Green strategy from waste to value-added-chemical production: efficient biosynthesis of 6-hydroxy-3-succinoyl-pyridine by an engineered biocatalyst

Reduction of nicotine content in tobacco through microbial degradation: research progress and potential applications

Originally native to South America, tobacco and is now distributed worldwide as a major cash crop. Nicotine is the main harmful component of tobacco leaves, cigarette smoke and tobacco waste, which severely affects not only the flavor of the tobacco leaf, but also causes great damage to human health. As the anti-smoking movement continued to grow since the 1950s, and consumers become more aware of their health and environmental protection, the world tobacco industry has been committed to research, develop and produce low nicotine cigarette products with relatively low risk to human health. Among various approaches, the use of microorganisms to reduce nicotine content and improve tobacco quality has become one of the most promising methods. Due to increasing interest in nicotine-degrading microorganisms (NDMs), this article reviews recent reports on NDMs, nicotine-degrading enzymes, regulation of nicotine-degrading bacterial consortia and optimization of fermentation conditions, aiming to provide updated references for the in-depth research and application of microorganisms for the degradation of nicotine.

Insights into Pharmacological Activities of Nicotine and 6-Hydroxy-L-nicotine, a Bacterial Nicotine Derivative: A Systematic Review

The purported cognitive benefits associated with nicotine and its metabolites in the brain are a matter of debate. In this review, the impact of the pharmacologically active metabolite of a nicotine derivative produced by bacteria named 6-hydroxy-L-nicotine (6HLN) on memory, oxidative stress, and the activity of the cholinergic system in the brain was examined. A search in the PubMed, Science Direct, Web of Science, and Google Scholar databases, limiting entries to those published between 1992 and 2023, was conducted. The search focused specifically on articles about nicotine metabolites, memory, oxidative stress, and cholinergic system activity, as well as enzymes or pathways related to nicotine degradation in bacteria. The preliminary search resulted in 696 articles, and following the application of exclusion criteria, 212 articles were deemed eligible for inclusion. This review focuses on experimental studies supporting nicotine catabolism in bacteria, and the chemical and pharmacological activities of nicotine and its metabolite 6HLN.

Characterization on nicotine degradation and research on heavy metal resistance of a strain Pseudomonas sp. NBB

The remediation of polluted sites containing multiple contaminants like nicotine and heavy metals poses significant challenges, due to detrimental effects like cell death. In this study, we isolated a new strain Pseudomonas sp. NBB capable of efficiently degrading nicotine even in high level of heavy metals. It degraded nicotine through pyrrolidine pathway and displayed minimum inhibitory concentrations of 2 mM for barium, copper, and lead, and 5 mM for manganese. In the presence of 2 mM Ba2+ or Pb2+, 3 g L-1 nicotine could be completely degraded within 24 h. Moreover, under 0.5 mM Cu2+ or 5 mM Mn2+ stress, 24.13% and 72.56% of nicotine degradation were achieved in 60 h, respectively. Strain NBB tolerances metal stress by various strategies, including morphological changes, up-regulation of macromolecule transporters, cellular response to DNA damage, and down-regulation of ABC transporters. Notably, among the 153 up-regulated genes, cds_821 was identified as manganese exporter (MneA) after gene disruption and recovery experiments. This study presents a novel strain capable of efficiently degrading nicotine and displaying remarkable resistance to heavy metals. The findings of this research provide valuable insights into the potential application of nicotine bioremediation in heavy metal-contaminated areas.

Nicotine metabolism pathway in bacteria: mechanism, modification, and application

Nicotine is a harmful pollutant mainly from the waste of tobacco factories. It is necessary to remove nicotine via high efficient strategies such as bioremediation. So far, an increasing number of nicotine degrading strains have been isolated. However, their degrading efficiency and tolerance to high content nicotine is still not high enough for application in real environment. Thus, the modification of nicotine metabolism pathway is obligated and requires comprehensive molecular insights into whole cell metabolism of nicotine degrading strains. Obviously, the development of multi-omics technology has accelerated the mechanism study on microbial degradation of nicotine and supplied more novel strategy of strains modification. So far, three pathways of nicotine degradation, pyridine pathway, pyrrolidine pathway, and the variant of pyridine and pyrrolidine pathway (VPP pathway), have been clearly identified in bacteria. Muti-omics analysis further revealed specific genome architecture, regulation mechanism, and specific genes or enzymes of three pathways, in different strains. Especially, muti-omics analysis revealed that functional modules coexisted in different genome loci and played additional roles on enhanced degradation efficiency in bacteria. Based on the above discovery, genomic editing strategy becomes more feasible to greatly improve bacterial degrading efficiency of nicotine.

