Metabolic engineering of Pseudomonas bharatica CSV86T to degrade Carbaryl (1-naphthyl-N-methylcarbamate) via the salicylate-catechol route.

Pseudomonas bharatica CSV86T displays the unique property of preferential utilization of aromatic compounds over simple carbon sources like glucose and glycerol and their co-metabolism with organic acids. Well-characterized growth conditions, aromatic compound metabolic pathways and their regulation, genome sequence, and advantageous eco-physiological traits (indole acetic acid production, alginate production, fusaric acid resistance, organic sulfur utilization, and siderophore production) make it an ideal host for metabolic engineering. Strain CSV86T was engineered for Carbaryl (1-naphthyl-N-methylcarbamate) degradation via salicylate-catechol route by expression of a Carbaryl hydrolase (CH) and a 1-naphthol 2-hydroxylase (1NH). Additionally, the engineered strain exhibited faster growth on Carbaryl upon expression of the McbT protein (encoded by the mcbT gene, a part of Carbaryl degradation upper operon of Pseudomonas sp. C5pp). Bioinformatic analyses predict McbT to be an outer membrane protein, and Carbaryl-dependent expression suggests its probable role in Carbaryl uptake. Enzyme activity and protein analyses suggested periplasmic localization of CH (carrying transmembrane domain plus signal peptide sequence at the N-terminus) and 1NH, enabling compartmentalization of the pathway. Enzyme activity, whole-cell oxygen uptake, spent media analyses, and qPCR results suggest that the engineered strain preferentially utilizes Carbaryl over glucose. The plasmid-encoded degradation property was stable for 75-90 generations even in the absence of selection pressure (kanamycin or Carbaryl). These results indicate the utility of P. bharatica CSV86T as a potential host for engineering various aromatic compound degradation pathways.IMPORTANCEThe current study describes engineering of Carbaryl metabolic pathway in Pseudomonas bharatica CSV86T. Carbaryl, a naphthalene-derived carbamate pesticide, is known to act as an endocrine disruptor, mutagen, cytotoxin, and carcinogen. Removal of xenobiotics from the environment using bioremediation faces challenges, such as slow degradation rates, instability of the degradation phenotype, and presence of simple carbon sources in the environment. The engineered CSV86-MEC2 overcomes these disadvantages as Carbaryl was degraded preferentially over glucose. Furthermore, the plasmid-borne degradation phenotype is stable, and presence of glucose and organic acids does not repress Carbaryl metabolism in the strain. The study suggests the role of outer membrane protein McbT in Carbaryl transport. This work highlights the suitability of P. bharatica CSV86T as an ideal host for engineering aromatic pollutant degradation pathways.

Development of efficient modules for recombinant protein expression and periplasmic localisation in Pseudomonas bharatica CSV86T.

Escherichia coli has been widely employed as a host for heterologous protein expression. However, due to certain limitations, alternative hosts like Pseudomonas, Lactococcus and Bacillus are being explored. Pseudomonas bharatica CSV86T, a novel soil isolate, preferentially degrades wide range of aromatics over simple carbon sources like glucose and glycerol. Strain also possesses advantageous eco-physiological traits, making it an ideal host for engineering xenobiotic degradation pathways, which necessitates the development of heterologous expression systems. Based on the efficient growth, short lag-phase and rapid metabolism of naphthalene, Pnah and Psal promoters (regulated by NahR) were selected for expression. Pnah was found to be strong and leaky as compared to Psal, using 1-naphthol 2-hydroxylase (1NH, ∼66 kDa) as reporter gene in strain CSV86T. The Carbaryl hydrolase (CH, ∼72 kDa) from Pseudomonas sp. C5pp was expressed under Pnah in strain CSV86T and could successfully be translocated to the periplasm due to the presence of the Tmd + Sp sequence. The recombinant CH was purified from the periplasmic fraction and the kinetic characteristics were found to be similar to the native protein from strain C5pp. These results potentiate the suitability of P. bharatica CSV86T as a desirable host, while Pnah and the Tmd + Sp can be employed for overexpression and periplasmic localisation, respectively. Such tools find application in heterologous protein expression and metabolic engineering applications.

