A specific bacterium is capable of producing a highly pure form of cellulose, a structural polymer usually associated with plants. This microscopic organism weaves intricate fibers, creating a substance with properties that have captured the attention of scientists. This process provides a versatile material with a growing list of applications.
The Cellulose-Producing Bacterium
Acetobacter xylinum is a species of Gram-negative bacteria known for its ability to produce cellulose. This bacterium is aerobic, meaning it requires oxygen to live, and is commonly found in environments where sugars are present, such as on fruits and in fermented beverages. The cellulose it creates, often called bacterial cellulose, is chemically identical to the cellulose found in plants but possesses a different physical structure. Its fibers are finer, creating a material with higher purity, strength, and water-holding capacity.
This organism was long known as Acetobacter xylinum, but scientific classification has evolved. Following phylogenetic analysis, it has had several name changes, including Gluconacetobacter xylinus. Today, its officially recognized scientific name is Komagataeibacter xylinus, though the older name is still frequently used in commercial and historical contexts.
This reclassification distinguishes it from other acetic acid bacteria. While other bacteria can produce cellulose, K. xylinus is considered one of the most efficient and is the most studied for this purpose. The distinct properties of its cellulose make it a subject of intense research and development, setting it apart from its plant-based counterpart.
Mechanism of Bacterial Cellulose Synthesis
Komagataeibacter xylinus absorbs sugars, such as glucose, from its liquid growth medium to use as a carbon source. Inside the bacterial cell, a series of enzymatic reactions convert this sugar into precursor molecules. These precursors are then directed to pores located on the bacterium’s outer membrane.
From these pores, the bacterium extrudes linear chains of cellulose. Individual glucose units are linked together into long polymers, forming what are known as cellulose nanofibrils. These fibrils are incredibly fine, with diameters measuring only a few nanometers. This biological mechanism is a controlled form of natural 3D printing on a microscopic scale.
As bacteria in the colony perform this action simultaneously, the extruded nanofibrils intertwine and layer upon one another. This collective effort results in the formation of a dense, web-like matrix of interconnected fibers. This creates a strong, gelatinous mat, called a pellicle, that forms on the surface of the liquid medium where the bacteria are growing.
Culinary and Food Production Roles
The cellulose pellicle from Komagataeibacter xylinus is a component in several traditional foods and beverages. Its most widely recognized application is in the fermentation of kombucha, a fermented tea drink. Here, the pellicle is commonly known as a SCOBY, which stands for Symbiotic Culture Of Bacteria and Yeast. The SCOBY houses K. xylinus along with various yeast species that work together to ferment the sweetened tea, with the pellicle growing thicker with each batch.
Another culinary use is in the creation of nata de coco, a dessert originating from the Philippines. This food product consists of chewy, translucent cubes made of bacterial cellulose. To produce it, K. xylinus is cultured in coconut water, and the resulting thick pellicle is harvested, cleaned, and cut into cubes. A similar dessert, nata de piña, is made using pineapple juice instead of coconut water.
Beyond these well-known examples, the bacterium plays a role in the production of certain types of vinegar. As an acetic acid bacterium, K. xylinus can be part of the mother of vinegar, a biofilm that facilitates the conversion of ethanol into acetic acid. The cellulose it produces helps to structure this biofilm, keeping the bacteria at the surface of the liquid where they have access to oxygen.
Biomedical and Industrial Innovations
The properties of bacterial cellulose have led to its adoption in biomedical and industrial fields. Its high purity and biocompatibility make it suitable for medical applications. Advanced wound dressings are a prominent example, as the cellulose gel can maintain a moist environment for healing while protecting the wound from infection. It is also used as a temporary artificial skin for burn victims due to its high water content and soothing properties.
In tissue engineering, bacterial cellulose serves as a scaffold material. Its porous, three-dimensional structure can support cell growth, providing a framework for regenerating tissues like cartilage, bone, and blood vessels. It is also explored for use in new medical implants and devices because it is strong, flexible, and not typically rejected by the human body.
Beyond medicine, this biomaterial is used in various industries:
- A sustainable textile, often marketed as vegan leather, due to its durability and leather-like texture.
- High-performance diaphragms for headphones due to its unique acoustic properties.
- Specialized filtration membranes.
- A substrate for flexible electronic circuits.