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Armen Trchounian

Bio: Armen Trchounian is an academic researcher from Yerevan State University. The author has contributed to research in topics: Fermentation & Rhodobacter sphaeroides. The author has an hindex of 33, co-authored 224 publications receiving 3674 citations. Previous affiliations of Armen Trchounian include Russian-Armenian (Slavonic) University & Chiba University.


Papers
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Journal ArticleDOI
TL;DR: Formate hydrogen lyase from Escherichia coli is a membrane-bound complex that oxidizes formic acid to carbon dioxide and molecular hydrogen, which depends on the external pH and the presence of formate.
Abstract: Formate hydrogen lyase from Escherichia coli is a membrane-bound complex that oxidizes formic acid to carbon dioxide and molecular hydrogen. Under anaerobic growth conditions and fermentation of sugars (glucose), it exists in two forms. One form is constituted by formate dehydrogenase H and hydrogenase 3, and the other one is the same formate dehydrogenase and hydrogenase 4; the presence of small protein subunits, carriers of electrons, is also probable. Other proteins may also be involved in formation of the enzyme complex, which requires the presence of metal (nickel-cobalt). Its formation also depends on the external pH and the presence of formate. Activity of both forms requires F0F1-ATPase; this explains dependence of the complex functioning on proton-motive force. It is also possible that the formate hydrogen lyase complex will exhibit its own proton-translocating function.

128 citations

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TL;DR: The results obtained indicate that these essential oils have antioxidant, antibacterial and antifungal activity and can be used as natural antioxidant and antimicrobial agents in medicine, food industry and cosmetics.
Abstract: The plants belonging to the Ocimum genus of the Lamiaceae family are considered to be a rich source of essential oils which have expressed biological activity and use in different area of human activity. There is a great variety of chemotypes within the same basil species. Essential oils from three different cultivars of basil, O. basilicum var. purpureum, O. basilicum var. thyrsiflora, and O. citriodorum Vis. were the subjects of our investigations. The oils were obtained by steam distillation in a Clevenger-type apparatus. The gas chromatography mass selective analysis was used to determine their chemical composition. The antioxidant activities of these essential oils were measured using 1,1-diphenyl-2-picrylhydrazyl assays; the tyrosinase inhibition abilities of the given group of oils were also assessed spectophotometrically, and the antimicrobial activity of the essential oils was determined by the agar diffusion method, minimal inhibitory concentrations were expressed. According to the results, the qualitative and quantitative composition of essential oils was quite different: O. basilicum var. purpureum essential oil contained 57.3% methyl-chavicol (estragol); O. basilicum var. thyrsiflora oil had 68.0% linalool. The main constituents of O. citriodorum oil were nerol (23.0%) and citral (20.7%). The highest antioxidant activity was demonstrated by O. basilicum var. thyrsiflora essential oil. This oil has also exhibited the highest tyrosinase inhibition level, whereas the oil from O. citriodorum cultivar demonstrated the highest antimicrobial activity. The results obtained indicate that these essential oils have antioxidant, antibacterial and antifungal activity and can be used as natural antioxidant and antimicrobial agents in medicine, food industry and cosmetics.

112 citations

Journal ArticleDOI
TL;DR: Recent new data that have been obtained with Escherichia coli, Clostridium beijerinskii, Rhodobacter sphaeroides and other bacteria are reviewed and further approaches and strain-improvement could increase H2 production in a cost-effective way.
Abstract: Hydrogen (H2) is an effective, environmentally friendly and renewable source of fuel that can be produced during dark- and photo-fermentation by different facultative and obligate anaerobic and purple bacteria and microalgae. This product is known as biohydrogen. It has the advantage of variable yield at low temperature (for mesophiles growing best at moderate temperature) and relatively low production cost, if compared with thermochemical methods. To develop fermentative H2 production biotechnology using cheap carbonaceous by-products and utilization of organic wastes, the selection or construction of effective bacterial strains and optimization of technology process conditions are required. Here we review recent new data that have been obtained with Escherichia coli, Clostridium beijerinskii, Rhodobacter sphaeroides and other bacteria. Activities of [Ni-Fe]-hydrogenases of dark-fermentative bacteria and [Mo]-nitrogenase and [Ni-Fe]-hydrogenase of photo-fermentative species have been examined after growth with different carbon sources, using pure cultures, as well as co-culture and mixed-cultures technologies. Importantly, H2 production from cheap and readily available substrates like crude glycerol or different industrial, agricultural and other carbon-based wastes by bacteria is a sustainable technology. Consequently further approaches and strain-improvement could increase H2 production in a cost-effective way, and they will lead to both small- and large-scale H2 production. Moreover, they will provide significant economic and environmental benefits for renewable and sustainable energy supply in the near future.