Bioinsecticide Production from Cigarette Wastes

Tobacco, one of the most significant nonfood crops, is critical to agriculture worldwide. The tobacco processing business creates a significant amount of hazardous tobacco waste containing nicotine, and only a tiny portion of it gets recycled. Nicotine, the primary component of tobacco products such as cigarettes, is an alkaloid and can be used as an insecticide. This research aims to extract nicotine from discarded cigarette butts and utilize it as an insecticide. Extraction, emulsification, and efficiency testing on cabbage aphids are all part of the procedure. The initial extraction tests used a solvent combination of ethanol and methanol in various ratios, with a 3 : 1 ratio yielding the best results. Temperature (30–60°C), extraction length (4–6 hrs), and sodium hydroxide concentration (1–3 M) are the independent variables studied for extraction parameters, and the optimal conditions are determined using Design-Expert, response surface approach central composite design (RSM-CCD). In addition, artificial neural network (ANN) studies with MATLAB were used to accurately forecast extraction yield. The extracted product was evaluated using a gas chromatography–mass spectrometry (GC-MS) and a UV/visible spectrophotometer. The ideal crude extract yield and nicotine content were 17.75 and 3.26%, respectively, at the optimal conditions of temperature 60°C, time 4 hrs, and NaOH concentration 2.83 M with desirability of 0.832. The nicotine extracted was emulsified by combining the crude extract with a combination of palm oil and surfactants. Density, viscosity, pH, flash point, and surface tension of the emulsified concentration were measured and reported as 1.01 ± 0.01 g/ml, 585.33 ± 2.52 mPa s, 9.37 ± 0.03, 87.96 C, and 34.10 mN/m, respectively. On the cabbage aphid, the emulsified concentrated extract performed best at a ratio of 1 : 100 (emulsified concentrated to solvent).

Pollutant Degrading Enzyme: Catalytic Mechanisms and Their Expanded Applications

The treatment of environmental pollution by microorganisms and their enzymes is an innovative and socially acceptable alternative to traditional remediation approaches. Microbial biodegradation is often characterized with high efficiency as this process is catalyzed via degrading enzymes. Various naturally isolated microorganisms were demonstrated to have considerable ability to mitigate many environmental pollutants without external intervention. However, only a small fraction of these strains are studied in detail to reveal the mechanisms at the enzyme level, which strictly limited the enhancement of the degradation efficiency. Accordingly, this review will comprehensively summarize the function of various degrading enzymes with an emphasis on catalytic mechanisms. We also inspect the expanded applications of these pollutant-degrading enzymes in industrial processes. An in-depth understanding of the catalytic mechanism of enzymes will be beneficial for exploring and exploiting more degrading enzyme resources and thus ameliorate concerns associated with the ineffective biodegradation of recalcitrant and xenobiotic contaminants with the help of gene-editing technology and synthetic biology.

Time-Dependent Analysis of Paenarthrobacter nicotinovorans pAO1 Nicotine-Related Proteome

Paenarthrobacter nicotinovorans is a soil Gram-positive nicotine-degrading microorganism (NDM) that harbors a 165 kb pAO1 catabolic megaplasmid. The nicotine catabolic genes on pAO1 have been sequenced, but not all the details on the regulation and interplay of this pathway with the general metabolism of the cell are available. To address this issue at the protein level, a time-based shotgun proteomics study was performed. P. nicotinovorans was grown in the presence or absence of nicotine, and the cells were harvested at three different time intervals: 7, 10, and 24 h after inoculation. The cells were lysed, separated on SDS-PAGE, and digested by in-gel digestion using trypsin, and the resulting peptide mixture was analyzed using nanoliquid chromatography tandem mass spectrometry. We found an extensive number of proteins that are both plasmidal- and chromosomal-encoded and that work together in the energetic metabolism via the Krebs cycle and nicotine pathway. These data provide insight into the adaptation of the bacterial cells to the nicotine metabolic intermediates and could serve as a basis for future attempts to genetically engineer the pAO1-encoded catabolic pathway for increased bioremediation efficiency or for the production of valuable chemicals. The mass-spectrometry-based proteomics data have been deposited to the PRIDE partner repository with the data set identifier PXD012577.

Additional Role of Nicotinic Acid Hydroxylase for the Transformation of 3-Succinoyl-Pyridine by Pseudomonas sp. Strain JY-Q

