New Technology Makes Bioethanol With Only Cellulose, Microorganisms

Aug 12, 2008 20:43 Yousuke Ogasawara, Nikkei Electronics

Gekkeikan Sake Co Ltd developed a technology to produce bioethanol from inedible plants using only microorganisms. This was realized by the company's new technology to produce a large quantity of cellulolytic enzymes through solid culture of koji mold (aspergilli).

According to the company, it implanted genes that produce cellulose-degrading enzyme into koji mold, and at the same time discovered a base sequence called "promoter," which largely contributes to the production of the enzyme, on the chromosomes. Gekkeikan calls the koji mold with this property the "super koji mold."

This super koji mold breaks down solid cellulose in chaff and rice straws into glucose, which is required for alcohol fermentation. Existing methods require chemicals, such as sulfuric acid or processing using pressurized high-temperature water.

For production of bioethanol from inedible plants, cellulose has to be broken down into glucose as the first step. In existing methods, for breaking down of cellulose into glucose, chemicals such as sulfuric acid, supercritical water or subcritical water (both in high temperature and pressure) had to be used. This is because cellulose is chemically stable and has a rigid structure.

With these methods, a large amount of water is needed to liquefy the raw materials and substantial energy was required for distillation after fermentation, according to the company.

In Japanese sake brewing, koji mold breeds on rice in solid state and produces an enzyme that breaks down rice starch into glucose (liquefying, saccharization). The glucose is fermented by the yeast, producing alcohol.

Gekkeikan was inspired by this sake brewing process to develop the koji mold that breeds on solid state materials and dissolves cellulose into glucose. This method does not require a large amount of water and at the same time reduces the energy consumed for distillation after fermentation.

The company developed the "super yeast," which dissolves water-soluble cellulose (cello-oligosaccharide) into glucose for alcohol fermentation, in March 2008 (See related article). Previously, pretreatment by subcritical water was necessary for dissolving solid cellulose into water-soluble cellulose, even when the super mold was used.

If the super koji mold and the super yeast are used in combination, the super koji mold roughly breaks down cellulose into water-soluble cellulose, then the super yeast ferments it into alcohol.

Gekkeikan will work on the development of a super koji mold capable of producing larger amounts of the cellulose-dissolving enzyme. It also plans to promote research for enhancing safety, including the possibility of incorporating a gene derived from koji mold into a super koji mold for the production of the cellulose-dissolving enzyme, according to the company.

The research is being conducted as part of NEDO's (the New Energy and Industrial Technology Development Organization) "High-Efficiency Biomass Energy Conversion Technology Development" project in collaboration with Kobe University and Osaka University.

Gekkeikan and its partners will disclose the research results at the 2008 Convention organized by the Society for Biotechnology, Japan. The convention takes place at Tohoku Gakuin University in Sendai, Miyagi, August 27 to 29, 2008. The presentation will be made on August 28.

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