Chitosan-modified fluorescent dye for simple, fast, and in-situ measurement of fungal cell growth in the presence of insoluble compounds

The measurement of fungal cell growth in submerged culture systems containing insoluble compounds is essential yet difficult due to the interferences from the insoluble compounds like biopolymers. Here, we developed a fluorescent strategy based on chitosan-modified fluorescein isothiocyanate (GC-FITC) to monitor the cell growth of lignocellulosic fungi cultivated on biopolymers. GC-FITC could stain only lignocellulosic fungi (Tricoderma reesei, Penicillium oxalicum, Aspergillus nidulans, and Neurospora crassa), but not biopolymers (cellulose, xylan, pectin, or lignin), excluding the interferences from these insoluble biopolymer. Moreover, a linear relationship was observed between the fluorescence intensity of GC-FITC absorbed by lignocellulosic fungi and the biomass of lignocellulosic fungi. Therefore, GC-FITC was leveraged to monitor the cell growth of lignocellulosic fungi when using biopolymers like cellulose as the carbon sources, which is faster, more convenient, time-saving, and cost-effective than the existing methods using protein/DNA content measurement. GC-FITC offers a powerful tool to detect fungal growth in culture systems with insoluble materials.

Process-induced cell cycle oscillations in CHO cultures: Online monitoring and model-based investigation

The influence of process strategies on the dynamics of cell population heterogeneities in mammalian cell culture is still not well understood. We recently found that the progression of cells through the cell cycle causes metabolic regulations with variable productivities in antibody-producing Chimese hamster ovary (CHO) cells. On the other hand, it is so far unknown how bulk cultivation conditions, for example, variable nutrient concentrations depending on process strategies, can influence cell cycle-derived population dynamics. In this study, process-induced cell cycle synchronization was assessed in repeated-batch and fed-batch cultures. An automated flow cytometry set-up was developed to measure the cell cycle distribution online, using antibody-producing CHO DP-12 cells transduced with the cell cycle-specific fluorescent ubiquitination-based cell cycle indicator (FUCCI) system. On the basis of the population-resolved model, feeding-induced partial self-synchronization was predicted and the results were evaluated experimentally. In the repeated-batch culture, stable cell cycle oscillations were confirmed with an oscillating G1 phase distribution between 41% and 72%. Furthermore, oscillations of the cell cycle distribution were simulated and determined in a (bolus) fed-batch process with up to 25 × 1 0 6 cells/ml. The cell cycle synchronization arose with pulse feeding only and ceased with continuous feeding. Both simulated and observed oscillations occurred at higher frequencies than those observable based on regular (e.g., daily) sample analysis, thus demonstrating the need for high-frequency online cell cycle analysis. In summary, we showed how experimental methods combined with simulations enable the improved assessment of the effects of process strategies on the dynamics of cell cycle-dependent population heterogeneities. This provides a novel approach to understand cell cycle regulations, control cell population dynamics, avoid inadvertently induced oscillations of cell cycle distributions and thus to improve process stability and efficiency.