Nicotine and nicotinic acid (NA) are both considered to be representatives of N-heterocyclic aromatic compounds, and their degradation pathways have been revealed in Pseudomonas species. However, the cooccurrence of these two pathways has only been observed in Pseudomonas sp. strain JY-Q. The nicotine pyrrolidine catabolism pathway of strain JY-Q consists of the functional modules Nic1, Spm, and Nic2. The module enzyme, 3-succinoylpyridine monooxygenase (Spm), catalyzes transformation of 3-succinoyl-pyridine (SP) to 6-hydroxy-3-succinoyl-pyridine (HSP). There exist two homologous but not identical Spm enzymes (namely, Spm1 and Spm2) in JY-Q. However, when spm1 and spm2 were both in-frame deleted, the mutant still grew well in basic salt medium (BSM) supplemented with nicotine as the sole carbon/nitrogen nutrition, suggesting that there exists an alternative pathway responsible for SP catabolism in JY-Q. NicAB, an enzyme accounting for NA hydroxylation, contains reorganized domains similar to those of Spm. When the JY-Q_nicAB gene (nicAB in strain JY-Q) was introduced into another Pseudomonas strain, one that is unable to degrade NA, the resultant recombinant strain exhibited the ability to transform SP to HSP, but without the ability to metabolize NA. Here, we conclude that NicAB in strain JY-Q exhibits an additional role in SP transformation. The other genes in the NA cluster, NicXDFE (Nic2 homolog), then also exhibit a role in subsequent HSP metabolism for energy yield. This finding also suggests that the cooccurrence of nicotine and NA degradation genes in strain JY-Q represents an advantage for JY-Q, making it more effective and flexible for the degradation of nicotine.IMPORTANCE 3-Succinoyl-pyridine (SP) and 6-hydroxy-3-succinoyl-pyridine (HSP) are both valuable chemical precursors to produce insecticides and hypotensive agents. SP and HSP could be renewable through the nicotine microbial degradation pathway, in which 3-succinoylpyridine monooxygenases (Spm) account for transforming SP into HSP in Pseudomonas sp. strain JY-Q. However, when two homologous Spm genes (spm1 and spm2) were knocked out, the mutant retained the ability to degrade nicotine. Thus, in addition to Spm, JY-Q should have an alternative pathway for SP conversion. In this research, we showed that JY-Q_NicAB was responsible for this alternative SP conversion. Both of the primary functions for nicotinic acid dehydrogenation and the additional function for SP metabolism were detected in a recombinant strain harboring JY-Q_NicAB. As a result, both nicotinic acid and nicotine degradation pathways in JY-Q contribute to its remarkable nicotine tolerance and nicotine degradation availability. These findings also provide one more metabolic engineering strategy for accumulation for value-added intermediates.

Nutrient uptake, yield and taste of oilseed rape (Brassica napus L.) and soil chemical properties following amendment with uncomposted and composted tobacco waste and cattle manure

The inadequacy of the nutrient supply of most tropical and sub-tropical soils may be curbed through organic material recycling, thus reducing the need for mineral fertiliser use. To promote tobacco waste recycling in a smallholder food-cash crop production system, nutrient uptake, dry biomass yield and taste of oilseed rape (Brassica napus L.) and soil chemical properties were determined on a sandy loam soil under field conditions. The experiment was a randomised complete block design with three blocks and eight treatments, namely, control (no amendment), mineral fertiliser (121, 30.8, 24.6 kg/ha N, P and K, respectively), uncomposted tobacco leaf scrap (TSC) and compost of TSC and cattle manure (TSC-CM) at 5, 20 and 40 t/ha. N, P and K uptake and dry biomass yield of oilseed rape were higher (p<0.05) than control with 40 t/ha TSC-CM and mineral fertiliser application at 3 weeks after transplanting (WAT), while significant improvements with TSC were observed from 5 WAT. Mineral N, extractable P and exchangeable K were higher than control with TSC-CM at 20 t/ha and 40 t/ha at 3 WAT, and higher with TSC at 9 WAT. Soil organic carbon was more improved with TSC application than TSC-CM at 9 WAT. Organoleptic testing revealed an intensely bitter taste in oilseed rape with mineral fertiliser, 20 t/ha and 40 t/ha TSC at 3 WAT, although it diminished with time. A trade-off of nutrient uptake, yield, taste of oilseed rape and soil properties improvement is attainable with application of TSC-CM at 40 t/ha, while if composting is not feasible, TSC application at 20 t/ha is a viable alternative. Thus, judicious utilisation of tobacco waste offers a viable solution to the problem of low soil fertility on sandy soils and can reduce the need for mineral fertiliser use, while promising sustainable soil management.

Photoenzymatic Hydrogenation of Heteroaromatic Olefins Using 'Ene'-Reductases with Photoredox Catalysts

Flavin-dependent 'ene'-reductases (EREDs) are highly selective catalysts for the asymmetric reduction of activated alkenes. This function is, however, limited to enones, enoates, and nitroalkenes using the native hydride transfer mechanism. Here we demonstrate that EREDs can reduce vinyl pyridines when irradiated with visible light in the presence of a photoredox catalyst. Experimental evidence suggests the reaction proceeds via a radical mechanism where the vinyl pyridine is reduced to the corresponding neutral benzylic radical in solution. DFT calculations reveal this radical to be "dynamically stable", suggesting it is sufficiently long-lived to diffuse into the enzyme active site for stereoselective hydrogen atom transfer. This reduction mechanism is distinct from the native one, highlighting the opportunity to expand the synthetic capabilities of existing enzyme platforms by exploiting new mechanistic models.

