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Decomposition of rice chaff using a cocultivation system of Thermobifida fusca and Ureibacillus thermosphaericus
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1  Graduate School of Science and Engineering, Soka University


Lignocellulosic biomass comprises cellulose, hemicellulose, and lignin and is a potential source of fuels and chemicals. Although this complex biomass is known to be a persistent compound, it can be cooperatively decomposed by a microbial consortium in nature. The cellulolytic and hemicellulolytic bacterium Thermobifida fusca and the lignolytic bacterium Ureibacillus thermosphaericus are moderately thermophilic and have similar optimal growth temperatures and pH values. In this study, the coculture of T. fusca and U. thermosphaericuswere used for the biodegradation of rice chaff at 50ºC.

The bacterial strains were incubated in the modified Brock’s basal salts medium (pH 8.0) supplemented with yeast extract (0.5%) and rice chaff (0.5%) at 50ºC for 7 days. The concentration of reducing sugars and the enzymatic activities of laccase, lignin peroxidase, cellulase, and xylanase in the supernatant of the culture medium were measured every day. The viable cells in each culture were counted as colony forming units.

The cell density of the coculture reached 4.6 × 108 CFU/mL on the second day and maintained a concentration of >3.3 × 107 CFU/mL throughout the study period. The concentrations of the reducing sugars in the cultures of T. fusca and U. thermosphaericus as well as in the mixed culture of the two strains after 7 days of incubation were 0.047 mg/mL, 0.040 mg/mL, and 0.195 mg/mL, respectively, indicating that the decomposition of rice chaff was enhanced in the coculture. Based on the results, it is thought that the lignin surrounding the cellulose was decomposed by laccase and lignin peroxidase secreted from U. thermosphaericus resulting that cellulose and hemicellulose in the rice chaff were easily decomposed by the enzymes from T. fusca.

Keywords: Lignocellulose; cocultivation; moderately thermophilic bacteria; laccase; lignin peroxidase; cellulase; xylanase