CO Metabolism by a Thermophilic Actinomycete, Streptomyces Strain G26

SUMMARY: Streptomyces G26, isolated from compost, is a moderately thermophilic actinomycete and a facultative autotroph capable of aerobic growth on CO or on CO2/H2. Soluble extracts of CO-grown mycelium contained enzymes of the Calvin cycle together with a CO oxidoreductase; the latter was present in heterotrophically grown mycelium at only 1% of the level found in CO-grown cultures. The CO oxidoreductase of Streptomyces G26 was unique in its ability to rapidly reduce low-potential acceptors such as the viologen dyes in addition to acceptors with E o’ values between + 11 mV and +429 mV. Although complete purification of the enzyme proved difficult, evidence is presented that extracts contained only one CO oxidoreductase. The partially purified enzyme had a very low apparent K m for CO, comparable with the CO oxidoreductase from Pseudomonas thermocarboxydovorans. Highest activities were observed at pH 7.2 and 60–65 °C. The enzyme was inactivated by methanol, suggesting that it is a molybdenum hydroxylase like the CO oxidoreductases from other aerobic bacteria.