What is a bacteriophage and how/why do they work and how long do they live?

Hi Grthumongous,

Bacteriophages are extremely important right now for both the
treatment of bacterial disease and for genetic cloning experiments. 
They are, as purkinje notes below, viruses that get into a bacterium
and then are replicated by the bacterium.  This can kill (by breaking
apart, or lysing) the bacterium, or may just sit around and cohabit
with the bacterium's own genetic material.  Because they are not
technically "living" (though there is some debate on this!), viruses
don't have a lifespan per se.  Depending on the phage in question, the
virus could be around for a very short period or a very long time. 
Some well-known phages are lambda and T4.

Here are some nice encyclopedia articles on bacteriophages:

Wikipedia: Phage
http://en.wikipedia.org/wiki/Bacteriophage

Columbia Encyclopedia: Bacteriophage
http://www.bartleby.com/65/ba/bacterio.html

For a bit more in-depth information, here are lecture notes and class
pages for a variety of molecular biology courses:

University of South Carolina Microbiology and Immunology On-Line: Bacteriology
http://www.med.sc.edu:85/mayer/phage.htm

Indiana Biolab: Beginners Introduction to Bacteriophages
http://www.disknet.com/indiana_biolab/p000.htm

Western Kentucky University Biology 220: Bacteriophage
http://bioweb.wku.edu/courses/biol22000/35Bacteriophages/default.html


The encyclopedia articles I found by going to the Wikipedia
(www.wikipedia.org) and Bartleby reference (www.bartleby.com).  The
courses I found by doing a search for "bacteriophage introduction"
(this found a lot of websites).  Please let me know if I can clarify
this answer any!

Librariankt

thanks librariankt.
I remember a 1990s PBS show (Nova?) where a decrepit under-funded
post-Soviet lab was arguably the world leader in this approach at the
time.

And thanks to early responder purkinje for their input.

A bacteriophage is a virus which infects bacteria. It is made of a
protein shell and usually DNA inside (but sometimes RNA, which gets
reverse transcribed into DNA). It latches onto protein receptors in
the bacterial membrane and injects its contents (the DNA or RNA) into
the cell, and the cell replicates that DNA. Then there are two
pathways-- the virus can either replicate and make new viri, lysing
the cell, or it can just incorporate itself into DNA (I should
probably check on the details of that; I can't remember exactly).
Because it is not a cellular entity, it can live a very, very long
time unless it is heated up or treated chemically, or until the
protein shell degrades, or until its host dies.

I forgot to add-- this website relates too:
http://answers.google.com/answers/threadview?id=343424

Wow, you are the first person to say thanks, and I have answered
(well, ok, I've commented, but my comments are better answers than the
answerers give) almost 100 questions on here! Thanks.