Proteomic characterization of transient expression and secretion of a stress-related metalloprotease in high cell density culture of Bacillus megaterium

Intracellular and extracellular proteome analysis was carried out by combined two-dimensional gel electrophoresis and mass spectrometric analysis (2DE/MS) for high cell density fed-batch culture of recombinant Bacillus megaterium strains. In the early feeding phase with a constant growth rate of 0.12 h−1 under glucose limitation, high expression and secretion of a metalloprotease (referred as Bmg1465) was detected. The transient appearance of this metalloprotease was found both as cell-associated and as secreted into the culture medium. Searching homologous proteins for functional assignment led to an unambiguous identification of Bmg1465 as a zinc-binding metalloprotease of the type immune inhibitor A (InhA). Metalloproteases of this type are currently considered as typical virulence factors associated with pathogenic Bacillus species. The result raises questions concerning the intrinsic function(s) of Bmg1465 in B. megaterium, which has the GRAS status, with respect to its stress response in high cell density culture.