Regulatory Mechanism of Nicotine Degradation in Pseudomonas putida

We report the entire process underlying the NicR2 regulatory mechanism from association between free NicR2 and two promoters to dissociation of the NicR2-promoter complex. NicR2 can bind to another promoter, Pspm, which controls expression of nicotine-degrading genes that are not controlled by the Phsp promoter. We identified specific nucleotides of the Pspm promoter responsible for NicR2 binding. HSP was further demonstrated as an antagonist, which prevents the binding of NicR2 to the Pspm and Phsp promoters, by locking NicR2 in the derepression conformation. The competition between NicR2 and RNA polymerase is essential to initiate transcription of nicotine-degrading genes. This study extends our understanding of molecular mechanisms in biodegradation of environmental pollutants and toxicants.

Nicotine, a toxic and addictive alkaloid from tobacco, is an environmental pollutant in areas near cigarette production facilities. Over the last decade, our group has studied, in depth, the pyrrolidine pathway of nicotine degradation in Pseudomonas putida S16. However, little is known regarding whole mechanism(s) regulating transcription of the nicotine degradation pathway gene cluster. In the present study, we comprehensively elucidate an overall view of the NicR2-mediated two-step mechanism regulating 3-succinoyl-pyridine (SP) biotransformation, which involves the association of free NicR2 with two promoters and the dissociation of NicR2 from the NicR2-promoter complex. NicR2 can bind to another promoter, Pspm, and regulate expression of the nicotine-degrading genes in the middle of nic2 gene cluster, which are not controlled by the previously reported Phsp promoter. We identified the function of the inverted repeat bases on the two promoters responsible for NicR2 binding and found out that the –35/–10 motif for RNA polymerase is overlapped by the NicR2 binding site. We clarify the exact role of 6-hydroxy-3-succinoyl-pyridine (HSP), which acts as an antagonist and may prevent binding of free NicR2 to the promoters but cannot release NicR2 from the promoters. Finally, a regulatory model is proposed, which consists of three parts: the interaction between NicR2 and two promoters (Pspm and Phsp), the interaction between NicR2 and two effectors (HSP and SP), and the interaction between NicR2 and RNA polymerase.

Microbial Degradation of Nicotinamide by a Strain Alcaligenes sp. P156

A novel Alcaligenes sp. strain P156, which can utilize nicotinamide as its sole source of carbon, nitrogen and energy, was enriched and isolated from soil in a solid waste treatment plant. Aerobic growth and degradation with nicotinamide were characterized. Seven nicotinamide degradation-related genes were obtained by sequence alignment from the genome sequence of strain P156. Four genes, designated naaA, naaD, naaE and naaF, were cloned and heterologously expressed. Nicotinamide degradation is initiated by deamination to form nicotinic acid catalyzed by the nicotinamidase NaaA, which shares highest amino acid sequence identity (27.2%) with nicotinamidase from Arabidopsis thaliana. Nicotinic acid is converted to 6-hydroxynicotinic acid, which is further oxidized to 2,5-dihydroxypyridine (2,5-DHP). 2,5-DHP is then transformed to a ring-cleavage product, N-formylmaleamic acid, by an Fe²⁺ dependent dioxygenase NaaD. N-formylmaleamic acid is transformed to fumaric acid through maleamic acid and maleic acid by NaaE and NaaF, respectively. To our knowledge, this is the first report of the complete microbial degradation of nicotinamide in bacteria. Nicotinamide is considered as a model compound for the study of microbial degradation of pyridinic compounds, and the nicotinamide degrading related genes in strain P156 were distributed differently from the reported similar gene clusters. Therefore, this study contribute to the knowledge on the degradation of pyridinic compounds.

Transcriptome analysis of genes and metabolic pathways associated with nicotine degradation in Aspergillus oryzae 112822

BACKGROUND

Nicotine-degrading microorganisms (NDMs) have recently received much attention since they can consume nicotine as carbon and nitrogen source for growth. In our previous work, we isolated an efficient nicotine-degrading fungus Aspergillus oryzae 112822 and first proposed a novel demethylation pathway of nicotine degradation in fungi. However, the underlying mechanisms of the demethylation pathway remain unresolved. In the present study, we performed a comparative transcriptome analysis to elucidate the molecular mechanisms of nicotine tolerance and degradation in A. oryzae 112822.

RESULTS

We acquired a global view of the transcriptional regulation of A. oryzae 112822 exposed to nicotine and identified 4381 differentially expressed genes (DEGs) by nicotine treatment. Candidate genes encoding cytochrome P450 monooxygenases (CYPs), FAD-containing amine oxidase, molybdenum cofactor (Moco)-containing hydroxylase, and NADH-dependent and FAD-containing hydroxylase were proposed to participate in the demethylation pathway of nicotine degradation. Analysis of these data also revealed that increased energy was invested to drive nicotine detoxification. Nicotine treatment led to overproduction of reactive oxygen species (ROS), which formed intracellular oxidative stress that could induce the expression of several antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and peroxiredoxin (Prx). Thioredoxin system was induced to restore the intracellular redox homeostasis. Several glutathione S-transferases (GSTs) were induced, most likely to participate in phase II detoxification of nicotine by catalyzing the conjugation of glutathione (GSH) to active metabolites. The toxin efflux pumps, such as the ATP-Binding Cassette (ABC) transporters and the major facilitator superfamily (MFS) transporters, were overexpressed to overcome the intracellular toxin accumulation. By contrast, the metabolic pathways related to cellular growth and reproduction, such as ribosome biogenesis and DNA replication, were inhibited by nicotine treatment.

