Kinetics of two subgroups of propionate-using organisms in anaerobic digestion

A novel method for measuring the kinetics of a subgroup of organisms growing in mixed culture was used to measure the kinetics of propionate-using organisms in a mixed-population anaerobic digester. It was shown that there are at least two subgroups of propionate-using organisms with distinctly different growth kinetics. Both subgroups could grow without reducing sulfate. The slower-growing subgroup had a Ks of 11 mg/liter and a mumax of 0.0054 h-1 which is similar to the mumax reported for Syntrophobacter wolinii. The faster-growing group had a mumax of 0.050 h-1 and a Ks of 330 mg/liter. The slower-growing group was inhibited by a pH shock from 7.0 to 6.0, whereas the faster-growing group was less sensitive to the pH shock.