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Mercury (Hg) methylation and demethylation is supposed to simultaneously exist in the environment and form a cycle, which determines the net production of methylmercury (MeHg). Exploring the mechanisms of MeHg formation and degradation, and its final fate in the natural environment is essential to understanding the biogeochemical cycle of Hg. However, MeHg demethylation has been less studied in the past years comparing with Hg methylation, particularly in anaerobic microorganisms whose demethylation role has been under-evaluated. This review described the current state of knowledge on biotic (microorganisms) and abiotic demethylation (photodegradation, chemical degradation) of MeHg. The decomposition of MeHg performed by microorganisms has been identified as two different pathways, reductive demethylation (RD) and oxidative demethylation (OD). Anaerobic and aerobic microorganisms involved in the process of RD and OD, influencing factors as well as research background and histories are systematically described in this review. It is predicted that the photodegradation mechanism, as well as anaerobic microorganisms involved in MeHg formation and degradation cycle will be the focus of future research.
Hongxia Du; Ming Ma; Yasuo Igarashi; Dingyong Wang. Biotic and Abiotic Degradation of Methylmercury in Aquatic Ecosystems: A Review. Bulletin of Environmental Contamination and Toxicology 2019, 102, 605 -611.
AMA StyleHongxia Du, Ming Ma, Yasuo Igarashi, Dingyong Wang. Biotic and Abiotic Degradation of Methylmercury in Aquatic Ecosystems: A Review. Bulletin of Environmental Contamination and Toxicology. 2019; 102 (5):605-611.
Chicago/Turabian StyleHongxia Du; Ming Ma; Yasuo Igarashi; Dingyong Wang. 2019. "Biotic and Abiotic Degradation of Methylmercury in Aquatic Ecosystems: A Review." Bulletin of Environmental Contamination and Toxicology 102, no. 5: 605-611.
Mercury (Hg) deposition in the forest ecosystem is a significant source of input for methyl Hg (MeHg) and total Hg (THg) to the subtropical forest field and downstream aquatic systems. Wet deposition, litterfall, runoff, and fluxes with forest soil percolate of MeHg and THg were sampled for two years in a watershed forest of southwest China. Results showed that the depositions of THg and MeHg through litterfall and throughfall were 86 µg m−2 yr−1 and 0.8 µg m−2 yr−1 respectively, with litterfall acting as a predominant route for the input of both THg and MeHg. The estimated fluxes of THg and MeHg in the throughfall and litterfall were 3 and 4 times greater than those in the precipitation. Methylmercury in the decomposed litter migrates during its erosion by surface runoff and the concentrations of MeHg were quite consistent with that in the surface runoff. Methylmercury mainly accumulated in the lower layer of the litter and upper layer of the soil (Oi), and its transfer through the soil cross-section was delayed. THg retention was not consistent with MeHg, probably with lower soil layers (Oe and Oa) storing and enriching THg in the forest ecosystem. The forest floor of the lower soil is an effective sink for THg but not for MeHg. Methylmercury accumulated in decomposing litter and upper soil layer might transfer with soil percolate, possessing potential ecological risks for residents living around the downstream aquatic systems.
Hongxia Du; Ming Ma; Tao Sun; Siwei An; Yasuo Igarashi; Dingyong Wang. Methyl and Total Mercury in Different Media and Associated Fluxes in a Watershed Forest, Southwest China. International Journal of Environmental Research and Public Health 2018, 15, 2618 .
AMA StyleHongxia Du, Ming Ma, Tao Sun, Siwei An, Yasuo Igarashi, Dingyong Wang. Methyl and Total Mercury in Different Media and Associated Fluxes in a Watershed Forest, Southwest China. International Journal of Environmental Research and Public Health. 2018; 15 (12):2618.
Chicago/Turabian StyleHongxia Du; Ming Ma; Tao Sun; Siwei An; Yasuo Igarashi; Dingyong Wang. 2018. "Methyl and Total Mercury in Different Media and Associated Fluxes in a Watershed Forest, Southwest China." International Journal of Environmental Research and Public Health 15, no. 12: 2618.
