A novel nicotinoprotein aldehyde dehydrogenase involved in polyethylene glycol degradation

Potential routes of plastics biotransformation involving novel plastizymes revealed by global multi-omic analysis of plastic associated microbes

Despite increasing efforts across various disciplines, the fate, transport, and impact of synthetic plastics on the environment and public health remain poorly understood. To better elucidate the microbial ecology of plastic waste and its potential for biotransformation, we conducted a large-scale analysis of all publicly available meta-omic studies investigating plastics (n = 27) in the environment. Notably, we observed low prevalence of known plastic degraders throughout most environments, except for substantial enrichment in riverine systems. This indicates rivers may be a highly promising environment for discovery of novel plastic bioremediation products. Ocean samples associated with degrading plastics showed clear differentiation from non-degrading polymers, showing enrichment of novel putative biodegrading taxa in the degraded samples. Regarding plastisphere pathogenicity, we observed significant enrichment of antimicrobial resistance genes on plastics but not of virulence factors. Additionally, we report a co-occurrence network analysis of 10 + million proteins associated with the plastisphere. This analysis revealed a localized sub-region enriched with known and putative plastizymes-these may be useful for deeper investigation of nature's ability to biodegrade man-made plastics. Finally, the combined data from our meta-analysis was used to construct a publicly available database, the Plastics Meta-omic Database (PMDB)-accessible at plasticmdb.org. These data should aid in the integrated exploration of the microbial plastisphere and facilitate research efforts investigating the fate and bioremediation potential of environmental plastic waste.

Advances in Functionalization of Bioresorbable Nanomembranes and Nanoparticles for Their Use in Biomedicine

Bioresorbable nanomembranes (NMs) and nanoparticles (NPs) are powerful polymeric materials playing an important role in biomedicine, as they can effectively reduce infections and inflammatory clinical patient conditions due to their high biocompatibility, ability to physically interact with biomolecules, large surface area, and low toxicity. In this review, the most common bioabsorbable materials such as those belonging to natural polymers and proteins for the manufacture of NMs and NPs are reviewed. In addition to biocompatibility and bioresorption, current methodology on surface functionalization is also revisited and the most recent applications are highlighted. Considering the most recent use in the field of biosensors, tethered lipid bilayers, drug delivery, wound dressing, skin regeneration, targeted chemotherapy and imaging/diagnostics, functionalized NMs and NPs have become one of the main pillars of modern biomedical applications.

A landfill serves as a critical source of microplastic pollution and harbors diverse plastic biodegradation microbial species and enzymes: Study in large-scale landfills, China

Microplastics (MPs) are emerging pollutants. Landfills store up to 42% of worldwide plastic waste and serve as an important source of MPs. However, the study of MPs distribution and the plastic biodegradation potential in landfills is limited. In this study, the distribution of abundance, size, morphology and polymer type of MPs and plastics biodegradation species in refuse samples along landfill depths were extensively investigated within a large-scale landfill in Shenzhen, China. In addition, plastics biodegradation enzymes were evaluated in seven Chinese large-scale landfills leachate. MPs distribution pattern was investigated in all refuse samples. The abundance of MPs in refuse samples varied between 81 and 133 items/g. The size of MPs in all samples varied between 0.03 and 5 mm, and the average sizes were 1.2 mm ± 0.1 mm. The main morphology and polymer type were fragments and cellophane, respectively. Landfill depth was significantly negatively correlated with the relative abundance of MPs size 1-5 mm (p < 0.05) and was positively correlated with the relative abundance of MPs size < 0.2 mm (p < 0.05), suggesting that plastics were broken down during municipal solid waste decomposition. The multiple regression on matrices analysis further showed the landfill depths and plastic morphology significantly impact the MPs distribution. The strains, Lysinibacillus massiliensis (with relative abundance of 1.8%) for low-density polyethylene and polystyrene biodegradation, and Pseudomonas stutzeri (0.1%) for low density polythene and polypropylene biodegradation, were detected on the plastic surface with high relative abundance. Furthermore, 75 plastic degradation species and their associated 31 enzymes (breakdown 24 plastics) were discovered in seven landfills leachate samples.

