(A) Copy number of the sigB gene in L. monocytogenes EGD-e grown in BHI medium for 3 h, 4 h, 8 h and 16 h. Data shown here is representative of three independent biological replicates. (B) Immuno-blot analysis quantifying σB from L. monocytogenes EGD-e at different growth phases. Proteins were isolated from cultures of L. monocytogenes EGD-e grown for 3 h (lane 1), 4 h (lane 2), 8 h (lane 3) and 16 h (lane 4) in BHI at 37°C and σB was detected using rabbit polyclonal anti-serum produced against S. aureus COL σB. The L. monocytogenes ΔsigB deletion mutant (lane 5) was used as negative control and S. aureus COL (lane 6) was used as positive control for specific binding of the antibody. Molecular masses (in kilodaltons) of prestained SDS-PAGE standard marker (Bio-Rad) are indicated on the left and σB is marked on the right.