The Experts below are selected from a list of 876 Experts worldwide ranked by ideXlab platform
Helga Ertesvag - One of the best experts on this subject based on the ideXlab platform.
-
functional characterization of three azotobacter chroococcum alginate modifying enzymes related to the azotobacter vinelandii alge mannuronan c 5 epimerase family
Scientific Reports, 2020Co-Authors: Agnieszka Maria Gawin, Olav Andreas Aarstad, Finn Lillelund Aachmann, Lisa Tietze, Trygve Brautaset, Helga ErtesvagAbstract:Bacterial alginate initially consists of 1-4-linked β-D-mannuronic acid residues (M) which can be later epimerized to α-L-guluronic acid (G). The family of AlgE mannuronan C-5-epimerases from Azotobacter vinelandii has been extensively studied, and three genes putatively encoding AlgE-type epimerases have recently been identified in the genome of Azotobacter chroococcum. The three A. chroococcum genes, here designated AcalgE1, AcalgE2 and AcalgE3, were recombinantly expressed in Escherichia coli and the gene products were partially purified. The catalytic activities of the enzymes were stimulated by the addition of calcium ions in vitro. AcAlgE1 displayed epimerase activity and was able to introduce long G-blocks in the alginate substrate, preferentially by attacking M residues next to pre-existing G residues. AcAlgE2 and AcAlgE3 were found to display lyase activities with a substrate preference toward M-alginate. AcAlgE2 solely accepted M residues in the positions - 1 and + 2 relative to the cleavage site, while AcAlgE3 could accept either M or G residues in these two positions. Both AcAlgE2 and AcAlgE3 were bifunctional and could also catalyze epimerization of M to G. Together, we demonstrate that A. chroococcum encodes three different AlgE-like alginate-modifying enzymes and the biotechnological and biological impact of these findings are discussed.
Sheng-tao Yang - One of the best experts on this subject based on the ideXlab platform.
-
toxicity and environmental impact of multi walled carbon nanotubes to nitrogen fixing bacterium azotobacter chroococcum
Journal of environmental chemical engineering, 2021Co-Authors: Bowei Ouyang, Ailimire Yilihamu, Peng Ouyang, Dong Liu, Dongyan Zhang, Sheng-tao YangAbstract:Abstract With the large-scale production and wide applications of carbon nanotubes (CNTs), they are inevitably entering the environment and bringing unknown threats to environmental organisms. Nitrogen-fixing bacteria dominate 80% of the nitrogen fixation in nitrogen cycle. Herein, we investigated the toxicity and environmental impact of multi-walled CNTs (MWCNTs) to nitrogen-fixing bacterium Azotobacter chroococcum. MWCNTs slightly inhibited the growth of A. chroococcum and induced small increase of death rate at high concentrations. MWCNTs did not penetrate the cell walls of A. chroococcum and no cytoplasm loss was observed. MWCNTs were only observed surrounding the A. chroococcum cells. According to oxidative stress assays, MWCNTs induced meaningful oxidative damage at 0.5 mg/mL after 6 d exposure, but the oxidative damage diminished at 14 d. MWCNTs did not affect the nitrogen fixation activity of A. chroococcum and the soil nitrogen contents. Our findings provided the fundamental data for the environmental safety of CNTs to nitrogen-fixing bacteria.
-
Interaction between graphene oxide and nitrogen-fixing bacterium Azotobacter chroococcum: Transformation, toxicity and nitrogen fixation
Carbon, 2020Co-Authors: Ailimire Yilihamu, Bowei Ouyang, Peng Ouyang, Yitong Bai, Qiangqiang Zhang, Mengyao Shi, Xin Guan, Sheng-tao YangAbstract:Abstract Nitrogen is an essential element and 80% of nitrogen fixation from atmosphere is achieved by biological nitrogen fixation. When graphene enters the environment, it would inevitably interact with nitrogen-fixing bacteria and might disturb the nitrogen cycle. Herein, the interaction between graphene oxide (GO) and nitrogen-fixing bacterium Azotobacter chroococcum was studied to reveal the potential impact of graphene materials on biological nitrogen fixation. After incubation with A. chroococcum, GO was separated, washed and characterized by different techniques. The toxicity of GO to A. chroococcum was monitored by colony-forming unit (CFU) counting, growth curve, live/dead staining and ultrastructural observations. The nitrogen fixation activity of A. chroococcum was measured by acetylene reduction assay and the soil nitrogen contents were measured. GO was immediately reduced by cell secretions and kept stable thereafter. GO stimulated A. chroococcum growth at low concentrations and showed inhibitive effect at high concentrations. GO induced cell death and cell wall break at high concentration. The toxicological mechanism was assigned to membrane damage and oxidative stress. In the presence of soil, GO showed similar concentration-dependent but alleviated toxicity, while the soil nitrogen contents slightly increased at high concentrations. Our results collectively indicated that GO was bio-reduced and toxic to nitrogen-fixation bacteria.