Co-inducible Catabolism of 2-Naphthol Initiated by Hydroxylase CehC1C2 in Rhizobium sp. X9 Removed Its Ecotoxicity.

2-Naphthol, which originates from various industrial activities, is widely disseminated through the discharge of industrial wastewater and is, thus, harmful to the water ecosystem, agricultural production, and human health. In this study, the carbaryl degrading strain Rhizobium sp. X9 was proven to be able to degrade 2-naphthol and reduce its toxicity to rice (Oryza sativa) and Chlorella ellipsoidea. Two-component hydroxylase CehC1C2 is responsible for the initial step of degradation and generates 1,2-dihydroxynaphthalene, which is further degraded by the ceh cluster. The transcription of gene cluster cehC1C2 could be induced when both 2-naphthol and glucose were added. A bioinformatic analysis revealed that two transcriptional regulators, the inhibitor CehR2 and the activator CehR3, could be involved in this process. Our study elucidated the molecular mechanism of microbial degradation of 2-naphthol and provided an effective strategy for the in situ remediation of 2-naphthol contamination in the environment.

Display of a novel carboxylesterase CarCby on Escherichia coli cell surface for carbaryl pesticide bioremediation.

BACKGROUND: Carbamate pesticides have been widely used in agricultural and forestry pest control. The large-scale use of carbamates has caused severe toxicity in various systems because of their toxic environmental residues. Carbaryl is a representative carbamate pesticide and hydrolase/carboxylesterase is the initial and critical enzyme for its degradation. Whole-cell biocatalysts have become a powerful tool for environmental bioremediation. Here, a whole cell biocatalyst was constructed by displaying a novel carboxylesterase/hydrolase on the surface of Escherichia coli cells for carbaryl bioremediation. RESULTS: The carCby gene, encoding a protein with carbaryl hydrolysis activity was cloned and characterized. Subsequently, CarCby was displayed on the outer membrane of E. coli BL21(DE3) cells using the N-terminus of ice nucleation protein as an anchor. The surface localization of CarCby was confirmed by SDS-PAGE and fluorescence microscopy. The optimal temperature and pH of the engineered E. coli cells were 30 °C and 7.5, respectively, using pNPC4 as a substrate. The whole cell biocatalyst exhibited better stability and maintained approximately 8-fold higher specific enzymatic activity than purified CarCby when incubated at 30 °C for 120 h. In addition, ~ 100% and 50% of the original activity was retained when incubated with the whole cell biocatalyst at 4 ℃ and 30 °C for 35 days, respectively. However, the purified CarCby lost almost 100% of its activity when incubated at 30 °C for 134 h or 37 °C for 96 h, respectively. Finally, approximately 30 mg/L of carbaryl was hydrolyzed by 200 U of the engineered E. coli cells in 12 h. CONCLUSIONS: Here, a carbaryl hydrolase-containing surface-displayed system was first constructed, and the whole cell biocatalyst displayed better stability and maintained its catalytic activity. This surface-displayed strategy provides a new solution for the cost-efficient bioremediation of carbaryl and could also have the potential to be used to treat other carbamates in environmental bioremediation.

The Potential Binding Interaction and Hydrolytic Mechanism of Carbaryl with the Novel Esterase PchA in Pseudomonas sp. PS21.

Microbial bioremediation is a very potent and eco-friendly approach to alleviate pesticide pollution in agricultural ecosystems, and hydrolase is an effective element for contaminant degradation. In the present study, a novel Mn2+-dependent esterase, PchA, that efficiently hydrolyzes carbamate pesticides with aromatic structures was identified from Pseudomonas sp. PS21. The hydrolytic activity was confirmed to be related closely to the core catalytic domain, which consists of six residues. The crucial residues indirectly stabilized the position of carbaryl via chelating Mn2+ according to the binding model clarified by molecular simulations, and the additional hydrophobic interactions between carbaryl with several hydrophobic residues also stabilized the binding conformation. The residue Glu398, by serving as the general base, might activate a water molecule and facilitate PchA catalysis. This work offers valuable insights into the binding interaction and hydrolytic mechanism of carbaryl with the hydrolase PchA and will be crucial to designing strategies leading to the protein variants that are capable of degrading related contaminants.