CONCLUSION

These results revealed that complex regulation networks, involving detoxification, transport, and oxidative stress response accompanied by increased energy investment, were developed for nicotine tolerance and degradation in A. oryzae 112822. This work provided the first insight into the metabolic regulation of nicotine degradation and laid the foundation for further revealing the molecular mechanisms of the nicotine demethylation pathway in filamentous fungi.

Plant Molecular Farming - Integration and Exploitation of Side Streams to Achieve Sustainable Biomanufacturing

Plants have unique advantages over other systems such as mammalian cells for the production of valuable small molecules and proteins. The benefits cited most often include safety due to the absence of replicating human pathogens, simplicity because sterility is not required during production, scalability due to the potential for open-field cultivation with transgenic plants, and the speed of transient expression potentially providing gram quantities of product in less than 4 weeks. Initially there were also significant drawbacks, such as the need to clarify feed streams with a high particle burden and the large quantities of host cell proteins, but efficient clarification is now readily achieved. Several additional advantages have also emerged reflecting the fact that plants are essentially biodegradable, single-use bioreactors. This article will focus on the exploitation of this concept for the production of biopharmaceutical proteins, thus improving overall process economics. Specifically, we will discuss the single-use properties of plants, the sustainability of the production platform, and the commercial potential of different biomass side streams. We find that incorporating these side streams through rational process integration has the potential to more than double the revenue that can currently be achieved using plant-based production systems.

Proteomics based analysis of the nicotine catabolism in Paenarthrobacter nicotinovorans pAO1

Paenarthrobacter nicotinovorans is a nicotine-degrading microorganism that shows a promising biotechnological potential for the production of compounds with industrial and pharmaceutical importance. Its ability to use nicotine was linked to the presence of the catabolic megaplasmid pAO1. Although extensive work has been performed on the molecular biology of nicotine degradation in this bacterium, only half of the genes putatively involved have been experimentally linked to nicotine. In the current approach, we used nanoLC-MS/MS to identify a total of 801 proteins grouped in 511 non-redundant protein clusters when P. nicotinovorans was grown on citrate, nicotine and nicotine and citrate as the only carbon sources. The differences in protein abundance showed that deamination is preferred when citrate is present. Several putative genes from the pAO1 megaplasmid have been shown to have a nicotine-dependent expression, including a hypothetical polyketide cyclase. We hypothesize that the enzyme would hydrolyze the N1-C6 bond from the pyridine ring with the formation of α-keto- glutaramate. Two chromosomally-encoded proteins, a malate dehydrogenase, and a D-3-phosphoglycerate dehydrogenase were shown to be strongly up-regulated when nicotine was the sole carbon source and could be related to the production the α-keto-glutarate. The data have been deposited to the ProteomeXchange with identifier PXD008756.

An enzymatic approach reverses nicotine dependence, decreases compulsive-like intake, and prevents relapse

Tobacco use disorder is the leading cause of disease and preventable death worldwide, but current medications that are based on pharmacodynamics have low efficacy. Novel pharmacokinetic approaches to prevent nicotine from reaching the brain have been tested using vaccines, but these efforts have failed because antibody affinity and concentration are not sufficient to completely prevent nicotine from reaching the brain. We provide preclinical evidence of the efficacy of an enzymatic approach to reverse nicotine dependence, reduce compulsive-like nicotine intake, and prevent relapse in rats with a history of nicotine dependence. Chronic administration of NicA2-J1, an engineered nicotine-degrading enzyme that was originally isolated from Pseudomonas putida S16, completely prevented nicotine from reaching the brain and reversed somatic signs of withdrawal, hyperalgesia, and irritability-like behavior in nicotine-dependent rats with a history of escalation of nicotine self-administration. NicA2-J1 also decreased compulsive-like nicotine intake, reflected by responding despite the adverse consequences of contingent footshocks, and prevented nicotine- and stress (yohimbine)-induced relapse. These results demonstrate the efficacy of enzymatic therapy in treating nicotine addiction in advanced animal models and provide a strong foundation for the development of biological therapies for smoking cessation in humans.

