GROWTH AND RESPIRATORY OXIDATION OF REDUCED SULFUR-COMPOUNDS BY INTACT-CELLS OF THIOBACILLUS-NOVELLUS (TYPE STRAIN) GROWN ON THIOSULFATE

Thiobacillus novellus (type strain) was grown chemolithoautrophically on thiosulfate in batch cultures under microaerophilic conditions. Und er these conditions, T. novellus grew exponentially (mu = 0.05-0.06 h- 1). The respiratory oxidation rates of tetrathionate, thiosulfate, ele mental sulfur (S-degrees), and sulfite were measured respirometrically with an oxygen electrode, with exponentially growing cells. Cells gro wing on thiosulfate as the unique energy source retain thiosulfate-oxi dizing activity, S-degrees-oxidizing activity (SOA), and very high sul fite-oxidizing activity, but lack respiratory tetrathionate-oxidizing activity. HQNO (50 mum), an inhibitor of the quinone-cytochrome b regi on, strongly inhibited the SOA (70%), moderately the sulfite-oxidizing activity (45%), and poorly the thiosulfate-oxidizing activity (15%), 1 mm KCN totally inhibited (>89%) all respiratory activities. This stu dy confirms that in Thiobacillus novellus, as well as in other Thiobac illi, SOA is present in cells grown with thiosulfate as sole electron donor. SOA appears not to be an oxygenase; it is linked to the respira tory chain, and the electrons are probably released in the quinone-cyt ochrome b region.