Bacterial Variation

Types of Bacterial Variation 1)Phenotypic variation: Changes in the bacterial characters in response to environmental conditions: o Reversible when the environmental cause is removed. o Not heritable (no genetic changes). Examples: o Penicillin interferes with cell wall synthesis. o Phenol interferes with development of flagella.

2)Genotypic variation: Changes in the bacterial characters due to changes in the genetic constitution of the bacterial cell: o Irreversible. o Heritable among bacterial generations. Causes: o Mutation. o Gene transfer.

Change in the sequence of nitrogenous bases in the bacterial DNA due to: o Insertion of new bases. o Deletion of bases. o Substitution of one base for another: Transition: substitution of purine with purine or pyrimidine with another pyrimidine. Transversion: substitution of purine with pyrimidine or the reverse. Gene mutation Mutation may occur spontaneously or induced by agents like x-rays, UV light, alkylating agents.

T GCA T GCA T GCA T GCAA T GCA T ACA Insertion Deletion Substitution Mutation

Transfer of DNA within the bacterial cells by:  Transposons (jumping genes). Transfer of DNA between the bacterial cells by:  Transformation.  Conjugation.  Transduction:  Generalized  Specialized Gene transfer

 When bacterial cells dye, their DNA is released into the surrounding medium.  The adjacent bacterial cells will uptake this free DNA. Transformation

 Conjugation occurs between F+ donor cell which is the bacterial cell carrying F plasmid and F- recipient cell which does not contain F plasmid.  The F+ cell will form sex pilus by its F plasmid.  The pilus arising from F+ cell attaches to a receptor on the surface of F- cell.  One strand of F plasmid is transferred through the pilus from F+ cell to F- cell.  Each single strand acts as a template for synthesis of the complementary strand.  Thus at the end of conjugation, the 2 bacterial cells will be F+ carrying F plasmid. Conjugation

 During the lytic cycle of bacteriophage replication, the bacterial DNA becomes fragmented.  During assembly of the phage, by accident, any fragment of the bacterial DNA may be enclosed within the phage head instead of phage DNA.  The phage will transmit this fragment to other bacterial cells. Generalized transduction

 During the lysogenic cycle of bacteriophage replication, the prophage may be induced to detach from the bacterial chromosome to start a lytic cycle.  During detachment, the prophage may carry with it a fragment of the adjacent genetic material of the bacterial chromosome.  The prophage will transmit this specific fragment of bacterial chromosome to other bacterial cells. Specialized transduction

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