Frieder Schauer - One of the best experts on this subject based on the ideXlab platform.
-
Study of enzymatic properties of phenol oxidase from nitrogen-fixing Azotobacter chroococcum
AMB Express, 2011Co-Authors: Susanne Herter, Marlen Schmidt, Mark L Thompson, Annett Mikolasch, Frieder SchauerAbstract:Azotobacter chroococcum is a widespread free-living soil bacterium within the genus of Azotobacter known for assimilation of atmospheric nitrogen and subsequent conversion into nitrogenous compounds, which henceforth enrich the nitrogen content of soils. A. chroococcum SBUG 1484, isolated from composted earth, exhibits phenol oxidase (PO) activity when growing under nitrogen-fixing conditions. In the present study we provide incipient analysis of the crude PO activity expressed by A. chroococcum SBUG 1484 within comparative analysis to fungal crude PO from the white-rot fungus Pycnoporus cinnabarinus SBUG-M 1044 and tyrosinase (PPO) from the mushroom Agaricus bisporus in an attempt to reveal desirable properties for exploitation with future recombinant expression of this enzyme. Catalytic activity increased with pre-incubation at 35°C; however 70% of activity remained after pre-treatment at 50°C. Native A. chroococcum crude PO exhibited not only strong preference for 2,6-dimethoxyphenol, but also towards related methoxy-activated substrates as well as substituted ortho -benzenediols from over 40 substrates tested. Presence of CuSO_4 enhanced crude phenol oxidase activity up to 30%, whereas NaN_3 (0.1 mM) was identified as the most inhibiting substance of all inhibitors tested. Lowest inhibition of crude PO activity occurred after 60 minutes of incubation in presence of 15% methanol and ethanol with 63% and 77% remaining activities respectively, and presence of DMSO even led to increasing oxidizing activities. Substrate scope and inhibitor spectrum strongly differentiated A. chroococcum PO activity comprised in crude extracts from those of PPO and confirmed distinct similarities to fungal PO.
-
a new phenol oxidase produced during melanogenesis and encystment stage in the nitrogen fixing soil bacterium azotobacter chroococcum
Applied Microbiology and Biotechnology, 2011Co-Authors: Susanne Herter, Marlen Schmidt, Mark L Thompson, Annett Mikolasch, Frieder SchauerAbstract:Laccases are copper-containing phenol oxidases that are commonly found in many types of plant, insect, fungi and bacteria. Whilst phenol oxidases have been well characterized in fungal species, laccase-type enzymes originating from bacteria have been much less well defined. Bacteria belonging to the family Azotobacteraceae share many morphological characteristics with strains already known to exhibit polyphenol and phenol oxidase activity; and hence the aim of this work was to identify and characterize a novel laccase from the isolated strain Azotobacter chroococcum SBUG 1484 in an attempt to provide further understanding of the roles such enzymes play in physiological development. Laccase activity was clearly observed through oxidation of 2,6-dimethoxyphenol, other typical substrates including: methoxy-monophenols, ortho- and para-diphenols, 4-hydroxyindole, and the non-phenolic compound para-phenylenediamine. A. chroococcum SBUG 1484 showed production of a cell-associated phenol oxidase when grown under nitrogen-fixing conditions, and was also observed when cells enter the melanogenic and encystment stages of growth. Catechol which is structurally related to melanin compounds was also released from Azotobacter cells into the surrounding culture medium during nitrogen-fixing growth. From our results we propose that a membrane-bound laccase plays an important role in the formation of melanin, which was monitored to correlate with progression of A. chroococcum SBUG 1484 cells into the encystment stage of growth.
Agnieszka Maria Gawin - One of the best experts on this subject based on the ideXlab platform.