Draft genome of Gongronella butleri reveals the genes contributing to its biodegradation potential

BACKGROUND

Gongronella butleri is a fungus with many industrial applications including the composting of solid biowaste. Kerala Agricultural University, India, has developed a microbial consortium of which GbKAU strain of G. butleri is a major component. Even with great industrial significance, genome of this fungus is not published, and the genes and pathways contributing to the applications are not understood. This study had the objective to demonstrate the solid biowaste decomposing capability of the strain, to sequence and annotate the genome, and to reveal the genes and pathways contributing to its biodegradation potential.

RESULTS

Strain GbKAU of G. butleri isolated and purified from the organic compost was found to produce higher levels of laccase and amylase, compared to Bacillus subtilis which is being widely used in biosolid waste management. Both were shown to be equally efficient in the in vivo composting capabilities. Whole genome sequencing has given ~11 million paired-end good quality reads. De novo assembly using dual-fold approach has yielded 44,639 scaffolds with draft genome size of 29.8 Mb. A total of 11,428 genes were predicted and classified into 359 groups involved in diverse pathways, of which 14 belonged to the enzymes involved in the degradation of macromolecules. Seven previously sequenced strains of the fungus were assembled and annotated. A direct comparison showed that the number of genes present in those strains was comparable to our strain, while all the important biodegrading genes were conserved across the genomes. Gene Ontology analysis had classified the genes according to their molecular function, biological process, and cellular component. A total of 104,718 SSRs were mined and classified to mono- to hexa-nucleotide repeats. The variant analysis in comparison with the closely related genus Cunninghamella has revealed 1156 variants.

CONCLUSIONS

Apart from demonstrating the biodegradation capabilities of the GbKAU strain of G. butleri, the genome of this industrially important fungus was sequenced, de novo assembled, and annotated. GO analysis has classified the genes based on their functions, and the genes involved in biodegradation were revealed. Biodegradation potential, genome features in comparison with other strains, and the functions of the identified genes are discussed.

Highly Stable, Cold-Active Aldehyde Dehydrogenase from the Marine Antarctic Flavobacterium sp. PL002

Stable aldehyde dehydrogenases (ALDH) from extremophilic microorganisms constitute efficient catalysts in biotechnologies. In search of active ALDHs at low temperatures and of these enzymes from cold-adapted microorganisms, we cloned and characterized a novel recombinant ALDH from the psychrotrophic Flavobacterium PL002 isolated from Antarctic seawater. The recombinant enzyme (F-ALDH) from this cold-adapted strain was obtained by cloning and expressing of the PL002 aldH gene (1506 bp) in Escherichia coli BL21(DE3). Phylogeny and structural analyses showed a high amino acid sequence identity (89%) with Flavobacterium frigidimaris ALDH and conservation of all active site residues. The purified F-ALDH by affinity chromatography was homotetrameric, preserving 80% activity at 4 °C for 18 days. F-ALDH used both NAD+ and NADP+ and a broad range of aliphatic and aromatic substrates, showing cofactor-dependent compensatory KM and kcat values and the highest catalytic efficiency (0.50 µM−1 s−1) for isovaleraldehyde. The enzyme was active in the 4–60 °C-temperature interval, with an optimal pH of 9.5, and a preference for NAD+-dependent reactions. Arrhenius plots of both NAD(P)+-dependent reactions indicated conformational changes occurring at 30 °C, with four(five)-fold lower activation energy at high temperatures. The high thermal stability and substrate-specific catalytic efficiency of this novel cold-active ALDH favoring aliphatic catalysis provided a promising catalyst for biotechnological and biosensing applications.

Draft genome of Meyerozyma guilliermondii strain vka1: a yeast strain with composting potential

Background

Meyerozyma guilliermondii is a yeast which could be isolated from a variety of environments. The vka1 strain isolated and purified from the organic compost was found to have composting potential. To better understand the genes assisting the composting potential in this yeast, whole genome sequencing and sequence annotation were performed.

