Conditions are described that support anaerobic dark chemotrophic grow
th of heliobacteria. Growth was pyruvate-dependent and was best in wel
l-buffered pyruvate media supplemented with yeast extract. Heliobacter
ial cells grown in darkness synthesized bacteriochlorophyll g and caro
tenoids and fermented pyruvate to acidic products, CO2, and in some ca
ses, H-2. All recognized species of heliobacteria as well as several n
ewly isolated strains were capable of dark anaerobic growth, suggestin
g that this growth mode may be ecologically important for survival of
these organisms in their soil habitat.