Biodegradation of cyclohexylamine by Brevibacterium oxydans IH-35A

Reaction of cyclamate with hypochlorous acid in vitro and formation of chlorcyclohexylamine and cyclohexylamine

In this work, we investigated the reaction of cyclamate with hypochlorous acid (HOCl) in simulated gastric juice. The reaction products were detected by high-performance liquid chromatography diode array detection (HPLC-DAD) and ultra-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS). We also explored the changes in product concentration as a function of reaction time, cyclamate and HOCl concentrations. Cyclamate reacted with hypochlorous acid instantly in the simulated gastric fluid. N, N-dichlorcyclohexylamine and cyclohexylamine were both detected when the HOCl concentration was at millimole. Cyclohexylamine can only be found when HOCl concentration was at micromole. N, N-dichlorcyclohexylamine and cyclohexylamine concentrations both increased when cyclamate concentration increased under the millimole level of HOCl. As an important reactive oxygen species, hypochlorous acid (HClO) is produced in various physiological processes. The abnormal rise of the HClO level is associated with many inflammatory diseases. Chronic gastritis associated with Helicobacter pylori is a multistep, progressive, life-long inflammation. So, chronic gastritis infected with H. pylori may cause cyclamate metabolizing into cyclohexylamine in vivo.

Cloning and characterization of four enzymes responsible for cyclohexylamine degradation from Paenarthrobacter sp. TYUT067

Paenarthrobacter sp. TYUT067 is a soil bacterium that can degrade and use cyclohexylamine as the sole source of carbon and energy. However, the responsible enzymes involved in cyclohexylamine degradation by TYUT067 have not been cloned and characterized in detail yet. In this study, four possible cyclohexylamine degradation genes, one cyclohexylamine oxidase (Pachao), two cyclohexanone monooxygenases (Pachms) and one lactone hydrolase (Pamlh) were successfully cloned and heterologous expressed in Escherichia coli T7 host cells. The four enzymes were purified and characterized. The optimal pH and temperature of the purified enzymes toward their own substrates were 7.0 (PaCHAO), 8.0 (PaCHM1), 9.0 (PaCHM2 and PaMLH) and 30 °C (PaCHAO and PaMLH), 40 °C (PaCHM2) and 45 °C (PaCHM1), respectively, with K_M of 1.1 mM (PaCHAO), 0.1 mM (PaCHM1), 0.1 mM (PaCHM2) and 0.8 mM (PaMLH), and yielding a catalytic efficiency k_cat/K_M of 16.1 mM^-1 s^-1 (PaCHAO), 1.0 mM^-1 s^-1 (PaCHM1), 5.0 mM^-1 s^-1 (PaCHM2) and 124.4 mM^-1 s^-1 (PaMLH). In vitro mimicking the cyclohexylamine degradation pathway was conducted by using the combined three cyclohexylamine degradation enzymes (PaCHAO, PaCHM2 and PaMLH) with 10-50 mM cyclohexylamine, 100% conversion of cyclohexylamine could be finished within 12 h without any detected intermediates. The current study confirmed the enzymes responsible for cyclohexylamine degradation in TYUT067 for the first time, provide basic information for further investigation and application of these specific enzymes in pollution control.

Biodegradation of Polystyrene by Three Bacterial Strains Isolated from the Gut of Superworms (Zophobas atratus larvae)

AIMS

To isolate polystyrene degrading bacteria from the gut of superworms and investigate their ability to degrade polystyrene (PS).

METHODS AND RESULTS

Three PS degrading bacteria identified as Pseudomonas sp. EDB1, Bacillus sp. EDA4, and Brevibacterium sp. EDX were successfully isolated from the gut of superworms (Zophobas atratus Larvae) that ingest PS. Incubating PS with each strain for 30-day led to the formation of biofilm on the PS film. Scanning Electron Microscopy (SEM) revealed considerable damage (in terms of pits formation) on the surface of the PS films. FTIR analysis suggested the incorporation of carbonyl group into the carbon backbone of PS. Decreasing of WCA of microbial treated PS film confirmed a chemical change from hydrophobicity to hydrophilicity on the PS surface. Based on these results, we conclude that all isolates had the ability to degrade PS.

CONCLUSIONS

Brevibacterium sp. EDX (GenBank MZ32399) was isolated as the most efficient PS-degrading strain based on the most changing in both PS surface morphology (SEM and WCA analyses) and chemical modification (FTIR analysis) in its PS degradation process.

SIGNIFICANCE AND IMPACT OF THE STUDY

This was the first study to describe the PS degradation by Brevibacterium sp. EDX, and thus provided for its development in plastic remediation process.

