Growth kinetics of the thermophilic fungus Thermomyces lanuginosus

Abstract

The growth kinetics and morphology of a thermophile fungus, Thermomyces lanuginosus , were studied at 50 °C in semi-solid and liquid (stationary, shake flask, and fermenter culture) media; complex (yeast plus soluble starch: YPS) and defined media (yeast-free, with NH 4 -N) were used. On YPS agar, the colony radial growth rate was 367 ± 5 m h −1 (mean ± s.e. ) as compared with 217 ± 4 m h −1 on the defined medium. In liquid culture growth was biphasic. In YPS medium in shake flask cultures at 220 rpm the initial specific growth rate (μ 1 ) until 8 h was 0·89 h −1 decreasing thereafter (μ 2 ) to 0·46 h −1 , and in stationary cultivation μ 1 and μ 2 were 0·55 and 0·28 h −1 respectively. Growth in a 2 l (1·5 l working volume) fermenter was also biphasic (μ 1 , 0·84 h −1 ; μ 2 , 0·35 h −1 ). The hyphal growth unit length ( G ) on solid medium (YPS) was 156 ± 7 m. In liquid culture the G -value seemed to be inversely related to the shear stress, showing a decrease from 188 ± 5 m (stationary culture) to 116 ± 12 m (400 rpm, shake flask). In fermenter at 900 rpm G was 85 ± 2 m. The mean hyphal diameter after 14 h of growth was: stationary culture, 1·77 ± 0·05 m; shake flask culture, 1·11 ± 0·06 m; in fermenter, 1·20 ± 0·06 m after 13·5 h.