Streptomyces thermoautotrophicus sp. nov., a Thermophilic CO- and H 2 -Oxidizing Obligate Chemolithoautotroph

Abstract

The novel thermophilic CO- and H 2 -oxidizing bacterium UBT1 has been isolated from the covering soil of a burning charcoal pile. The isolate is gram positive and obligately chemolithoautotrophic and has been named Streptomyces thermoautotrophicus on the basis of G+C content (70.6 ± 0.19 mol%), a phospholipid pattern of type II, MK-9(H 4 ) as the major quinone, and other chemotaxonomic and morphological properties. S. thermoautotrophicus could grow with CO ( t d = 8 h), H 2 plus CO 2 ( t d = 6 h), car exhaust, or gas produced by the incomplete combustion of wood. Complex media or heterotrophic substrates such as sugars, organic acids, amino acids, and alcohols did not support growth. Molybdenum was required for CO-autotrophic growth. For growth with H 2 , nickel was not necessary. The optimum growth temperature was 65°C; no growth was observed below 40°C. However, CO-grown cells were able to oxidize CO at temperatures of 10 to 70°C. Temperature profiles of burning charcoal piles revealed that, up to a depth of about 10 to 25 cm, the entire covering soil provides a suitable habitat for S. thermoautotrophicus . The K m was 88 μl of CO liter −1 and V max was 20.2 μl of CO h −1 mg of protein −1 . The threshold value of S. thermoautotrophicus of 0.2 μl of CO liter −1 was similar to those of various soils. The specific CO-oxidizing activity in extracts with phenazinemethosulfate plus 2,6-dichlorophenolindophenol as electron acceptors was 246 μmol min −1 mg of protein −1 . In exception to other carboxydotrophic bacteria, S. thermoautotrophicus CO dehydrogenase was able to reduce low potential electron acceptors such as methyl and benzyl viologens.