Figure 1

Screening for natural bacterial consortia with high cellulosic ethanol production and identification of P. taiwanensis . (A) Screening of consortia with cellulose degradation and ethanol production capabilities. In total, 16 consortia were collected from the locations listed in Additional file 1: Table S1, and their cellulose degradation and ethanol production performance was determined by culturing with 7 g/L α-cellulose for 6 days at 55°C. The error bars represent the SD (n = 3). (B) Community structure differences between HL and HP as determined using PCR-DGGE. Total DNA was extracted from fermentation cultures at the point when ethanol reached its highest titer, and partial 16S rDNA was then used for DGGE analysis. Left arrows indicate the strongest bands that were unique to the HP consortium; the corresponding strains are represented as follows: C.tp (Clostridium thermopalmarium), C.sp (Clostridium sporogenes), C.ts (Clostridium thermosuccinogenes), A.ce (Acetivibrio cellulolyticus), C.st (Clostridium stercorarium), T.ts (Thermoanaerobacterium thermosaccharolyticum), and P.tw (Pseudoxanthomonas taiwanensis). (C) The seven strains in B were cultured, and each was added to the HL consortium at a biomass ratio of 8.5:1 HL:strain. The co-fermentations were performed at 55°C for 7 days. The maximal ethanol titers are shown. The strain abbreviations under each column represent the co-fermentation of HL with the specified strains. HL represents fermentation by consortium HL without any added strains. The error bars represent the SD (n = 3). (D) P. taiwanensis boosts ethanol production by consortium HL in a dose-dependent manner. Co-fermentations were conducted with different proportions of P. taiwanensis and with α-cellulose as a carbon source at 55°C for 7 days with HL and HP as controls. The ratio in the legend represents the biomass proportion of the consortium and the single strains. The error bars represent the SD (n = 3).