Biodegradation of alicyclic amines by a newly isolated hypersaline tolerant strain Paenarthrobacter sp. TYUT067

Alicyclic amines are widely used in several types of industries, and considerable attention has been devoted to possible environmental pollution by alicyclic amines in hypersaline industrial wastewater. In this study, a new hypersaline tolerant bacterial TYUT067 capable of growing in liquid basal salt medium with cyclohexylamine (CHAM) as the sole carbon source and energy source, was isolated from soil, and discovered with highly efficient CHAM degrading ability. The strain TYUT067 was identified as Paenarthrobacter sp. based on 16S rDNA gene sequence, and its degradation characteristic was examined. The results revealed that the isolated TYUT067 could grow well under pH range of 6.5-10.0, temperature from 20 °C to 30 °C. For degradation of 60 mM of cyclohexylamine, 100% degradation could be finished within 120 h. The TYUT067 could degrade 10 mM CHAM under hypersaline conditions (3-5% NaCl, w/v), revealed the hypersaline tolerance of TYUT067. Different type of amines was also tested with TYUT067, the degradations of >90% were achieved toward several alicyclic amines. The current results suggested that TYUT067 was a potential species could be efficiently used for the degradation of alicyclic amines and might be applicable to a hypersaline wastewater treatment system for the removal of alicyclic amines.

Enantioselective Cascade Biocatalysis for Deracemization of Racemic β-Amino Alcohols to Enantiopure (S)-β-Amino Alcohols by Employing Cyclohexylamine Oxidase and ω-Transaminase

Optically active β-amino alcohols are very useful chiral intermediates frequently used in the preparation of pharmaceutically active substances. Here, a novel cyclohexylamine oxidase (ArCHAO) was identified from the genome sequence of Arthrobacter sp. TYUT010-15 with the R-stereoselective deamination activity of β-amino alcohol. ArCHAO was cloned and successfully expressed in E. coli BL21, purified and characterized. Substrate-specific analysis revealed that ArCHAO has high activity (4.15 to 6.34 U mg^-1 protein) and excellent enantioselectivity toward the tested β-amino alcohols. By using purified ArCHAO, a wide range of racemic β-amino alcohols were resolved, (S)-β-amino alcohols were obtained in >99 % ee. Deracemization of racemic β-amino alcohols was conducted by ArCHAO-catalyzed enantioselective deamination and transaminase-catalyzed enantioselective amination to afford (S)-β-amino alcohols in excellent conversion (78-94 %) and enantiomeric excess (>99 %). Preparative-scale deracemization was carried out with 50 mM (6.859 g L^-1 ) racemic 2-amino-2-phenylethanol, (S)-2-amino-2-phenylethanol was obtained in 75 % isolated yield and >99 % ee.

Tetracycline degradation by Klebsiella sp. strain TR5: Proposed degradation pathway and possible genes involved

Microorganisms with high tetracycline (TC) degradation efficiencies are required for biological processes for TC-containing wastewater treatment. With multiple enrichment cultures, a TC-degrading strain TR5 was isolated from chicken manure mixture in a large broiler farm, which was identified as Klebsiella pneumoniae by 16S rRNA gene sequencing and biochemical properties. Strain TR5 could degrade TC quickly (∼90% within 36 h) with the initial TC concentration of 200 mg/L under optimized conditions via single-factor experiment coupled with RSM. Strain TR5 could detoxify TC and generate much less toxic products as long as cultured more than one day. Three TC-degrading pathways were proposed based on 8 possible products. A transformant containing a plasmid from TR5 acquired TC-degrading ability, indicating that TC-degrading genes were located on this plasmid. Complete sequencing of pYK5 showed that isomerase-, oxidoreductase-, and transferases-encoding genes were found and were inferred to be involved in TC degradation. TR5 may not degrade TC completely and it can utilize some carbon-containing compounds derived from TC via the effect of formylglutathione hydrolase-encoding gene. Our findings showed that strain TR5 could be a promising agent for wastewater treatment, and genes involved in TC degradation are worthy of further investigations for enzyme preparations development.

Complete Genome Sequence of Mameliella alba Strain KU6B, a Cyclohexylamine-Utilizing Marine Bacterium

Here, we report the complete genome sequence of Mameliella alba strain KU6B, a bacterium newly isolated from seawater of Boso Peninsula in Japan that is capable of utilizing cyclohexylamine. The complete genome contained a 5,386,988-bp circular chromosome and three circular plasmids of 256,516, 112,434, and 76,727 bp.

Here, we report the complete genome sequence of Mameliella alba strain KU6B, a bacterium newly isolated from seawater of Boso Peninsula in Japan that is capable of utilizing cyclohexylamine. The complete genome contained a 5,386,988-bp circular chromosome and three circular plasmids of 256,516, 112,434, and 76,727 bp.

