Electron donors and acceptors for members of the family Beggiatoaceae

The family Beggiatoaceae comprises large, colorless sulfur bacteria, which are best known for their chemolithotrophic metabolism, the oxidation of reduced sulfur compounds with oxygen or nitrate. This thesis contributes to a more comprehensive understanding of the ecophysiology of these organisms with several studies on different aspects of their dissimilatory metabolism. Section 2 proposes a general model of sulfur compound oxidation in this family and Section 3 presents a possible rationale for sulfur respiration under strongly sulfidic conditions. Section 4 describes physiological and genomic studies, showing that members of the family Beggiatoaceae can use molecular hydrogen as an electron donor. The possible influence of hydrogen oxidation on the metabolic plasticity of the Beggiatoaceae is discussed and environmental settings are pointed out, in which hydrogen oxidation could be important for these organisms. Section 5 compares the energetics of hydrogen and sulfur oxidation.