Main groups of microorganisms are
a. PRIONS
They are small protenaceous infectious particles which don't have nucleic acids, discovered in sheep. It exist in two configuration ie
Prp and prp-c infectious agents. The first one is infectious found in infected organisms and the second one is non disease causing found in brain of all adult mammals. Prp- sc prion protein discovered in sheep.
b. VIROIDS
They are subviral pathogenic particles consisting of short stranded of naked RNA. They have no protective protein coat( capsid) around nucleic acids, so don't have any definite shape. Their RNA strand has 300- 400 nucleotide internally paired, RNA strand remain in circular configuration. It has no a codon that codes for polypeptides for protein coat. Ex. Plant disease ( Chrysanthemum stunts) .
c.
VIRUSES They are submicroscopic obligates, intracellular parasites ie they essentially required a living host cell in order to multiply. A simple virus is called virion, nucleic acids is the genetic material having protein coat. It contains a single type of nucleic acids ie either DNA OR RNA.
d. MYCOPLASMA
They are prokaryotes with out cell wall. Hence they are pleomorphic. They are also smallest cells. They are cultivated using organic media sterols. They contain both RNA and DNA.
e. BACTERIA
They forms the largest groups of Prokaryote,, vary greatly in their cell shape, cell arrangements, motility, oxygen requirements, nutritional and metabolic properties and reactions to Gram's stain. They varied enable them to develop on a very wide range of organic and inorganic substrates . By modern molecular techniques it's divided into two groups ie
1. Archaebacteria-
single celled bacteria,are simple , capable of living in extremely conditions like ocean depths, volcanic sites, salt brine etc . These are the oldest bacteria known while the earth formed. Characterised by absence of muramic acids and D- amino acids in their cell walls., absence of fatty acids in their membranes, presence of several subunits in the RNA polymerase. Besides this many of their membranes is monolayered. They are resistance to antibiotics- chloramphenicol.
2. Eubacteria-single celled bacteria and complex microorganisms normally called bacteria. Capable of living in normal conditions ie soil, water, living and non living organisms. Characterized by presence of N- acetylmuramic acid and N- acetylglucosamine in their cell walls.lipids present in their cell membranes are straight chain molecules connected with ester linkages forming bilayered structure. In this bacteria DNA polymerase is made-up of four sub units. Photosynthesis is anoxygenic.
f. CYANOBACTERIA
They are prokaryotes, resemble like algae in the presence of chl and oxygenic photosynthesis. Many bacteria have specialised celled heterocysts which contains nitrogen fixing enzymes.
g. RICKETTSIAS
Smallest prokaryotes, are usually rod shape commonly called coccobacilli, but exist in many alternative forms. Unlike most bacteria, it's difficult to stain it wit ordinary alkaline dyes. So it is stained with Giemsa's stain. Mucopolysaccharides is the main constituents of their cell walls. Like virus they're also obligate intracellular parasites. Most of them transfer to human body through insects and ticks( A parasite) .
All the best......
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