Re: What are the most commonly used microbial polysaccharides in industry?

There are many widely used polysaccharides.  Starches and pectins are 
important in the food industry.  Cellulose is important in the paper and 
pulp industry.  But I think that your question is directed towards 
polysaccharides that are used because their chemical and structural 
properties make them important hydrocolloids.  These extracts are used as 
food thickeners and stabilizers.  They can act as emulsifying agents in 
foods, cosmetics, and paints.  They can be used to help recover oil from 
wells.  There is quite an extensive list of uses for these hydrocolloids.

Carrageenan is a structural polysaccharide from red seaweed (Rhodophyceae).  
Chief sources are Chondrus crispus and Gigartina stellata harvested from 
the ocean.  Several different types exist based on sulfate concentration.  
Xantham gum is an extracellular polysaccharide from the bacterium 
Xanthomonas campestris.

Alginate and algin are gelling polysaccharides extracted from giant brown 
seaweed (giant kelp, Macrocystis pyrifera) or from horsetail kelp 
(Laminaria digitata) or from sugar kelp (Laminaria saccharina).  
Polysaccharides similar to alginate are secreted by Pseudomonas aeruginosa 
and Azotobacter vinelandii.  

Agar is a complex polysaccharide extracted from the agarocytes of red algae 
(Rhodophyceae).  Genera include Gelidium, Gracilaria, Acanthopeltis, 
Ceramium, and Pterocladia found in the Pacific and Indian Oceans and Japan 
Sea.  Agar can be separated into a neutral gelling fraction, agarose, and a 
sulfated non-gelling fraction, agaropectin.  Again, different classes of 
agar are determined by their sulfate content.

Locust bean gum is another extract useful in food and cosmetics 
manufacturing.  It is extracted from the ground kernel endosperms of tree 
pods of Ceratonia siliqua.  It is a complex mixture of proteins, 
carbohydrates, ash, fat, and fiber.  Guar gum is similar but is derived 
from Cyamopsis tetragonolobus endosperms.

A number of other microbially derived polysaccharides are in use for 
specific applications.  These include materials from the red alga 
Porphyridium and from cyanobacteria like Spirulina.