Cellulose is the main component of plant cell wall. Some bacteria produce cellulose (celled biocellulose or bacterial cellulose). Plant cellulose and bacterial cellulose have the same chemical structure, but different physical and chemical properties. Figure 1 shows an electron microscopic image of biocellulose and plant cellulose. Bacterial cellulose is produced by an acetic acid-producing bacterium, Acetobacter xylinum. The diameter of biocellulose is about 1/100 of that of plant cellulose and Young's modulus of biocellulose is almost equivalent to that of aluminum. Therefore, biocellulose is expected to be a new biodegradable biopolymer.
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| Fig. 1. Bacterial cellulose and plant cellulose. | |
In the mass production of biocellulose, conventionally an agitated reactor is used. In our laboratory, we applied an airlift reactor to produce bacterial cellulose because this reactor is simple in structure, its energy requirement is low, its shear stress to cells is small, and the possibility of contamination is low. Figure 2 shows a 50-liter airlift reactor. In the airlift reactor, the productivity of bacterial cellulose was equivalent to that in conventional agitated reactors and its energy requirement was one-tenth of that in agitated reactors. The bacterial cellulose produced in an airlift reactor formed a unique pellet-type cellulose.
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| Fig. 2. 50 liter airlift reactor. |
All genes responsible for biocellulose synthesis have been cloned and their characterization is under way. Figure 3 shows the predicted steps of bacterial cellulose synthesis when glucose is used as the carbon source. The analysis of genes will lead to higher productivity of bacterial cellulose and to new biocellulose with different properties.
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| Fig. 3. The predicted pathway of cellulose synthesis and secretion when glucose is taken into Gluconacetobactor xylinum from the outside of the cell. |
Preservation of forest resources is essential to prevent global warming because the increase in CO2 concentration can be stopped only by the absorption of CO2 by plants and trees. However, the use of trees for the production of paper and construction materials has continuously depleated forest resources. Bacterial cellulose is the only alternative for plant cellulose because bacteria produce bacterial cellulose in a few days, while trees need more than 30 years to realize full growth. In this respect, bacterial cellulose is the key material for preventing global warming and preservation of the nature.