Native roles of Baeyer–Villiger monooxygenases in the microbial metabolism of natural compounds

Baeyer–Villiger monooxygenases function in the primary metabolism of atypical carbon sources, as well as the synthesis of complex microbial metabolites.

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 (CHAO_YT–02) was 48% identical to its homolog from Brevibacterium oxydans IH-35A (CHAO_IH–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 K_m and V_max 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 CHAO_YT–02 and CHAO_IH–35 were compared. Our results are helpful to elucidate the mechanism of microbial degradation of CHAM in the strain YT-02. In addition, CHAO_YT–02, as a potential biocatalyst, is promising in controlling CHAM pollution and deracemization of chiral amines.

Draft Genome Sequence of Cyclohexylamine-Degrading Strain Acinetobacter sp. YT-02 Isolated

Acinetobacter sp. YT-02, a Gram-negative bacterium isolated from the activated sludge from a sodium N-cyclohexylsulfamate production plant, has the ability to degrade cyclohexylamine. It was classified as a member of Acinetobacter sp., a Gram-negative bacterium, sharing a 16S rRNA gene sequence identity of 99% with Acinetobacter guangdongensis strain 1NM-4. It could degrade 10 mmol/L cyclohexylamine within 22 h. Based on the identified metabolite, the metabolic pathway of cyclohexylamine could be postulated as it was degraded via cyclohexanone. Draft genome sequence of this strain (2,993, 647 bp of chromosome length) is presented here. We further identified the genes encoding the enzymes involved in cyclohexylamine oxidation to cyclohexanone and the subsequent downstream metabolic pathway of cyclohexanone oxidation. Strain YT-02 has the potentiality to be applied in the treatment of the pollutant cyclohexylamine, and it could also be treated as a research material to study the degradation mechanism of cyclohexylamine.

Complete genome sequence of the cyclohexylamine-degrading Pseudomonas plecoglossicida NyZ12

Pseudomonas plecoglossicida NyZ12 (CCTCC AB 2015057), a Gram-negative bacterium isolated from soil, has the ability to degrade cyclohexylamine. The complete genome sequence of this strain (6,233,254bp of chromosome length) is presented, with information about the genes of characteristic enzymes responsible for cyclohexylamine oxidation to cyclohexanone and the integrated gene cluster for the metabolic pathway of cyclohexanone oxidation to adipate.

Structural analysis of a novel cyclohexylamine oxidase from Brevibacterium oxydans IH-35A

Cyclohexylamine oxidase (CHAO) is a flavoprotein first described in Brevibacterium oxydans strain IH-35A that carries out the initial step of the degradation of the industrial chemical cyclohexylamine to cyclohexanone. We have cloned and expressed in Escherichia coli the CHAO-encoding gene (chaA) from B. oxydans, purified CHAO and determined the structures of both the holoenzyme form of the enzyme and a product complex with cyclohexanone. CHAO is a 50 kDa monomer with a PHBH fold topology. It belongs to the flavin monooxygenase family of enzymes and exhibits high substrate specificity for alicyclic amines and sec-alkylamines. The overall structure is similar to that of other members of the flavin monooxygenase family, but lacks either of the C- or N-terminal extensions observed in these enzymes. Active site features of the flavin monooxygenase family are conserved in CHAO, including the characteristic aromatic cage. Differences in the orientations of residues of the CHAO aromatic cage result in a substrate-binding site that is more open than those of its structural relatives. Since CHAO has a buried hydrophobic active site with no obvious route for substrates and products, a random acceleration molecular dynamics simulation has been used to identify a potential egress route. The path identified includes an intermediate cavity and requires transient conformation changes in a shielding loop and a residue at the border of the substrate-binding cavity. These results provide a foundation for further studies with CHAO aimed at identifying features determining substrate specificity and for developing the biocatalytic potential of this enzyme.

Cyclohexylamine oxidase as a useful biocatalyst for the kinetic resolution and dereacemization of amines

The biocatalytic performance of a cloned cyclohexylamine oxidase derived from Brevibacterium oxydans IH-35A towards structurally different amines was investigated. Cycloalkyl primary amines, alkyl aryl amines, and α-carbon-substituted aliphatic amines were identified as suitable substrates for the biocatalyst based on an activity assay. Kinetic resolutions of several amines by either recombinant whole cells or crude enzyme extracts prepared therefrom gave enantiomerically pure (R)-amines besides the corresponding ketones. When cyclohexylamine oxidase in combination with a borane–ammonia complex as reducing agent was applied to the deracemization of several substrates, excellent enantiomeric ratios (>99:1) and good isolated yields (62%–75%) of the corresponding (R)-amines were obtained.

