Bacteria from the species of Aerobacter, Acetobacter, Achromobacter, Agrobacterium, Alacaligenes, Azotobacter, Pseudomonas, Rhizobium and Sarcina synthesize cellulose. Only the Acetobacter species produce enough cellulose to justify commercial interest. The most extensively studied member of the Acetobacter species is A. xylinus, formerly known as A. xylinum. SEM micrograph of the wet structure of microbial cellulose.

Bacterial cellulose x 20000 (a) and plant cellulose x 200 (b). Acetobacter are of particular importance commercially, because: - they are used in the production of vinegar (intentionally converting the ethanol in the wine to acetic acid) - they can destroy wine which it infects by producing excessive amounts of acetic acid or ethyl acetate - they are used to intentionally acidify beer during long maturation periods Advantages Over Plant Cellulose Some advantages of microbial cellulose over plant cellulose include: Finer structure No hemicellulose or lignin need to be removed Longer fiber length: much stronger Can be grown to virtually any shape Disadvantages for Commercial Use Some issues that prevented larger scale commerciaization so far include: High price (about 100 x more than plant cellulose) Because of high priced substrates: sugars Low volumetric yields Lack of large scale production capacity Potential Future Improvements a b Bacterial cellulose x 20000 (a) and plant cellulose x 200 (b). Plant cellulose and bacterial cellulose have the same chemical structure, but different physical and chemical properties. 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.

Cellulose is found in plants as microfibrils (2-20 nm diameter and 100 - 40 000 nm long). These form the structurally strong framework in the cell walls. Celluloseis mostly prepared from wood pulp Structural unit Cellulose is a linear polymer of β-(1 4)-D-glucopyranose units in 4C1 conformation. The fully equatorial conformation of β-linked glucopyranose residues stabilizes the chair structure, minimizing its flexibility (e.g. relative to the slightly more flexible α-linked glucopyranose residues in amylose). Cellulose cellulose, since it is not bonded to other substances, is not chemically modified after isolation from wood a-cellulose wood cellulose that is insoluble in strong NaOH (17.5%) b-cellulose soluble in strong NaOH, but precipitates when neutralized g-cellulose material remaining soluble after neutralization Direct Isolation Methods nitric acid in ethanol acidified acetyl-acetone and dioxane Cl2 and NO2 in DMSO or SO2 in DMSO

Cellulose Biosynthetic Pathway in Acetobacter xylinum Glc, glucose; G6P, glucose-6-phosphate; G1P, glucose-1-phosphate; PGA,phosphogluconic acid; Frc, fructose; F1P, fructose-1-phosphate; FDP, fructose- 1,6- phosglucomutase; UGP, UDP-glucose pyrophosphorylase; PGH, phosphoglucomutase; UGP, UDP-glucose pyrophorylase; G6PD, glucose-6- phosphate dehy-drogenase; PGI, phosphoglucose isomerase; FHK, fructose hexokinase; 1 PFk,fructose-1-phosphate kinase; FBP, fructose bis-phosphatase; PTS, phosphotransferase system; EMP, Embden-Myerhoff pathway. The predicted pathway of cellulose synthesis and secretion when glucose is taken into Gluconacetobactor xylinum from the outside of the cell. http://www.res.titech.ac.jp/~junkan/english/cellulose/index.html (14-3-2008)

Future aspects 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.