Stimulation by cysteine on growth of Clostridium thermoaceticum in minimal medium

Summary An acetate-tolerant strain of Clostridium thermoaceticum (ATCC 31490), characterized as growing on a tryptone-yeast extract complex medium, was adapted to grow in a minimal medium containing glucose as sole carbon source. After five sequential batch cultures involving reducing and deleting organic materials from the original complex medium, the bacterium could grow on minimal medium with a supplement of nicotinic acid. However, growth and homoacetogenesis from glucose was remarkably retarded compared with that observed in the original complex medium. This could be strikingly improved up to the original level by replacing sodium thioglycolate (a reducing agent in the original medium) with L-cysteinHCI supplemented to the minimal medium. Cysteine played an important role in stimulating growth and homoacetogenesis by not only supplying H₂S as a sulphur source via cysteine desulphydrase (EC 4.4.1.1) but also maintaining a proper redox potential (—370 and —400 mV) in the growth phase during culture. Methionine could not serve as a sulphur source.Offprint requests to: Shiro Nagai