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 justifycommercial interest. The most extensively studied member of theAcetobacter species is A. xylinus, formerly known as A. xylinum.

SEM micrograph of the wet structure of microbial cellulose.

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 CelluloseSome advantages of microbial cellulose over plant cellulose include:Finer structureNo hemicellulose or lignin need to be removedLonger fiber length: much strongerCan be grown to virtually any shape

Disadvantages for Commercial UseSome issues that prevented larger scale commerciaization so far include:High price (about 100 x more than plant cellulose)

Because of high priced substrates: sugarsLow volumetric yields

Lack of large scale production capacityPotential Future Improvements

a b

Bacterial cellulose x 20000 (a) and plant cellulose x 200 (b).

Plant cellulose and bacterial cellulose have the same chemicalstructure, 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 celluloseand Young's modulus of biocellulose is almost equivalent to that ofaluminum. Therefore, biocellulose is expected to be a newbiodegradable 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 thecell walls. Celluloseis mostly prepared from wood pulp

Structural unit

Cellulose is a linear polymer of β-(1 4)-D-glucopyranose units in 4C1conformation. The fully equatorial conformation of β-linkedglucopyranose residues stabilizes the chair structure, minimizing itsflexibility (e.g. relative to the slightly more flexible α-linkedglucopyranose residues in amylose).

Cellulose

cellulose, since it is not bonded to other substances, is notchemically modified after isolation from wooda-cellulose

wood cellulose that is insoluble in strong NaOH (17.5%)b-cellulose

soluble in strong NaOH, but precipitates when neutralizedg-cellulose

material remaining soluble after neutralizationDirect Isolation Methods

nitric acid in ethanolacidified acetyl-acetone and dioxaneCl2 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, fructosehexokinase; 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 intoGluconacetobactor xylinum from the outside of the cell.

http://www.res.titech.ac.jp/~junkan/english/cellulose/index.html (14-3-2008)

Future aspectsPreservation of forest resources is essential to prevent global warming

because the increase in CO2 concentration can be stopped only by theabsorption of CO2 by plants and trees.

However, the use of trees for the production of paper and constructionmaterials has continuously depleated forest resources.

Bacterial cellulose is the only alternative for plant cellulose becausebacteria produce bacterial cellulose in a few days, while trees need morethan 30 years to realize full growth. In this respect, bacterial cellulose isthe key material for preventing global warming and preservation of thenature.