Publications by authors named "Hor-Gil Hur"

107 Publications

Non-specific degradation of chloroacetanilide herbicides by glucose oxidase supported Bio-Fenton reaction.

Chemosphere 2021 Dec 23;292:133417. Epub 2021 Dec 23.

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, Republic of Korea. Electronic address:

Bio-Fenton reaction supported by glucose oxidase (GOx) for producing HO was applied to degrade persistent chloroacetanilide herbicides in the presence of Fe (Ⅲ)-citrate at pH 5.5. There were pH decrease to 4.3, the production of 8 mM HO and simultaneous consumption to produce •OH radicals which non-specifically degraded the herbicides. The degradation rates followed the order acetochlor ≈ alachlor ≈ metolachlor > propachlor ≈ butachlor with the degradation percent of 72.8%, 73.4%, 74.0%, 47.4%, and 43.8%, respectively. During the Bio-Fenton degradation, alachlor was dechlorinated and filtered into catechol via the production of intermediates formed through a series of hydrogen atom abstraction and hydrogen oxide radical addition reactions. The current Bio-Fenton reaction leading to the production of •OH radicals could be applied for non-specific oxidative degradation to various persistent organic pollutants under in-situ environmental conditions, considering diverse microbial metabolic systems able to continuously supply HO with ubiquitous Fe(II) and Fe(III) and citrate.
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http://dx.doi.org/10.1016/j.chemosphere.2021.133417DOI Listing
December 2021

Higher abundance of core antimicrobial resistant genes in effluent from wastewater treatment plants.

Water Res 2022 Jan 19;208:117882. Epub 2021 Nov 19.

Faculty of Biotechnology, College of Applied Life Sciences, SARI, Jeju National University, Jeju 63243, Republic of Korea. Electronic address:

Wastewater treatment plants (WWTPs) receive sewage water from a variety of sources, including livestock farms, hospitals, industries, and households, that contain antimicrobial resistant bacteria (ARB) and antimicrobial resistant genes (ARGs). Current treatment technologies are unable to completely remove ARB and ARGs, which are eventually released into the aquatic environment. This study focused on the core resistome of urban WWTPs that are persistent through wastewater treatment processes. We adopted the Hiseq-based metagenomic sequencing approach to identify the core resistome, their genetic context, and pathogenic potential of core ARGs in the influent (IN) and effluent (EF) samples of 12 urban WWTPs in South Korea. In this study, the abundance of ARGs ranged from 0.32 to 3.5 copies of ARGs per copy of the 16S rRNA gene, where the IN samples were relatively higher than the EF samples, especially for the macrolide-lincosamide-streptogramin (MLS)- and tetracycline- resistant genes. On the other hand, there were 43 core ARGs sharing up to 90% of the total, among which the relative abundance of sul1, APH(3'')-lb, and RbpA was higher in EF than in IN (p < 0.05). Moreover, tetracycline and sulfonamide-related core ARGs in both EF and IN were significantly more abundant on plasmids than on chromosomes (p < 0.05). We also found that the majority of core ARGs were carried by opportunistic pathogens such as Acinetobacter baumannii, Enterobacter cloacae, and Pseudomonas aeruginosa in both IN and EF. In addition, phages were the only mobile elements whose abundance correlated with that of core ARGs in EF, suggesting that transduction may play a major role in disseminating ARGs in the receiving water environment of the urban WWTP. The persistent release of core ARGs with pathogenic potential into environmental water is of immediate concern. The mobility of ARGs and ARBs in the environment is a major public health concern. These results should be taken into consideration when developing policy to mitigate environmental dissemination of ARG by WWTPs.
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http://dx.doi.org/10.1016/j.watres.2021.117882DOI Listing
January 2022

Layers of Uranium Phosphate Nanorods and Nanoplates Encrusted on Fungus Cladosporium sp. Strain F1 Hyphae.

Microbes Environ 2021 ;36(4)

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology.

The hyphae of Cladosporium sp. strain F1 (CFGR 2020-301-00084) were heavily encrusted with pre-synthesized uranium phosphate minerals under a wide range of pH conditions. SEM and TEM images showed that nanorods and nanoplates of uranium phosphate minerals at pH 4 and 5 and at pH 6, 7, and 8, respectively, were tightly adsorbed along the hyphae of Cladosporium sp. strain F1, while only a few uranium phosphate minerals were observed on the hyphae of Aspergillus niger VKMF 1119. Based on the physical mobility and chemical stability of uranium phosphate minerals under in situ oxidizing environmental conditions, the application of Cladosporium sp. strain F1 has potential as a novel strategy for the remediation of uranium contamination in sediments and aquifers under a wide range of pH conditions where larger amounts of phosphate are present in the environment.
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http://dx.doi.org/10.1264/jsme2.ME21036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8674443PMC
December 2021

Direct and Indirect Reduction of Cr(VI) by Fermentative Fe(III)-Reducing sp. Strain Cellu-2a.

J Microbiol Biotechnol 2021 Nov;31(11):1519-1525

Department of Bioenvironmental Chemistry, Jeonbuk National University, Jeonju 54896, Republic of Korea.

Hexavalent chromium (Cr(VI)) is recognized to be carcinogenic and toxic and registered as a contaminant in many drinking water regulations. It occurs naturally and is also produced by industrial processes. The reduction of Cr(VI) to Cr(III) has been a central topic for chromium remediation since Cr(III) is less toxic and less mobile. In this study, fermentative Fe(III)-reducing bacterial strains (Cellu-2a, Cellu-5a, and Cellu-5b) were isolated from a groundwater sample and were phylogenetically related to species of by 16S rRNA gene analysis. One selected strain, Cellu-2a showed its capacity of reduction of both soluble iron (ferric citrate) and solid iron (hydrous ferric oxide, HFO), as well as aqueous Cr(VI). The strain Cellu-2a was able to reduce 15 μM Cr(VI) directly with glucose or sucrose as a sole carbon source under the anaerobic condition and indirectly with one of the substrates and HFO in the same incubations. The heterogeneous reduction of Cr(VI) by the surface-associated reduced iron from HFO by Cellu-2a likely assisted the Cr(VI) reduction. Fermentative features such as large-scale cell growth may impose advantages on the application of bacterial Cr(VI) reduction over anaerobic respiratory reduction.
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http://dx.doi.org/10.4014/jmb.2107.07038DOI Listing
November 2021

Degradation of sulfonated polyethylene by a bio-photo-fenton approach using glucose oxidase immobilized on titanium dioxide.