Isolation and characterization of the cotinine-degrading bacterium Nocardioides sp. Strain JQ2195

Cotinine, the primary nicotine metabolite, not only more stable and more difficult to degrade in the environment but is a potential health risk to human. To date, little is known about the biodegradation process of cotinine. In this study, a bacterial strain JQ2195 was isolated from municipal wastewater and was identified as Nocardioides sp. based on morphological, physiological characteristics, and 16 S rRNA gene phylogenetic analysis. This strain utilized cotinine as a sole carbon source and degraded 0.5 g L^-1 cotinine completely within 32 h. Optimum degradation of cotinine by JQ2195 was at 30 °C and pH 7.0. Two cotinine degradation intermediates were identified as 6-hydroxy-cotinine and 6-hydroxy-3-succinoylpyridine by UV/VIS spectroscopy and liquid chromatography coupled with time-of-flight mass spectrometry. In addition, about half of cotinine was transformed to 6-hydroxy-3-succinoylpyridine which was a value-added compound for biocatalysis. When 2,6-dichlorophenolindophenol was used as an electron acceptor, the cell-free extract containing the inducible cotinine dehydrogenase could convert cotinine into 6-hydroxy-cotinine with the activity 40 ± 6 mUnmg^-1.

An enzymatic advance in nicotine cessation therapy

A nicotine-degrading enzyme termed NicA2 was altered (NicA2-J1) through fusion of an albumin binding domain to increase its half-life. Examination of NicA2-J1 in vivo demonstrated a complete blockade of brain nicotine access, which in turn blunted nicotine's psychoactive effects. These data further support development of pharmacokinetic nicotine cessation therapeutics.

Genomic and transcriptomic analyses of Agrobacterium tumefaciens S33 reveal the molecular mechanism of a novel hybrid nicotine-degrading pathway

Agrobacterium tumefaciens S33 is able to degrade nicotine via a novel hybrid of the pyridine and pyrrolidine pathways. It can be utilized to remove nicotine from tobacco wastes and transform nicotine into important functionalized pyridine precursors for some valuable drugs and insecticides. However, the molecular mechanism of the hybrid pathway is still not completely clear. Here we report the genome analysis of strain S33 and its transcriptomes grown in glucose-ammonium medium and nicotine medium. The complete gene cluster involved in nicotine catabolism was found to be located on a genomic island composed of genes functionally similar but not in sequences to those of the pyridine and pyrrolidine pathways, as well as genes encoding plasmid partitioning and replication initiation proteins, conjugal transfer proteins and transposases. This suggests that the evolution of this hybrid pathway is not a simple fusion of the genes involved in the two pathways, but the result of a complicated lateral gene transfer. In addition, other genes potentially involved in the hybrid pathway could include those responsible for substrate sensing and transport, transcription regulation and electron transfer during nicotine degradation. This study provides new insights into the molecular mechanism of the novel hybrid pathway for nicotine degradation.

Whole cell biocatalysts: essential workers from Nature to the industry

Microorganisms have been exposed to a myriad of substrates and environmental conditions throughout evolution resulting in countless metabolites and enzymatic activities. Although mankind have been using these properties for centuries, we have only recently learned to control their production, to develop new biocatalysts with high stability and productivity and to improve their yields under new operational conditions. However, microbial cells still provide the best known environment for enzymes, preventing conformational changes in the protein structure in non-conventional medium and under harsh reaction conditions, while being able to efficiently regenerate necessary cofactors and to carry out cascades of reactions. Besides, a still unknown microbe is probably already producing a compound that will cure cancer, Alzeihmer's disease or kill the most resistant pathogen. In this review, the latest developments in screening desirable activities and improving production yields are discussed.

Green route to synthesis of valuable chemical 6-hydroxynicotine from nicotine in tobacco wastes using genetically engineered Agrobacterium tumefaciens S33

BACKGROUND

Tobacco is widely planted as an important nonfood economic crop throughout the world, and large amounts of tobacco wastes are generated during the tobacco manufacturing process. Tobacco and its wastes contain high nicotine content. This issue has become a major concern for health and environments due to its toxicity and complex physiological effects. The microbial transformation of nicotine into valuable functionalized pyridine compounds is a promising way to utilize tobacco and its wastes as a potential biomass resource. Agrobacterium tumefaciens S33 is able to degrade nicotine via a novel hybrid of the pyridine and pyrrolidine pathways, in which several intermediates, such as 6-hydroxynicotine, can be used as renewable precursors to synthesize drugs and insecticides. This provides an opportunity to produce valuable chemical 6-hydroxynicotine from nicotine via biocatalysis using strain S33.

RESULTS

To accumulate the intermediate 6-hydroxynicotine, we firstly identified the key enzyme decomposing 6-hydroxynicotine, named 6-hydroxynicotine oxidase, and then disrupted its encoding gene in A. tumefaciens S33. With the whole cells of the mutant as a biocatalyst, we tested the possibility to produce 6-hydroxynicotine from the nicotine of tobacco and its wastes and optimized the reaction conditions. At 30 °C and pH 7.0, nicotine could be efficiently transformed into 6-hydroxynicotine by the whole cells cultivated with glucose/ammonium/6-hydroxy-3-succinoylpyridine medium. The molar conversion and the specific catalytic rate reached approximately 98% and 1.01 g 6-hydroxynicotine h^-1 g^-1 dry cells, respectively. The product could be purified easily by dichloromethane extraction with a recovery of 76.8%, and was further confirmed by UV spectroscopy, mass spectroscopy, and NMR analysis.

