Introductory Microbiology

Cysts and Archaebacteria

• Cysts are dormant, thick walled, descication resistant forms that develops by differentiation of a vegetative cell and which can later germinate under suitable conditions. In some ways cysts resembles endospores; however, their structure and chemical composition are different and they do not have the high heat resistance of endospores. The classic example of a cyst is the structurally complex type produced by the genus Azotobacter.

Archaebacteria
• The archaebacteria are unusual organisms and the group is known to include 3 different kinds of bacteria, the methanogenes, the extreme halophiles and the thermoacidophiles.

Sl.No.	Cellular organization	Archae bacteria	Eubacteria
1	Cell wall	Variety of types not containing muramic acid	Variety with one type, contain muramic acid
2	Membrane lipids	Ether linked, branched aliphatic chains	Ester linked, straight aliphatic chains
3	Thymine in common arm of t-RNA	Absent	present in t-RNA's of most sps.
4	Sensitivity to chloramphenicol	Insensitive	sensitive
5	Structure of RNA polymerase core	Ten subunits	four subunits

Table: The major differences between archaebacteria and eubacteria