Results

The genome of M. guilliermondii vka1 strain was sequenced using a hybrid approach, on Illumina Hiseq-2500 platform at 100× coverage followed by Nanopore platform at 20× coverage. The de novo assembly using dual-fold approach had given draft genome of 10.8 Mb size. The genome was found to contain 5385 genes. The annotation of the genes was performed, and the enzymes identified to have roles in the degradation of macromolecules are discussed in relation to its composting potential. Annotation of the genome assembly of the related strains had revealed the unique biodegradation related genes in this strain. Phylogenetic analysis using the rDNA region has confirmed the position of this strain in the Ascomycota family. Raw reads are made public, and the genome wide proteome profile is presented to facilitate further studies on this organism.

Conclusions

Meyerozyma guilliermondii vka1 strain was sequenced through hybrid approach and the reads were de novo assembled. Draft genome size and the number of genes in the strain were assessed and discussed in relation to the related strains. Scientific insights into the composting potential of this strain are also presented in relation to the unique genes identified in this strain.

Evaluation on the removal performance of dichloromethane and toluene from waste gases using an airlift packing reactor

Biological removal of dichloromethane (DCM) from pharmaceutical industry is limited by its recalcitrance. In this study, an airlift packing reactor (ALPR), which combined the suspended and fixed-film microbial growth system, was set up to remove DCM and co-existed toluene. The removal performance of the ALPR for DCM was greater than traditional airlift reactor (ALR). The maximum elimination capacity (EC_max) of the ALPR for DCM reached 108 g m^-3 h^-1 with removal efficiency (RE) of 41%, increased by 145% if compared to the ALR. The EC_max for toluene was 172 g m^-3 h^-1 with RE of 70%, decreased by 25% if compared to the ALR, which was mainly due to the higher liquid-phase biomass in the ALR. The results of high-throughput sequencing showed that the microbial composition on the packings of the ALPR had a large difference from its liquid-phase or the liquid-phase of the ALR. Gemmobacter, Rhizomicrobium, Chitinophaga, Vampirovibrio, and Fodinicurvata were genera with great abundance fixed on the packings and Rhizomicrobium, Chitinophaga, Vampirovibrio, and Fodinicurvata are first to be reported in VOCs biological removal. This study indicated that the ALPR can augment the microbial community and effectively improve the removal of recalcitrant VOCs.

Examining the Use of Nanocellulose Composites for the Sorption of Contaminants of Emerging Concern: An Experimental and Computational Study

The occurrence of contaminants of emerging concern (CECs) in water is an environmental issue that must be addressed to avoid damage to ecosystems and human health. Inspired by this current issue, in this work, we fabricated nanocellulose (NC) particles grafted with the block copolymer Jeffamine ED 600 (NC-Jeffamine) capable of adsorbing acetaminophen, sulfamethoxazole, and N,N-diethyl-meta-toluamide (DEET) from aqueous solution by electrostatic interactions. NC-Jeffamine composites were prepared by carboxylation of the NC surface via 2,2,6,6-tetramethyl-1-piperidinyloxy oxidation followed by the covalent attachment of Jeffamine using the N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide/N-hydroxysulfosuccinimide sodium salt reaction. The reaction was followed and confirmed by Fourier transform infrared and conductometric titration. The physical characterization was performed by thermogravimetric analysis, Brunauer-Emmett-Teller analysis, scanning electron microscopy, dynamic light scattering, and Z-potential analysis. This material was used to study the adsorption profile of three CECs in deionized water, namely, acetaminophen, sulfamethoxazole, and DEET. The adsorption isotherms were obtained at pH 3, 7, and 9, where the best adsorption results corresponded to pH 9 because of the uniform dispersion of the adsorbate in solution. A computational study based on the density functional theory determined that the possible interactions of the CECs with the adsorbent material were related to hydrogen bonds and/or van der Waals forces. The calculated binding energies were used as a descriptor to characterize the optimum adsorption site of CECs onto NC-Jeffamine.

