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Complete genome sequence of hyperthermophilic archaeon Thermococcus sp. ES1
Jung, J.H.,Kim, Y.T.,Jeon, E.J.,Seo, D.H.,Hensley, S.A.,Holden, J.F.,Lee, J.H.,Park, C.S. Elsevier Science Publishers 2014 Journal of biotechnology Vol.174 No.-
Thermococcus sp. strain ES1 is an anaerobic, hyperthermophilic archaeon from a hydrothermal vent that catabolizes sugars and peptides and produces H<SUB>2</SUB>S from S<SUP>o</SUP>, H<SUB>2</SUB>, acetate and CO<SUB>2</SUB> as its primary metabolites. We present the complete genome sequence of this strain (1,957,742bp) with a focus on its substrate utilization and metabolite production capabilities. The sequence will contribute to the development of heterotrophic archaea for bioenergy production and biogeochemical modeling in hydrothermal environments.
Jeon, E.J.,Jung, J.H.,Seo, D.H.,Jung, D.H.,Holden, J.F.,Park, C.S. IPC Science and Technology Press ; Elsevier Scienc 2014 Enzyme and microbial technology Vol.60 No.-
Maltose-forming α-amylase is a glycoside hydrolase family 57 (GH57) member that is unique because it displays dual hydrolysis activity toward α-1,4- and α-1,6-glycosidic linkages and only recognizes maltose. This enzyme was previously identified only in Pyrococcus sp. ST04 (PSMA); however, we recently found two homologs subgroups in Thermococcus species. One subgroup (subgroup A) showed relatively high amino acid sequence similarity to PSMA (>71%), while the other subgroup (subgroup B) showed lower homology with PSMA (<59%). To characterize the subgroup B maltose-forming α-amylase from Thermococcus species (TCMA), we cloned the CL1_0868 gene from Thermococcus sp. CL1 and then successfully expressed the gene in Escherichia coli. Although TCMA has a different oligomeric state relative to PSMA, TCMA showed similar substrate specificity. However, TCMA was shown to hydrolyze maltooligosaccharides more easily than PSMA. Also, TCMA displayed different optimum conditions depending on the glycosidic linkage of the substrate. TCMA had the highest activity at 85<SUP>o</SUP>C and at pH 5.0 for α-1,4-glycosidic linkage hydrolysis whereas it showed its maximal activity to cleave α-1,6-glycosidic linkages at 98<SUP>o</SUP>C and pH 6.0.
Kim, Y.T.,Jung, J.H.,Stewart, L.C.,Kwon, S.W.,Holden, J.F.,Park, C.S. Elsevier Publishing Services 2015 MARINE GENOMICS Vol.24 No.3
Methanocaldococcus bathoardescens JH146<SUP>T</SUP> is a hyperthermophilic and obligate hydrogenotrophic methanogen isolated from low-temperature (26<SUP>o</SUP>C) hydrothermal vent fluid at Axial Seamount in the northeastern Pacific Ocean. It is most closely related to the N<SUB>2</SUB>-fixing methanogen Methanocaldococcus sp. FS406-22; however, they differ in that JH146 cannot fix N<SUB>2</SUB> or reductively assimilate nitrate. In this study, we present the complete genome sequence of strain JH146<SUP>T</SUP> (1,607,556bp) with its 1635 protein coding genes, and 41 RNA genes. Our analysis focuses on its methane production via the acetyl-CoA pathway and its deleted gene clusters related to nitrogen assimilation. This study extends our understanding of methanogenesis at high temperatures and the impact of these organisms on the biogeochemistry of subseafloor hydrothermal environments and the deep sea.
THE EVOLUTION OF STAR FORMATION HISTORIES OF QUIESCENT GALAXIES
Pacifici, Camilla,Kassin, Susan A.,Weiner, Benjamin J.,Holden, Bradford,Gardner, Jonathan P.,Faber, Sandra M.,Ferguson, Henry C.,Koo, David C.,Primack, Joel R.,Bell, Eric F.,Dekel, Avishai,Gawiser, Er American Astronomical Society 2016 The Astrophysical Journal Vol.832 No.1
<P>Although there has been much progress in understanding how galaxies evolve, we still do not understand how and when they stop forming stars and become quiescent. We address this by applying our galaxy spectral energy distribution models, which incorporate physically motivated star formation histories (SFHs) from cosmological simulations, to a sample of quiescent galaxies at 0.2 < z < 2.1. A total of 845 quiescent galaxies with multi-band photometry spanning rest-frame ultraviolet through near-infrared wavelengths are selected from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) data set. We compute median SFHs of these galaxies in bins of stellar mass and redshift. At all redshifts and stellar masses, the median SFHs rise, reach a peak, and then decline to reach quiescence. At high redshift, we find that the rise and decline are fast, as expected, because the universe is young. At low redshift, the duration of these phases depends strongly on stellar mass. Low-mass galaxies (log(M*/M-circle dot) similar to 9.5) grow on average slowly, take a long time to reach their peak of star formation (greater than or similar to 4 Gyr), and then the declining phase is fast (less than or similar to 2 Gyr). Conversely, high-mass galaxies (log(M*/M-circle dot) similar to 11) grow on average fast (less than or similar to 2 Gyr), and, after reaching their peak, decrease the star formation slowly (greater than or similar to 3). These findings are consistent with galaxy stellar mass being a driving factor in determining how evolved galaxies are, with high-mass galaxies being the most evolved at any time (i.e., downsizing). The different durations we observe in the declining phases also suggest that low- and high-mass galaxies experience different quenching mechanisms, which operate on different timescales.</P>