Two LysR Family Transcriptional Regulators, McbH and McbN, Activate the Operons Responsible for the Midstream and Downstream Pathways, Respectively, of Carbaryl Degradation in Pseudomonas sp. Strain XWY-1.

Previously, a LysR family transcriptional regulator, McbG, that activates the mcbBCDEF gene cluster involved in the upstream pathway (from carbaryl to salicylate) of carbaryl degradation in Pseudomonas sp. strain XWY-1 was identified by us (Z. Ke, Y. Zhou, W. Jiang, M. Zhang, et al., Appl Environ Microbiol 87:e02970-20, 2021, https://doi.org/10.1128/AEM.02970-20). In this study, we identified McbH and McbN, which activate the mcbIJKLM cluster (responsible for the midstream pathway, from salicylate to gentisate) and the mcbOPQ cluster (responsible for the downstream pathway, from gentisate to pyruvate and fumarate), respectively. They both belong to the LysR family of transcriptional regulators. Gene disruption and complementation study reveal that McbH is essential for transcription of the mcbIJKLM cluster in response to salicylate and McbN is indispensable for the transcription of the mcbOPQ cluster in response to gentisate. The results of electrophoretic mobility shift assay (EMSA) and DNase I footprinting showed that McbH binds to the 52-bp motif in the mcbIJKLM promoter area and McbN binds to the 58-bp motif in the mcbOPQ promoter area. The key sequence of McbH binding to the mcbIJKLM promoter is a 13-bp motif that conforms to the typical characteristics of the LysR family. However, the 12-bp motif that is different from the typical characteristics of the LysR family regulator binding site sequence is identified as the key sequence for McbN to bind to the mcbOPQ promoter. This study revealed the regulatory mechanisms for the midstream and downstream pathways of carbaryl degradation in strain XWY-1 and further our knowledge of (and the size of) the LysR transcription regulator family. IMPORTANCE The enzyme-encoding genes involved in the complete degradation pathway of carbaryl in Pseudomonas sp. strain XWY-1 include mcbABCDEF, mcbIJKLM, and mcbOPQ. Previous studies demonstrated that the mcbA gene, responsible for hydrolysis of carbaryl to 1-naphthol, is constitutively expressed and that the transcription of mcbBCDEF was regulated by McbG. However, the transcription regulation mechanisms of mcbIJKLM and mcbOPQ have not been investigated yet. In this study, we identified two LysR-type transcriptional regulators, McbH and McbN, which activate the mcbIJKLM cluster (responsible for the degradation of salicylate to gentisate) and the mcbOPQ cluster (responsible for the degradation of gentisate to pyruvate and fumarate), respectively. The 13-bp motif is critical for McbH to bind to the promoter of mcbIJKLM, and 12-bp motif different from the typical characteristics of the LysR-type transcriptional regulator (LTTR) binding sequence affects the binding of McbN to the promoter. These findings help to expand the understanding of the regulatory mechanism of microbial degradation of carbaryl.

McbG, a LysR Family Transcriptional Regulator, Activates the mcbBCDEF Gene Cluster Involved in the Upstream Pathway of Carbaryl Degradation in Pseudomonas sp. Strain XWY-1.

