Inhibitory effect of acetic acid on growth of hyperthermophilic archaeon Pyrococcus furiosus

The growth inhibition of Pyrococcus furiosus by acetic acid was stronger than that by hydrogen and could be described by a non-competitive inhibition model in which the inhibition constants of undissociated acetic acid, K(p) and n, were estimated to be 0.69 mM (25 mM total acetic acid at pH 6.5; pKa=4.96; 98 degrees C) and 1.0, respectively. In order to reduce the acetic acid inhibition, repeated-batch culturing was performed using a filtration module. This yielded 0.49 g of dry cells l(-1) after growth for 12 h after inoculation. It became impossible, however, to continue repeated-batch culturing manually because the time intervals for medium replacement became too short. In order to automatically maintain a low concentration of acetic acid, a perfusion culture was carried out in which medium feeding coupled to a pH-auxostat was performed. In this perfusion culture, it was possible to maintain the acetic acid concentration below 7.6 mM during exponential growth of P. furiosus, resulting in 1.8 g of dry cells l(-1) at 15 h after inoculation.