INHIBITION OF RESPIRATORY OXIDATION OF REDUCED SULFUR-COMPOUNDS BY INTACT-CELLS OF THIOBACILLUS-DENITRIFICANS (STRAIN RT) GROWN ON THIOSULFATE

Thiobacillus denitrificans strain RT, an obligate sulfur-oxidizing che molithoautotroph, was grown under microaerophilic conditions with thio sulfate as the only energy source. The rates of tetrathionate, thiosul fate, elemental sulfur (S-degrees) and sulfite oxidation were measured respirometrically with an oxygen electrode, using actively growing ce lls. Cells oxidized thiosulfate, elemental sulfur (S-degrees) and sulf ite, but not tetrathionate. The thiosulfate-oxidizing activity and ele mental sulfur-oxidizing activity (SOA) were almost totally inhibited b y 50 muM myxothiazol (>80%), an inhibitor of the quinone-cytochrome b region, and by 10 muM of the uncoupler carbonyl cyanide m-chlorophenyl hydrazone (CCCP) (>82%). Sulfite-oxidizing activity was also significa ntly inhibited (>60%) by 50 muM myxothiazol and 10 muM CCCP. 1 mM KCN totally inhibited (>90%) all respiratory activities. This study confir ms that a sulfur-oxidizing activity appears during microaerophilic gro wth of Thiobacillus denitrificans strain RT on thiosulfate. The SOA is linked to the respiratory chain, probably releasing electrons in the quinone-cytochrome b region.