Microbial cellulose

Microbial cellulose, sometimes called bacterial cellulose, is a form of cellulose that is produced by bacteria. It is widely used in the traditional Filipino dessert Nata de coco. Microbial cellulose was first confirmed as cellulose in 1886.^[1]

Production

Bacteria from the genera Aerobacter, Acetobacter, Achromobacter, Agrobacterium, Alacaligenes, Azotobacter, Pseudomonas, Rhizobium, and Sarcina synthesize cellulose.^[2] However, only the Gluconacetobacter produce enough cellulose to justify commercial interest. The most extensively studied species is Gluconacetobacter xylinus, formerly known as Acetobacter xylinum and since reclassified into a different genus.^[2]

G. xylinus extrudes glycan chains from pores into the growth medium. These aggregate into microfibrils, which bundle to form microbial cellulose ribbons. Various kinds of sugars are used as substrate. Production occurs mostly at the interface of liquid and air.

Differences with plant cellulose

Some advantages of microbial cellulose over plant cellulose include:

• Finer and more intricate structure
• No hemicellulose or lignin to be removed
• Longer fiber length: much stronger and wider
• Can be grown to virtually any shape and thickness
• Can be produced on a variety of substrates
• The formula of the media used and the strain of Acetobacter xylinum will determine the quality of the pellicle
• More absorbent per unit volume

Disadvantages for commercial use

Some issues that have prevented large-scale commercialization so far include:

• High price (about 50 x more than plant cellulose)
  • Because of high-price substrates: sugars
  • Low volumetric yields
• Lack of large-scale production capacity
• Timely expansion and maintenance of the cell culture for production

A wet microbial cellulose pellicle being removed from a culture.

Functions

One continuing mystery surrounding microbial cellulose is its exact biological function. A. xylinus recently renamed as "Gluconacetobacter xylinus" is a successful and prevalent bacterium in nature, frequently finding a home in rotting fruits and sweetened liquids. The most familiar form of microbial cellulose is that of a pellicle on the top of a static cultured growth media. It has, thus, been hypothesized that cellulose acts as a floatation device, bringing the bacteria to the oxygen-rich air-media interface. This hypothesis has largely been discredited by experiments conducted on submerged oxygen-permeable silicone tubes that show that cellulose grows well submerged if enough oxygen is present.^[3] Others suspect that cellulose is used to immobilize the bacteria in an attempt to keep it near the food source, or as a form of protection against ultraviolet light.^[4]

Uses

Medical

Microbial cellulose is biocompatible and non-toxic, making it a good candidate material for medical applications.^[5] So far it has found a commercial role in some wound dressings. There is on-going research to evaluate a possible role for bacterial cellulose in the following applications:

• Scaffolds for tissue engineering
• Synthetic dura mater^[6]
• Bladder neck suspension
• Soft tissue replacement
• Artificial blood vessels

Non medical

• Matrix for electronic paper
• High-strength paper
• Diet foods
• Desserts: nata de coco
• Substrates for OLEDs
• Sony has use microbial cellulose as an acoustic membrane in high-end earphones^[7]
• It has a proposed use as a gloss surface finish in magazines^[8]

References