MICROBIAL ERMENTATION IN THE CELL-TAINER BIOREACTOR
Interest in microbial expression systems such as E. coli and Pichia pastoris, is increasing. That's the case not only for traditional products such as enzymes but also for production of biopharmaceuticals
and the manufacturing of platform chemicals. Bulk fermentation products are produced on large scales of up to 400 – 800 m3 in stirred bioreactors, but for screening and pre-culture purposes, the single-use bioreactors offer the advantage of fast
turnaround, speed in early stage development, and late stage development (scale-down experiments). The limited infrastructure
required (no autoclaves or SIP/CIP) is also a key advantage for single-use equipment.
Figure 4 shows microbial culture in a 10L fed-batch performed in the CELL-tainer single-use bioreactor. The profile shows
results that are comparable with those seen in stirred fermentors up to 100 L working volumes (5).
Figure 4. Cultivation of E.coli in a 10 L fed-batch in the CELL-tainer bioreactor. OD550 = biomass concentration in optical
density units measured at 550 nm.
In addition to the pH and DO sensor, a device for measuring glucose and lactate is available, using the Trace Analytics (
http://www.trace.de/) technology of a dialysis membrane. The dialysis membrane is integrated in the bottom of the bag, comparable to the pH and
DO sensors. The device is an integrated part of the gamma-irradiated bag (see figure 5).
Figure 5. Single-use dialysis membrane. (COURTESY: TRACE ANALYTICS GMBH/CELLUTION BIOTECH BV.)
In an E. coli fermentation, using glucose as substrate, online and offline data are compared (see figure 6). There is only a slight, negligible
discrepancy between on-line and off-line data. The off-line data are based on an enzymatic method in collected samples using
an autosampler. The discrepancy is easy to explain: the off-line data show lower values because of the metabolic activity
that continues after a sample till analysis takes place (2–5 minutes before the sample is –5 °C). The online measurements
are highly accurate because there is continuous equilibrium between the culture and the cell-free dialysate. The ability of
online measurement of an important parameter such as glucose (and lactate) offers the possibility to develop advanced on-line
control strategies, thus making the single-use bioreactor increasingly suitable for process development.
Figure 6. Comparison of in-line and on-line glucose measurement in an E.coli culture using the ContiTRACE dialysis membrane
plug integrated in the CELL-tainer.
Single-use bioreactors offer the advantage of fast installation, lower investments in infrastructure, and a significant decrease
of validation costs. Similarly a comparison of operational costs of a 5-day microbial process as performed in a 15L autoclavable,
in a 15L SIP bioreactor, versus the process in the single-use CELL-tainer, reveals significantly lower costs in the single-use
system per run (see figure 7). This includes the costs of bags (fully equipped with sensors). Because the single use CELL-tainer
bioreactor has a fast turnaround time, in the same bioreactor system, 40% more runs/year can be made, when compared to an
Figure 7. Relative operational cost comparison of 15-L bioreactors of different types.