Interspecific mycelial interactions between white rot fungi are always accompanied by increased production of laccase. In this study, the potential of white rot fungiDichomitus squalensfor enhancing laccase production during interaction with two other white rot fungiTrametes versicolororPleurotus ostreatuswas identified. To probe the mechanism of laccase induction and the role of laccase played during the combative interaction, we analyzed the laccase induction response to stressful conditions during fungal interaction related to the differential gene expression profile. We further confirmed the expression patterns of 16 selected genes by qRT-PCR analysis. We noted that many differential expression genes (DEGs) encoding proteins were involved in xenobiotics detoxification and ROS generation or reduction, including aldo/keto reductase, glutathione S-transferases, cytochrome P450 enzymes, alcohol oxidases and dehydrogenase, manganese peroxidase and laccase. Furthermore, many DEG-encoding proteins were involved in antagonistic mechanisms of nutrient acquisition and antifungal properties, including glycoside hydrolase, glucanase, chitinase and terpenoid synthases. DEGs analysis effectively revealed that laccase induction was likely caused by protective responses to oxidative stress and nutrient competition during fungal interspecific interaction.
Zi Xuan Zhong; Nan Nan Li; Bing Hui He; Yasuo Igarashi; Feng Luo. Transcriptome analysis of differential gene expression inDichomitus squalensduring interspecific mycelial interactions and the potential link with laccase induction. 2018, 359646 .
AMA StyleZi Xuan Zhong, Nan Nan Li, Bing Hui He, Yasuo Igarashi, Feng Luo. Transcriptome analysis of differential gene expression inDichomitus squalensduring interspecific mycelial interactions and the potential link with laccase induction. . 2018; ():359646.
Chicago/Turabian StyleZi Xuan Zhong; Nan Nan Li; Bing Hui He; Yasuo Igarashi; Feng Luo. 2018. "Transcriptome analysis of differential gene expression inDichomitus squalensduring interspecific mycelial interactions and the potential link with laccase induction." , no. : 359646.
H-NS family proteins encoded on the chromosome of Pseudomonas putida KT2440 (TurA and TurB) and the IncP-7 plasmid pCAR1 (Pmr) commonly have an N-terminal dimerization/oligomerization domain constituted by a central and a terminal dimerization sites. To clarify the dimerization manner at the central dimerization sites of the three homologs, we performed chemical cross-linking analyses with protein variants inactivated at the terminal dimerization site. Comparison of the hetero-dimer ratios among them suggested stronger affinities between the central dimerization sites of TurA and TurB monomers than between TurA and Pmr or TurB and Pmr. Furthermore, analyses of the interaction between truncated TurB containing only a functional terminal dimerization site and full-length proteins suggested that TurB exhibited higher affinities for oligomer complex formation with TurB itself and TurA but not Pmr. Altogether, we revealed stronger interaction between the N-terminal domains of TurA and TurB than between either of them and Pmr.
Zongping Sun; Delyana Vasileva; Chiho Suzuki-Minakuchi; Kazunori Okada; Feng Luo; Yasuo Igarashi; Hideaki Nojiri. Differential protein-protein binding affinities of H-NS family proteins encoded on the chromosome of Pseudomonas putida KT2440 and IncP-7 plasmid pCAR1. Bioscience, Biotechnology, and Biochemistry 2018, 82, 1640 -1646.
AMA StyleZongping Sun, Delyana Vasileva, Chiho Suzuki-Minakuchi, Kazunori Okada, Feng Luo, Yasuo Igarashi, Hideaki Nojiri. Differential protein-protein binding affinities of H-NS family proteins encoded on the chromosome of Pseudomonas putida KT2440 and IncP-7 plasmid pCAR1. Bioscience, Biotechnology, and Biochemistry. 2018; 82 (9):1640-1646.
Chicago/Turabian StyleZongping Sun; Delyana Vasileva; Chiho Suzuki-Minakuchi; Kazunori Okada; Feng Luo; Yasuo Igarashi; Hideaki Nojiri. 2018. "Differential protein-protein binding affinities of H-NS family proteins encoded on the chromosome of Pseudomonas putida KT2440 and IncP-7 plasmid pCAR1." Bioscience, Biotechnology, and Biochemistry 82, no. 9: 1640-1646.
