design: Bacterial cultures were centrifuged at 6000 g for 20 min, and pellets were discarded. The supernatants were filtered using a 0.22 m pore filter. The supernatants were concentrated by tangential flow filtration system. The filtrate was pelleted by ultracentrifugation at 100,000g for 2h at 4. The final pellets were resuspended in PBS and stored at 80. Total RNA was isolated by phenol-chloroform extraction method with trizol reagent.