Biomass concentrations were determined by measuring the
OD600 with a Shimadzu PC2103 photometer, where in this case
one OD600 unit refers to 0.365 g/kg cell dry weight. Glucose concentration
was determined enzymatically with a Yellow Springs
BiochemistryAnalyzerYSI 2700. The formation ofthe target protein
GFP was monitored offline with a Hitachi F2600 fluorescence photometer
using 395 nm as the excitation and 511 nm as the detection
wavelength.
All fermentation experiments reported were carried out in a
15-L Biostat C (Sartorius Stedim Biotech) fermenter with an initial
volume of V = 5 L and an inner diameter T = 200 mm. The fermenter
was equipped with two or three impellers on the same central
shaft. Gas was supplied with an open tube sparger centrally placed
below the lowest impeller. The clearance between bottom and gas
sparger was 25 mm, between gas sparger and first impeller 40 mm,
and 60 mm between each impeller. Different impeller types were
investigated: Rushton turbines (D6) as well as 6 blade concave disk
impellers (CD6) according to.