H-NS family proteins are nucleoid-associated proteins that form oligomers on DNA and function as global regulators. They are found in both bacterial chromosomes and plasmids, and were suggested to be candidate effectors of the interaction between them. TurA and TurB are the predominantly expressed H-NS family proteins encoded on the chromosome of Pseudomonas putida KT2440, while Pmr is encoded on the carbazole-degradative incompatibility group P-7 plasmid pCAR1. Previous transcriptome analyses suggested that they function cooperatively, but play different roles in the global transcriptional network. In addition to differences in protein interaction and DNA-binding functions, cell expression levels are important in clarifying the detailed underlying mechanisms. Here, we determined the precise protein amounts of TurA, TurB, and Pmr in KT2440 in the presence and absence of pCAR1. The intracellular amounts of TurA and TurB in KT2440 and KT2440(pCAR1) were determined by quantitative western blot analysis using specific antibodies. The amount of TurA decreased from the log phase (~80,000 monomers per cell) to the stationary phase (~20,000 monomers per cell), while TurB was only detectable upon entry into the stationary phase (maximum 6000 monomers per cell). Protein amounts were not affected by pCAR1 carriage. KT2440(pCAR1pmrHis), where histidine-tagged Pmr is expressed under its original promotor, was used to determine the intracellular amount of Pmr, which was constant (~30,000 monomers per cell) during cell growth. Quantitative reverse transcription PCR demonstrated that the transcriptional levels of turA and turB were consistent with protein expression, though the transcriptional and translational profiles of Pmr differed. The amount of TurB increases as TurA decreases, and the amount of Pmr does not affect the amounts of TurA and TurB. This is consistent with our previous observation that TurA and TurB play complementary roles, whereas Pmr works relatively independently. This study provides insight into the molecular mechanisms underlying reconstitution of the transcriptional network in KT2440 by pCAR1 carriage.
Zongping Sun; Delyana Vasileva; Chiho Suzuki-Minakuchi; Kazunori Okada; Feng Luo; Yasuo Igarashi; Hideaki Nojiri. Growth phase-dependent expression profiles of three vital H-NS family proteins encoded on the chromosome of Pseudomonas putida KT2440 and on the pCAR1 plasmid. BMC Microbiology 2017, 17, 1 -9.
AMA StyleZongping Sun, Delyana Vasileva, Chiho Suzuki-Minakuchi, Kazunori Okada, Feng Luo, Yasuo Igarashi, Hideaki Nojiri. Growth phase-dependent expression profiles of three vital H-NS family proteins encoded on the chromosome of Pseudomonas putida KT2440 and on the pCAR1 plasmid. BMC Microbiology. 2017; 17 (1):1-9.
Chicago/Turabian StyleZongping Sun; Delyana Vasileva; Chiho Suzuki-Minakuchi; Kazunori Okada; Feng Luo; Yasuo Igarashi; Hideaki Nojiri. 2017. "Growth phase-dependent expression profiles of three vital H-NS family proteins encoded on the chromosome of Pseudomonas putida KT2440 and on the pCAR1 plasmid." BMC Microbiology 17, no. 1: 1-9.
Previous research found that the water-level fluctuating zone (WLFZ) of the Three Gorges Reservoir (TGR) was an Hg-sensitive area. However, little research has been conducted on the distribution of Hg-methylating microorganisms in this area. The goal of this research was to provide an initial description of the distribution of the dsrB (for sulfate-reducing bacteria) and hgcA (one gene confirmed for Hg methylation) genes. Different types of soil were selected to analyze the abundance of the dsrB and hgcA in different periods, in inundated soil (SI, ≤155 m, which becomes sediment during the wet period, SS) and in non-inundated soil (≥175 m, SN) from Shibao, a typical WLFZ of the TGR. A significant positive correlation was observed between dsrB and hgcA abundance and MeHg concentrations, suggesting that microorganisms with these genes contribute to Hg methylation. Principal component analysis (PCA) indicated that dsrB diversity was highest in SI, followed by SS; SS had the highest diversity of hcgA. Six phylogenetic trees were constructed and showed that more strains were present in SI than in SS. HgcA sequences in SS were confined to three evolutionarily distant clades, δ-Proteobacteria, a methanogen group, and a Clostridia group, which was relatively rare among most clades.
