This paper examines the interactions between Synechococcus, heterotrophic bacteria and viruses however primarily looks at how viruses affect the growth rate of Synechococcus. The study includes four experiments of which one takes place in the Western Gulf of Mexico (1995) and three taking place in the North West Mediterranean (2003, 2004, 2005). In these sites Synechococcus can contribute greater than 50% of primary production so understanding their growth rates would help in our understanding of nutrient and energy flow in these areas.
The basic approach in all the experiments was to collect seawater samples in Go-Flow bottles and then serially dilute these untreated samples to reduce grazing (0.2um filtered water) and viral cell lysis (ultra-filtered water). In the 2004/2005 experiments they also wanted to see the effect of heat-inactivated virus' might have on Synechococcus growth rates. They did this by adding heat-inactivated virus' and bacteria into ultra-filtered seawater using a flow cytometer to get correct concentration. The abundance of Synechococcus was measured using a epifluorescence microscope with green-light excitation in the 1995 experiment and using flow cytometry in the 2003/2004/2005 experiments. However its important to note that I have seriously simplified what they actually did and that the methods did vary slightly between experiments.
In the 1995/2003/2004 experiments the growth rate of Synechococcus was higher in untreated samples compared to the virus free dilutions however in 2004 this was not significant. Also in the 2004 and 2005 heat-inactivated virus experiment growth rates of Synechococcus were significantly higher in the untreated virus samples compared to heat-inactivated samples.
Despite slightly different methods being used these experiments do suggest that active virus' do have a beneficial effect on Synechococcus growth. Viral lysis mortality in Synechococcus has been shown in other studies to be very small when compared to viral lysis of heterotrophic bacteria. It is therefore possible that active virus' are promoting Synechococcus growth by supplying nutrients and removing competition from heterotrophic bacteria. However it is very important to note that although this study strongly suggests virus' have a positive effect on Synechococcus growth it does not prove the mechanics behind this. Overall I thought the paper was very interesting as it shows that virus' are not only important for controlling bacteria populations through cell lysis but possibly also by supplying nutrients for cyanobacteria like Synechococcus which are incredibly important for primary production.
A review of: Markus G. Weinbauer et al. (2011): Synechococcus growth in the ocean may depend on the lysis of heterotrophic bacteria. Journal of Plankton Research, vol. 33, no. 10, pg 1465-1476.
1 comment:
Hi Matt,
In the paper you have reviewed, you mention that the authors looked into the growth rates of the Synechococcus, It’s very interesting that the authors almost suggest that the viruses and the bacterium are symbiotic as the viruses cannot fix carbon but do use the fixed carbon produced by such cyanobacteria which as we know are photosynthetic, and they suggest that the viruses may provide nutrients and controls of competition. This would mean that the Synechococcus can then concentrate solely on growth and photosynthesis. It would have been interesting if the authors also measured CO2 to see if this is the case. This links to what I have read about viruses so far about them shaping microbial communities and also what Lee commented on my post about dissolved organic matter (DOM) and that most of this comes from viral lysis of other microbes.
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