Bacterial Capsule

"Bacterial Capsule"

Many bacteria are sorruonded by a layer of gelatinous material that has been termed the capsule / slime layer or glycocalyx. Some bacteria do procude this prominent outer layer/ some do not they are usually composed of polysacchrides polypeptide or glycoprotein.

Functions

The capsule can perform many functions for bacterial cell.

• As capsule contain 99% water a thick capsule protects the cell from dehydration
• The capsule enhances the pathogenicity by protecting if from engulfment and digestion by phagocytes of the host.
• The glycocalyx helps the bacteria to adhere to surface. This property is helpful in development of disease.
• They serve reservoir of food
• Capsules block attachment of bacteriophage
• They promote the stability of bacterial suspension  by preventing the cells from setting out.

Bacterial Endospore : An Extremely Resistant Stage

Some genera of aerobic and anaerobic bacteria are characterized by producing intracellular thick walled, refractile , cryptobiolic inactive cell types.

Endospore formation and resistance :

The process of conversion of a negatative cell into spore when nutritional condition become favourable is called sporutation or sporogenesis.

The regetative cell under such conditions degenerates releasing an independent cell, the spore

It can revert to normal metabolically active vegetative cell only when the environmental conditions become favourable. This process is known as Germination.Complete transformation of a vegetative cell into a sporamgium and then into a spore requires 6 to 8 hours in most spore forming species.

The bacterial cell produces only one spore in the cytoplasm either at the pole ( polar spore ) near the pole ( sub polar spore ) or in the center ( central spore ).

The spore contains calcium and dipicolinic acid in large amount. The water molecules in spore are bound state. They can resist boiling , dessication , staining , disinfectants , radiations e.t.c. the working temperature for autoclave is 121C which is enough to kill all spores in 15 minutes spores can remain viable for years even 500 years

Medical significance of bacterial spores.

The majority of spore forming bacteria are relatively harmless , several bacterial pathogens are sporeformers. Infact some aspects of the disease they cause are related to the persistence and resistance of their spores.

When the spore of these species are embedded in a wound that conatins dead tissues they can germinate grow and release potent toxins.

Spore – Forming Species

• Bacillus. Anthracis ( Anthrax )
• Clostridium Tetani ( Tetanus )
• Clostridium Perfringens ( Gas gangrene )
• Clostridium Botulinum ( Botulism )

Differences between vegetative cell and spore

Vegetative cell	Endospore
norrefractile	High refractile
Usually stained by ordinary dyes	Not stained by ordinary dyes
Sensitive to various physical and chemical agents	Higly resistant
Killed at 60 C in 10 Minutes by moist heat	Killed at 121 C in 15 minutes by moist heat
Free Water 95-98 %	Bound water 5-10 %
Metabolic activation high	Metabolic activation low or practivally absent

Reproduction in Bacteria

Bacteria like all forms of life reproduce in order to propagate and maintain their kind sexes in bacteria are not differentiated, so sexual reproduction does not take place. Bacteria reproduce asexually by any one of the method.

1. Binary Fission
2. Budding
3. Fragmentation

Binary Fission :

Cell division takes place when the condition for growth are optimul and favourable. The most common mode of division in bacteria is binary fission.

A complex series of inter-related steps are involved in the process of binary fission.

1. Elongation of cell
2. Duplicastion of chromosome
3. distritbution Of chromosome after replication
4. formation of transevers septum
5. separation of daughter cells

Elongation of cell :

Just before the cell undergoes fission it elongates in size due to synthesis of new building materials like nuclear material , protein enzymes and cell wall building blocks

Duplication of chromosomes :

In bacteria cell division and DNA replication are closely Co,ordinated in order to ensure that each daughter cell gets an equal share of the chromosomes.

Distribution of chromosomes :

The nucleotide , during cell division attaches to central mesosomes. The mesosomes increase in size and structure during the process of DNA and make sure that the two daughter cells get a copy each of chromosome.

Formation of transverse septum :

The septum formation begins only after the DNA