106 citations

Journal ArticleDOI
TL;DR: A novel approach would be the use of glycerol as feedstock in fermentation processes leading to H2 production, reduced fuels and other chemicals with higher yields than those obtained by common sugars.
Abstract: Molecular hydrogen (H(2)) can be produced via hydrogenases during mixed-acid fermentation by bacteria. Escherichia coli possesses multiple (four) hydrogenases. Hydrogenase 3 (Hyd-3) and probably 4 (Hyd-4) with formate dehydrogenase H (Fdh-H) form two different H(2)-evolving formate hydrogen lyase (FHL) pathways during glucose fermentation. For both FHL forms, the hycB gene coding small subunit of Hyd-3 is required. Formation and activity of FHL also depends on the external pH ([pH](out)) and the presence of formate. FHL is related with the F(0)F(1)-ATPase by supplying reducing equivalents and depending on proton-motive force. Two other hydrogenases, 1 (Hyd-1) and 2 (Hyd-2), are H(2)-oxidizing enzymes during glucose fermentation at neutral and low [pH](out). They operate in a reverse, H(2)-producing mode during glycerol fermentation at neutral [pH](out). Hyd-1 and Hyd-2 activity depends on F(0)F(1). Moreover, Hyd-3 can also work in a reverse mode. Therefore, the operation direction and activity of all Hyd enzymes might determine H(2) production; some metabolic cross-talk between Hyd enzymes is proposed. Manipulating of different Hyd enzymes activity is an effective way to enhance H(2) production by bacteria in biotechnology. Moreover, a novel approach would be the use of glycerol as feedstock in fermentation processes leading to H(2) production, reduced fuels and other chemicals with higher yields than those obtained by common sugars.

91 citations

Journal ArticleDOI
TL;DR: It is suggested that Kup is the major K+ uptake system in E. coli upon hyper‐osmotic stress at a low pH.

90 citations


Cited by
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Journal Article
TL;DR: A diagnosis of gestational diabetes mellitus (GDM) (diabetes diagnosed in the second or third trimester of pregnancy that is not clearly overt diabetes) or chemical-induced diabetes (such as in the treatment of HIV/AIDS or after organ transplantation)
Abstract: 1. Type 1 diabetes (due to b-cell destruction, usually leading to absolute insulin deficiency) 2. Type 2 diabetes (due to a progressive insulin secretory defect on the background of insulin resistance) 3. Gestational diabetes mellitus (GDM) (diabetes diagnosed in the second or third trimester of pregnancy that is not clearly overt diabetes) 4. Specific types of diabetes due to other causes, e.g., monogenic diabetes syndromes (such as neonatal diabetes and maturity-onset diabetes of the young [MODY]), diseases of the exocrine pancreas (such as cystic fibrosis), and drugor chemical-induced diabetes (such as in the treatment of HIV/AIDS or after organ transplantation)

2,339 citations

Journal ArticleDOI
TL;DR: Providing a future energy supply that is secure and CO_2-neutral will require switching to nonfossil energy sources such as wind, solar, nuclear, and geothermal energy and developing methods for transforming the energy produced by these new sources into forms that can be stored, transported, and used upon demand.
Abstract: Two major energy-related problems confront the world in the next 50 years. First, increased worldwide competition for gradually depleting fossil fuel reserves (derived from past photosynthesis) will lead to higher costs, both monetarily and politically. Second, atmospheric CO_2 levels are at their highest recorded level since records began. Further increases are predicted to produce large and uncontrollable impacts on the world climate. These projected impacts extend beyond climate to ocean acidification, because the ocean is a major sink for atmospheric CO2.1 Providing a future energy supply that is secure and CO_2-neutral will require switching to nonfossil energy sources such as wind, solar, nuclear, and geothermal energy and developing methods for transforming the energy produced by these new sources into forms that can be stored, transported, and used upon demand.

