The power of the small – Marine Viruses
Viruses appear in the news a lot, many of us will know about annual flu season (caused by the influenza virus), the relatively recent outbreak of the Ebola virus in west Africa and also human immunodeficiency virus (HIV) the cause of AIDS. But viruses in the sea? They get a bit less attention, but are incredibly important.
Before we get in to marine viruses, let’s begin with what is a virus? A virus is an infectious intracellular parasite, meaning that it needs to get inside a living cell to replicate. It is essentially genetic information encapsulated in a protein coat. Due to the requirement of needing a ‘host’ cell, it is often said that viruses are not actually “alive” as they do not have the capability of self-replication like a bacterial cell.
Viruses are the most abundant biological entities in the oceans, there are approximately 10 million viruses per millilitre in surface seawater. If you were to take all of the carbon in marine viruses, it would be the equivalent of 75 million blue whales. If you took the average size of a marine virus and put them end to end then they would span 10 million light years. They are in such vast numbers, and so diverse, but we are only just beginning to fully appreciate how they regulate life in the oceans.
Viruses affect marine communities through various ways, there is of course the death of the cell, in a process known as lysis. This is where the cell essentially explodes and releases hundreds of viruses into the environment to look for a new host to infect. This is very important for the turning over of nutrients in the upper oceans, as the lysis of these cells causes the nutrients to be returned to the water column where they can be used again by bacteria or phytoplankton (microscopic marine plants).
Lytic life cycle of viruses
Viruses are also able to insert themselves into the genome of their hosts and affect the genes they are expressing, essentially controlling how the cell behaves. Finally, as viruses move between different cells rapidly they can act as methods of gene transfer. It has been discovered that some viruses of marine photosynthetic organisms actually carry with them almost all of the genes required for efficient photosynthesis.
Cartoon summarising the three major interactions of viruses with their hosts in the oceans.
I hope this article has hopefully shown to you the importance of viruses within the oceans, that they are not just disease causing agents but can regulate nutrient cycles and genetic transfer and that they are incredible interesting!
Photo 1 credit: http://linxc10.wix.com/microbes#!viruses/c1wjk
Photo 2 credit: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/V/Viruses.html
Photo 3 credit: Breitbart, M. 2012. Marine viruses: truth or dare. Ann. Rev. Mar. Sci. 4: 425–48.