Membrane bioreactor treatment of a simulated metalworking fluid wastewater containing ethylenediaminetetraacetic acid and dicyclohexylamine

Membrane bioreactors (MBRs) have been installed at automotive plants to treat metalworking fluid (MWF) wastewaters, which are known to contain toxic and/or recalcitrant organic compounds. A laboratory study was conducted to evaluate treatment of a simulated wastewater prepared from a semisynthetic MWF, which contains two such compounds, dicyclohexylamine (DCHA) and ethylenediaminetetraacetic acid (EDTA). Primary findings were as follows: During stable operating periods, almost all chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), and EDTA were removed (by > 96%). During somewhat unstable periods, COD removal was still extremely robust, but removal of EDTA and TKN were sensitive to prolonged episodes of low dissolved oxygen. Nitrogen mass balance suggested 30 to 40% TKN removal by assimilation and 60 to 70% by nitrification (including up to 34% TKN removal via subsequent denitrification). Dicyclohexylamine appeared to be readily biodegraded. Maximum DCHA and EDTA degradation rates between pH 7 and 8 were found. An Arthrobacter sp. capable of growth on DCHA as the sole source of carbon and energy was isolated.

Influence of artificial sweeteners on the kinetic and metabolic behavior of Lactobacillus delbrueckii subsp. bulgaricus

The addition of artificial sweeteners to a LAPT (yeast extract, peptone, and tryptone) medium without supplemented sugar increased the growth rate and final biomass of Lactobacillus delbrueckii subsp. bulgaricus YOP 12 isolated from commercial yogurt. Saccharin and cyclamate were consumed during microorganism growth, while the uptake of aspartame began once the medium was glucose depleted. The pH of the media increased as a consequence of the ammonia released into the media supplemented with the sweeteners. The L. delbrueckii subsp. bulgaricus strain was able to grow in the presence of saccharin, cyclamate, or aspartame, and at low sweetener concentrations, the microorganism could utilize cyclamate and aspartame as an energy and carbon source.

The selection of mixed microbial inocula in environmental biotechnology: Example using petroleum contaminated tropical soils

The impact of inorganic N and P additions on a tropical soil contaminated with petroleum hydrocarbons was investigated using molecular and culture techniques. Microcosms were incubated for 42 days and sampled at 0, 1, 7, 28 and 42 days. Changes in bacterial community structure were determined using denaturing gradient gel electrophoresis (DGGE) of the rRNA following reverse transcription PCR using primers specific to the V3 region of the 16S rRNA gene. To identify which components of the microbial community were changing during incubation, PCR amplicons were resolved using DGGE and the banding patterns analyzed using stepwise discriminant function analysis (SDA). SDA showed that the number of bands needed to recover the differences between samples over time could be reduced from the initial 11 bands for the 16S rRNA transcript to 3 bands. Sequences originating from the rRNA gels (16S rRNA transcripts) were recovered in clades containing known cultured isolates of Bacillus marisflavi, Microbacterium oxydans and Pseudomonas oleovorans. Isolation studies on these soils using lubricant oil as a carbon source yielded 317 bacterial isolates, 3 of which showed high sequence similarity (>96%) with the 16S rRNA transcripts identified using SDA as being important in differentiating between bacterial communities over time. These isolates were then tested singly and in combination for their ability to degrade lubricant oil. These analyses demonstrated that the consortium selected using the combined molecular-SDA approach was more effective at degrading the lubricant in both liquid media and in contaminated sand than the single isolates.

Purification and characterization of a novel cyclohexylamine oxidase from the cyclohexylamine-degrading Brevibacterium oxydans IH-35A

Cyclohexylamine oxidase (CHAO) from a cell extract of Brevibacterium grown on cyclohexylamine was purified 50.2-fold, to electrophoretic homogeneity, by serial chromatographies. The molecular mass of the native enzyme was estimated to be approximately 50 kDa by gel filtration and SDS-PAGE. The optimum pH was 7.4 and the stable pH range was 6.0 to 7.0. The enzyme was thermostable up to 30 degrees C. The enzyme was found to be highly specific for the deamination of alicyclic monoamines such as cyclopentylamine, cycloheptylamine, and N-methylcyclohexylamine and aliphatic monoamines, such as sec-butylamine. The apparent K(m) value for cyclohexylamine was 1.23 mM. The enzyme was inhibited by flavin enzyme inhibitors such as quinine and quinacrine. The N-terminal 27 amino acid residues were determined as Gly-Ser-Val-Thr-Pro-Asp-Pro-Asp-Val-Asp-Val-Ile-Ile-His-Gly-Ala-Gly-Ile-Ser-Gly-Ser-Ala-Ala-Ala-Lys-Ala-Leu-, revealing homology to conventional flavin-containing amine oxidases (EC 1.4.3.4).