1b). Ethanol was the primary fermentation product; and most of it was produced during the first day and the yield increased continuously. The content of acetic acid increased significantly, especially during the first 3 days. Like ethanol, butyric acid was mainly
produced during the first day and thereafter maintained a constant level. Cellobiose was detected on the third day, and with a peak value of 0.02 g L−1 on the fourth day. Glucose was only detected on the second day, with a concentration of 0.02 g L−1. see more The low concentration of the cellobiose and glucose indicated their immediate consumption. A minor proportion of butanol was detected on the 10th day, with a concentration of 0.016 g L−1. Normally, butanol is produced by mesophilic anaerobic bacteria such as Clostridium acetobutylicum; however, the thermophilic bacterial mixtures (60 °C) studied here also showed butanol production, indicating the
presence of thermophilic butanol-producing species in the community. However, other fermentation products still remained to be determined. Note that FP degradation was not a secondary consequence of using l-cysteine and bicarbonate as primary carbon source. This was confirmed using a medium with FP as the sole carbon source (without l-cysteine and bicarbonate); the degradation of FP was not changed except SB431542 that the decomposing rate was slower. The enzyme activity of the fermentation supernatant was compared with that of C. thermocellum LQR1. The FPase and CMCase activities of the community were two times higher than that of C. thermocellum LQR1 and beta-xylosidase of the community was much more active. The activities of xylanase, beta-glucosidase and pNPCase RANTES of C. thermocellum LQR1 were also higher (Table 1). To identify the community members, a 16S rRNA gene library of the cellulolytic consortium was constructed. Diversity levels were determined with a cutoff value of 97% sequence similarity. A total of 16 OTUs were represented
in the clone library after 50 clones were surveyed. Rarefaction analysis of the 16S rRNA clone library is shown in Fig. 2. The most abundant OTUs accounted for 42% and 18% of the clone library, and shared similarity with the type strain C. thermocellum ATCC 27405, which is known for its high cellulolytic ability due to cellulosome formation. Although the 16S rRNA gene similarities of these closes were around 87–89%, we believe that they were mainly responsible for cellulose degradation. In other studies, Clostridium straminisolvens-like sequences accounted for a large portion of cellulolytic enrichments (Izquierdo et al., 2010). In our results, one OTU accounted for only 2% of the clone library and was most similar to C. straminisolvens. However, in contrast to other cellulolytic enrichments, all sequences from the OTUs represented novel species.