TraeALDH7B1-5A, encoding aldehyde dehydrogenase 7 in wheat, confers improved drought tolerance in Arabidopsis

TraeALDH7B1 - 5A , encoding aldehyde dehydrogenase 7 in wheat, conferred significant drought tolerance to Arabidopsis , supported by molecular biological and physiological experiments. Drought stress significantly affects wheat yields. Aldehyde dehydrogenase (ALDH) is a family of enzymes catalyzing the irreversible conversion of aldehydes into acids to decrease the damage caused by abiotic stresses. However, no wheat ALDH member has been functionally characterized to date. Here, we obtained a differentially expressed EST encoding ALDH7 from a cDNA-AFLP library of wheat that was treated with polyethylene glycol 6000. The three full-length homologs of TraeALDH7B1 were isolated by searching the NCBI database and by homolog-based cloning method. Using nulli-tetrasomic lines we located them on wheat chromosomes 5A, 5B and 5D, and named them as TraeALDH7B1-5A, -5B and -5D, respectively. Gene expression profiles indicated that the expressions of all three genes were induced in roots, leaves, culms and spikelets under drought and salt stresses. Enzymatic activity analysis showed that TraeALDH7B1-5A had acetaldehyde dehydrogenase activity. For further functional analysis, we developed transgenic Arabidopsis lines overexpressing TraeALDH7B1-5A driven by the cauliflower mosaic virus 35S promoter. Compared with wild type Arabidopsis, 35S::TraeALDH7B1-5A plants significantly enhanced the tolerance to drought stress, which was demonstrated by up-regulation of stress responsive genes and physiological evidence of primary root length, maintenance of water retention and contents of chlorophyll and MDA. The combined results indicated that TraeALDH7B1-5A is an important drought responsive gene for genetic transformation to improve drought tolerance in crops.

Enabling nanomaterial, nanofabrication and cellular technologies for nanoneuromedicines

Nanoparticulate delivery systems represent an area of particular promise for nanoneuromedicines. They possess significant potential for desperately needed therapies designed to combat a range of disorders associated with aging. As such, the field was selected as the focus for the 2014 meeting of the American Society for Nanomedicine. Regenerative, protective, immune modulatory, anti-microbial and anti-inflammatory products, or imaging agents are readily encapsulated in or conjugated to nanoparticles and as such facilitate the delivery of drug payloads to specific action sites across the blood-brain barrier. Diagnostic imaging serves to precisely monitor disease onset and progression while neural stem cell replacement can regenerate damaged tissue through control of stem cell fates. These, taken together, can improve disease burden and limit systemic toxicities. Such enabling technologies serve to protect the nervous system against a broad range of degenerative, traumatic, metabolic, infectious and immune disorders. From the clinical editor: Nanoneuromedicine is a branch of nanomedicine that specifically looks at the nervous system. In the clinical setting, a fundamental hurdle in nervous system disorders is due to an inherent inability of nerve cells to regenerate after damage. Nanotechnology can offer new approaches to overcome these challenges. This review describes recent developments in nanomedicine delivery systems that would affect stem cell repair and regeneration in the nervous system.

Dichloromethane removal and microbial variations in a combination of UV pretreatment and biotrickling filtration

Biofiltration of hydrophobic and/or recalcitrant volatile organic compounds in industry is currently limited. A laboratory-scale system integrating ultraviolet (UV) photodegradation and a biotrickling filter (BTF) was developed to treat dichloromethane (DCM), and this was compared to BTF alone. A combined UV-BTF approach permitted faster biofilm formation and greater removal than BTF. DCM distribution and its photodegradation intermediates revealed that the lower filter of the UV-BTF contributed more to CO2 production; the upper filter assisted more with DCM removal. The UV-BTF kept secretion of extracellular polymeric substances at a normal level with an evenly distributed biomass. Pyrosequencing analysis showed that the dominant population in the combined biofilter was more diverse than that in BTF alone. Our data provide a foundation for understanding the effect of UV pretreatment on BTF performance and the microbial community.

