Connecion of the NAD+-Reducing Hydrogenases to Various Bioenergetic Pathways in the Purple Sulfur Photosynthetic Microbe, Thiocapsa Roseopersicina BBS

  • Gabor Rakhely, Department of Biotechnology, University of Szeged, Szeged, Hungary, Institute of Biophysics, Biological Research Centre,, Hungary
  • Judit Balogh, Institute of Biophysics, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary, Hungary
  • Rita Béres, Department of Biotechnology, University of Szeged, Szeged, Hungary, Hungary
  • Dora Latinovics, Department of Biotechnology, University of Szeged, Szeged, Hungary, Hungary
  • Dr Gergely Maroti, Department of Biotechnology, University of Szeged, Szeged, Hungary, Hungary
  • Dr Laszlo Nagy, Institute of Medical Physics and Biophysics, University of Szeged, Szeged, Hungary, Hungary
  • Julia Novak, Department of Biotechnology, University of Szeged, Szeged, Hungary, Hungary
  • Prof Kornel Kovacs, Department of Biotechnology, University of Szeged, Szeged, Hungary, Institute of Biophysics, Biological Research Centre,, Hungary

    • Thiocapsa rosoepersicina BBS, a purple sulfur anaerobic photosynthetic bacterium utilizes reduced sulfur compound for its growth. The strain accumulates elementary sulfur globules and can synthesize various storage materials like glycogen or polyhydroxyalkanoates.
    T. roseopersicina BBS, as world recorder, contains five NiFe hydrogenases (HynS-Isp1-Isp2-HynL, HupSLC, HupUV, Hox1EFUYH and Hox2FUYH) having various physiological roles [1]. The cells, grown in the presence elevated thiosulfate in the medium, can evolve hydrogen under illumination only, while in dark, low thiosulfate concentration stimulates the hydrogen production. In both cases, the NAD+-reducing Hox1 hydrogenase is responsible for the hydrogen evolution [2]. The HoxYH subunit of this hydrogenase is responsible for the proton reduction/hydrogen oxidation, while the hoxFU genes encode for the diaphorase subunits. The fifth subunit, the HoxE, likely has an electron transferring role. The in vivo hydrogen evolving capacity could be significantly reduced by using Nuo and photosynthesis inhibitors, hence, it seems that the Hox1 hydrogenase has direct connection to the respiratory chain, photosynthesis and sulfur metabolism [3].
    In the genome, recently sequenced, a second NAD+-reducing hydrogenase – composed of four subunits - could be identified. This second soluble enzyme, named as Hox2 could evolve or oxidize hydrogen in cells grown in the presence of glucose, therefore it seemed to be related to the (photo)fermentative processes.
    Taking into account for genomic and experimental data, an integrated network could be established, which connected the hydrogen, sulfur and nitrogen metabolism to photosynthesis, respiration, fermentation and metabolism of various storage materials.