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

The growth inhibition of Pyrococcus furiosus by acetic acid was stronger th an that by hydrogen and could be described by a non-competitive inhibition model in which the inhibition constants of undissociated acetic acid, Kp an d 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 aci d inhibition, repeated-batch culturing was performed using a filtration mod ule. This yielded 0.49g of dry cells l(-1) after growth for 12h after inocu lation. It became impossible, however, to continue repeated-batch culturing manually because the time intervals for medium replacement became too shor t. 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 maint ain 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 inoculati on.