Treatment of gaseous alpha-pinene by a combined system containing photo oxidation and aerobic biotrickling filtration

Biofiltration of hydrophobic and/or recalcitrant volatile pollutants is intrinsically limited. In the present study, a combined ultraviolet-biotrickling filter (UV-BTF) was developed to improve the removal of these compounds, and a single BTF as the control was operated under the same conditions. The experimental results showed that the UV-BTF provided higher removal efficiencies than the single BTF at an inlet concentration range of 600-1500 mg m(-3) under shorter residence times. The maximum elimination capacities (ECs) obtained were 94.2 mg m(-3)h(-1) and 44 mg m(-3)h(-1) in the combined UV-BTF and single BTF, respectively. The mass ratio of carbon dioxide produced to α-pinene removed in the UV-BTF was approximately 2.74, which was much higher than that of the single BTF (1.99). Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis indicated that there was more complicated microbial community in the UV-BTF than that in the single BTF. In addition, we investigated the effect of starvation or stagnation on re-acclimation and removal performance from an engineering standpoint. The results showed that the combined UV-BTF could deal with fluctuating conditions or periods without any flow (air or liquid) supply much better than the single BTF.

Gene cloning, expression, and characterization of a novel acetaldehyde dehydrogenase from Issatchenkia terricola strain XJ-2

Acetaldehyde is a known mutagen and carcinogen. Active aldehyde dehydrogenase (ALDH) represents an important mechanism for acetaldehyde detoxification. A yeast strain XJ-2 isolated from grape samples was found to produce acetaldehyde dehydrogenase with a high activity of 2.28 U/mg and identified as Issatchenkia terricola. The enzyme activity was validated by oxidizing acetaldehyde to acetate with NAD(+) as coenzyme based on the headspace gas chromatography analysis. A novel acetaldehyde dehydrogenase gene (ist-ALD) was cloned by combining SiteFinding-PCR and self-formed adaptor PCR. The ist-ALD gene comprised an open reading frame of 1,578 bp and encoded a protein of 525 amino acids. The predicted protein of ist-ALD showed the highest identity (73%) to ALDH from Pichia angusta. The ist-ALD gene was expressed in Escherichia coli, and the gene product (ist-ALDH) presented a productivity of 442.3 U/mL cells. The purified ist-ALDH was a homotetramer of 232 kDa consisting of 57 kDa-subunit according to the SDS-PAGE and native PAGE analysis. Ist-ALDH exhibited the optimal activity at pH 9.0 and 40°C, respectively. The activity of ist-ALDH was enhanced by K(+), NH4(+), dithiothreitol, and 2-mercaptoethanol but strongly inhibited by Ag(+), Hg(2+), Cu(2+), and phenylmethyl sulfonylfluoride. In the presence of NAD(+), ist-ALDH could oxidize many aliphatic, aromatic, and heterocyclic aldehydes, preferably acetaldehyde. Kinetic study revealed that ist-ALDH had a k (cat) value of 27.71/s and a k (cat)/K (m) value of 26.80 × 10(3)/(mol s) on acetaldehyde, demonstrating ist-ALDH, a catalytically active enzyme by comparing with other ALDHs. These studies indicated that ist-ALDH was a potential enzymatic product for acetaldehyde detoxification.

Biomedical Applications of Biodegradable Polymers

Utilization of polymers as biomaterials has greatly impacted the advancement of modern medicine. Specifically, polymeric biomaterials that are biodegradable provide the significant advantage of being able to be broken down and removed after they have served their function. Applications are wide ranging with degradable polymers being used clinically as surgical sutures and implants. In order to fit functional demand, materials with desired physical, chemical, biological, biomechanical and degradation properties must be selected. Fortunately, a wide range of natural and synthetic degradable polymers has been investigated for biomedical applications with novel materials constantly being developed to meet new challenges. This review summarizes the most recent advances in the field over the past 4 years, specifically highlighting new and interesting discoveries in tissue engineering and drug delivery applications.

