Viruses every day (Suttle, 2007). Viruses however to

Viruses
are abundant in every environment on earth from high up in the atmosphere to
the deepest depths of the ocean. Approximately 71% of the earth is covered by
water, of which 96.5% is in the ocean where the true power of viruses can be
seen. Viruses have the highest abundance of any other life form in the ocean,
occurring at approximately ten billion per litre of water with a vast range of
genetic diversity (Fuhrman, 1999). Microorganisms make up 90% of the biomass in
the ocean and are essential to nutrient and energy cycles. Yet, approximately
20% of this living biomass is lost to viruses every day (Suttle, 2007). Viruses
however to do not just affect microorganisms, they can cause mortality in almost
every lifeform in the ocean such as bacteria, archaea and eukaryotic organisms (Rohwer
and Thurber, 2009).
The development of methods to estimate the abundance and diversity of viruses
in the ocean has proved to be quite difficult for researchers. It was once
thought that the quantity of viruses in the ocean was linked to prokaryotic
abundance and activity but researchers have now found dissimilarity occurring
between them in different marine environments. 
Researchers have also found it difficult to quantify the exact effects
viruses have on heterotrophic and autotrophic communities in the ocean (Suttle,
2007).
However in recent years our knowledge of the vast range of viruses in the
marine environment has grown by using metagenomics processes. The relationship
between viruses and the organisms that they effect appears to limit and control
the genetic diversity of viruses in that area (Suttle, 2007). Recent studies
have revealed that viruses are capable of manipulating entire life histories
and future evolution of the organism that have infected, which shows that they
are of major importance in the marine food web. Since viruses can impact
bacteria, archaea and eukaryotic communities, they have the ability to change
the composition of almost any organism in our oceans (Rohwer and Thurber,
2009).

 

A virus is a small particle with RNA or DNA
genetic material which can be single or double stranded surrounded by a protein
coat and is generally about 20-200nm in length. The infectious virus particle
is composed of a nucleic acid surrounded by a protein shell (Lodish et al., 2000). Viruses need a host to
reproduce and multiply as they cannot do it by themselves. With almost every
cellular organism being vulnerable to infection by a vast array of viruses,
this makes viruses one of the most diverse and dangerous entities on earth. Viruses
use the hosts exposed cellular structures as a method to attach and enter the
organism, while using passive transport to come in contact with a host (Fuhrman,
1999).

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

The three major types of
reproduction in viruses are: Lytic infection, chronic infection and lysogeny.
Lytic infection is when the host cell is penetrated by a lytic phage. A nucleic
acid is injected into the cell which encourages the host cell to produce
multiple progeny viruses. The cell will then burst causing the death of the
cell, which allows the process to start once again as the virus particles that
are released can infect other cells of the host (Clyde and Glaunsinger, 2010).
Chronic infection does not result in the fatality of the cell. Instead, the
progeny virus can be released out of the cell through budding or extrusion over
numerous generations (Fuhrman, 1999). Lysongeny (also referred to as the
lysogenic cycle) is when the host cell can carry the cell of the virus in a
relatively stable state. The nucleic acid of the virus is reproduced with the
genome of the host cell and is called a prophage. However, a stressful event to
the host cell can trigger a change from the lysogenic cycle to lytic infection
(Guttman, 2001).

 

 

 

 

 

The bacterial virus “phage” was discovered by Frederick
W. Thwort in 1915 and also discovered by Félix d’Hérelle in 1917 in France, independently of each
other. Some say that d’Hérelle’s claims that he had no knowledge of
Thworts earlier discovery when he published his work in 1917 are false (Duckworth, 1976). In 1979 Francisco Torella
and Richard Morita discovered that there are many morphological similarities
between phage and marine viral particles and that they are extremely abundant in
the ocean with approximately 100,000 occurring in every millilitre of water. In
the 1990’s, a lot of research was put into diversity and abundance of marine
phage and the ecological effect these viruses have on marine plankton
communities. Research showed that viruses and protists gave major contributions
to the global biogeochemical cycle. Soon the very first marine viral genomes
were sequenced and developed what we know today as metagenomics to characterize
the different types of DNA and RNA viruses in the water (Rohwer and Thurber,
2009). The timeline shown in the figure below shows the major events that have occurred
in the research of marine viruses.