J Hazard Mater 2022 02 28;423(Pt A):127067. Epub 2021 Aug 28.

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Republic of Korea. Electronic address:

Polyethylene (PE) plastics are highly recalcitrant and resistant to photo-oxidative degradation due to its chemically inert backbone structure. We applied two novel reactions such as, Bio-Fenton reaction using glucose oxidase (GOx) enzyme alone and Bio-Photo-Fenton reaction using GOx immobilized on TiO nanoparticles (TiO-GOx) under UV radiation, for (bio)degradation of pre-activated PE with sulfonation (SPE). From both the reactions, GC-MS analyses identified small organic acids such as, acetic acid and butanoic acid as a major metabolites released from SPE. In the presence of UV radiation, 21 fold and 17 fold higher amounts of acetic acid (4.78 mM) and butanoic acid (0.17 mM) were released from SPE after 6 h of reaction using TiO-GOx than free GOx, which released 0.22 mM and 0.01 mM of acetic acid and butanoic acid, respectively. Our results suggest that (bio)degradation and valorization of naturally weathered and oxidized PE using combined reactions of biochemistry, photochemistry and Fenton chemistry could be possible.
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http://dx.doi.org/10.1016/j.jhazmat.2021.127067DOI Listing
February 2022

Structure and substrate specificity determinants of NfnB, a dinitroaniline herbicide-catabolizing nitroreductase from Sphingopyxis sp. strain HMH.

J Biol Chem 2021 10 30;297(4):101143. Epub 2021 Aug 30.

Department of Agricultural Biotechnology, Seoul National University, Seoul, Republic of Korea; Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul, Republic of Korea. Electronic address:

Nitroreductases are emerging as attractive bioremediation enzymes, with substrate promiscuity toward both natural and synthetic compounds. Recently, the nitroreductase NfnB from Sphingopyxis sp. strain HMH exhibited metabolic activity for dinitroaniline herbicides including butralin and pendimethalin, triggering the initial steps of their degradation and detoxification. However, the determinants of the specificity of NfnB for these herbicides are unknown. In this study, we performed structural and biochemical analyses of NfnB to decipher its substrate specificity. The homodimer NfnB is a member of the PnbA subgroup of the nitroreductase family. Each monomer displays a central α + β fold for the core domain, with a protruding middle region and an extended C-terminal region. The protruding middle region of Val75-Tyr129 represents a structural extension that is a common feature to members of the PnbA subgroup and functions as an opening wall connecting the coenzyme FMN-binding site to the surface, therefore serving as a substrate binding site. We performed mutational, kinetic, and structural analyses of mutant enzymes and found that Tyr88 in the middle region plays a pivotal role in substrate specificity by determining the dimensions of the wall opening. The mutation of Tyr88 to phenylalanine or alanine caused significant changes in substrate selectivity toward bulkier dinitroaniline herbicides such as oryzalin and isopropalin without compromising its activity. These results provide a framework to modify the substrate specificity of nitroreductase in the PnbA subgroup, which has been a challenging issue for its biotechnological and bioremediation applications.
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http://dx.doi.org/10.1016/j.jbc.2021.101143DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8484813PMC
October 2021

Emergence of High Level Carbapenem and Extensively Drug Resistant ST746 Producing NDM-5 in Influent of Wastewater Treatment Plant, Seoul, South Korea.

Front Microbiol 2021 23;12:645411. Epub 2021 Mar 23.

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology, Gwangju, South Korea.

High level carbapenem and extensively drug resistant (XDR) strain N7, which produces a variant of New Delhi metallo-β-lactamase (NDM-5), was isolated from the influent of the Jungnang wastewater treatment plant located on Han River, Seoul, South Korea. Phenotypic and genotypic resistances to carbapenem were tested using agar and broth dilution methods, and polymerase chain reaction. Whole-genome sequencing was performed to characterize the genetic structure of strain N7. strain N7, which harbors the gene, showed high level of carbapenem resistance at concentrations of doripenem (512 mg/L) and meropenem (256 mg/L), and XDR to 15 antibiotics. Based on the genomic sequence analysis, two plasmids, a hybrid IncHI2/N-type and an IncX3 type, were present. The former contains a cluster ( - --) bracketed by multi-insertional sequences, IS, IS, IS, and IS. The latter carries the following resistance genes: , , and , and . The chromosome, contig3, and contig5 also carry and , and and , respectively. Strain N7 also harbors virulence factors such as , , , , and . This study demonstrates the emergence of high level carbapenem resistant XDR strain N7 containing in aquatic environment, Seoul, South Korea. Due to the presence of mobile genetic elements, this strain could horizontally transfer resistance genes, including to environmental bacteria. Thus, it is necessary to conduct continuous surveillance for carbapenem resistance in various aquatic environments.
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http://dx.doi.org/10.3389/fmicb.2021.645411DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8021692PMC
March 2021

Metagenomic exploration of antibiotic resistome in treated wastewater effluents and their receiving water.

Sci Total Environ 2021 Apr 5;765:142755. Epub 2020 Oct 5.