Gene cloning and biochemical characterization of a NAD(P)+ -dependent aldehyde dehydrogenase from Bacillus licheniformis

A putative aldehyde dehydrogenase (ALDH) gene, ybcD (gene locus b1467), was identified in the genome sequence of Bacillus licheniformis ATCC 14580. B. licheniformis ALDH (BlALDH) encoded by ybcD consists of 488 amino acid residues with a molecular mass of approximately 52.7 kDa. The coding sequence of ybcD gene was cloned in pQE-31, and functionally expressed in recombinant Escherichia coli M15. BlALDH had a subunit molecular mass of approximately 53 kDa and the molecular mass of the native enzyme was determined to be 220 kDa by FPLC, reflecting that the oilgomeric state of this enzyme is tetrameric. The temperature and pH optima for BlALDH were 37 degrees C and 7.0, respectively. In the presence of either NAD(+) or NADP(+), the enzyme could oxidize a number of aliphatic aldehydes, particularly C3- and C5-aliphatic aldehyde. Steady-state kinetic study revealed that BlALDH had a K (M) value of 0.46 mM and a k (cat) value of 49.38/s when propionaldehyde was used as the substrate. BlALDH did not require metal ions for its enzymatic reaction, whereas the dehydrogenase activity was enhanced by the addition of disulfide reductants, 2-mercaptoethanol and dithiothreitol. Taken together, this study lays a foundation for future structure-function studies with BlALDH, a typical member of NAD(P)(+)-dependent aldehyde dehydrogenases.

Novel Polyoxyethylene-Containing Glycolipids Are Synthesized in Corynebacterium matruchotii and Mycobacterium smegmatis Cultured in the Presence of Tween 80

The addition of polyoxyethylene sorbitan monooleate (Tween 80) to a culture of mycobacteria greatly influences cell permeability and sensitivity to antibiotics but very little is known regarding the underlying mechanism. Here we show that Corynebacterium matruchotii (surrogate of mycobacteria) converts Tween 80 to a structural series of polyoxyethylenic acids which are then used to form novel series-2A and series-2B glycolipids. Minor series-3 glycolipids were also synthesized. The polyoxyethylenic acids replaced corynomycolic acids in the cell wall. Correspondingly the trehalose dicorynomycolate content was reduced. MALDI mass spectrometry, MS-MS, ¹H-NMR, and ¹³C-NMR were used to characterize the series-2 glycolipids. Series-2A glycolipid is trehalose 6-C_36:2-corynomycolate-6′-polyoxyethylenate and series-2B glycolipid is trehalose 6-C_36:2-corynomycolate-6′-furan ring-containing polyoxyethylenate. Mycobacterium smegmatis grown in the presence of Tween 80 also synthesizes series-2 type glycolipids. The synthesis of these novel glycolipids in corynebacteria and mycobacteria should result in gross changes in the cell wall permeability and drug sensitivity.

Cloning and heterologous expression of two aryl-aldehyde dehydrogenases from the white-rot basidiomycete Phanerochaete chrysosporium

We identified two aryl-aldehyde dehydrogenase proteins (PcALDH1 and PcALDH2) from the white-rot basidiomycete Phanerochaete chrysosporium. Both PcALDHs were translationally up-regulated in response to exogenous addition of vanillin, one of the key aromatic compounds in the pathway of lignin degradation by basidiomycetes. To clarify the catalytic functions of PcALDHs, we isolated full-length cDNAs encoding these proteins and heterologously expressed the recombinant enzymes using a pET/Escherichia coli system. The open reading frames of both PcALDH1 and PcALDH2 consisted of 1503 nucleotides. The deduced amino acid sequences of both proteins showed high homologies with aryl-aldehyde dehydrogenases from other organisms and contained ten conserved domains of ALDHs. Moreover, a novel glycine-rich motif "GxGxxxG" was located at the NAD(+)-binding site. The recombinant PcALDHs catalyzed dehydrogenation reactions of several aryl-aldehyde compounds, including vanillin, to their corresponding aromatic acids. These results strongly suggested that PcALDHs metabolize aryl-aldehyde compounds generated during fungal degradation of lignin and various aromatic xenobiotics.

