Index >>Bacterial Fungal Cells>>Capsules and Slimes

Capsules and Slimes  -

Many procaryotic organisms synthesise loose amorphous organic exopolymers which are deposited outside the cell wall called the capsules or the slime.

The term capsule refers to the layer tightly attached to the cell wall while the slime layer is the loose structure often diffuses into the growth medium.

These structures are not essential for the growth and survival of the bacterial cells but their presence confers certain advantages to the bacterial cells posses these structures,

In fact many bacteria do not produce neither capsule nor a slime and those which can produce can lose the ability to synthesize the components without any ill effects.

In some they are homopolymers of either amino acids or sugars while in others they are heteropolysaccharides which may be substituted.

In B. anthracis the capsule consists of a polymer of only D-glutamic acid while in some other bacilli, it may be a polymer of both D-and L-glutamic acids.

In acetic acid bacteria, the capsule consists of cellulose which contains glucose as the basic unit.

In Leuconostoc, the capsule is a homopolymer consisting of either only fructose (Levan) or glucose (Dextran).

Some Gram negative bacteria may not produce a capsule yet, may have smooth colonies.

This is because of the presence of an outer membrane in these organisms.

The capsular substances have immunological specificity and this has permitted distinction between closely related bacteria which cannot be otherwise distinguished from one another.

Even within a species immunological subspecies or types have been recognized based on the capsular antigens and these differences have been used in typing many

It is still not known as to why in some bacteria the exopolymers are in the form of capsules while in others they are in the form of slime.

Mutation of capsular to slime forming bacteria has been known. Although major chemical differences between the capsule and the slime polymers from wild type and slime forming

Klebsiella are not detected, some minor differences do exist suggesting that the structural integrity of the capsule and slime are determined by the presence of distinct components.