Microbial analysis
We collected Yandou and other soybean samples from one
household located in the suburb of the city of Xuzhou, Jiangsu
province. Each time, 10 g of sample was transferred into 30 ml
sterile LB broth, shaken vigorously, and held in boiling water
(100 C) for 20 min to kill all vegetative microbial cells. After cooling
down to room temperature, an aliquot of the supernatant was
serially diluted and plated on L-agar plates. Colony morphology
was recorded after incubation at 30 C for 24 h, and Gram-staining
was performed to help identify individual colonies. Controls
without boiling treatment were also included for each sample.