Unimolecular micelles based on hydrophobically derivatized hyperbranched polyglycerols: biodistribution studies

We recently reported the synthesis and testing of a new class of unimolecular micelles based on hyperbranched polyglycerols as second generation synthetic plasma expanders and as general drug delivery vehicles. A detailed biodistribution study of two derivatized hyperbranched polyglycerols of different molecular weights derivatized with hydrophobic groups and short poly(ethylene glycol) chains is reported in this article. In mice, these materials are nontoxic with circulation half-lives as high as 31 h, controllable by manipulating the molecular weight and the degree of PEG derivatization. Organ accumulation is low, presumably due to the "pegylation" effect. Thermal degradation and hydrolysis data suggest that these polymers are highly stable with a long shelf life, a major advantage for a pharmaceutical product. Degradation under acidic conditions has been observed for these polymers.

Involvement of PEG-carboxylate dehydrogenase and glutathione S-transferase in PEG metabolism by Sphingopyxis macrogoltabida strain 103

Sphingopyxis terrae and the Sphingopyxis macrogoltabida strains 103 and 203 are able to degrade polyethylene glycol (PEG). They possess the peg operon, which is responsible for the conversion of PEG to PEG-carboxylate-coenzyme A (CoA). The upstream (3.0 kb) and downstream (6.5 kb) regions of the operon in strain 103 were cloned and sequenced. The structure was well conserved between S. macrogoltabida strain 203 and S. terrae, except that two sets of transposases are absent in strain 203. The downstream region contains the genes for PEG-carboxylate dehydrogenase (PCDH), glutathione S-transferase (GST), tautomerase, and a hypothetical protein. The genes for pcdh and gst were transcribed constitutively and monocistronically, indicating that their transcription is independent of the operon regulation. PCDH and GST were expressed in Escherichia coli and characterized biochemically. PCDH is a homotetramer of 64-kDa subunits and contains one molecule of flavin adenine dinucleotide per subunit. The enzyme dehydrogenates PEG-carboxylate to yield glyoxylate, suggesting that the enzyme is the third enzyme involved in PEG degradation. GST is a homodimer of 28-kDa subunits. GST activity was noncompetitively inhibited by acyl-CoA and PEG-carboxylate-CoA, suggesting the interaction of GST with them. The proposed role for GST is to buffer the toxicity of PEG-carboxylate-CoA.

Cloning, expression, and characterization of an aldehyde dehydrogenase from Escherichia coli K-12 that utilizes 3-Hydroxypropionaldehyde as a substrate

3-Hydroxypropionaldehyde (3-HPA), an intermediary compound of glycerol metabolism in bacteria, serves as a precursor to 3-Hydroxypropionic acid (3-HP), a commercially valuable platform chemical. To achieve the effective conversion of 3-HPA to 3-HP, an aldH gene encoding an aldehyde dehydrogenase in Escherichia coli K-12 (AldH) was cloned, expressed, and characterized for its properties. The recombinant AldH exhibited broad substrate specificity for various aliphatic and aromatic aldehydes. AldH preferred NAD+ over NADP+ as a cofactor for the oxidation of most aliphatic aldehydes tested. Among the aldehydes used, the specific activity was highest (38.1 U mg(-1) protein) for 3-HPA at pH 8.0 and 37 degrees C. The catalytic efficiency (kcat) and the specificity constant (kcat/Km) for 3-HPA in the presence of NAD+ were 28.5 s(-1) and 58.6x10(3) M(-1) s(-1), respectively. The AldH activity was enhanced in the presence of disulfide reductants such as dithiothreitol (DTT) or 2-mercaptoethanol, while several metal ions, particularly Hg2+, Ag+, Cu2+, and Zn2+, inhibited AldH activity. This study illustrates that AldH is a potentially useful enzyme in converting 3-HPA to 3-HP.