Hongxia Du; Ming Ma; Tao Sun; Xianzhu Dai; Caiyun Yang; Feng Luo; Dingyong Wang; Yasuo Igarashi. Mercury-methylating genes dsrB and hgcA in soils/sediments of the Three Gorges Reservoir. Environmental Science and Pollution Research 2016, 24, 5001 -5011.
AMA StyleHongxia Du, Ming Ma, Tao Sun, Xianzhu Dai, Caiyun Yang, Feng Luo, Dingyong Wang, Yasuo Igarashi. Mercury-methylating genes dsrB and hgcA in soils/sediments of the Three Gorges Reservoir. Environmental Science and Pollution Research. 2016; 24 (5):5001-5011.
Chicago/Turabian StyleHongxia Du; Ming Ma; Tao Sun; Xianzhu Dai; Caiyun Yang; Feng Luo; Dingyong Wang; Yasuo Igarashi. 2016. "Mercury-methylating genes dsrB and hgcA in soils/sediments of the Three Gorges Reservoir." Environmental Science and Pollution Research 24, no. 5: 5001-5011.
Hongxia Du; Yasuo Igarashi; Dingyong Wang. [Transmembrane transport of inorganic mercury in microorganisms--a review]. ACTA MICROBIOLOGICA SINICA 2014, 54, 1 .
AMA StyleHongxia Du, Yasuo Igarashi, Dingyong Wang. [Transmembrane transport of inorganic mercury in microorganisms--a review]. ACTA MICROBIOLOGICA SINICA. 2014; 54 (10):1.
Chicago/Turabian StyleHongxia Du; Yasuo Igarashi; Dingyong Wang. 2014. "[Transmembrane transport of inorganic mercury in microorganisms--a review]." ACTA MICROBIOLOGICA SINICA 54, no. 10: 1.
Conversion of industrial processes to more nature-friendly modes is a crucial subject for achieving sustainable development. Utilization of hydrogen-oxidation reactions by hydrogenase as a driving force of bioprocess reaction can be an environmentally ideal method because the reaction creates no pollutants. We expressed NAD-dependent alcohol dehydrogenase from Kluyveromyces lactis in a hydrogen-oxidizing bacterium: Ralstonia eutropha. This is the first report of hydrogen-driven in vivo coupling reaction of the alcohol dehydrogenase and indigenous soluble NAD-reducing hydrogenase. Asymmetric reduction of hydroxyacetone to (R)-1,2-propanediol, which is a commercial building block for antibacterial agents, was performed using the transformant as the microbial cell catalyst. The two enzymes coupled in vitro in vials without a marked decrease of reactivity during the 20 hr reaction because of the hydrogenase reaction, which generates no by-product that affects enzymes. Alcohol dehydrogenase was expressed functionally in R. eutropha in an activity level equivalent to that of indigenous NAD-reducing hydrogenase under the hydrogenase promoter. The hydrogen-driven in vivo coupling reaction proceeded only by the transformant cell without exogenous addition of a cofactor. The decrease of reaction velocity at higher concentration of hydroxyacetone was markedly reduced by application of an in vivo coupling system. Production of (R)-1,2-propanediol (99.8% e.e.) reached 67.7 g/l in 76 hr with almost a constant rate using a jar fermenter. The reaction velocity under 10% PH2 was almost equivalent to that under 100% hydrogen, indicating the availability of crude hydrogen gas from various sources. The in vivo coupling system enabled cell-recycling as catalysts. Asymmetric reduction of hydroxyacetone by a coupling reaction of the two enzymes continued in both in vitro and in vivo systems in the presence of hydrogen. The in vivo reaction system using R. eutropha transformant expressing heterologous alcohol dehydrogenase showed advantages for practical usage relative to the in vitro coupling system. The results suggest a hopeful perspective of the hydrogen-driven bioprocess as an environmentally outstanding method to achieve industrial green innovation. Hydrogen-oxidizing bacteria can be useful hosts for the development of hydrogen-driven microbial cell factories.
