Isolation and growth physiology of novel thermoactinomycetes

A total of 34 thermophilic isolates identified as members of the genus Thermoactinomyces by a range of chemotaxonomic, microscopic and determinative biochemical tests, were isolated from two acid soils. Growth studies in shake flask and fermenter identified the isolates to be moderately acidophilic with growth occurring between pH 4.5 and 6.0 with optima at pH 5.0. The isolates differed considerably from known Thermoactinomyces cultures in their pH profile, colony morphology and in several biochemical tests. Extracellular enzyme activities are identified and partially characterized in terms of their thermostability, pH and temperature profiles from crude supernatant fluid samples. Optimal protease, amylase and pullulanase activity was observed at pH 5.0-5.5 and 75-80 degrees C with each showing T(50) values of 10, 30 and 30 min, respectively. A highly thermotolerant extracellular esterase was also identified which retained 50% activity after 8 h at 90 degrees C. This is the first report of an acidophilic member of the genus Thermoactinomyces.