5.5. Expression of heterologous proteins in Paenibacillus larvae
The understanding of phenotypic differences within the species P. larvae (Genersch and Otten, 2003; Genersch et al., 2005; Neuendorf et al., 2004; Rauch et al., 2009) and the role of genotype-specific putative virulence factors (Fünfhaus et al., 2009; Fünfhaus and Genersch, 2012) have been hampered by the lack of molecular tools allowing genetic manipulation of this pathogen.
To functionally analyse putative virulence factors during bacterial pathogenesis, the corresponding genes need to be disrupted, manipulated, or labelled for specific visualisation. Likewise, the expression of homologous or heterologous proteins in P. larvae would be a valuable tool to further study the molecular pathogenesis of P. larvae infections. Recently, the first protocol for the expression of a foreign protein (green fluorescent protein, GFP) in P. larvae has been described (Poppinga and Genersch, 2012). Since GFP expression is one of the most successful molecular tools to specifically label proteins and to visualize them under native conditions (Tsien, 1998), this can be considered a breakthrough in AFB research. Constitutive expression of GFP in P. larvae will help to visualize and quantify bacterial cells in larval experiments. Additionally, GFP-fused virulence factors that are expressed during infection can be detected and visualised in and/or outside the bacterial cell.