FERMENTATION STUDIES WITH THERMOPHILIC ARCHAEA IN PURE CULTURE AND INSYNTROPHY WITH A THERMOPHILIC METHANOGEN

Two heterotrophic, thermophilic, sulfur-reducing archaea were isolated from the Guaymas Basin hydrothermal vent. The fermentation of protein aceous and carbohydrate substrates was examined at 85-degrees-C for ea ch isolate in the presence and absence of elemental sulfur and in cocu lture with a thermophilic methanogen. The heterotrophic isolates diffe red with respect to their requirement for sulfur. Both heterotrophic i solates exhibited a mixed organic acid fermentation from proteinaceous substrates; however, acetate was the sole organic acid produced from carbohydrate fermentation. In coculture fermentations with a thermophi lic methanogen, the heterotrophic isolates exhibited enhanced growth a nd fermentation. Interspecies hydrogen transfer and elemental sulfur-r eduction may be important microbial processes in deep-sea hydrothermal vent community metabolism.