CONCLUSIONS

We successfully developed a novel biocatalytic route to 6-hydroxynicotine from nicotine by blocking the nicotine catabolic pathway via gene disruption, which provides an alternative green strategy to utilize tobacco and its wastes as a biomass resource by converting nicotine into valuable hydroxylated-pyridine compounds.

Molybdenum-containing nicotine hydroxylase genes in a nicotine degradation pathway that is a variant of the pyridine and pyrrolidine pathways

Ochrobactrum sp. strain SJY1 utilizes nicotine as a sole source of carbon, nitrogen, and energy via a variant of the pyridine and pyrrolidine pathways (the VPP pathway). Several strains and genes involved in the VPP pathway have recently been reported; however, the first catalyzing step for enzymatic turnover of nicotine is still unclear. In this study, a nicotine hydroxylase for the initial hydroxylation step of nicotine degradation was identified and characterized. The nicotine hydroxylase (VppA), which converts nicotine to 6-hydroxynicotine in the strain SJY1, is encoded by two open reading frames (vppAS and vppAL [subunits S and L, respectively]). The vppA genes were heterologously expressed in the non-nicotine-degrading strains Escherichia coli DH5α and Pseudomonas putida KT2440; only the Pseudomonas strain acquired the ability to degrade nicotine. The small subunit of VppA contained a [2Fe-2S] cluster-binding domain, and the large subunit of VppA contained a molybdenum cofactor-binding domain; however, an FAD-binding domain was not found in VppA. Resting cells cultivated in a molybdenum-deficient medium had low nicotine transformation activity, and excess molybdenum was detected in the purified VppA by inductively coupled plasma-mass spectrometry analysis. Thus, it is demonstrated that VppA is a two-component molybdenum-containing hydroxylase.

Sustainable production of valuable compound 3-succinoyl-pyridine by genetically engineering Pseudomonas putida using the tobacco waste

Treatment of solid and liquid tobacco wastes with high nicotine content remains a longstanding challenge. Here, we explored an environmentally friendly approach to replace tobacco waste disposal with resource recovery by genetically engineering Pseudomonas putida. The biosynthesis of 3-succinoyl-pyridine (SP), a precursor in the production of hypotensive agents, from the tobacco waste was developed using whole cells of the engineered Pseudomonas strain, S16dspm. Under optimal conditions in fed-batch biotransformation, the final concentrations of product SP reached 9.8 g/L and 8.9 g/L from aqueous nicotine solution and crude suspension of the tobacco waste, respectively. In addition, the crystal compound SP produced from aqueous nicotine of the tobacco waste in batch biotransformation was of high purity and its isolation yield on nicotine was 54.2%. This study shows a promising route for processing environmental wastes as raw materials in order to produce valuable compounds.

Protein retention on plasma-treated hierarchical nanoscale gold-silver platform

Dense arrays of gold-supported silver nanowires of about 100 nm in diameter grown directly in the channels of nanoporous aluminium oxide membrane were fabricated and tested as a novel platform for the immobilization and retention of BSA proteins in the microbial-protective environments. Additional treatment of the silver nanowires using low-temperature plasmas in the inductively-coupled plasma reactor and an atmospheric-pressure plasma jet have demonstrated that the morphology of the nanowire array can be controlled and the amount of the retained protein may be increased due to the plasma effect. A combination of the neutral gold sublayer with the antimicrobial properties of silver nanowires could significantly enhance the efficiency of the platforms used in various biotechnological processes.

Functional Identification of a Novel Gene, moaE, for 3-Succinoylpyridine Degradation in Pseudomonas putida S16

Microbial degradation of N-heterocyclic compounds, including xanthine, quinoline, nicotinate, and nicotine, frequently requires molybdenum hydroxylases. The intramolecular electron transfer chain of molybdenum hydroxylases consists of a molybdenum cofactor, two distinct [2Fe-2S] clusters, and flavin adenine dinucleotide. 3-Succinoylpyridine monooxygenase (Spm), responsible for the transformation from 3-succinoylpyridine to 6-hydroxy-3-succinoylpyridine, is a crucial enzyme in the pyrrolidine pathway of nicotine degradation in Pseudomonas. Our previous work revealed that the heterotrimeric enzyme (SpmA, SpmB, and SpmC) requires molybdopterin cytosine dinucleotide as a cofactor for their activities. In this study, we knocked out four genes, including PPS_1556, PPS_2936, PPS_4063, and PPS_4397, and found that a novel gene, PPS_4397 encoding moaE, is necessary for molybdopterin cytosine dinucleotide biosynthesis. Resting cell reactions of the moaE deletion mutant incubated with 3 g l⁻¹ nicotine at 30 °C resulted in accumulation of 3-succinoylpyridine, and the strain complemented by the moaE gene regained the ability to convert 3-succinoylpyridine. In addition, reverse transcription-quantitative polymerase chain reaction analysis indicated that the transcriptional levels of the genes of moaE, spmA, and spmC of Pseudomonas putida S16 were distinctly higher when grown in nicotine medium than in glycerol medium.