Takahiro Oda; Koji Oda; Hiroaki Yamamoto; Akinobu Matsuyama; Masaharu Ishii; Yasuo Igarashi; Hirofumi Nishihara. Hydrogen-driven asymmetric reduction of hydroxyacetone to (R)-1,2-propanediol by Ralstonia eutropha transformant expressing alcohol dehydrogenase from Kluyveromyces lactis. Microbial Cell Factories 2013, 12, 2 -2.
AMA StyleTakahiro Oda, Koji Oda, Hiroaki Yamamoto, Akinobu Matsuyama, Masaharu Ishii, Yasuo Igarashi, Hirofumi Nishihara. Hydrogen-driven asymmetric reduction of hydroxyacetone to (R)-1,2-propanediol by Ralstonia eutropha transformant expressing alcohol dehydrogenase from Kluyveromyces lactis. Microbial Cell Factories. 2013; 12 (1):2-2.
Chicago/Turabian StyleTakahiro Oda; Koji Oda; Hiroaki Yamamoto; Akinobu Matsuyama; Masaharu Ishii; Yasuo Igarashi; Hirofumi Nishihara. 2013. "Hydrogen-driven asymmetric reduction of hydroxyacetone to (R)-1,2-propanediol by Ralstonia eutropha transformant expressing alcohol dehydrogenase from Kluyveromyces lactis." Microbial Cell Factories 12, no. 1: 2-2.
A cylindrical bioelectrochemical reactor (BER) containing carbon fiber textiles (CFT; BER + CFT) has characteristics of bioelectrochemical and packed-bed systems. In this study, utility of a cylindrical BER + CFT for degradation of a garbage slurry and recovery of biogas was investigated by applying 10% dog food slurry. The working electrode potential was electrochemically regulated at −0.8 V (vs. Ag/AgCl). Stable methane production of 9.37 L-CH4 · L−1 · day−1 and dichromate chemical oxygen demand (CODcr) removal of 62.5% were observed, even at a high organic loading rate (OLR) of 89.3 g-CODcr · L−1 · day−1. Given energy as methane (372.6 kJ · L−1 · day−1) was much higher than input electric energy to the working electrode (0.6 kJ · L−1 · day−1) at this OLR. Methanogens were highly retained in CFT by direct attachment to the cathodic working electrodes (52.3%; ratio of methanogens to prokaryotes), compared with the suspended fraction (31.2%), probably contributing to the acceleration of organic material degradation and removal of organic acids. These results provide insight into the application of cylindrical BER + CFT in efficient methane production from garbage waste including a high percentage of solid fraction.
Daisuke Sasaki; Kengo Sasaki; Atsushi Watanabe; Masahiko Morita; Yasuo Igarashi; Naoya Ohmura. Efficient production of methane from artificial garbage waste by a cylindrical bioelectrochemical reactor containing carbon fiber textiles. AMB Express 2013, 3, 17 -17.
AMA StyleDaisuke Sasaki, Kengo Sasaki, Atsushi Watanabe, Masahiko Morita, Yasuo Igarashi, Naoya Ohmura. Efficient production of methane from artificial garbage waste by a cylindrical bioelectrochemical reactor containing carbon fiber textiles. AMB Express. 2013; 3 (1):17-17.
Chicago/Turabian StyleDaisuke Sasaki; Kengo Sasaki; Atsushi Watanabe; Masahiko Morita; Yasuo Igarashi; Naoya Ohmura. 2013. "Efficient production of methane from artificial garbage waste by a cylindrical bioelectrochemical reactor containing carbon fiber textiles." AMB Express 3, no. 1: 17-17.
Masahiro Yamamoto; Hiroyuki Arai; Masaharu Ishii; Yasuo Igarashi. Erratum to “Characterization of two different 2-oxoglutarate:ferredoxin oxidoreductases from Hydrogenobacter thermophilus TK-6” [Biochem. Biophys. Res. Commun. 312 (2003) 1297–1302]. Biochemical and Biophysical Research Communications 2004, 314, 660 .
AMA StyleMasahiro Yamamoto, Hiroyuki Arai, Masaharu Ishii, Yasuo Igarashi. Erratum to “Characterization of two different 2-oxoglutarate:ferredoxin oxidoreductases from Hydrogenobacter thermophilus TK-6” [Biochem. Biophys. Res. Commun. 312 (2003) 1297–1302]. Biochemical and Biophysical Research Communications. 2004; 314 (2):660.