Faculty of Biotechnology, College of Applied Life Sciences, SARI, Jeju National University, Jeju 63243, Republic of Korea. Electronic address:

Environmental dissemination of antimicrobial resistance is a global health problem. Antimicrobial-resistant bacteria and antibiotic-resistant genes (ARGs) are constantly released into the environment through effluents (EFs) from wastewater treatment plants (WWTPs). Thus, requiring a better understanding of the selection and fate of ARGs in wastewater treatment processes. Therefore, we investigated the impacts of urban WWTP EFs on receiving water in the context of their resistomes and mobilomes. We used a HiSeq-based short read metagenomic approach to address the dynamics and diversity of ARGs in WWTP EF as well as the upstream (UP) and downstream (DN) river waters, followed by an investigation of plasmid-mediated ARGs. The abundance of ARGs at each site varied from 7.2 × 10 to 7.4 × 10 ARG copies per 16S rRNA gene copy, and EF samples showed the highest abundance, followed by DN and UP water samples. ARG diversity ranged from 121 to 686 types per site, and EF had the most diverse ARGs. Commonly identified ARGs in the EF and DN samples were clinically important and were absent in UP samples. The abundance of ARGs, mobile genetic elements (MGEs), and plasmid contigs found only in EF and DN were positively correlated with each other, indicating the importance of mobilomes in the dissemination of ARGs in the environment. Moreover, the proportions of plasmid-mediated ARGs was highest in the EF samples, followed by the DN and UP samples. These findings suggest that WWTP EF may act as a driving factor shaping the resistomes and mobilomes of receiving waters. In particular, a higher abundance of plasmid-mediated ARGs in WWTP EF suggests higher transmissibility in the DN environment.
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http://dx.doi.org/10.1016/j.scitotenv.2020.142755DOI Listing
April 2021

A novel pathway for initial biotransformation of dinitroaniline herbicide butralin from a newly isolated bacterium Sphingopyxis sp. strain HMH.

J Hazard Mater 2021 01 17;402:123510. Epub 2020 Jul 17.

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, Republic of Korea. Electronic address:

Butralin (N-sec- Butyl-4-tert-butyl-2,6-dinitroaniline) is a highly persistent dinitroaniline herbicide frequently detected in the environment. In this study, butralin-degrading soil bacterium, Sphingopyxis sp. strain HMH was isolated from agricultural soil samples. Based on whole genome sequence analysis of the strain HMH, the gene encoding a nitroreductase NfnB was identified and expressed in Escherichia coli (E. coli), and protein was purified to homogeneity. NfnB is a flavin-nitroreductase, found to be a functional tetramer, composed of subunit molecular mass of 25 kDa. The metabolites from butralin degradation by strain HMH and purified NfnB were identified using ultra performance liquid chromatography high resolution mass spectrometry (UPLC-HRMS), and a novel mechanism of butralin degradation was proposed. NfnB selectively nitro-reduced butralin into N- (sec-Butyl)-4-(tert-butyl)-6-nitrobenzene- 1,2-diamine, followed by formation of 5-(tert-Butyl)-3 -nitrobenzene-1,2-diamine and butanone by N- dealkylation through possible hydroxylation reaction onto the carbon linked amine of the N-(sec-Butyl) moiety. In our study, we could not detect the hydroxylated product 2-(2-Amino-4-tert-butyl-6-nitro- phenylamino)-butan-2-ol) (carbinolamine), instead its Schiff base product (E)-2-(Butan-2-yildeneamino)-5- (tert-butyl)-3-nitroaniline was detected. The release of butanone was further confirmed by derivatization with 2,4- dinitrophenylhydrazine (DNPH) followed by MS analysis. In conclusion, this study explores a novel multi-functional flavin- nitroreductase family enzyme NfnB, catalyzing unique and sequential nitroreduction and N-dealkylation through oxidative hydroxylation of dinitroaniline herbicide butralin.
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http://dx.doi.org/10.1016/j.jhazmat.2020.123510DOI Listing
January 2021

Complete Genome Sequence of a Plant-Derived Phenylpropanoid-Degrading Bacterium, Pseudomonas putida JYR-1.

Microbiol Resour Announc 2020 Jan 2;9(1). Epub 2020 Jan 2.

Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing, China

JYR-1 was isolated from soil contaminated with industrial oil because of its ability to utilize -anethole as a carbon and energy source. The complete genome is 5.41 Mb with 4,834 protein-coding genes. Study of this isolate will provide insight into biotransformation pathways for phenylpropanoids.
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http://dx.doi.org/10.1128/MRA.01152-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6940283PMC
January 2020

Cupriavidus sp. strain Ni-2 resistant to high concentration of nickel and its genes responsible for the tolerance by genome comparison.

Arch Microbiol 2019 Dec 11;201(10):1323-1331. Epub 2019 Jul 11.

Department of Bioenvironmental Chemistry, Chonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju-si, Jeollabuk-do, 54896, Republic of Korea.

The widespread use of metals influenced many researchers to examine the relationship between heavy metal toxicity and bacterial resistance. In this study, we have inoculated heavy metal-contaminated soil from Janghang region of South Korea in the nickel-containing media (20 mM Ni) for the enrichment. Among dozens of the colonies acquired from the several transfers and serial dilutions with the same concentrations of Ni, the strain Ni-2 was chosen for further studies. The isolates were identified for their phylogenetic affiliations using 16S rRNA gene analysis. The strain Ni-2 was close to Cupriavidus metallidurans and was found to be resistant to antibiotics of vancomycin, erythromycin, chloramphenicol, ampicillin, gentamicin, streptomycin, and kanamycin by disk diffusion method. Of the isolated strains, Ni-2 was sequenced for the whole genome, since the Ni-resistance seemed to be better than the other strains. From the genome sequence we have found that there was a total of 89 metal-resistance-related genes including 11 Ni-resistance genes, 41 heavy metal (As, Cd, Zn, Hg, Cu, and Co)-resistance genes, 22 cation-efflux genes, 4 metal pumping ATPase genes, and 11 metal transporter genes.
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http://dx.doi.org/10.1007/s00203-019-01700-5DOI Listing
December 2019

Seasonal Mixing-Driven System in Estuarine-Coastal Zone Triggers an Ecological Shift in Bacterial Assemblages Involved in Phytoplankton-Derived DMSP Degradation.

Microb Ecol 2020 Jan 29;79(1):12-20. Epub 2019 May 29.