Although enzyme-encoding genes involved in the degradation of carbaryl have been reported in Pseudomonas sp. strain XWY-1, no regulator has been identified yet. In the mcbABCDEF cluster responsible for the upstream pathway of carbaryl degradation (from carbaryl to salicylate), the mcbA gene is constitutively expressed, while mcbBCDEF is induced by 1-naphthol, the hydrolysis product of carbaryl by McbA. In this study, we identified McbG, a transcriptional activator of the mcbBCDEF cluster. McbG is a 315-amino-acid protein with a molecular mass of 35.7 kDa. It belongs to the LysR family of transcriptional regulators and shows 28.48% identity to the pentachlorophenol (PCP) degradation transcriptional activation protein PcpR from Sphingobium chlorophenolicum ATCC 39723. Gene disruption and complementation studies reveal that mcbG is essential for transcription of the mcbBCDEF cluster in response to 1-naphthol in strain XWY-1. The results of the electrophoretic mobility shift assay (EMSA) and DNase I footprinting show that McbG binds to the 25-bp motif in the mcbBCDEF promoter area. The palindromic sequence TATCGATA within the motif is essential for McbG binding. The binding site is located between the -10 box and the transcription start site. In addition, McbG can repress its own transcription. The EMSA results show that a 25-bp motif in the mcbG promoter area plays an important role in McbG binding to the promoter of mcbG This study reveals the regulatory mechanism for the upstream pathway of carbaryl degradation in strain XWY-1. The identification of McbG increases the variety of regulatory models within the LysR family of transcriptional regulators.IMPORTANCEPseudomonas sp. strain XWY-1 is a carbaryl-degrading strain that utilizes carbaryl as the sole carbon and energy source for growth. The functional genes involved in the degradation of carbaryl have already been reported. However, the regulatory mechanism has not been investigated yet. Previous studies demonstrated that the mcbA gene, responsible for hydrolysis of carbaryl to 1-naphthol, is constitutively expressed in strain XWY-1. In this study, we identified a LysR-type transcriptional regulator, McbG, which activates the mcbBCDEF gene cluster responsible for the degradation of 1-naphthol to salicylate and represses its own transcription. The DNA binding site of McbG in the mcbBCDEF promoter area contains a palindromic sequence, which affects the binding of McbG to DNA. These findings enhance our understanding of the mechanism of microbial degradation of carbaryl.

Hydrolase CehA and a Novel Two-Component 1-Naphthol Hydroxylase CehC1C2 are Responsible for the Two Initial Steps of Carbaryl Degradation in Rhizobium sp. X9.

Carbaryl is a widely used carbamate pesticide in agriculture. The strain Rhizobium sp. X9 possesses the typical carbaryl degradation pathway in which carbaryl is mineralized via 1-naphthol, salicylate, and gentisate. In this study, we cloned a carbaryl hydrolase gene cehA and a novel two-component 1-naphthol hydroxylase gene cehC1C2. CehA mediates carbaryl hydrolysis to 1-naphthol and CehC1, an FMNH2 or FADH2-dependent monooxygenase belonging to the HpaB superfamily, and hydroxylates 1-naphthol in the presence of reduced nicotinamide-adenine dinucleotide (FMN)/flavin adenine dinucleotide (FAD), and the reductase CehC2. CehC1 has the highest amino acid similarity (58%) with the oxygenase component of a two-component 4-nitrophenol 2-monooxygenase, while CehC2 has the highest amino acid similarity (46%) with its reductase component. CehC1C2 could utilize both FAD and FMN as the cofactor during the hydroxylation, although higher catalytic activity was observed with FAD as the cofactor. The optimal molar ratio of CehC1 to CehC2 was 2:1. The Km and Kcat/Km values of CehC1 for 1-naphthol were 74.71 ± 16.07 µM and (8.29 ± 2.44) × 10-4 s-1·µM-1, respectively. Moreover, the enzyme activities and substrate spectrum between CehC1C2 and previously reported 1-naphthol hydroxylase McbC were compared. The results suggested that McbC had a higher 1-naphthol hydroxylation activity, while CehC1C2 had a broader substrate spectrum.

Production of a specific monoclonal antibody for 1-naphthol based on novel hapten strategy and development of an easy-to-use ELISA in urine samples.

1-naphthol (1-NAP) is the main metabolite of pesticide carbaryl and naphthalene, and is also a genotoxic and carcinogenic intermediate in the synthesis of organic compound, dyes, pigment and pharmaceutical industry. In this work, two novel haptens were designed and synthesized for developing a competitive indirect enzyme-linked immunosorbent assay (ciELISA) method for 1-NAP in urine samples. The assay showed a limit of detection of 2.21 ng/mL and working range from 4.02 ng/mL to 31.25 ng/mL for 1-NAP in optimized working buffer. The matrix effect of samples was eliminated via 15-fold dilution of optimized working buffer. Good average recoveries (102.4%-123.4%) with a coefficient of variation from 11.7% to 14.7% was obtained for spiked urine samples. Subsequent instrument verification test showed good correlation between the results of ciELISA and high-performance liquid chromatography. The developed ciELISA is a high-throughput tool to monitor 1-NAP in urine, which can provide technical support for the establishment of biological exposure level for the exposure to carbaryl, naphthalene and other related pollutants.

