Disruption of bacterial cells by sonication and bead beating.

Bacterial cultures were sonicated 18 times on ice for 2 s × 50 at 300 W. For the bead beating disruption protocol, 1 ml bacterial culture was transferred to a 2-ml screw-cap tube containing 1 g of 0.1-mm glass beads (Sigma, St. Louis, MO, USA). The mixture was subjected to 15 bursts (1 min each), followed by a cooling period on ice (4 min) with the Mini-BeadBeater (BioSpec Products, Inc.).