E. huxleyi virus hitching rides on zooplankton- Yeehhhaaw

Marine viruses are known to accelerate the turnover of marine phytoplankton biomass and nutrient recycling in the oceans. Frada et al. 2014 initially recognised that natural viral dispersal rates don’t match up with the rapid viral- mediated decline of algal blooms that often cover thousands of square kilometers of the ocean’s surface. Elucidating the mechanisms that govern the increased dissemination of marine phytoplankton blooms is key for understanding viral- driven biogeochemical processes. Emiliania huxleyi, a bloom- forming cocolithophore that plays an important role in the carbon cycle, is infected and killed by the E. huxleyi virus (EhV). In this experiment, it is shown that calanoid copepods (a common zooplankton which feeds on phytoplankton) and Artemia salina (a model organism) can accumulate and mediate the transmission of viruses in more than one way. Other important discoveries were also made whilst they were investigating this.

Copepods were first collected from two bloom locations in the North Pacific, and by using PCR, >80% of the copepods micro- biomes were found to contain similar sequence composition of EhV’s. This also led to the isolation of a new infectious EhV strain- which was therefore used in the experiments. It would have been useful if the authors identified the different species of copepods so other research could then bridge off of this with the same species, but I understand that this is a time consuming and difficult task.

It was shown that EhV’s can be dispersed by detachment off copepods surfaces and/or via viral- dense fecal pellets (FP). Viruses remained viable over a period of 1 day (up to 28hrs) post-feeding on EhV infected algal cells. It was also shown that the passage through zooplankton (A. salina cultured in the lab) guts actually prolonged EhV’s half-life of infectivity by 35%, relative to free virions in seawater, potentially enhancing viral transmission. From these results the authors proposed that zooplankton, swimming through topographically adjacent phytoplankton micro-patches and migrating daily over large areas across physically separated water masses can serve as viral vectors, boosting host to virus contact rates and potentially accelerating the demise of biologically important phytoplankton blooms. They also proposed that the infection via grazers will be most pronounced at the initiation phase of a bloom, where host-cell densities are low and effective contact rates are highly constrained. I personally can’t get my head around that zooplankton can travel far enough in a day to another adjacent phytoplankton bloom, but it has been previously shown that zooplankton can swim at speeds of tens of millimetres per second- so it can be achieved. 

It is likely that zooplankton are following the scent trails of diffused info chemicals to encourage them to migrate between algal patches. If we can find a way to detect these phytoplankton info chemicals, there is potential to be able to predict the spread and direction of virus infections.

What I found most interesting about this paper was the discovery that the half -life of the virus increased when transported through A. salina’s gut. This could be due to the FP coating against light exposure and dissolved enzymes or other chemicals, as these factors can dramatically reduce viral infectivity. This paper has highlighted that there is a research gap in studying how marine viruses are transported other than physical processes and the phenomenon witnessed here is likely to be generalised to other microbial groups at sea, however research is needed to confirm this. There has been various research linking climate change factors to a potential change in microbe diversity, abilities and densities in the worlds oceans, so to determine how viruses will be transferred in the future it is important to look at other viruses and zooplankton and linking with previous climatic research.

Frada, M. J., Schatz, D., Farstey, V., Ossolinski, J. E., Sabanay, H., Ben-Dor, S.,  & Vardi, A. (2014). Zooplankton May Serve as Transmission Vectors for Viruses Infecting Algal Blooms in the Ocean. Current Biology 24, 2592-2597. 

A Pdf. version was kindly given to me by the authors.