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology, Gwangju, 61005, Republic of Korea.

The coastal zone has distinguishable but tightly connected ecosystems from rivers to the ocean and globally contributes to nutrient cycling including phytoplankton-derived organic matter. Particularly, bacterial contributions to phytoplankton-derived dimethylsulfoniopropionate (DMSP) degradation have been recently evaluated by using advanced sequencing technologies to understand their role in the marine microbial food web. Here, we surveyed the bacterial diversity and community composition under seasonal water mixing in the bay of Gwangyang (GW), a semi-enclosed estuary at the southern tip of the Korea Peninsula. We detected phylogenetic dissimilarities among season-specific habitats in GW and their specific bacterial taxa. Additionally, bacterial contribution to degradation of phytoplankton-derived DMSP from estuarine to coastal waters at euphotic depths in GW was investigated as the presence or absence of DMSP demethylation gene, encoded by dmdA. Among the operational taxonomic units (OTUs) in GW bacterial communities, the most dominant and ubiquitous OTU1 was affiliated with the SAR11 clade (SAR11-OTU). The population dynamics of SAR11-OTU in dmdA-detected GW waters suggest that water mass mixing plays a major role in shaping bacterial communities involved in phytoplankton-derived DMSP demethylation.
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http://dx.doi.org/10.1007/s00248-019-01392-wDOI Listing
January 2020

High genetic diversity of Vibrio parahaemolyticus isolated from tidal water and mud of southern coast of South Korea.

FEMS Microbiol Ecol 2019 03;95(3)

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology, 123 Cheomdangwagi-ro, Oryong-dong, Buk-gu, 61005 Gwangju, South Korea.

A horizontal, fluorophore-enhanced, repetitive extragenic palindromic-polymerase chain reaction (rep-PCR) DNA fingerprinting technique was adapted to examine the genotypic richness and source differentiation of Vibrio parahaemolyticus (n = 1749) isolated from tidal water and mud of southern coast of South Korea. The number of unique genotypes observed from June (163, 51.9%), September (307, 63.9%), December (205, 73.8%) and February (136, 74.7%), indicating a high degree of genetic diversity. Contrary, lower genetic diversity was detected in April (99, 46.8%), including predominant genotypes comprised >30 V. parahaemolyticus isolates. Jackknife analysis indicated that 65.1% tidal water isolates and 87.1% mud isolates were correctly assigned to their source groups. Sixty-nine isolates of pathogenic V. parahaemolyticus were clustered into two groups, separated by sampling month, source of isolation and serogroups. Serotypes O1, O4, O5, O10/O12 and O11 were the dominant serovariants, while serotypes O3/O13 were highly detected in April where there were no pathogenic V. parahaemolyticus isolates. Most of the V. parahaemolyticus isolates were resistant to ampicillin, ceftazidime and sulfamethoxazole. Interestingly, four V. parahaemolyticus isolates resistant to carbepenem did not contain the known carbapenemase-encoding gene, but possess an extended-spectrum β-lactamase blaTEM.
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http://dx.doi.org/10.1093/femsec/fiz022DOI Listing
March 2019

Characterization of a novel thermostable carboxylesterase from thermoalkaliphilic bacterium Bacillus thermocloaceae.

Biosci Biotechnol Biochem 2019 May 10;83(5):882-891. Epub 2019 Feb 10.

a School of Earth Sciences and Environmental Engineering , Gwangju Institute of Science and Technology (GIST) , Gwangju , Republic of Korea.

A novel thermostable carboxylesterase (Est5250) of thermoalkaliphilic bacterium Bacillus thermocloaceae was heterologously expressed in Escherichia coli and its biochemical properties were investigated. Est5250 showed optimum esterase activity at 60 °C and pH 8.0. The enzyme was highly thermostable at 60 °C, interestingly, the thermostability was enhanced in the presence of Ca, retaining more than 60% of its original activity after 12 h of pre-incubation. Est5250 was active in the presence of 1% (v/v) of organic solvents and 0.1% (v/v) of non-ionic detergents. The enzyme activity was significantly enhanced up to 167% and 159% in the presence of 2-mercaptoethanol and dithiothreitol, respectively. Est5250 showed high substrate specificity for short-chain p-nitrophenyl-esters. Kinetic constants, K and k, for p-nitrophenyl-acetate were 185.8 μM and 186.6 s, respectively. Est5250 showed outstanding thermostability and tolerance to various organic solvents under thermoalkaliphilic conditions, suggesting that it would be a highly suitable biocatalyst for various biotechnological applications. Abbreviations: B. thermocloaceae sp.: Bacillus thermocloaceae; E. coli: Escherichia coli; NP: nitrophenyl; DMSO: dimethyl sulfoxide; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; DMF: dimethyl formamide; EGTA: ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid; CTAB: cetrimonium bromide; PMSF: phenylmethylsulfonyl fluoride; DEPC: diethyl pyrocarbonate; 2-ME: 2-mercaptoethanol; DTT: dithiothreitol.
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http://dx.doi.org/10.1080/09168451.2019.1574555DOI Listing
May 2019

Biogenic Hematite from Bacteria: Facile Synthesis of Secondary Nanoclusters for Lithium Storage Capacity.

ACS Appl Mater Interfaces 2019 Feb 6;11(7):6948-6957. Epub 2019 Feb 6.

School of Earth Sciences and Environmental Engineering , Gwangju Institute of Science and Technology , Gwangju 61005 , Republic of Korea.