Structure and conservation of a polyethylene glycol-degradative operon in sphingomonads

Sphingopyxis terrae, and Sphingopyxis macrogoltabida strains 103 and 203, can degrade polyethylene glycols (PEGs). They differ in the following respects: (i) different substrate specificities (chain length) of assimilable PEG, (ii) PEG-inducible or constitutive PEG-degradative proteins, and (iii) symbiotic or axenic degradation of PEG. S. terrae was able to incorporate PEG 6000, but strain 103 could not incorporate more than PEG 4000, suggesting that the difference in assimilable PEG chain length depends on the ability to take up substrate. PEG-degradative genes (pegB, C, D, A, E and R) from these strains were cloned. Their primary structures shared a high homology of more than 99 %. The peg genes encode a TonB-dependent receptor (pegB), a PEG-aldehyde dehydrogenase (pegC), a permease (pegD), a PEG dehydrogenase (pegA) and an acyl-CoA ligase (pegE), and in the opposite orientation, an AraC-type transcription regulator (pegR). The peg operon was flanked by two different sets of transposases. These three strains contained large plasmids and the operon was located in one of the large plasmids in S. terrae. The peg genes could be detected in other PEG-degrading sphingomonads. These results suggest that the peg genes have evolved in a plasmid-mediated manner. An insertion of a transposon gene (pegF) between pegD and pegA in strain 203 was found, which caused the constitutive expression of pegA in this strain.

Dual regulation of a polyethylene glycol degradative operon by AraC-type and GalR-type regulators in Sphingopyxis macrogoltabida strain 103

The genes for polyethylene glycol (PEG) catabolism (pegB,C,D,AandE) inSphingopyxis macrogoltabidastrain 103 were shown to form a PEG-inducible operon. ThepegRgene, encoding an AraC-type regulator in the downstream area of the operon, is transcribed in the reverse direction. The transcription start sites of the operon were mapped, and three putativeσ70-type promoter sites were identified in thepegB,pegAandpegRpromoters. A promoter activity assay showed that thepegBpromoter was induced by PEG and oligomeric ethylene glycols, whereas thepegAandpegRpromoters were induced by PEG. Deletion analysis of thepegBpromoter indicated that the region containing the activator-binding motif of an AraC/XylS-type regulator was required for transcription of thepegBCDAEoperon. Gel retardation assays demonstrated the specific binding of PegR to thepegBpromoter. Transcriptional fusion studies ofpegRwithpegAandpegBpromoters suggested that PegR regulates the expression of thepegBCDAEoperon positively through its binding to thepegBpromoter, but PegR does not bind to thepegApromoter. Two specific binding proteins for thepegApromoter were purified and identified as a GalR-type regulator and an H2A histone fragment (histone-like protein, HU). The binding motif of a GalR/LacI-type regulator was found in thepegAandpegRpromoters. These results suggested the dual regulation of thepegBCDAEoperon through thepegBpromoter by an AraC-type regulator, PegR (PEG-independent), and through thepegAandpegRpromoters by a GalR/LacI-type regulator together with HU (PEG-dependent).

Purification, characterization and cloning of aldehyde dehydrogenase from Rhodococcus erythropolis UPV-1

The enzyme responsible for formaldehyde removal in industrial wastewaters by cells of Rhodococcus erythropolis UPV-1 was identified as a broad-specific aldehyde dehydrogenase (EC 1.2.1.3). The enzyme was purified to electrophoretic homogeneity from ethanol-grown cells with a specific activity of 19.5 U mg-1 protein and an activity recovery of 56%. The enzyme showed an isoelectric point (pI) of 5.3 and was a trimer of 162 kDa consisting of three identical 54-kDa subunits. It was specific for NAD+ and showed hyperbolic kinetics for this coenzyme (Km=90 microM), but sigmoidal kinetics for the aliphatic aldehydes used as substrates. The enzyme affinity for aldehydes increased with their hydrocarbon chain length, ranging from 333 microM for formaldehyde to 85 nM for n-octanal. The corresponding calculated Hill coefficients were in the 1.55-2.77 range. With n-propanal as substrate, the optimum pH and temperature for activity were 9.5-10.0 and 47.5 degrees C, respectively, with an Ea for catalysis of 28.6 kJ mol-1. NAD+ protected the enzyme against thermal inactivation, but aldehydes were ineffective. The activity was severely inhibited by p-hydroxymercuribenzoate, indicating that a thiol was essential for catalysis. The 1,524-bp aldhR gene encoding a 507-amino-acid protein was expressed in cells of Escherichia coli M15 as a hexahistidine-tagged protein.