Figure 4.

Growth phenotypes of M. jannaschii strains grown with sulfide or sulfite as medium reductant and sulfur source. The study was performed as described previously (Mukhopadhyay et al., 1999; Johnson and Mukhopadhyay, 2005) using 530 ml sealed serum bottles, each containing 100 ml medium and a mixture of H₂ and CO₂ (80:20, v/v) in the head space at a pressure of 3 × 10⁵ Pa (Mukhopadhyay et al., 1999; Johnson and Mukhopadhyay, 2005). Sulfite or sulfide concentration, 2 mM. When sulfite was used as sulfur source, after sulfite addition but prior to inoculation, the medium was pre-incubated at 80°C for 14 h to achieve adequate reduction as evidence by the clearing of the color of resazurin; resazurin is a redox indicator commonly used in methanogen media (Balch et al., 1979). Pre-warmed and pre-reduced media were inoculated with 2 ml of an overnight culture developed under the test condition, with one exception. For testing the ability of BM10 to grow with sulfite as sulfur source, the inoculum was developed with sulfide. Each reported optical density value is an average from measurements with two independent cultures.