Process dynamics analysis
Sampling a fermenter to measure biomass and product-titer, is like judging expert-skills on country-level. The summed behaviour of millions of cells does not tell you what is really going on at single-cell level. But this is key to understand your cubic-meter process:
Do all cells produce at same level, or are there distinct sub-populations of highly productive and less productive cells? Are there factors impacting relative size of these sub-populations over time? Do the sub-populations change when switching to another feed-solution? Do these sub-populations arise or change when switching to another substrate-charge? ... Single-cell analysis might tell you!
To illustrate the situation, have a look at the FACS-plots below: Both represent the same strain, but cultivation-conditions were slightly different between left and right scenario. It is clearly visible, that in the right-handed plot, a sub-population arises, which represents less-productive cells. In fact, overall titer and yield from the cultivation represented by the right-handed plot were significantly lower compared to the left-handed scenario.
FACS-plots, representing cells of an industrial production strain. The sensor-mediated fluoresence emission (indicating productivity) at the Y-axis is plotted against the forward scatter (a parameter for cell-size) at the X-axis. Each dot represents one single cell. The closer a dot is located to the top of the Y-axis, the more productive a cell is.