Introduction

The gum or slime producing properties of microorganisms have been known for centuries. These exocellular polymers, a common feature of the microorganisms, are found in the form of a discrete capsule surrounding the microbial cell or secreted as an amorphous mass into the surrounding medium. These microbial polysaccharides or biopolymers have unique and novel properties which are finding a wide range of applications in the food, pharmaceutical, and other industries and are rapidly emerging as a new and important source of commercial hydrocolloids. Microorganisms produce three distinct types of polysaccharides: extracellular polysaccharides, structural polysaccharides, and intracellular storage polysaccharides. The extracellular polysaccharides in many cases are water-soluble polymers having unique and useful hydrocolloid properties and can be classified into two types: capsules that are part of the cell wall and slimes that accumulate outside of the cell wall and diffuse continuously into the culture medium. The polysaccharides produced by the slime formers are usually highly viscous polymers with interesting functional properties.