide degradation was 35 ℃ and 8.0, respectively. The pathway of napropamide degradation was elucidated based on metabolites identification by GC-MS. The main degradation products of napropamide by LGY06 were α-naphthol and propylacetanilide. The meta-bolism of napropamide by strain LGY06 involved dealkylation and oxidation (or hydrolyzation). Under the laboratory control conditions, the bacterial strain LGY06 could effectively enhance the degradation of napropamide in soil. Compared with the un-inoculated controls, the half-life of napropamide in sterilized soil, non-rhizosphere soil, and rhizosphere soil inoculated with the strain LGY06 was shorted by 79.5%, 36.6% and 41.1%, respectively.