In industrial fermentation processes, product formation is always accompanied by biomass production. Since biomass formation, basically, goes at the expense of product formation, it would be beneficial to decouple growth from product formation in non-biomass driven applications. This project aims to investigate zero growth product formation with a genomics-based approach. In most industrial fermentations, the microorganisms will be present in this physiological state for the majority of the process
This project aims to investigate zero growth physiology in four different biological systems, baker’s yeast – Saccharomyces cerevisiae –, filamentous fungi (Aspergillus niger), the lactic acid bacterium, Lactobacillus plantarum and the solvent-tolerant biocatalyst, Pseudomonas putida. This is done by studying the gradual changes that occur at the transcriptome and metabolome levels when the microorganisms go from a growing to a non-growing state. This transition is realized by retentostat cultivation, i.e. a cell-recycling fermentor where substrate is fed at a constant rate while cells are retained in the fermentor by means of an internal filtration device. In such a fermentation system, the biomass concentration, ultimately, reaches a steady-state where all substrate provided is used for maintenance purposes. Initial transcriptome analysis of S. cerevisiae and L. plantarum shows differential expression of several hundreds of genes under these “Zero Growth” conditions. Currently, the metabolite profiles under these conditions are being investigated. The study will provide a scientific basis for the rational improvement of product formation by this micro-organism at zero growth rate (i.e. without formation of excess biomass).