1,651 citations

Journal ArticleDOI
TL;DR: An updated genome‐scale reconstruction of the metabolic network in Escherichia coli K‐12 MG1655 with increased scope and computational capability is presented, expected to broaden the spectrum of both basic biology and applied systems biology studies of E. coli metabolism.
Abstract: An updated genome-scale reconstruction of the metabolic network in Escherichia coli K-12 MG1655 is presented. This updated metabolic reconstruction includes: (1) an alignment with the latest genome annotation and the metabolic content of EcoCyc leading to the inclusion of the activities of 1260 ORFs, (2) characterization and quantification of the biomass components and maintenance requirements associated with growth of E. coli and (3) thermodynamic information for the included chemical reactions. The conversion of this metabolic network reconstruction into an in silico model is detailed. A new step in the metabolic reconstruction process, termed thermodynamic consistency analysis, is introduced, in which reactions were checked for consistency with thermodynamic reversibility estimates. Applications demonstrating the capabilities of the genome-scale metabolic model to predict high-throughput experimental growth and gene deletion phenotypic screens are presented. The increased scope and computational capability using this new reconstruction is expected to broaden the spectrum of both basic biology and applied systems biology studies of E. coli metabolism.

1,445 citations

Journal ArticleDOI
TL;DR: The transfer of hydrogen and formate between bacteria and archaea that helps to sustain growth in syntrophic methanogenic communities is reviewed and the process of reverse electron transfer is described, which is a key requirement in obligately syntrophic interactions.
Abstract: Interspecies electron transfer is a key process in methanogenic and sulphate-reducing environments. Bacteria and archaea that live in syntrophic communities take advantage of the metabolic abilities of their syntrophic partner to overcome energy barriers and break down compounds that they cannot digest by themselves. Here, we review the transfer of hydrogen and formate between bacteria and archaea that helps to sustain growth in syntrophic methanogenic communities. We also describe the process of reverse electron transfer, which is a key requirement in obligately syntrophic interactions. Anaerobic methane oxidation coupled to sulphate reduction is also carried out by syntrophic communities of bacteria and archaea but, as we discuss, the exact mechanism of this syntrophic interaction is not yet understood.

1,052 citations

01 Jan 2004
TL;DR: In this paper, a probiotic strain L. acidophilus M92 was examined for autoaggregation ability and cell surface hydrophobicity, which suggests the possible role of cell surface layer (S-layer) proteins, approximated at 45 kDa.
Abstract: The ability of probiotic bacteria to adhere to the intestinal epithelium play an important role in colonization of the gastrointestinal tract, preventing their elimination by peristalsis and providing a competitive advantage in this ecosystem. To identify bacterial traits related to adhesion the probiotic strain L. acidophilus M92 was examined for autoaggregation ability and cell surface hydrophobicity L. acidophilus M92 exhibits a strong autoaggregation phenotype and also coaggregation with some pathogen microorganisms that may form a barrier that prevents their colonization. The examined probiotic strain manifests a good degree of hydrophobicity determined by microbial adhesion to hydrocarbons. Aggregation and hydrophobicity were abolished upon exposure of the cells to pronase, which suggests the possible role of cell surface layer (S-layer) proteins, approximated at 45 kDa, in a L. acidophilus M92. The relationship between autoaggregation and adhesion ability to intestinal tissue was investigated by observing the adhesivity of L. acidophilus M92 to porcine ileal epithelial cells. Removal of the S-layer proteins by extraction with 5 M LiCl reduced autaggregation and in vitro adhesion of this strain.

605 citations