Identification and characterization of a novel bacterial carbohydrate esterase from the bacterium Pantoea ananatis Sd-1 with potential for degradation of lignocellulose and pesticides.

OBJECTIVE: Identification and characterization of a novel bacterial carbohydrate esterase (PaCes7) with application potential for lignocellulose and pesticide degradation. RESULTS: PaCes7 was identified from the lignocellulolytic bacterium, Pantoea ananatis Sd-1 as a new carbohydrate esterase. Recombinant PaCes7 heterologously expressed in Escherichia coli showed a clear preference for esters with short-chain fatty acids and exhibited maximum activity towards α-naphthol acetate at 37 °C and pH 7.5. Purified PaCes7 exhibited its catalytic activity under mesophilic conditions and retained more than 40% activity below 30 °C. It displayed a relatively wide pH stability from pH 6-11. Furthermore, the enzyme was strongly resistant to Mg2+, Pb2+, and Co2+ and activated by K+ and Ca2+. Both P. ananatis Sd-1 and PaCes7 could degrade the pesticide carbaryl. Additionally, PaCes7 was shown to work in combination with cellulase and/or xylanase in rice straw degradation. CONCLUSIONS: The data suggest that PaCes7 possesses promising biotechnological potential.

Identification of the key amino acid sites of the carbofuran hydrolase CehA from a newly isolated carbofuran-degrading strain Sphingbium sp. CFD-1.

A novel carbofuran-degrading strain CFD-1 was isolated and preliminarily identified as Sphingbium sp. This strain was able to utilize carbofuran as the sole carbon source for growth. The carbofuran hydrolase gene cehA was cloned from strain CFD-1 and expressed in Escherichia coli. CehA could hydrolyze carbamate pesticides including carbofuran and carbaryl efficiently, while it showed poor hydrolysis ability against isoprocarb, propoxur, oxamyl and aldicarb. CehA displayed maximal enzymatic activity at 40 °C and pH 7.0. The apparent Km and Kcat values of CehA for carbofuran were 133.22 ±â€¯5.70 µM and 9.48 ±â€¯0.89 s-1, respectively. The site-directed mutation experiment showed that His313, His315, His453 and His495 played important roles in the hydrolysis of carbofuran by CehA. Furthermore, the sequence of cehA is highly conserved among different carbofuran-degrading strains, and there are mobile elements around cehA, indicating that it may be transferred horizontally between different strains.

Variability in Assembly of Degradation Operons for Naphthalene and its derivative, Carbaryl, Suggests Mobilization through Horizontal Gene Transfer.

In the biosphere, the largest biological laboratory, increased anthropogenic activities have led microbes to evolve and adapt to the changes occurring in the environment. Compounds, specifically xenobiotics, released due to such activities persist in nature and undergo bio-magnification in the food web. Some of these compounds act as potent endocrine disrupters, mutagens or carcinogens, and therefore their removal from the environment is essential. Due to their persistence, microbial communities have evolved to metabolize them partially or completely. Diverse biochemical pathways have evolved or been assembled by exchange of genetic material (horizontal gene transfer) through various mobile genetic elements like conjugative and non-conjugative plasmids, transposons, phages and prophages, genomic islands and integrative conjugative elements. These elements provide an unlimited opportunity for genetic material to be exchanged across various genera, thus accelerating the evolution of a new xenobiotic degrading phenotype. In this article, we illustrate examples of the assembly of metabolic pathways involved in the degradation of naphthalene and its derivative, Carbaryl, which are speculated to have evolved or adapted through the above-mentioned processes.

Single-particle enumeration-based ultrasensitive enzyme activity quantification with fluorescent polymer nanoparticles.

