Abstract
Aquifex aeolicus is a hyperthermophilic, chemolithoautotrophic, hydrogen-oxidizing, and microaerophilic bacterium growing at 85 degrees C. We have shown that it can grow on an H2/S degrees medium and produce H2S from sulfur in the later exponential phase. The complex carrying the sulfur reducing activity (electron transport from H2 to S degrees ) has been purified and characterized. It is a membrane-bound multiprotein complex containing a [NiFe] hydrogenase and a sulfur reductase connected via quinones. The sulfur reductase is encoded by an operon annotated dms (dimethyl sulfoxide reductase) that we have renamed sre and is composed of three subunits. Sequence analysis showed that it belongs to the Me2SO reductase molybdoenzyme family and is similar to the sulfur/polysulfide/thiosulfate/tetrathionate reductases. The study of catalytic properties clearly demonstrated that it can reduce tetrathionate, sulfur, and polysulfide, but cannot reduce Me2SO and thiosulfate, and that NADPH increases the sulfur reducing activity. To date, this is the first characterization of a supercomplex from a bacterium that couples hydrogen oxidation and sulfur reduction. The distinctive feature in A. aeolicus is the cytoplasmic localization of the sulfur reduction, which is in accordance with the presence of sulfur globules in the cytoplasm. Association of this sulfur-reducing complex with a hydrogen-oxygen pathway complex (hydrogenase I, bc1 complex) in the membrane suggests that subcomplexes involved in respiratory chains in this bacterium are part of supramolecular organization.
Highlights
Sulfur compounds are vital processes for many bacteria and essential steps in the global sulfur cycle
Growth of A. aeolicus with Elemental Sulfur or Thiosulfate—In this work, we show that A. aeolicus can grow in an H2/CO2/O2 atmosphere with S° with a high final cell concentration (A600 ϭ 1.2 on S° against A600 ϭ 0.8 on S2O3) (Fig. 1)
One unit of sulfur reductase (SR) activity corresponds to the uptake of 1 mol of H2S/min, and 1 unit of hydrogenase activity corresponds to the uptake of 1 mol of H2/min
Summary
Organism and Growth Conditions—A. aeolicus was grown at 85 °C in 2-liter bottles under 1.4 bars of H2/CO2 (80:20) in SME medium, modified according to Ref. 23, at pH 6.8 in the presence of thiosulfate (1 g/liter) or S° (7.5 g/liter) and harvested in the late exponential growth phase. Proteins were eluted with a 50 mM step gradient of 0 –350 mM NaCl. The 50 –100 mM NaCl fraction contained the hydrogenase and the sulfur reductase activities. The 50 –100 mM NaCl fraction contained the hydrogenase and the sulfur reductase activities This fraction was loaded onto a hydroxylapatite column (2 ϫ 12 cm, Bio-Gel; Bio-Rad) equilibrated in buffer A containing NaCl at a concentration of 75 mM. A calibration curve had been made previously using Na2S (30) As this method does not take account the loss of sulfide through reactions with sulfur, the activities determined are underestimated. Denaturing Gel Electrophoresis—100 g of purified complex was loaded on a 4% polyacrylamide stacking, 10% running SDS gel (Protean II XL cell; Bio-Rad). Sequence Alignment—Multiple sequence alignments were done using ClustalW (36) at pbil.univ-lyon1.fr/
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
