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Cellulose is a very significant member of the polysaccharide family because of its presence in plant and algal cell walls. Some species of the bacteria also produce cellulose, such as Acetobacter sp., Komagataeibacter sp., and Agrobacterium sp. The main difference between celluloses from plant and bacterial origins are the absence of hemicellulose and lignin in the bacterial type, thus avoiding the need for harsh pre-treatment procedures commonly used for cellulose purification among the plant systems [8, 9].

Table 3.1 Types, sources, monomers, and linkages found in common polysaccharides.

Type	Sources	Monomers	Linkage	References
Cellulose	Seaweed, bacteria	Glucose	β(1→4)	[8, 10]
Chitosan	Shrimps, crabs, fungi	N-acetyl glucosamine, glucosamine	β(1→4)	[13]
Alginate	Seaweed	β-D-mannuronate, α-L-guluronate	β(1→4)	[208]
Carrageenan	Seaweed	Galactose, 3,6-anhydrogalactose, ester bound sulfate	–	[208]
Agar	Seaweed	3,6-anhydro-α-lgalactopyranose, β-dgalactopyranose	–	[208]
Porphyran	Seaweed	β-D-galactose, α-Lgalactose, 3,6-anhydro- α-L-galactose		[40]
Fucoidan	Seaweed	Fucose	α(1→3) (backbone), α(1→3) α(1→4) (residues)	[208]
Ulvan	Seaweed	Rhamnose, glucuronic acid, fucose,	–	[208]
EPS*	Microalgae	Various	Various	[208]

*EPS: Exopolysaccharides.

Seaweeds can typically contain 2–13% (w/w) of crude cellulose, with brown algae leading the group [10]. In comparison, cotton is a well-known example of natural pure cellulose fiber with more than 90% (w/w) cellulose content [11] and widely used in the textile industry, while plant fibers can contain ~26–85% (w/w) cellulose [12]. For commercial purposes, cellulose obtained from bacterial fermentation is more appropriate due to the higher growth rate of bacteria and the possibility of genetic and/or media manipulation for enhancing the content.

Chemically, cellulose consists of glucose residues linked to β (1→4); it is a water-insoluble, linear molecule deprived of branching or coiling. Cellulose can be broke into its constituent glucose moieties by mineral acid treatment or enzymatic hydrolysis [2].