Ammonia production from yeast extract and its effect on growth of the hyperthermophilic archaeon Sulfolobus solfataricus

Utilization of yeast extract and formation of byproduct metabolite were investigated for hyperthermophilic archaeon Sulfolobus solfataricus (DSM 1617). In both batch and fed-batch cultivations of S. solfataricus, maximal cell density, NH4+ ion production and pH change were highly dependent on the ratio of yeast extract to glucose in the medium. Variation of NH 4+ ion level was identified as a major cause of pH change during cultivation, and acidification of culture broth was attributed to consumption of NH4+ ions rather than formation of acid byproducts. It was also observed that increase of NH4+ ion concentrations in the medium resulted in greater degree of growth inhibition.