Conditions for vigorous growth on sulfide and reactor-scale cultivation protocols for the thermophilic green sulfur bacterium Chlorobium tepidum

We describe a reactor-scale cultivation protocol for the fastest-growing an d only known thermophilic member of the family Chlorobiaceae, Chlorobium te pidum. We discovered that C. tepidum would grow with sulfide as the sole el ectron source at rates and,vith final cell yields comparable to those found with thiosulfate only if the sulfide concentration was maintained below 0. 1 mM and the culture redox potential was at -300 +/- 20 mV. Such was also t he requirement for growth in a photobioreactor when thiosulfate (optimum le vel, 12 mM) was used as the preferred electron source. For cultivation of C . tepidum on a 5- to 500-ml scale, we used the system of Balch and Wolfe (A ppl. Environ. Microbiol. 32:781-791, 1976) using stopper sealed serum tubes and bottles as an alternative to the methods commonly used for the cultiva tion of phototrophic anaerobes and obtained consistent results.