Expanding the genetic tool box for Cupriavidus necator by a stabilized L-rhamnose inducible plasmid system

The Gram negative bacterium Cupriavidus necator is well known for the accumulation of poly(3-hydroxybutyrate) and its fast lithoautotrophic growth, leading in high cell densities. Although the host was engineered for the heterologous production of diverse chemicals and biopolymers in recent years, tool box of stabilized inducible expression systems is still limited. To avoid plasmid loss during fermentation processes and to allow expression of complex proteins, a tunable L-rhamnose inducible system was established and characterized using enhanced green fluorescent protein (eGFP). The construct was stabilized by a previously established partitioning system. An increase of fluorescence signal intensity in different media was shown with inducer concentrations up to 11mM L-rhamnose. The strongest effects were measured at quite low concentrations - high tunability was observed between 0 and 0.4-1mM (depending on the medium used). Expression is tightly regulated and could be increased over 140-fold in complex medium and approximately 60-fold in minimal medium due to induction with 11mM L-rhamnose. Varying induction times were characterized regarding growth behavior and expression pattern, taking into consideration problems that may arise during expression of toxic proteins. The novel plasmid expands the tool box for engineering the highly flexible production host C. necator.