Friday, October 8, 2010


So, I haven't posted in a while. I foolishly thought that I would have oodles of free time once I quit my job and started grad school, but that has not been the case. TAing takes up a lot of time. I don't know how some people manage to get their PhD while teaching the whole time; I'm counting myself lucky that I will probably only have to teach this semester. 3 hours of class time X 2 sections, plus 3 hours of "office hours", 1 1/2 hours of TA meeting . . . and grading and creating quizzes and homework. It easily adds up to the promised 20 hours per week, and is the biggest consumer of my time at the moment. Behind that is my research work and the one class I am taking.

The work I'm doing in the lab is a short-term project called a rotation; the expectation is that I will have completed it by the end of the semester. Even though I will probably stay in the same lab for my thesis, this is not my thesis work. I've decided to try to work in a bit more literature reading in order to benefit my rotation research and help me decide what I will want to work on for my thesis eventually. So I've set myself a goal of reading one non-required journal article each weekend. "Non-required" meaning I've picked it myself because it seems interesting, not because it is required for a class or my supervisor or advisor told me to read it.

This week's selection is "Changes in Membrane Fatty Acid Composition during Entry of Vibrio vulnificus into the Viable But Nonculturable State". Day AP, Oliver JD. Journal of Microbiology. 2004 Jun;42(2):69-73.

Vibrio vulnificus is the organism I am studying for my project. It is a shellfish bacterium related to Vibrio cholerae, which causes cholera. V. vulnificus causes more than 95% of all seafood-related fatalities in the U.S., and it undergoes a transformation in the winter.

Cold temperatures cause it to become dormant to the point where it cannot be grown in the lab on normal media, yet if it is introduced into animals it still causes infection. My job this semester is to elucidate the molecular mechanism for this change. Interestingly, there are all sorts of papers showing that V. vulnificus does become dormant and what physiological changes it undergoes, but none investigating how to resuscitate it from dormancy (other than warming it back up, which seems a bit obvious), or why it is not culturable in this state.

The Day and Oliver paper was quite short, and simply showed a a change in the makeup of the fatty acids that comprise the cell membrane while the cells were going into the VBNC state. Their hypothesis is that in order to maintain membrane fluidity at lower temperatures, more unsaturated fatty acids (which have a lower melting point) are needed. In addition to measuring fatty acid ratios during entry into VBNC, they also inhibited fatty acid production by treatment with an antibiotic, cerulenin. The cells that could not produce additional fatty acids due to this treatment died after incubation at 5 degrees Celsius, indicating that this change in membrane composition is required to maintain viability. However, this only addresses one side of the VBNC (Viable But Nonculturable) state--we still don't know why the cells are not culturable if they are still alive. That's what I'm working on.

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