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Genetic Engineering & Biotechnology News | GENengnews.com | APRIL 15, 2017 | 25 data were probably caused by slightly deviating growth in each shake flask and following vari- ances in cell aggregation in each of the sampling cultures. The formula y = 0.1075 x + 0.12257 was used to calibrate the biomass signal ampli- tude measured with the SFR vario and convert it into cell dry weight concentration. In Figure 3, the calibrated online biomass values in g/L over time of two independent experiments are plotted together with the re- spective offline measurement values for cell dry weight and settled cell volume. All mea- surement methods show the same trend in biomass development. Online measurements show linear growth after a short exponential phase, which is typi- cal for plant cells in suspension culture. Fur- thermore, online measurements reveal differ- ent growth patterns of S. fruticosa in the two experiments, with a longer exponential phase in experiment 2. These variations might also be caused by different starting cell densities. This finding could not be derived from the offline data, and shows clearly the advantage of the online measurement system. In the on- line data of both experiments, maximum bio- mass values were reached after about 200h cultivation period. Offline data show differ- ent points of maximum biomass at 200h for experiment 2 and 250h for experiment 1. As mentioned before, samples for offline measurements were taken from separate cul- tures, so not-quite-synchronized growth in the different shake flasks might have caused these variations. The oxygen sensor spot integrated in the shake flasks read with the SFR vario deliv- ered a very good online signal, compared to the readings of amperometric sensors used to monitor plant cell culture in bioreactors, which have a very high noise ratio (data not shown). The online oxygen measurements show a constant decrease in the oxygen level for the first 100h of the cultivation period and it remained at a minimum of about 50% O 2 -saturation during the growth phase, in- dicating high metabolic activity of the cells (Figure 4). The slight fluctuations might indicate met- abolic processes of the plant cells during their linear growth phase that have not been inves- tigated so far. After the maximum biomass was reached, metabolic activity of the cells stopped and the oxygen saturation level in the culture medium started to increase again. Conclusion The applicability of online measurements with the SFR vario for plant cell-suspension culture monitoring was proven with a S. fruticosa cell-suspension culture. The online data are consistent with gravimetrically de- termined offline values, while giving a more detailed view of culture performance com- pared to the single-spot offline measurements. Combined with online oxygen monitoring, valuable information about the metabolic be- havior of the cultures could be obtained. More tests with other plant cell lines form- ing larger aggregates are planned, to further apply online biomass monitoring with the SFR vario in plant cell culture. U N S T O P P A B L E P U L S E 100x more sensitivity, down to the femtogram. 20x faster: separate up to 200,000 base pairs in about 1 hour. SHATTER ALL EXPECTATIONS IN GENOMIC DISCOVERY. Automating genomic discover y A AT I - U S . C O M Bioprocessing P. Scherhag is a graduate student at HTW Dresden, Dr. G.T. John (firstname.lastname@example.org) is director of marketing & innovations at PreSens, Dr.-Ing. C. Haas is a research associate at Technical University (Dresden), and Dr.rer.nat. J.-U. Ackermann is a professor of chemical engineering at HTW Dresden. Website: www.presens.de. Tutorial Figure 3. Calibrated online biomass values measured with the SFR vario (in g/L, blue lines), and offline values of cell dry weight (green lines) and settled cell volume (red dots and circles) for two independent experimental runs of S. fruticosa culture in 250 mL shake flasks; online and offline measured values show the same trend in biomass development. Figure 4. Calibrated online biomass data and dissolved oxygen measurement in S. fruticosa culture in two independent experimental runs recorded with the SFR vario.