Physiological Characterization of Sulfolobus acidocaldarius in a Controlled Bioreactor Environment

The crenarchaeal model organism Sulfolobus acidocaldarius is typically cultivated in shake flasks. Although shake flasks represent the state-of-the-art for the cultivation of this microorganism, in these systems crucial process parameters, like pH or substrate availability, are only set initially, but cannot be controlled during the cultivation process. As a result, a thorough characterization of growth parameters under controlled conditions is still missing for S. acidocaldarius. In this study, we conducted chemostat cultivations at 75 °C using a growth medium containing L-glutamate and D-glucose as main carbon sources. Different pH values and dilution rates were applied with the goal to physiologically characterize the organism in a controlled bioreactor environment. Under these controlled conditions a pH optimum of 3.0 was determined. Washout of the cells occurred at a dilution rate of 0.097 h^-1 and the optimal productivity of biomass was observed at a dilution rate of 0.062 h^-1. While both carbon sources were taken up by S. acidocaldarius concomitantly, a 6.6-fold higher affinity for L-glutamate was shown. When exposed to suboptimal growth conditions, S. acidocaldarius reacted with a change in the respiratory behavior and an increased trehalose production rate in addition to a decreased growth rate.