A New Strategy for Smoking Cessation: Characterization of a Bacterial Enzyme for the Degradation of Nicotine

Smoking is the leading cause of preventable diseases; thus, effective smoking cessation aids are crucial for reducing the prevalence of cigarette smoking and smoking-related illnesses. In our current campaign we offer a nicotine-degrading enzyme from Pseudomonas putida, NicA2, a flavin-containing protein. To explore its potential, a kinetic evaluation of the enzyme was conducted, which included determination of K(m), k(cat), buffer/serum half-life, and thermostability. Additionally, the catabolism profile of NicA2 was elucidated to assess the potential toxicity of the nicotine-derived products. In characterizing the enzyme, a favorable biochemical profile of the enzyme was discovered, making NicA2 a prospective therapeutic candidate. This approach provides a new avenue for the field of nicotine addiction therapy.

Plasma treatment for next-generation nanobiointerfaces

Energy deficiency, global poverty, chronic hunger, chronic diseases, and environment conservation are among the major problems threatening the whole mankind. Nanostructure-based technologies could be a possible solution. Such techniques are now used for the production of many vitally important products including cultured and fermented food, antibiotics, various medicines, and biofuels. On the other hand, the nanostructure-based technologies still demonstrate low efficiency and controllability, and thus still are not capable to decisively address the global problems. Furthermore, future technologies should ensure lowest possible environmental impact by implementing green production principles. One of the most promising approaches to address these challenges are the sophisticatedly engineered biointerfaces. Here, the authors briefly evaluate the potential of the plasma-based techniques for the fabrication of complex biointerfaces. The authors consider mainly the atmospheric and inductively coupled plasma environments and show several examples of the artificial plasma-created biointerfaces, which can be used for the biotechnological and medical processes, as well as for the drug delivery devices, fluidised bed bioreactors, catalytic reactors, and others. A special attention is paid to the plasma-based treatment and processing of the biointerfaces formed by arrays of carbon nanotubes and graphene flakes.

Nicotine-degrading microorganisms and their potential applications

Nicotine-degrading microorganisms (NDMs) are a special microbial group which can use nicotine as the sole carbon and nitrogen source for growth. Since the 1950s, the bioconversion of nicotine by microbes has received increasing attention, and several NDMs have been identified, such as Arthrobacter nicotinovorans, Microsporum gypseum, Pellicularia filamentosa JTS-208, and Pseudomonas sp. 41. In recent years, increasing numbers of NDMs have been isolated and identified from tobacco plantation soil, leaf, and tobacco waste. Meanwhile, the metabolic pathway and degradation mechanism of nicotine have been elucidated in several NDMs, such as A. nicotinovorans, Agrobacterium tumefaciens S33, Aspergillus oryzae, and Pseudomonas putida S16. Moreover, several NDMs have been used in improving the quality of cigarettes, treating tobacco waste, and producing valuable intermediates of nicotine. Here, we summarize the diversity, phylogenetic analysis, and potential applications of NDMs.

Molecular mechanism of nicotine degradation by a newly isolated strain, Ochrobactrum sp. strain SJY1

A newly isolated strain, SJY1, identified as Ochrobactrum sp., utilizes nicotine as a sole source of carbon, nitrogen, and energy. Strain SJY1 could efficiently degrade nicotine via a variant of the pyridine and pyrrolidine pathways (the VPP pathway), which highlights bacterial metabolic diversity in relation to nicotine degradation. A 97-kbp DNA fragment containing six nicotine degradation-related genes was obtained by gap closing from the genome sequence of strain SJY1. Three genes, designated vppB, vppD, and vppE, in the VPP pathway were cloned and heterologously expressed, and the related proteins were characterized. The vppB gene encodes a flavin-containing amine oxidase converting 6-hydroxynicotine to 6-hydroxy-N-methylmyosmine. Although VppB specifically catalyzes the dehydrogenation of 6-hydroxynicotine rather than nicotine, it shares higher amino acid sequence identity with nicotine oxidase (38%) from the pyrrolidine pathway than with its isoenzyme (6-hydroxy-l-nicotine oxidase, 24%) from the pyridine pathway. The vppD gene encodes an NADH-dependent flavin-containing monooxygenase, which catalyzes the hydroxylation of 6-hydroxy-3-succinoylpyridine to 2,5-dihydroxypyridine. VppD shows 62% amino acid sequence identity with the hydroxylase (HspB) from Pseudomonas putida strain S16, whereas the specific activity of VppD is ∼10-fold higher than that of HspB. VppE is responsible for the transformation of 2,5-dihydroxypyridine. Sequence alignment and phylogenetic analysis suggested that the VPP pathway, which evolved independently from nicotinic acid degradation, might have a closer relationship with the pyrrolidine pathway. The proteins and functional pathway identified here provide a sound basis for future studies aimed at a better understanding of molecular principles of nicotine degradation.