Classes of plasmids:

a) Virulence plasmid

b) Drug resistance plasmid

c) Encode gene for bacterial conjugation.

Effects of plasmid on host phenotype

1. F factor: Increases fertility.
2. R factor: Increases resistance to antibiotics
3. Ti factor: Induce tumor in plants.

 

Important characteristics of normally occurring plasmids

a) Influence characteristics of their bacterial hosts.

b) Replicate independently the main chromosome.

c) Usually specific to one or a few species of bacteria.

d) Undergo reversible integration into bacterial chromosome.

e) Can be transferred by conjugation

f) Usually contain upto 40 genes

g) Don’t occur free in nature.