Cellulose degradation by co-cultivation of Bacillus licheniformis and Clostridium thermocellum

Abstract:

[Objective] To explore synergy mechanism of cellulose biodegradation and relationships among the bacterial consortium, we took an approach of artificial constructing composite consortia. [Methods] Some strains were isolated from a microbial community which could ferment lignocellulose to produce biogas at high temperature. One of strains was identified as Bacillus licheniformis by sequencing nearly complete 16S rRNA gene. The strains’ combination, which consisted of the Bacillus licheniformis and Clostridium thermocellum strain CTL-6, had strong filter paper cellulose degradation ability. [Results] Throughout the 9-day co-cultivation, the cumulative degradation amount of filter paper was 484.6 mg and relative degradation ratio was as high as 93.2%. Overall, the variation of pH decreased firstly and then gradually increased. The initial pH of the culture solution was 7.00. The pH dropped to the lowest value (about 6.57) in 3 d. At the end of the culture period (9 days), the pH was 7.73. The combination could produce cellulase and hemicellulase, and two kinds of enzyme activity all represented the rising trend. The maximum of cellulase activity and hemicellulase activity were 0.32 and 0.57 U/mL, respectively, on the day 9. Lactic acid, formic acid, acetic acid, propionic acid and butyric acid were detected by HPLC during the co-culture. Among the five organic acids, the propionic acid and butyric acid had higher metabolism yield and the maximum concentrations were 1 068.8 and 1 477.3 mg/L, respectively. In addition to propionic acid, the concentration change trends of other 4 organic acids had no significant correlation with the change of the filter paper degradation. The total concentration variation of the five organic acids was in accordance with the variation of pH. This result indicated that it probably existed some not-detected acidic substances, the concentration variation of which played a decisive role in the pH variation of the co-culture system. [Conclusion] Bacillus licheniformis could effectively promote the cellulolytic activity of Clostridium thermocellum CTL-6, and the strains’ combination could also be used to artificially construct composite microbial which was able to convert cellulose to produce methane.

Key words:Bacillus licheniformis, Clostridium thermocellum, Cellulose biodegradation, Synergism, Co-culture