What I did for the last year....

I've just returned from the GRC: Microbial Population Biology conference where I presented a poster on my work for the past year. In a few installments I'd like to reproduce this poster here.

My major question of interest was, "How does molecular stochasticity in the individual cell affect major life history traits?" To address this question, I used the enterobacteriophage lambda strain cI857 as a model. Under normal circumstances, cI857 integrates itself into E. coli's genome where it is passed horizontally to daughter cells. Most of the phage's genome is repressed at this point. However, after a temperature spike, the phage is induced into the lytic cycle. Here the "late" genes are expressed, including the lysis cassette and the genes that make phage babies.The lysis cassette contains four genes that produce five proteins. I'll focus just on two: holin and endolysin. The best available model suggests that holin integrates itself into the host's inner membrane. Over time, the holin concentration in the membrane rises, until it spontaneously condenses into a raft. Subsequently the holin undergoes a conformational change producing a hole in the inner membrane. This permits endolysin to attack and degrade the outer membrane, leading to host cell lysis and the release of phage babies into the surrounding medium. Thus holin, and its rate of production, is the main determinant of lysis time, or in life history theory, generation time. The rate of holin production depends on protein translation from low copy mRNA transcripts. Since a single mRNA transcript can produce multiple holin molecules, small changes in mRNA numbers can have large effects on holin production and, hence, the timing of lysis. My project looked at how differences in mRNA production and differences in holin structure led to variability in lysis timing. I'll discuss these in greater detail in a later post and show some of my data.

A cool animation sequence of the lytic cycle is available here.

Lead photo: Maria Schnos, Institute for Molecular Virology, University of Wisconsin, Madison

Genetic Map of the λ genome from CA Reinhart, W. Kentucky University.

Figure by me.