Acetylcholinesterase (AChE) plays a vital role in nerve conduction through rapidly hydrolyzing the neurotransmitter acetylcholine (ACh) and is correlated with Alzheimer's disease. In this work, a label-free single-particle enumeration (SPE) method for the quantitative detection of acetylcholinesterase (AChE) activity is developed. The design is based on the fluorescence resonance energy transfer (FRET) between fluorescent conjugated polymer nanoparticles (FCPNPs) and MnO2 nanosheets. The fluorescence of FCPNPs can be effectively quenched by MnO2 nanosheets via hydrogen bonding interaction. In the presence of acetylcholinesterase (AChE), acetylthiocholine (ATCh) could be hydrolyzed to thiocholine (TCh), which can reduce MnO2 to Mn2+ and trigger the decomposition of MnO2 nanosheets. As a result, the fluorescence of FCPNPs is restored. Taking advantage of the superior brightness and stable fluorescence emission from individual FCPNPs, the accurate quantification of AChE is achieved by statistically counting the fluorescent particles on the glass slide surface. A linear range from 5 to 1600 µU mL-1 is obtained for AChE assay and the limit-of-detection (LOD) is 1.02 µU mL-1, which is far below the spectroscopic measurements in bulk solution. In the human serum sample, satisfactory recovery efficiencies are determined in a range of 91.0%-103.0%. Furthermore, pesticide carbaryl as an inhibitor of AChE activity was detected. The LOD is 1.12 pg mL-1 with linear responses ranging from 5 to 300 pg mL-1, which demonstrates the feasibility of this approach for AChE inhibitor screening. As a consequence, the label-free SPE-based method affords a promising platform for the sensitive detection of target molecules in the future.

Carbaryl waste-water treatment by Rhodopseudomonas sphaeroides.

Carbaryl wastewater treatment and the resource recycling of biomass as sludge by Rhodopseudomonas sphaeroides (R. sphaeroides) with the assistance of starch processing wastewater (SPW) was investigated in this research. It was observed that carbaryl was not degraded under the 100, 500 mg/L COD groups. The addition of SPW assisted R. sphaeroides to degrade carbaryl efficiently. Carbaryl removal reached 100% after 5 days under the optimal group (3500 mg/L). Interestingly, carbaryl in the mixed wastewater began to be degraded after day 1. Further research indicated that cehA gene was expressed after day 1. Subsequently, carbaryl hydrolase was synthesized under gene regulation. Analysis revealed that cehA and carbaryl hydrolase were adaptive gene expressions and enzymes. Carbaryl as stimulus signal started cehA gene expression through signal transduction pathway. This process took one day for R. sphaeroides. However, organics in 100, 500 mg/L COD groups were deficient, which could not maintain R. sphaeroides growth for over one day. Organics in SPW provided sufficient carbon sources for R. sphaeroides under other groups. The method could complete the mixed (SPW and carbaryl) wastewater treatment, carbaryl removal, the resource recycling of R. sphaeroides biomass as sludge simultaneously.

Genome Analysis of Carbaryl-Degrading Strain Pseudomonas putida XWY-1.

Carbaryl was a widely used pesticide in the agriculture industry. The toxicity against non-target organisms and the environmental pollution it caused became the focus of public concern. However, the microbial mechanism of carbaryl degradation was not fully investigated. In the study, we reported the complete genome of the carbaryl-degrading Pseudomonas putida strain XWY-1, which consists of a chromosome (5.9 Mbp) and a plasmid (0.4 Mbp). The carbaryl degradation genes are located on the plasmid. The study on the genome will facilitate to further elucidate the carbaryl degradation and advance the potential biotechnological applications of P. putida strain XWY-1.

Carbaryl biodegradation by Xylaria sp. BNL1 and its metabolic pathway.

Although ascomycetes occupy a vaster niche in soil than the well-studied basidiomycetes, they have received limited attention in studies related to bioremediation. In this study, the degradation of carbaryl by Xylaria sp. was studied in different culture conditions and its possible metabolic pathway was elucidated. In liquid culture, 99% of the added carbaryl was eliminated when cytochrome P450 (CYP450) was active, which was similar to the degradation rate of Pleurotus ostreatus, a fungus with strong bioremediation ability. Mn2+ is beneficial to the degradation of carbaryl. Compared to the 72.17% degradation rate in sterile soil, 59.0% carbaryl was eliminated in non-sterile soil, which suggested that Xylaria sp. BNL1 can resist microorganismal infection. Furthermore, the intracellular fractions containing laccase, CYP450, and carbaryl esterase efficiently degraded carbaryl. The presence of carbaryl metabolites suggested that Xylaria sp. BNL1 initiated its attack on carbaryl via carbaryl esterase to release α-naphthol, which was further degraded to 1,4-naphthoquinone and benzoic acid by CYP450 and laccase. Thus, our study highlights the potential of using Xylaria sp. for bioremediation.

