. Two-stage continuous fermentation
The continuous fermentations were conducted in customized
1 l and 5 l bioreactor with working volume in the 500 ml and
1250 ml to obtain dilution rates of 0.1 and 0.04 h−1 respectively.
The fermentations in both reactors were started as batch, inoculated
with 5% preculture from the serum bottles. Before and
after inoculation, the reactors were gassed with nitrogen at a flow
rate of 20 ml min−1 to achieve anaerobiosis. Both reactors were
started as batch fermentations for 18–20 h until sufficient biomass
is produced, OD600 nm ≈
5, and then were connected for continuous
fermentation. The medium to the first reactor and broth to the
second reactor were pumped with peristaltic pumps (Reglo Digital
2 channels, Ismatec SA, Glattbrugg, Switzerland) to maintain constant
reactor volumes. The cells were kept in suspension using a
magnetic stirrer. pH control was adjusted by adding 1 M HCl or 2 M
NaOH.