Inhibitory effect of mineral ion accumulation on high density growth of the hyperthermophilic archaeon Sulfolobus solfataricus

A fed-batch operation for high density cultivation of Sulfolobus solfataric us (DSM 1617) in a bench-top fermenter using a feed medium composed of gluc ose and yeast extract was investigated. The highest maximal cell density ob tained in controlled fed-batch cultures was 21.7 g/l. Although higher yeast extract concentrations in the medium favored greater cell biomass yield, c ell growth ceased with low cell densities. It was observed that large amoun ts of inorganic ions, such as sulfate, ammonium, potassium and phosphate io ns, were accumulated in the culture broth at higher yeast extract concentra tions. This was due to either the addition of the titrant or feeding of yea st extract during cultivation. Fed-batch cultures with additional mineral s alts in the feed medium showed much lower cell biomass, indicating that acc umulation of inorganic ions has a significant inhibitory effect on the grow th of S. solfataricus. Inhibition of cell growth by the presence of mineral ions was further confirmed by the batch culture experiments. Some plausibl e mechanisms which can account for the growth inhibition at higher mineral ion concentrations have been suggested.