Lysozyme (0.2mg/ml; Sigma-Aldrich L7651) was added to the cell suspension by mixing with a metal spatula, and the suspension was warmed to 30°C for 10min. DNase (DN25; Sigma-Aldrich) was then added at 0.1mg/ml and MgCl2 added to 60mM to activate the enzyme. Cells were incubated for an additional 15 min at 30°C.