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Hur, Hor-Gil 한국응용생명화학회 2000 Journal of Applied Biological Chemistry (J. Appl. Vol.43 No.1
Burkholderia cepacia strain G4 (pHG-2) containing toluene 2-monooxygenase and toluene dioxygenase, was able to grow on toluene and accumulate cis-3-methyl-3,5-cyclohexadien-1,2-diol (cis-toluene dihydrodiol) in the liquid culture. The cis-toluene dihydrodiol produced was identical to the authentic compound, as judged through mass spectrometry and nuclear magnetic resonance analysis. Our results indicate that pHG-2 provides an economical means to produce chemically-important chiral synthons while growing on toluene.
Jiang, Shenghua,Hur, Hor-Gil Japanese Society of Microbial Ecology/The Japanese 2013 Microbes and environments Vol.28 No.3
<P>Uranium (VI) is considered to be one of the most widely dispersed and problematic environmental contaminants, due in large part to its high solubility and great mobility in natural aquatic systems. We previously reported that under anaerobic conditions, <I>Shewanella oneidensis</I> MR-1 grown in medium containing uranyl acetate rapidly accumulated long, extracellular, ultrafine U(VI) nanofibers composed of polycrystalline chains of discrete meta-schoepite (UO<SUP>3</SUP>·2H<SUB>2</SUB>O) nanocrystallites. Wild-type MR-1 finally transformed the uranium (VI) nanofibers to uranium (IV) nanoparticles via further reduction. In order to investigate the influence of the respiratory chain in the uranium transformation process, a series of mutant strains lacking a periplasmic cytochrome MtrA, outer membrane (OM) cytochrome MtrC and OmcA, a tetraheme cytochrome CymA anchored to the cytoplasmic membrane, and a trans-OM protein MtrB, were tested in this study. Although all the mutants produced U(VI) nanofibers like the wild type, the transformation rates from U(VI) nanofibers to U(IV) nanoparticles varied; in particular, the mutant with deletion in tetraheme cytochrome CymA stably maintained the uranium (VI) nanofibers, suggesting that the respiratory chain of <I>S. oneidensis</I> MR-1 is probably involved in the stability of extracellular U(VI) nanofibers, which might be easily treated via the physical processes of filtration or flocculation for the remediation of uranium contamination in sediments and aquifers, as well as the recovery of uranium in manufacturing processes.</P>
( Anamika Khanal ),( Hor-gil Hur ),( James K. Fredrickson ),( Ji-hoon Lee ) 한국미생물 · 생명공학회 2021 Journal of microbiology and biotechnology Vol.31 No.11
Hexavalent chromium (Cr(VI)) is recognized to be carcinogenic and toxic and registered as a contaminant in many drinking water regulations. It occurs naturally and is also produced by industrial processes. The reduction of Cr(VI) to Cr(III) has been a central topic for chromium remediation since Cr(III) is less toxic and less mobile. In this study, fermentative Fe(III)-reducing bacterial strains (Cellu-2a, Cellu-5a, and Cellu-5b) were isolated from a groundwater sample and were phylogenetically related to species of Cellulomonas by 16S rRNA gene analysis. One selected strain, Cellu-2a showed its capacity of reduction of both soluble iron (ferric citrate) and solid iron (hydrous ferric oxide, HFO), as well as aqueous Cr(VI). The strain Cellu-2a was able to reduce 15 μM Cr(VI) directly with glucose or sucrose as a sole carbon source under the anaerobic condition and indirectly with one of the substrates and HFO in the same incubations. The heterogeneous reduction of Cr(VI) by the surface-associated reduced iron from HFO by Cellu-2a likely assisted the Cr(VI) reduction. Fermentative features such as large-scale cell growth may impose advantages on the application of bacterial Cr(VI) reduction over anaerobic respiratory reduction.
Intracellular Uranium Accumulation by Shewanella sp. HN-41 under the Thiosulfate-Reducing Condition
Lee, Ji-Hoon,Hur, Hor-Gil The Korean Society for Applied Biological Chemistr 2014 Applied Biological Chemistry (Appl Biol Chem) Vol.57 No.1
A strain of genus Shewanella, one of representative dissimilatory Fe(III)-reducing bacteria, HN-41 precipitated intra- and extracellular needle-like uranium materials in the anaerobic incubation with uranyl acetate ($U(VI)O{_2}^{2+}$) and sodium thiosulfate ($S_2O_3^{2-}$) as the possible electron acceptors. In the absence of thiosulfate, strain HN-41 generated only fine-grained extracellular U precipitates, presumably mineral uraninite ($U(IV)O_2$). Electron microscopy showed that the needle-like U precipitates were associated with the inner and outer membranes of strain HN-41 cells incubated anaerobically with thiosulfate. Energy-dispersive X-ray spectroscopy and associated mapping analyses on a single intracellular needle-like particle indicated the compositions of U, P, and S, which lead to inference of the precipitates consisting of uraninite, phosphate, and sulfide. The results indicate that the presence of competing electron acceptors may significantly alter the forms and locations of U biomineralization products.
Ahyeon Cho,Alpana Joshi,Hor-Gil Hur,Ji-Hoon Lee The Korean Society for Microbiology and Biotechnol 2024 Journal of microbiology and biotechnology Vol.34 No.3
Root-nodule nitrogen-fixing bacteria are known for being specific to particular legumes. This study isolated the endophytic root-nodule bacteria from the nodules of legumes and examined them to determine whether they could be used to promote the formation of nodules in other legumes. Forty-six isolates were collected from five leguminous plants and screened for housekeeping (16S rRNA), nitrogen fixation (nifH), and nodulation (nodC) genes. Based on the 16S rRNA gene sequencing and phylogenetic analysis, the bacterial isolates WC15, WC16, WC24, and GM5 were identified as Rhizobium, Sphingomonas, Methylobacterium, and Bradyrhizobium, respectively. The four isolates were found to have the nifH gene, and the study confirmed that one isolate (GM5) had both the nifH and nodC genes. The Salkowski method was used to measure the isolated bacteria for their capacity to produce phytohormone indole acetic acid (IAA). Additional experiments were performed to examine the effect of the isolated bacteria on root morphology and nodulation. Among the four tested isolates, both WC24 and GM5 induced nodulation in Glycine max. The gene expression studies revealed that GM5 had a higher expression of the nifH gene. The existence and expression of the nitrogen-fixing genes implied that the tested strain had the ability to fix the atmospheric nitrogen. These findings demonstrated that a nitrogen-fixing bacterium, Methylobacterium (WC24), isolated from a Trifolium repens, induced the formation of root nodules in non-host leguminous plants (Glycine max). This suggested the potential application of these rhizobia as biofertilizer. Further studies are required to verify the N<sub>2</sub>-fixing efficiency of the isolates.