Genes in Viruses and Bacteria

Part 2

Counting Viruses

Viruses can only be cultured (grown for study) in the presence of living cells. To grow bacteriophages you must first start with a healthy layer or "lawn" of susceptible bacteria.

Only then can the virus be introduced the bacteria covered agar (usually in a petri dish). Each active virus infects just one bacterium, but within a few hours hundreds of bacteria will be infected and dying. The death and destruction of the bacteria leave a small but visible "hole" in the bacterial lawn.


Classification of Viruses

Microbiologists use a wide variety of characterists to identify and classify viruses including:

  • Shape - examples: polyhedral, spherical, rodshaped, polyhedral + tail
  • Nucleic acid content: DNA or RNA
  • Presence or absence of an envelop
  • type of host affected
  • method of transmission (vectors)

For a more through treatment of virus biology follow this link to an Introduction to Moleculuar Virology