Carbaryl as a Carbon and Nitrogen Source: an Inducible Methylamine Metabolic Pathway at the Biochemical and Molecular Levels in Pseudomonas sp. Strain C5pp.

Carbaryl is the most widely used carbamate family pesticide, and its persistent nature causes it to pollute both soil and water ecosystems. Microbes maintain the Earth's biogeochemical cycles by metabolizing various compounds present in the matter, including xenobiotics, as a sole source of carbon, nitrogen, and energy. Soil isolate Pseudomonas sp. strain C5pp metabolizes carbaryl efficiently as the carbon source. Periplasmic carbaryl hydrolase catalyzes the conversion of carbaryl to 1-naphthol and methylamine. 1-Naphthol was further used as a carbon source via gentisate, whereas the metabolic fate of methylamine is not known. Here, we demonstrate that strain C5pp showed efficient growth on carbaryl when supplied as a carbon and nitrogen source, suggesting that the methylamine generated was used as the nitrogen source. Genes involved in the methylamine metabolism were annotated and characterized at the biochemical and molecular level. Transcriptional and enzyme activity studies corroborate that the γ-glutamylmethylamide/N-methylglutamate (GMA/NMG) pathway is involved in the metabolism of carbaryl and methylamine as a nitrogen source. Compared to carbaryl, methylamine was found to be an effective inducer for the metabolic and transporter genes. Strain C5pp also harbored genes involved in sarcosine metabolism that were cotranscribed and induced by sarcosine. The presence of inducible pathways for metabolism of carbaryl as a nitrogen and carbon source helps in complete and efficient mineralization of carbaryl by strain C5pp, thereby maintaining the biogeochemical cycles.IMPORTANCE The degradation of xenobiotics plays a significant role in the environment to maintain ecological systems as well as to prevent the imbalance of biogeochemical cycles via carbon-nitrogen cycling. Carbaryl is the most widely used pesticide from the carbamate family. Pseudomonas sp. strain C5pp, capable of utilizing carbaryl as a carbon and nitrogen source for its growth, subsequently helps in complete remediation of carbaryl. Thus, it maintains the ecosystem by balancing the biogeochemical cycles. The metabolic versatility and genetic diversity of strain C5pp for the transformation of contaminants like carbaryl and 1-naphthol into less harmful products make it a suitable candidate from the perspective of bioremediation.

Cloning and expression of the carbaryl hydrolase gene mcbA and the identification of a key amino acid necessary for carbaryl hydrolysis.

Carbamate hydrolase is the initial and key enzyme for degradation of carbamate pesticides. In the present study, we report the isolation of a carbaryl-degrading strain Pseudomonas sp. XWY-1, the cloning of its carbaryl hydrolase gene (mcbA) and the characterization of McbA. Strain XWY-1 was able to utilize carbaryl as a sole carbon source and degrade it using 1-naphthol as an intermediate. Transposon mutagenesis identified a mutant of XWY-1M that was unable to hydrolyze carbaryl. The transposon-disrupted gene mcbA was cloned by self-formed adaptor PCR, then expressed in Escherichia coli BL21(DE3) and purified. McbA was able to hydrolyze carbamate pesticides including carbaryl, isoprocarb, fenobucarb, carbofuran efficiently, while it hydrolyzed aldicarb, and propoxur poorly. The optimal pH of McbA was 7.0 and the optimal temperature was 40°C. The apparent Km and kcat values of McbA for carbaryl were 77.67±12.31µM and 2.12±0.10s-1, respectively. Three amino acid residues (His467, His477 and His504) in the predicted polymerase/histidinol phosphatase-like domain were shown to be closely related to the activity of McbA, with His504 being the most important, as a replacement of His504 led to the complete loss of activity. This is the first study to identify key amino acids in McbA.

