Journal of Microbiology

Research Support, Non-U.S. Gov'ts

Dimethyl sulfoxide reduction by a hyperhermophilic archaeon Thermococcus onnurineus NA1 via a cysteine-cystine redox shuttle: Ae Ran Choi , Min-Sik Kim , Sung Gyun Kang , Hyun Sook Lee; J. Microbiol. 2016;54(1):31-38. Published online January 5, 2016; DOI: https://doi.org/10.1007/s12275-016-5574-1

Abstract: A variety of microbes grow by respiration with dimethyl sulfoxide (DMSO) as an electron acceptor, and several distinct DMSO respiratory systems, consisting of electron carriers and a terminal DMSO reductase, have been characterized. The heterotrophic growth of a hyperthermophilic archaeon Thermococcus onnurineus NA1 was enhanced by the addition of DMSO, but the archaeon was not capable of reducing DMSO to DMS directly using a DMSO reductase. Instead, the archaeon reduced DMSO via a cysteine-cystine redox shuttle through a mechanism whereby cystine is microbially reduced to cysteine, which is then reoxidized by DMSO reduction. A thioredoxin reductase-protein disulfide oxidoreductase redox couple was identified to have intracellular cystine-reducing activity, permitting recycle of cysteine. This study presents the first example of DMSO reduction via an electron shuttle. Several Thermococcales species also exhibited enhanced growth coupled with DMSO reduction, probably by disposing of excess reducing power rather than conserving energy.

Thionine Increases Electricity Generation from Microbial Fuel Cell Using Saccharomyces cerevisiae and Exoelectrogenic Mixed Culture: Mostafa Rahimnejad , Ghasem Darzi Najafpour , Ali Asghar Ghoreyshi , Farid Talebnia , Giuliano C. Premier , Gholamreza Bakeri , Jung Rae Kim , Sang-Eun Oh; J. Microbiol. 2012;50(4):575-580. Published online August 25, 2012; DOI: https://doi.org/10.1007/s12275-012-2135-0

Abstract: Microbial fuel cells (MFCs) have been shown to be capable of clean energy production through the oxidation of biodegradable organic waste using various bacterial species as biocatalysts. In this study we found Saccharomyces cerevisiae, previously known electrochemcially inactive or less active species, can be acclimated with an electron mediator thionine for electrogenic biofilm formation in MFC, and electricity production is improved with facilitation of electron transfer. Power generation of MFC was also significantly increased by thionine with both aerated and non-aerated cathode. With electrochemically active biofilm enriched with swine wastewater, MFC power increased more significantly by addition of thionine. The optimum mediator concentration was 500 mM of thionine with S. cerevisae in MFC with the maximum voltage and current generation in the microbial fuel cell were 420 mV and 700 mA/m2, respectively. Cyclic voltametry shows that thionine improves oxidizing and reducing capability in both pure culture and acclimated biofilm as compared to non-mediated cell. The results obtained indicated that thionine has great potential to enhance power generation from unmediated yeast or electrochemically active biofilm in MFC.

Effect of Natural Mediators on the Stability of Trametes trogii Laccase during the Decolourization of Textile Wastewaters: Rim Khlifi-Slama , Tahar Mechichi , Sami Sayadi , Abdelhafidh Dhouib; J. Microbiol. 2012;50(2):226-234. Published online April 27, 2012; DOI: https://doi.org/10.1007/s12275-012-1421-1

Abstract: The purpose of the present study was to determine the effect of natural mediators on the stability of the Trametes trogii crude laccase in the process of decolourization of textile effluents. Acetosyringone allowed the highest wastewaters decolourization rate of 25%. At higher concentrations of acetosyringone, the relative activity of laccase decreased approximately by between 38% and 88% after 5 days of incubation. T. trogii laccase was strongly inactivated at 3 mM syringaldehyde, after 3 days of incubation. However, laccase activity is more stable in the presence of the vanillin and m-coumarate. The T. trogii growth on solid effluentbased- medium was examined and evaluated by measuring the colony diameter in cm. T. trogii was completely inhibited on 100:0 and 80:20 effluent:water solid medium, however, colony diameter reached 5 cm on 60:40 effluent:water solid medium after 13–14 days incubation. When the textile effluent was pre-treated with laccase and laccase-acetosyringone system, the colony diameter of 2 cm of T. trogii on 80:20 effluent:water solid medium was reached after 14 and 10 days of incubation respectively.

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