Chlorella Virus has been challenging my stereotypes once again. In addition to the “bigger genome therefore bigger virus particle” assumption, I was clearly guilty of a “bigger virus therefore slow at replicating” assumption too. Its nothing I though explicitly, in fact had you asked me outright, I would have admitted that there is no real reason I can think of that a larger virus HAS to have a slower replication cycle. But I know I had this misperception because at some point I heard Dr. James Van Etten on TWIV say that infectious Chlorella Virus can be detected in the infected cell at 3-4 hours and it blew my mind. That’s pretty fast, I thought, I wonder how fast other viruses are. So I spent the weekend with my head in the literature.
First, some basic virology. There is a classic experiment called the “one step growth curve” where you add your virus to the cells such that all of the cells are infected approximately at the same instant, you then wash away any unbound virus and then occasionally harvest some of the cells to check for virus. If you are good enough, and depending on the virus, initially you will detect the input virus, but that will then disappear as the virus is uncoated and begins to replicate in the cells. Then there will be a period where you can’t detect any virus at all because the input virus has come undone inside the cell but no new viruses have been assembled – this is called the eclipse. Eventually, as viral gene expression continues, new viruses will assemble inside the cell and you will see increasing amounts of virus.
All of this how long and how much virus business is VERY dependent on the conditions you use, the strain of virus you are using, the particular lot of cells you are infecting, etc etc. It is almost meaningless to compare the eclipse periods of of different viruses, but that is what I am going to do below. I went through the literature and found data for each of the viruses shown, and looked for the EARLIEST that virus levels started to rise. I didn’t worry about the fact that these infections were done using different cells, or even with the same amount of input virus (critical variables in this kind of experiment)… I just wanted to get a very rough idea of “how fast they could go”.
So in the figure shown at left (from this paper) – for influenza virus – I saw that the virus levels convincingly rising at 3 hours post infection. That has to mean that, at least with this strain of influenza in these cells under these conditions, this virus CAN assemble new viruses in 3 hours. The end of the eclipse period here is ~3 hours.
So then here is my viral drag race. These numbers were plucked from various articles and suffer from the obvious limitations mentioned above. In other words, results may vary depending on how the experiment is done, but in general the following viruses can produce infectious daughter virions as early as this. I have personally worked with three of these viruses (Adenovirus, HCMV and HIV) and these numbers fit with what I observed in my own hands.
So Chlorella Virus is pretty damned fast.
I am going to be super lazy and just post the links now. Later I will clean this up a bit.
Klebsiella Phage vB: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3622015/#!po=11.6667
Phaeocystis globosa virus: Phaeocystis, major link in the biogeochemical cycling of climate-relevant elements: Major Link in the Biogeochemical Cycling of Climate-Relevant Elements (Google eBook)