Ferrihydrite, or iron(III) (oxyhydr)oxide (Fe(OH)), a representative scavenger of environmentally relevant toxic elements, has been repurposed as a low-cost and scalable precursor of well-developed hematite (α-FeO) secondary nanoclusters with a hierarchically structured morphology for lithium-ion anode materials. Here, we report that the bacteria Clostridium sp. C8, isolated from a methane-gas-producing consortium, can synthesize self-assembled secondary hematite nanoclusters (∼150 nm) composed of small nanoparticles (∼15 nm) through the molecular structural rearrangement of amorphous ferrihydrite under mild conditions. The biogenic hematite particles, wrapped with graphene oxide reduced in situ by the reducing bacteria Shewanella sp. HN-41 via one-pot synthesis, deliver an excellent reversible capacity of ∼1000 mA h g after 100 cycles at a current density of 1 A g. Furthermore, the heat-treated hematite/rGO exhibits a capacity of 820 mA h g at a high current density of 5 A g and a reversible capacity of up to 1635 mA h g at a current density of 100 mA g. This study provides an easy, eco-efficient, and scalable microbiological synthetic route to produce hierarchical hematite/rGO secondary nanoclusters with potential as high-performance Li-ion anode materials.
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http://dx.doi.org/10.1021/acsami.8b18894DOI Listing
February 2019

Biosynthesis of Nanomaterials by Species for Application in Lithium Ion Batteries.

Front Microbiol 2018 21;9:2817. Epub 2018 Nov 21.

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology, Gwangju, South Korea.

Nanomaterials exhibit extraordinary properties based on their size, shape, chemical composition, and crystal structure. Owing to their unique properties nanomaterials are preferred over their bulk counterparts for a number of applications. Although conventional physical and chemical routes were established for the massive production of nanomaterials, there are some drawbacks such as environmental burden and high cost that cannot be disregarded. Recently, there has been great interest toward the green synthesis of inorganic nanomaterials. It has been reported that dissimilatory metal reduction by microorganisms is a cost-effective process to remediate toxic organic and inorganic compounds under anaerobic conditions. Particularly, members of the genus have been utilized to produce various biogenic nanomaterials with unique micro/nanostructured morphologies through redox transformations as well as to remove harmful metals and metalloids in eco-efficient and environment-friendly methods under ambient conditions. In the present mini-review, we specifically address the active utilization of microbial respiration processes for the synthesis of novel functional biogenic nanomaterials by the members of the genus. This biosynthetic method may provide alternative approaches to produce electrode materials for sustainable energy storage applications.
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http://dx.doi.org/10.3389/fmicb.2018.02817DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6258770PMC
November 2018

Thermoalkaliphilic laccase treatment for enhanced production of high-value benzaldehyde chemicals from lignin.

Int J Biol Macromol 2019 Mar 16;124:200-208. Epub 2018 Nov 16.

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Republic of Korea. Electronic address:

Enzymatic conversion of lignin into high-value chemicals is a key step in sustainable and eco-friendly development of lignin valorization strategies. In the present study, a novel thermoalkaliphilic laccase, CtLac, from Caldalkalibacillus thermarum strain TA2.A1 was tested for the depolymerization of lignin and the production of value-added chemicals, using three different lignocellulosic biomass, organosolv lignin (OSL), and Kraft lignin. Seven valuable lignin monomers were identified from the CtLac-treated samples using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Remarkably, increases of 22.0%, 65.6%, and 27.3% of p-hydroxybenzaldehyde and increases of 111.1%, 93.5%, and 238.1% of vanillin were observed from rice straw, corn stover, and reed, respectively. Comparative analysis of lignin monomers released from rice straw, using Trametes versicolor laccase (TvL) and CtLac indicated efficient depolymerization of lignin by CtLac. CtLac treatment resulted in 2.3 fold and 5.6 fold, and 1.9 fold and 2.8 fold higher amounts of p-hydroxybenzaldehyde and vanillin from OSL and Kraft lignin, respectively, compared to CtLac-treated rice straw samples after 12 h reaction. OSL was the best substrate for the production of benzaldehyde chemicals using CtLac treatment. The results demonstrated potential application of bacterial laccase CtLac for valorization of biomass lignin into high-value benzaldehyde chemicals under thermoalkaliphilic conditions.
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http://dx.doi.org/10.1016/j.ijbiomac.2018.11.144DOI Listing
March 2019

Adsorption and Incorporation of Arsenic to Biogenic Lepidocrocite Formed in the Presence of Ferrous Iron during Denitrification by Paracoccus denitrificans.

Environ Sci Technol 2018 09 24;52(17):9983-9991. Epub 2018 Aug 24.

Pohang Accelerator Laboratory (PAL) , Pohang University of Science and Technology , Pohang 37673 , Republic of Korea.

We demonstrate adsorption and partial incorporation of arsenic, in its soluble form, either as arsenite or arsenate into lepidocrocite (γ-FeOOH), which was formed through nitrite-driven Fe(II) oxidation by Paracoccus denitrificans under nitrate-reducing conditions. Fe and As K-edge XANES and radial distribution functions of Fourier-transformed EXAFS spectra showed that portions of As were found to be incorporated in the biogenic lepidocrocite, in addition to higher portions of adsorbed As. We suggest that denitrifying bacteria such as Paracoccus denitrificans, studied here, could facilitate decrease of aqueous arsenic As(III) and/or As(V) through indirect Fe(II) oxidation to solid phase iron minerals, here as lepidocrocite, by the denitrification product nitrite in the presence of nitrate, ferrous iron, and arsenic, under certain environmental conditions where these materials could be found, such as in As-contaminated paddy soils and wetlands.
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http://dx.doi.org/10.1021/acs.est.8b02101DOI Listing
September 2018

Metagenomic analysis reveals the prevalence and persistence of antibiotic- and heavy metal-resistance genes in wastewater treatment plant.

J Microbiol 2018 Jun 1;56(6):408-415. Epub 2018 Jun 1.

Faculty of Biotechnology, School of life sciences, SARI, Jeju National University, Jeju, 63243, Republic of Korea.

