2.2 Microorganism
G. oxydans NL71 was derived from ATCC621. The strain was preserved in sorbitol-agar medium containing 50 g/L sorbitol, 5 g/L yeast extract and 15 g/L agar, at 4 ℃. The inoculum was cultivated in a baffled Erlenmeyer flask at 30 ℃ for 24-36 h, with continual agitation at 220 rpm using a shaking table (New Brunswick Scientific). The nutrient medium was composed of 100 g/L sorbitol and 10 g/L yeast extract. The cultured cells were centrifuged at 6000 rpm and 4 ℃, for 5-10 min by freezing centrifuge (Avanti J-26 XP, Beckman Coulter). The centrifuged cells were washed 3 times in sterile saline and sterile water for reserve, respectively(Zhou et al., 2018).