-
functional characterization of three azotobacter chroococcum alginate modifying enzymes related to the azotobacter vinelandii alge mannuronan c 5 epimerase family
Scientific Reports, 2020Co-Authors: Agnieszka Maria Gawin, Olav Andreas Aarstad, Finn Lillelund Aachmann, Lisa Tietze, Trygve Brautaset, Helga ErtesvagAbstract:Bacterial alginate initially consists of 1-4-linked β-D-mannuronic acid residues (M) which can be later epimerized to α-L-guluronic acid (G). The family of AlgE mannuronan C-5-epimerases from Azotobacter vinelandii has been extensively studied, and three genes putatively encoding AlgE-type epimerases have recently been identified in the genome of Azotobacter chroococcum. The three A. chroococcum genes, here designated AcalgE1, AcalgE2 and AcalgE3, were recombinantly expressed in Escherichia coli and the gene products were partially purified. The catalytic activities of the enzymes were stimulated by the addition of calcium ions in vitro. AcAlgE1 displayed epimerase activity and was able to introduce long G-blocks in the alginate substrate, preferentially by attacking M residues next to pre-existing G residues. AcAlgE2 and AcAlgE3 were found to display lyase activities with a substrate preference toward M-alginate. AcAlgE2 solely accepted M residues in the positions - 1 and + 2 relative to the cleavage site, while AcAlgE3 could accept either M or G residues in these two positions. Both AcAlgE2 and AcAlgE3 were bifunctional and could also catalyze epimerization of M to G. Together, we demonstrate that A. chroococcum encodes three different AlgE-like alginate-modifying enzymes and the biotechnological and biological impact of these findings are discussed.
Bowei Ouyang - One of the best experts on this subject based on the ideXlab platform.
-
toxicity and environmental impact of multi walled carbon nanotubes to nitrogen fixing bacterium azotobacter chroococcum
Journal of environmental chemical engineering, 2021Co-Authors: Bowei Ouyang, Ailimire Yilihamu, Peng Ouyang, Dong Liu, Dongyan Zhang, Sheng-tao YangAbstract:Abstract With the large-scale production and wide applications of carbon nanotubes (CNTs), they are inevitably entering the environment and bringing unknown threats to environmental organisms. Nitrogen-fixing bacteria dominate 80% of the nitrogen fixation in nitrogen cycle. Herein, we investigated the toxicity and environmental impact of multi-walled CNTs (MWCNTs) to nitrogen-fixing bacterium Azotobacter chroococcum. MWCNTs slightly inhibited the growth of A. chroococcum and induced small increase of death rate at high concentrations. MWCNTs did not penetrate the cell walls of A. chroococcum and no cytoplasm loss was observed. MWCNTs were only observed surrounding the A. chroococcum cells. According to oxidative stress assays, MWCNTs induced meaningful oxidative damage at 0.5 mg/mL after 6 d exposure, but the oxidative damage diminished at 14 d. MWCNTs did not affect the nitrogen fixation activity of A. chroococcum and the soil nitrogen contents. Our findings provided the fundamental data for the environmental safety of CNTs to nitrogen-fixing bacteria.
-
Interaction between graphene oxide and nitrogen-fixing bacterium Azotobacter chroococcum: Transformation, toxicity and nitrogen fixation
Carbon, 2020Co-Authors: Ailimire Yilihamu, Bowei Ouyang, Peng Ouyang, Yitong Bai, Qiangqiang Zhang, Mengyao Shi, Xin Guan, Sheng-tao YangAbstract:Abstract Nitrogen is an essential element and 80% of nitrogen fixation from atmosphere is achieved by biological nitrogen fixation. When graphene enters the environment, it would inevitably interact with nitrogen-fixing bacteria and might disturb the nitrogen cycle. Herein, the interaction between graphene oxide (GO) and nitrogen-fixing bacterium Azotobacter chroococcum was studied to reveal the potential impact of graphene materials on biological nitrogen fixation. After incubation with A. chroococcum, GO was separated, washed and characterized by different techniques. The toxicity of GO to A. chroococcum was monitored by colony-forming unit (CFU) counting, growth curve, live/dead staining and ultrastructural observations. The nitrogen fixation activity of A. chroococcum was measured by acetylene reduction assay and the soil nitrogen contents were measured. GO was immediately reduced by cell secretions and kept stable thereafter. GO stimulated A. chroococcum growth at low concentrations and showed inhibitive effect at high concentrations. GO induced cell death and cell wall break at high concentration. The toxicological mechanism was assigned to membrane damage and oxidative stress. In the presence of soil, GO showed similar concentration-dependent but alleviated toxicity, while the soil nitrogen contents slightly increased at high concentrations. Our results collectively indicated that GO was bio-reduced and toxic to nitrogen-fixation bacteria.