The increased antibiotic resistance among microorganisms has resulted into growing interest for investigating the wastewater treatment plants (WWTPs) as they are reported to be the major source in the dissemination of antibiotic resistance genes (ARGs) and heavy metal resistance genes (HMRGs) in the environment. In this study, we investigated the prevalence and persistence of ARGs and HMRGs as well as bacterial diversity and mobile genetic elements (MGEs) in influent and effluent at the WWTP in Gwangju, South Korea, using high-throughput sequencing based metagenomic approach. A good number of broad-spectrum of resistance genes (both ARG and HMRG) were prevalent and likely persistent, although large portion of them were successfully removed at the wastewater treatment process. The relative abundance of ARGs and MGEs was higher in effluent as compared to that of influent. Our results suggest that the resistance genes with high abundance and bacteria harbouring ARGs and MGEs are likely to persist more through the treatment process. On analyzing the microbial community, the phylum Proteobacteria, especially potentially pathogenic species belonging to the genus Acinetobacter, dominated in WWTP. Overall, our study demonstrates that many ARGs and HMRGs may persist the treatment processes in WWTPs and their association to MGEs may contribute to the dissemination of resistance genes among microorganisms in the environment.
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http://dx.doi.org/10.1007/s12275-018-8195-zDOI Listing
June 2018

Fecal pollution: new trends and challenges in microbial source tracking using next-generation sequencing.

Environ Microbiol 2018 09 5;20(9):3132-3140. Epub 2018 Aug 5.

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea.

In this minireview, we expand upon traditional microbial source tracking (MST) methods by discussing two recently developed, next-generation-sequencing (NGS)-based MST approaches to identify sources of fecal pollution in recreational waters. One method defines operational taxonomic units (OTUs) that are specific to a fecal source, e.g., humans and animals or shared among multiple fecal sources to determine the magnitude and likely source association of fecal pollution. The other method uses SourceTracker, a program using a Bayesian algorithm, to determine which OTUs have contributed to an environmental community based on the composition of microbial communities in multiple fecal sources. Contemporary NGS-based MST tools offer a promising avenue to rapidly characterize fecal source contributions for water monitoring and remediation efforts at a broader and more efficient scale than previous molecular MST methods. However, both NGS methods require optimized sequence processing methodologies (e.g. quality filtering and clustering algorithms) and are influenced by primer selection for amplicon sequencing. Therefore, care must be taken when extrapolating data or combining datasets. Furthermore, traditional limitations of library-dependent MST methods, including differential decay of source material in environmental waters and spatiotemporal variation in source communities, remain to be fully understood. Nevertheless, increasing use of these methods, as well as expanding fecal taxon libraries representative of source communities, will help improve the accuracy of these methods and provide promising tools for future MST investigations.
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http://dx.doi.org/10.1111/1462-2920.14281DOI Listing
September 2018

A novel laccase from thermoalkaliphilic bacterium Caldalkalibacillus thermarum strain TA2.A1 able to catalyze dimerization of a lignin model compound.

Appl Microbiol Biotechnol 2018 May 19;102(9):4075-4086. Epub 2018 Mar 19.

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, Republic of Korea.

In the present study, the gene encoding a multicopper oxidase, more precisely a laccase from the thermoalkaliphilic aerobic bacterium Caldalkalibacillus thermarum strain TA2.A1 (CtLac), was cloned and expressed in Escherichia coli. CtLac is a monomeric protein with a molecular weight of 57 kDa as determined by native polyacrylamide gel electrophoresis. The optimum pH and temperature for 2,6-dimethoxyphenol (2,6-DMP) oxidation were 8.0 and 70 °C, respectively. The kinetic constants K and k for 2,6-DMP were of 200 μM and 23 s, respectively. The enzyme was highly thermostable at 80 °C and retained more than 80% of its activity after 24 h preincubation under thermoalkaliphilic conditions. Remarkably, it showed a half-life of about 12 h at 90 °C. The enzyme activity was significantly enhanced by Cu and Mn and was not affected in the presence of most of the other metal ions. CtLac activity was stimulated in the presence of halides, organic solvents, and surfactants. Furthermore, the activity of CtLac on a dimeric lignin model compound, guaiacylglycerol-β-guaiacyl ether (GGGE) was investigated. Liquid chromatography-mass spectrometry analysis indicated that CtLac catalyzes dimerization of GGGE to form a C5-C5 biphenyl tetramer. The stability and activity of CtLac characterized herein under thermoalkaliphilic conditions make it a highly suitable biocatalyst for various biotechnological and industrial applications.
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http://dx.doi.org/10.1007/s00253-018-8898-4DOI Listing
May 2018

Inference on Paleoclimate Change Using Microbial Habitat Preference in Arctic Holocene Sediments.

Sci Rep 2017 08 29;7(1):9652. Epub 2017 Aug 29.

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology, Gwangju, 61005, Republic of Korea.

The present study combines data of microbial assemblages with high-resolution paleoceanographic records from Core GC1 recovered in the Chukchi Sea. For the first time, we have demonstrated that microbial habitat preferences are closely linked to Holocene paleoclimate records, and found geological, geochemical, and microbiological evidence for the inference of the sulphate-methane transition zone (SMTZ) in the Chukchi Sea. In Core GC1, the layer of maximum crenarchaeol concentration was localized surrounding the SMTZ. The vertically distributed predominant populations of Gammaproteobacteria and Marine Group II Euryarchaeota (MG-II) were consistent with patterns of the known global SMTZs. MG-II was the most prominent archaeal group, even within the layer of elevated concentrations of crenarchaeol, an archaeal lipid biomarker most commonly used for Marine Group I Thaumarchaeota (MG-I). The distribution of MG-I and MG-II in Core GC1, as opposed to the potential contribution of MG-I to the marine tetraether lipid pool, suggests that the application of glycerol dibiphytanyl glycerol tetraethers (GDGT)-based proxies needs to be carefully considered in the subsurface sediments owing to the many unknowns of crenarchaeol. In conclusion, microbiological profiles integrated with geological records seem to be useful for tracking microbial habitat preference, which reflect climate-triggered changes from the paleodepositional environment.
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http://dx.doi.org/10.1038/s41598-017-08757-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5575242PMC
August 2017

Inactivation efficiency of plasmid-encoded antibiotic resistance genes during water treatment with chlorine, UV, and UV/HO.

Water Res 2017 10 22;123:783-793. Epub 2017 Jun 22.

