Streptavidin is a protein obtained by the cultivation of the bacteria Streptomyces avidinii and Streptomyces lavendulae. It binds the vitamin biotin with an extremely high affinity. Due to its extraordinary binding properties, streptavidin is of central importance for a wide range of molecular techniques and is applied e.g. in the context of downstream processing of proteins, genome sequencing and molecular diagnostics. The interaction of biotin and streptavidin helps to circumvent radioactive labeling methods by the application of fluorescence markers associated to either one of the binding partners. However, substantial deficiencies in fermentative methods and downstream processing of streptavidin result in a high market price of the protein.

Current production processes lead to relatively low product concentrations. On the one hand, when cultivating inherently streptavidin-producing organisms fermentations are characterized by long cultivation periods due to their slow growth, caused among other reasons by a fungal-like morphology (see figure below). The limitation of heterologous streptavidin expression on the other hand results from toxic effects brought about by intracellular accumulation of the protein and resulting biotin deprivation. At the same time, the standard downstream processing procedure, namely affinity chromatography on iminobiotin columns, is based on an expensive purification material.

Hence, this PhD-project is aiming for the development of solutions for both of these problems in order to reduce product cost.

 
Spherical mycelium of Streptomyces avidinii grown in suspension culture, enlarged 100fold