Fluorescent reporter libraries as useful tools for optimizing microbial cell factories: a review of the current methods and applications

The use of genetically encoded fluorescent reporters allows speeding up the initial optimization
steps of microbial bioprocesses. These reporters can be used for determining
the expression level of a particular promoter, not only the synthesis of a specific protein
but also the content of intracellular metabolites. The level of protein/metabolite is thus
proportional to a fluorescence signal. By this way, mean expression profiles of protein/
metabolites can be determined non-invasively at a high-throughput rate, allowing the
rapid identification of the best producers. Actually, different kinds of reporter systems
are available, as well as specific cultivation devices allowing the on-line recording of the
fluorescent signal. Cell-to-cell variability is another important phenomenon that can be
integrated into the screening procedures for the selection of more efficient microbial cell
factories.