嫌気性細菌の機能を駆使したバイオマスの有効利用

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Anaerobic and cellulolytic bacteria such as Clostridium thermocellum, Clostridium josui and Clostridium paraputrificum were isolated from compost and soil and Ruminococcus albus was obtained from cow rumen. From these anaerobic bacteria, many genes encoding novel cellulases and xylanases were isolated, characterized, and expressed in Escherichia coli. From the characteristics of the genes and enzymes, we confirmed that cellulolytic anaerobes produce enzyme complex, I.e. cellulosome, which is known to consist of cohesin domains on the cellulase integrating protein (Cip or core protein) and dockerin domains on enzymes. Several dockerin and cohesin polypeptides were independently produced by E. coli and their cohesin-dockerin binding properties were determined with BIAcore by measuring surface plasmon resonance. Three pairs of cohesin-dockerin with different mutual binding specificities were selected. Two of the three genes encoding the respective cohesin were connected to one gene and expressed in E. coli to produce a chimera core protein, on which two dehydrogenases with the respective dockerin were arranged to catalyze CO_2 reduction to formic acid. This technique could contribute to the reduction of greenhouse gas. An endoglucanase from R. albus and a xylanase from Clostridium stercorarium were expressed in tobacco and rice plants. From both transgenic plants, the respective enzyme activity was detected in leaves, stems, and rice seeds, indicating that the CaMV35S promoter allows the expression of the proteins in any part of the plant. The digestibility of the transgenic rice plant in goat rumen was slightly accelerated. C. paraputrificum from seashore soil solubilized shrimp shells and chitin to generate hydrogen gas. The hydrogen productivity (1.7 mol H_2/mol glucose) of the organism was improved up to 1.8-fold by enforcing the hydrogenase gene using a modified vector of Clostridium perfringens. We also found that hydrogen-producing microflora isolated from soil, garbage, and dried pelletted garbage, known as refuse-derived fuel (RDF), are effective in converting biomass waste to hydrogen gas. All these results show that unutilized or waste biomass can be converted to valuable materials by using microbial functions.
社団法人日本生物工学会の論文
2005-01-25

嫌気性細菌の機能を駆使したバイオマスの有効利用

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