Table 3.

Relevant challenges encountered during plate screen development and proposed potential solutions

Common challenges in plate screen	96-well plate	Lab-scale bioreactor	Details	Potential solutions
Population size (total number of cells)	107 cells	1012 cells	Tank processes allow for an extended growth phase due to controlled environment	Match number of generations by adjusting the volume or density of the seed culture
pH control	Uncontrolled	Controlled base and/or acid addition	One-sided pH control is required for most fermentation process	Addition of buffering solutions, reduction of substrate/product concentration or biomass
Aeration	Uncontrolled	DO control through air/oxygen spargers and impeller speed adjustment	Oxygen transfer in plates is typically lower than in tanks	Characterize potential impact of oxygen limitation on strain performance. Reduction of oxygen uptake rate by adjustment of substrate concentration and cell density
Substrate load	Low	High	Strains may be sensitive to excess carbon and produce unwanted byproducts leading to changes in pH	Employ a glucose-limited main plate fermentation, either as batch or using glucose release system
Biomass concentration	Low	High	Oxygen transfer and process control capabilities in plates are limited	Include a scale-down factor in plate media composition
Carbon supply	Uncontrolled	Controlled	Bioreactors are equipped with controlled feeding mechanisms	Employ glucose release system and modify enzyme and substrate concentration to optimize release rate to generate fed-batch regimen
Evaporation	High risk	Low risk	Evaporation in plates can lead to significant differences in a culture volume	Determine the impact of evaporation on well-to-well CV at different time points. Minimize incubation time