Development of corn silk as a biocarrier for Zymomonas mobilis biofilms in ethanol production from rice straw

Z. mobilis cell immobilization has been proposed as an effective means of improving ethanol production. In this work, polystyrene and corn silk were used as biofilm developmental matrices for Z. mobilis ethanol production with rice straw hydrolysate as a substrate. Rice straw was hydrolyzed by dilute sulfuric acid (H2SO4) and enzymatic hydrolysis. The final hydrolysate contained furfural (271.95 +/- 76.30 ppm), 5-hydroxymethyl furfural (0.07 +/- 0.00 ppm), vanillin (1.81 +/- 0.00 ppm), syringaldehyde (5.07 +/- 0.83 ppm), 4-hydroxybenzaldehyde (4-HB) (2.39 +/- 1.20 ppm) and acetic acid (0.26 +/- 0.08 %). Bacterial attachment or biofilm formation of Z. mobilis strain TISTR 551 on polystyrene and delignified corn silk carrier provided significant ethanol yields. Results showed up to 0.40 +/- 0.15 g ethanol produced/g glucose consumed when Z. mobilis was immobilized on a polystyrene carrier and 0.51 +/- 0.13 g ethanol produced/g glucose consumed when immobilized on delignified corn silk carrier under batch fermentation by Z. mobilis TISTR 551 biofilm. The higher ethanol yield from immobilized, rather than free living, Z. mobilis could possibly be explained by a higher cell density, better control of anaerobic conditions and higher toxic tolerance of Z. mobilis biofilms over free cells.