Comparisons of microsomal cytochrome P450 content and enzymatic activity towards selected model substrates and insecticides in different tissues from the migratory locust (Locusta migratoria).

Cytochrome P450 monooxygenases (P450s) are important enzymes for biotransformations of various endogenous and xenobiotic substances in various organisms. In this study, we examined microsomal P450 protein content and enzymatic activity in four major detoxification tissues dissected from fifth-instar nymphs of the migratory locust (Locusta migratoria). The highest microsomal P450 protein content was found in the gastric caeca (a part of the midgut), followed by the midgut, Malpighian tubules and fat bodies. Microsomal P450s showed the highest aromatic hydroxylation, O-dealkylation and O-dearylation activities towards six of the seven model substrates examined in the fat bodies. Although the gastric caeca showed the highest P450 protein content, the enzymatic activities towards six of the seven model substrates were the lowest in this tissue. Further, the midgut, gastric caeca and fat bodies showed significant metabolic activities towards two pyrethroid insecticides (deltamethrin and fluvalinate), but no significant activities towards the other four insecticides (malathion, chlorpyrifos, carbaryl and methoprene). These results support our conclusions: 1) total P450 protein content alone cannot be reliably used to predict its enzymatic activity, and 2) insect P450 enzymatic activity is both tissue and substrate dependent.

Compartmentalization of the Carbaryl Degradation Pathway: Molecular Characterization of Inducible Periplasmic Carbaryl Hydrolase from Pseudomonas spp.

Pseudomonas sp. strains C5pp and C7 degrade carbaryl as the sole carbon source. Carbaryl hydrolase (CH) catalyzes the hydrolysis of carbaryl to 1-naphthol and methylamine. Bioinformatic analysis of mcbA, encoding CH, in C5pp predicted it to have a transmembrane domain (Tmd) and a signal peptide (Sp). In these isolates, the activity of CH was found to be 4- to 6-fold higher in the periplasm than in the cytoplasm. The recombinant CH (rCH) showed 4-fold-higher activity in the periplasm of Escherichia coli The deletion of Tmd showed activity in the cytoplasmic fraction, while deletion of both Tmd and Sp (Tmd+Sp) resulted in expression of the inactive protein. Confocal microscopic analysis of E. coli expressing a (Tmd+Sp)-green fluorescent protein (GFP) fusion protein revealed the localization of GFP into the periplasm. Altogether, these results indicate that Tmd probably helps in anchoring of polypeptide to the inner membrane, while Sp assists folding and release of CH in the periplasm. The N-terminal sequence of the mature periplasmic CH confirms the absence of the Tmd+Sp region and confirms the signal peptidase cleavage site as Ala-Leu-Ala. CH purified from strains C5pp, C7, and rCHΔ(Tmd)a were found to be monomeric with molecular mass of ∼68 to 76 kDa and to catalyze hydrolysis of the ester bond with an apparent Km and Vmax in the range of 98 to 111 µM and 69 to 73 µmol · min-1 · mg-1, respectively. The presence of low-affinity CH in the periplasm and 1-naphthol-metabolizing enzymes in the cytoplasm of Pseudomonas spp. suggests the compartmentalization of the metabolic pathway as a strategy for efficient degradation of carbaryl at higher concentrations without cellular toxicity of 1-naphthol.IMPORTANCE Proteins in the periplasmic space of bacteria play an important role in various cellular processes, such as solute transport, nutrient binding, antibiotic resistance, substrate hydrolysis, and detoxification of xenobiotics. Carbaryl is one of the most widely used carbamate pesticides. Carbaryl hydrolase (CH), the first enzyme of the degradation pathway which converts carbaryl to 1-naphthol, was found to be localized in the periplasm of Pseudomonas spp. Predicted transmembrane domain and signal peptide sequences of Pseudomonas were found to be functional in Escherichia coli and to translocate CH and GFP into the periplasm. The localization of low-affinity CH into the periplasm indicates controlled formation of toxic and recalcitrant 1-naphthol, thus minimizing its accumulation and interaction with various cellular components and thereby reducing the cellular toxicity. This study highlights the significance of compartmentalization of metabolic pathway enzymes for efficient removal of toxic compounds.