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 61005, Republic of Korea. Electronic address:

This study assessed the inactivation efficiency of plasmid-encoded antibiotic resistance genes (ARGs) both in extracellular form (e-ARG) and present within Escherichia coli (intracellular form, i-ARG) during water treatment with chlorine, UV (254 nm), and UV/HO. A quantitative real-time PCR (qPCR) method was used to quantify the ARG damage to amp (850 bp) and kan (806 bp) amplicons, both of which are located in the pUC4K plasmid. The plate count and flow cytometry methods were also used to determine the bacterial inactivation parameters, such as culturability and membrane damage, respectively. In the first part of the study, the kinetics of E. coli inactivation and ARG damage were determined in phosphate buffered solutions. The ARG damage occurred much more slowly than E. coli inactivation in all cases. To achieve 4-log reduction of ARG concentration at pH 7, the required chlorine exposure and UV fluence were 33-72 (mg × min)/L for chlorine and 50-130 mJ/cm for UV and UV/HO. After increasing pH from 7 to 8, the rates of ARG damage decreased for chlorine, while they did not vary for UV and UV/HO. The i-ARGs mostly showed lower rates of damage compared to the e-ARGs due to the protective roles of cellular components against oxidants and UV. The contribution of OH radicals to i-ARG damage was negligible in UV/HO due to significant OH radical scavenging by cellular components. In all cases, the ARG damage rates were similar for amp versus kan, except for the chlorination of e-ARGs, in which the damage to amp occurred faster than that to kan. Chlorine and UV dose-dependent ARG inactivation levels determined in a wastewater effluent matrix could be reasonably explained by the kinetic data obtained from the phosphate buffered solutions and the expected oxidant (chlorine and OH radicals) demands by water matrix components. These results can be useful in optimizing chlorine and UV-based disinfection systems to achieve ARG inactivation.
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http://dx.doi.org/10.1016/j.watres.2017.06.056DOI Listing
October 2017

Emergence of Klebsiella variicola positive for NDM-9, a variant of New Delhi metallo-β-lactamase, in an urban river in South Korea.

J Antimicrob Chemother 2017 04;72(4):1063-1067

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea.

Objectives: To examine the presence of pathogenic bacteria carrying New Delhi metallo-β-lactamase in the environment and to characterize the genome structures of these strains.

Methods: Phenotypic screening of antimicrobial susceptibility and WGS were conducted on three Klebsiella variicola strains possessing NDM-9 isolated from an urban river.

Results: Three carbapenem-resistant K. variicola isolated from Gwangju tributary were found to possess bla NDM-9 genes. Antimicrobial susceptibility testing indicated resistance of these strains to aminoglycosides, carbapenems, cephems, folate pathway inhibitors, fosfomycin and penicillins, but susceptibility to fluoroquinolones, phenicols, tetracyclines and miscellaneous agents. WGS revealed that the 108 kb IncFII(Y)-like plasmids carry bla NDM-9 sandwiched between IS 15 for the GJ1 strain, IS 26 for the GJ2 strain, IS 15D1 for the GJ3 strain and IS Vsa3 , and further bracketed by IS 26 and Tn AS3 along with the mercury resistance operon upstream and the class 1 integron composed of gene cassettes of aadA2 , dfrA12 and sul1 downstream. An aph(3')-Ia gene conferring resistance to aminoglycosides is located after the integrons. Chromosomally encoded bla LEN-13 , fosA , aqxA and oqxB genes, as well as plasmid-mediated bla TEM-1B and bla CTX-M-65 encoding ESBL, ant(3')-Ia and mph (A) genes, were also identified.

Conclusions: The findings of the present study provide us with the information that NDM-9 has been spreading into the environment. Dissemination of NDM-9 in the environment has raised a health risk alarm as this variant of NDM carries MDR genes with highly transferable mobile genetic elements, increasing the possibility of resistance gene transfer among microorganisms in the environment.
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http://dx.doi.org/10.1093/jac/dkw547DOI Listing
April 2017

Season-Specific Occurrence of Potentially Pathogenic Vibrio spp. on the Southern Coast of South Korea.

Appl Environ Microbiol 2017 02 17;83(3). Epub 2017 Jan 17.

School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea

Vibrio species are widely distributed in warm estuarine and coastal environments, and they can infect humans through the consumption of raw and mishandled contaminated seafood. In this study, we aimed to isolate and observe the distribution of enteropathogenic Vibrio spp. from environments of the southern coast of South Korea over a season cycle. A total of 10,983 isolates of Vibrio spp. were obtained from tidal water and mud samples over a 1-year period from five sampling sites along the southwest coast of South Korea. We found that Vibrio alginolyticus (n = 6,262) and Vibrio parahaemolyticus (n = 1,757) were ubiquitous in both tidal water and mud year round, whereas Vibrio cholerae (n = 24) and Vibrio vulnificus (n = 130) were seasonally specific to summer. While all V. cholerae isolates were nontoxigenic (non-O1 and non-O139), more than 88% of V. vulnificus isolates possessed the virulence factor elastolytic protease (encoded by vvp). Interestingly, V. parahaemolyticus, which was omnipresent in all seasons, contained the virulence factors thermostable direct hemolysin (encoded by tdh) and thermostable direct hemolysin-related hemolysin (encoded by trh) in larger amounts in June (29 trh-positive strains) and September (14 tdh-, 36 trh-, and 12 tdh- and trh-positive strains) than in December (4 trh-positive strains) and February (3 tdh-positive strains), and virulence factors were absent from isolates detected in April. To understand why virulence factors were detected only in the warm season and were absent in the cold season although the locations are static, long-term monitoring and particularly seasonal study are necessary.