Chicago/Turabian StyleMasahiro Yamamoto; Hiroyuki Arai; Masaharu Ishii; Yasuo Igarashi. 2004. "Erratum to “Characterization of two different 2-oxoglutarate:ferredoxin oxidoreductases from Hydrogenobacter thermophilus TK-6” [Biochem. Biophys. Res. Commun. 312 (2003) 1297–1302]." Biochemical and Biophysical Research Communications 314, no. 2: 660.
A thermophilic, chemolithoautotrophic hydrogen-oxidizing bacterium, Hydrogenobacter thermophilus TK-6, fixes carbon dioxide via the reductive TCA cycle. 2-Oxoglutarate:ferredoxin oxidoreductase (OGOR) is one of the key enzymes of this cycle. Strain TK-6 has two distinct OGOR enzymes termed For and Kor. These enzymes were purified and characterized following heterologous expression in Escherichia coli. The specific activity of For was approximately one-tenth of that of Kor. Additionally, For showed higher thermo-stability than Kor under both aerobic and anaerobic conditions. Western blot analysis showed that both of For and Kor were expressed when strain TK-6 was grown under aerobic conditions. In contrast, only Kor was expressed when the strain was grown under anaerobic conditions using nitrate as a terminal electron acceptor. These results indicate that For supports the optimal growth of strain TK-6 in the presence of oxygen.
Masahiro Yamamoto; Hiroyuki Arai; Masaharu Ishii; Yasuo Igarashi. Characterization of two different 2-oxoglutarate:ferredoxin oxidoreductases from Hydrogenobacter thermophilus TK-6. Biochemical and Biophysical Research Communications 2003, 312, 1297 -1302.
AMA StyleMasahiro Yamamoto, Hiroyuki Arai, Masaharu Ishii, Yasuo Igarashi. Characterization of two different 2-oxoglutarate:ferredoxin oxidoreductases from Hydrogenobacter thermophilus TK-6. Biochemical and Biophysical Research Communications. 2003; 312 (4):1297-1302.
Chicago/Turabian StyleMasahiro Yamamoto; Hiroyuki Arai; Masaharu Ishii; Yasuo Igarashi. 2003. "Characterization of two different 2-oxoglutarate:ferredoxin oxidoreductases from Hydrogenobacter thermophilus TK-6." Biochemical and Biophysical Research Communications 312, no. 4: 1297-1302.
A commercially available composter was operated using fixed composition of garbage with or without the addition of soybean oil. The composter was operated without adding seed microorganisms or bulking materials. Microflora within the composter were analyzed by denaturing gradient gel electrophoresis (DGGE) in the case of oil addition, or by 16/18 S rRNA gene sequencing of the isolated microorganisms in the case of no oil addition. The results showed that, irrespective of the addition of oil, the bacteria identified were all gram positive, and that lactobacilli seemed to be the key microorganisms. Based on the results, suitable microflora for use in a household composter are discussed.
Miho Aoshima; Mannix Salvador Pedro; Shin Haruta; Linxian Ding; Tomoko Fukada; Asuka Kigawa; Tohru Kodama; Masaharu Ishii; Yasuo Igarashi. Analyses of microbial community within a composter operated using household garbage with special reference to the addition of soybean oil. Journal of Bioscience and Bioengineering 2001, 91, 456 -461.
AMA StyleMiho Aoshima, Mannix Salvador Pedro, Shin Haruta, Linxian Ding, Tomoko Fukada, Asuka Kigawa, Tohru Kodama, Masaharu Ishii, Yasuo Igarashi. Analyses of microbial community within a composter operated using household garbage with special reference to the addition of soybean oil. Journal of Bioscience and Bioengineering. 2001; 91 (5):456-461.
Chicago/Turabian StyleMiho Aoshima; Mannix Salvador Pedro; Shin Haruta; Linxian Ding; Tomoko Fukada; Asuka Kigawa; Tohru Kodama; Masaharu Ishii; Yasuo Igarashi. 2001. "Analyses of microbial community within a composter operated using household garbage with special reference to the addition of soybean oil." Journal of Bioscience and Bioengineering 91, no. 5: 456-461.