1. College of Resource and EnvironmentCollege of ScienceState Key Laboratory of Agricultural MicrobiologyHuazhong Agricultural University Wuhan 430070 P. R. China
2. State Key Laboratory of Agricultural MicrobiologyCollege of Veterinary MedicineKey Laboratory of Preventive Veterinary Medicine in Hubei ProvinceThe Cooperative Innovation Center for Sustainable Pig ProductionHuazhong Agricultural University Wuhan 430070 P. R. China