Importance: The presence of enteropathogenic Vibrio species (Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus), which cause acute diarrheal infection, septicemia, and wound infections upon ingestion through food and water, is usually associated with temperature. The World Health Organization (WHO) has estimated that there are 1.4 to 4.3 million cases and 28,000 to 142,000 deaths per year worldwide caused by cholera disease. In South Korea alone, consumption is as much as 52.4 kg of fish and shellfish per year per capita. Our findings suggested that seasonally specific acceleration of these possible pathogenic Vibrio spp. may threaten seafood safety and increase the risk of illness in South Korea, where local people consume raw fish during warmer months.
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http://dx.doi.org/10.1128/AEM.02680-16DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5244290PMC
February 2017

Retraction Note to: Enhancement of the catalytic activity of ferulic acid decarboxylase from Enterobacter sp. Px6-4 through random and site-directed mutagenesis.

Appl Microbiol Biotechnol 2016 Nov;100(22):9807

School of Environmental Science and Engineering, Gwangju Institute of Science and Technology, Gwangju, 500-712, South Korea.

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http://dx.doi.org/10.1007/s00253-016-7877-xDOI Listing
November 2016

Synthesis of gold structures by gold-binding peptide governed by concentration of gold ion and peptide.

Biosci Biotechnol Biochem 2016 Aug 25;80(8):1478-83. Epub 2016 Apr 25.

d School of Environmental Science and Engineering , Gwangju Institute of Science and Technology , Gwangju , Republic of Korea.

Although biological synthesis methods for the production of gold structures by microorganisms, plant extracts, proteins, and peptide have recently been introduced, there have been few reports pertaining to controlling their size and morphology. The gold ion and peptide concentrations affected on the size and uniformity of gold plates by a gold-binding peptide Midas-11. The higher concentration of gold ions produced a larger size of gold structures reached 125.5 μm, but an increased amount of Midas-11 produced a smaller size of gold platelets and increased the yield percentage of polygonal gold particles rather than platelets. The mechanisms governing factors controlling the production of gold structures were primarily related to nucleation and growth. These results indicate that the synthesis of gold architectures can be controlled by newly isolated and substituted peptides under different reaction conditions.
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http://dx.doi.org/10.1080/09168451.2016.1176516DOI Listing
August 2016

Dynamic changes in the population structure of Escherichia coli in the Yeongsan River basin of South Korea.

FEMS Microbiol Ecol 2015 Nov 20;91(11). Epub 2015 Oct 20.

School of Environmental Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea

Although Escherichia coli has been used as an indicator to examine fecal contamination of aquatic environment, it also has been reported to become naturalized to secondary habitats, including soil, water and beach sand. A total of 2880 E. coli isolates obtained from surface water and sediment samples from the Yeongsan River in 2013 were genotyped by using the horizontal fluorophore-enhanced rep-PCR DNA fingerprinting technique. Although different E. coli genotypic groups were observed between surface water and sediments in the dry season, they were mingled and undifferentiated from each other in the rainy season. This indicates that there are frequent sediment resuspension events in the river basin. Moreover, the genotypic composition of the E. coli population in the Yeongsan River basin changes over months and years, implying that genotypic structure of E. coli populations dynamically fluctuates in the river environment. Consequently, our data suggests that the use of E. coli libraries for fecal source tracking needs to be reassessed to account for the changing structure of riverine E. coli populations.
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http://dx.doi.org/10.1093/femsec/fiv127DOI Listing
November 2015

Bacterial biogeography influenced by shelf-basin exchange in the Arctic surface sediment at the Chukchi Borderland.

Environ Microbiol 2016 Feb 2;18(2):668-78. Epub 2015 Dec 2.

School of Environmental Science and Engineering, Gwangju Institute of Science and Technology, Gwangju, 61005, Republic of Korea.

It has been known that continental shelves around the Arctic Ocean play a major role in the ventilation of the deep basins as a consequence of shelf-basin exchange. In the present study, we found that bacterial assemblage of the surface sediment was different from that of seawater while seawater harboured local bacterial assemblages in response to the Arctic hydrography. This finding suggests that the Arctic seafloor sediments may have distinctive bacterial biogeography. Moreover, the distribution of bacterial assemblages and physicochemical properties in surface sediments changed gradually from the Arctic continental shelf to deep-sea basin. Based on the results, bacterial biogeography in the Arctic seafloor sediments may be influenced by winnowing and re-deposition of surface sediments through the sediment gravity flow. The present study offers a deeper understanding of shelf convection and its role for the construction of bacterial assemblages in the Arctic Ocean.
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http://dx.doi.org/10.1111/1462-2920.13064DOI Listing
February 2016

Enhancement of the catalytic activity of ferulic acid decarboxylase from Enterobacter sp. Px6-4 through random and site-directed mutagenesis.

Appl Microbiol Biotechnol 2015 Nov 10;99(22):9473-81. Epub 2015 Jun 10.

School of Environmental Science and Engineering, Gwangju Institute of Science and Technology, Gwangju, 500-712, South Korea.

The enzyme ferulic acid decarboxylase (FADase) from Enterobacter sp. Px6-4 catalyzes the decarboxylation reaction of lignin monomers and phenolic compounds such as p-coumaric acid, caffeic acid, and ferulic acid into their corresponding 4-vinyl derivatives, that is, 4-vinylphenol, 4-vinylcatechol, and 4-vinylguaiacol, respectively. Among various ferulic acid decarboxylase enzymes, we chose the FADase from Enterobacter sp. Px6-4, whose crystal structure is known, and produced mutants to enhance its catalytic activity by random and site-directed mutagenesis. After three rounds of sequential mutations, FADase(F95L/D112N/V151I) showed approximately 34-fold higher catalytic activity than wild-type for the production of 4-vinylguaiacol from ferulic acid. Docking analyses suggested that the increased activity of FADase(F95L/D112N/V151I) could be due to formation of compact active site compared with that of the wild-type FADase. Considering the amount of phenolic compounds such as lignin monomers in the biomass components, successfully bioengineered FADase(F95L/D112N/V151I) from Enterobacter sp. Px6-4 could provide an ecofriendly biocatalytic tool for producing diverse styrene derivatives from biomass.
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http://dx.doi.org/10.1007/s00253-015-6717-8DOI Listing
November 2015
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