Bloom or bust

It is commonly known that viral lysis of marine organisms, such as microalgae and plankton, is an important source of carbon and nutrients such as nitrogen for bacteria in the oceans. This influx of organic matter fuels bacterial growth and shapes the way their communities form. In turn this has an effect on microbial loop processes and therefore marine food webs.

While most studies focus on post-lysis effects, a recent study by Sheik et al. (2013) looks at exactly how viral infection of the unicellular algae Phaeocystis globosa (which often form large blooms in polar regions), affects surrounding bacterial populations from the moment of infection to post-lysis stages.

To measure the bacterial communities surrounding P. globosa cells, a method called CARD-FISH (catalysed reporter deposition-fluorescence in-situ hybridization) was used. Measurements of the bacteria were taken at regular intervals, and this was able to provide evidence of increasing population numbers, especially of the gammaproteobacteria Alteromonas, just 5 – 8 hours after viral infection of P. globosa cells, before cell lysis at ~12 hours.

A combination of HISH and nanoSIMS was used to measure how much carbon and nitrogen was assimilated by the bacterial populations. This showed that ~20% of the measured C and N were leaked during early viral infection.

The leakage of organic matter from the infected but still intact cells resulted in colonization of the infected algae by bacteria. I think this is potentially due to the creation of a chemotactic gradient which attracts the bacteria towards the source of the organic matter, similar to how bacteria find sinking marine snow particles and plumes.

I believe this work is a step forward in understanding the degree to which viruses impact bacterial communities in the ocean. It is a detailed expansion of work already done on the effect of viral lysis on carbon and nitrogen cycling by bacteria. It not only manages to quantify the bacterial communities utilizing carbon and nitrogen released from infected algal particles, but also provides us with a new niche to study by looking at the bacteria which colonize infected algal particles. I think this paper can be used as a good base for better understanding the processes behind algal blooms and their effects on oceanic microbial processes.

Abdul R Sheik, C. P. (2013). Responses of the coastal bacterial community to viral infection of the algae Phaeocystis globosa. Multidisciplinary Journal of Microbial Ecology, 8, 212 - 225.