Heterogeneity in cell populations and possible implications on product heterogeneities

摘要

Chemical and biotechnological processes give access to non-natural substances. To improve economic efficiency, quality and resource efficiency in more and more complex processes, highly sufficient process monitoring, management and optimization is needed. Novel analytical techniques will lead to major improvements in this field. Up to now, single-cell dynamics are almost not taken in consideration so far in the field of biotechnology. In this work, an unsupervised image analysis technique was established and used to determine multidimensional cell properties in various cell cultures. As model processes, lipid production in different algal-biotechnological model cultivations were investigated. Single-cell analysis was based on epifluorescence microscopy with spectral information. Object recognition and single-cell characterization in the microscopic data was done via algorithms programmed in MATLAB®. Use of spectroscopic information from fluorescence microscopes enables quantitative determination of cell size and quantification of different cellular ingredients such as pigments and lipids in parallel. Reliability of the technique was proven via different reference analyses. Lipid enrichment was done via stress induction with e.g., nitrogen starvation. The cells showed strong response in relation of the applied stress on e.g., cellular growth, photosynthetic apparatus and pigment composition. On the single-cellular level, heterogeneity of the culture in multiple dimensions and correlations between different cellular properties were quantified over time. The algal cells show an unexpected heterogeneity in all single-cell parameters and exhibit very dynamic correlations between cell size, chlorophyll content, and lipid content. Furthermore, the cells differentiated into two distinct sub-populations with clearly different TAG productivities. Understanding and optimization of these single-cell dynamics will contribute to gain higher lipid yields in future and opens new perspectives in biotechnology and systems biology. Based on the described cell-to-cell heterogeneity the question raises how the product quality and quantity is possibly negatively influenced.