Hello marine biology students.
In this video we're going to start talking
about the diversity of life, specifically
viruses and prokaryotes.
[Intro Music]
So let's talk about the non-animal life in
the ocean.
We're going to start by discussing microscopic
organisms or microorganisms.
When we had looked at the tree of life previously,
you may have wondered where viruses were?
Well, it turns out that viruses are not on
the tree of life because viruses are not alive.
They do not meet all of the characteristics
of life and viruses could not pre-exist life,
the same way that a computer software could
not pre-exist computer hardware.
Without the machinery, it wouldn't be able
to do anything, including propagate.
Viruses are a product of cells, but they are
also found for every type of cell around.
They are a consequence and a result of cells
and they will copy themselves as long as there
are cells around.
When we've asked about viruses in the ocean,
we would define a virus as a non-cellular
infectious agent.
Viruses are not capable of reproduction without
a host.
When we look at the core structure of a virus,
it is made up of a nucleic acid core
and some sort of capsid or covering, a protein
coat.
This protein coat could be made up of numerous
protein subunits and arranged in a variety
of different shapes.
Among the viruses that are in the marine environment,
there are some notable types, such as retroviruses,
which store their genetic information in the
form of the nucleic acid RNA as opposed to
DNA.
Retroviruses have been known for a while,
but they do defy what's known as the Central
Dogma of Genetics, in that information is
supposed to flow from DNA to RNA to protein.
Well, retroviruses take their RNA information
and they actually make molecules of DNA from
it in the cells they're infecting.
Another type of virus are lysogenic viruses.
These lysogenic viruses actually insert their
own DNA into the genomic DNA of their host
and sometimes this insertion can result in
the virus being dormant or inactive for a
while, and then at some point in the future
coming out and start making more of itself.
Another category of viruses are the bacteriophages,
which specifically infect prokaryotic cells
and multiply within them.
After using some new methods of analysis,
we have found that viruses are actually quite
common in the marine environment, both in
the water and also within sediments, on surfaces,
and pretty much everywhere.
These viruses can infect marine bacteria,
plankton, seaweeds, plants and animals.
It turns out that few of these marine viruses
are pathogenic to humans, because humans aren't
the most common organisms in the marine environment.
The exception would be if raw human waste
or sewage is going into that water, then human
pathogens could be present.
But otherwise, the viruses that are present
are going to be those viruses that can be
copied by the cells in the environment.
One action of viruses is lysis or bursting
of infected cells, which results in the release
of those viruses into the water.
This method of destroying or rupturing cells
also results in the production of large amounts
of dissolved organic matter or DOM into the
marine environment, and DOM can be a major
food source for many marine bacteria.
Here we see a picture of one of the more bizarre
marine viruses.
This is known as a megavirus and it's surprisingly
big.
In fact, it's bigger than many bacterial cells.
These megaviruses have been found to infect
oceanic amoeba.
Most viruses are far smaller than this and
wouldn't be able to be seen with a traditional
microscope, but megaviruses are the exception.
Now, when we look at these major groups of
life, these domains, we have Domain Bacteria,
Domain Archaea, and Domain Eukarya.
Viruses can infect all of these types of cells,
but again, viruses are not on this Tree of
Life.
We're going to spend some time talking about
the prokaryotic domains, Domain Bacteria and
Domain Archaea.
What are some characteristics of Archaea 
and Bacteria?
First off, these cells are prokaryotic, in
that they do not have a nucleus.
They have genetic material, they have cytoplasm
and a plasma membrane and ribosomes, but they
do not have internal organelle compartments,
especially not one that stores their genomic
DNA.
They have a single chromosome, which is normally
circular.
They'll likely have cell walls in addition
to their plasma membrane and they have great
metabolic diversity.
They can get the energy from their environment
in a variety of different ways.
This is normally limited in more complex organisms.
So the first of these groups we'll talk about
are the Archaea.
These are ancient organisms, in fact there
are fossils of Archaea that date back 3.8
billion years.
They're one of the first forms of life on
this planet.
Archaea themselves have a variety of metabolic
types, with some getting energy from methane,
some getting energy from hydrothermal vents,
others doing chemosynthesis, a variety of
different ways to get their energy.
Now, it turns out that Archaea are pretty
widely distributed at sea, although they can
end up living in environments that other forms
of life are not able to.
They can tolerate wide ranges in temperature,
salinity, and even desiccation or drying out.
They can be found in many areas including
near hydrothermal vents and salt flats, two
very extreme environments.
And here we can see a micrographic image of
some of these Archaea.
These are methanogenic bacteria that live
near deep sea hydrothermal vents.
Next, we'll spend a little bit of time talking
about marine bacteria.
They come in a variety of shapes, including
spirals, spheres, rods, and even ring shaped
bacteria.
Their cell wall structure is semi-rigid, but
permeable.
When it comes to size, they are normally microscopic,
but there are some examples of large cells
in marine bacteria, often in oxygen-poor environments.
As with the archaea, we see a wide variety
of metabolic types.
Bacteria are very abundant worldwide.
Here in these images we can see one of those
ring-shaped bacteria that are found in the
marine environment and then in the other slide
we can also see one of these extremely large
bacterial cells.
The little yellow granules within those cells
are sulfur.
When we talk about the ecological role that
prokaryotes play in the marine environment,
they often spend a lot of time breaking down
dead organic matter.
This forms detritus, minute particles of organic
matter that are available as nutrition for
other organisms.
As we're going to see in many marine environments,
suspension feeders and deposit feeders are
filtering detritus out of the sea water as
a food source.
There are some bacteria which are photosynthetic,
including cyanobacteria, and these can play
a very important role in marine environments.
They are one of the primary producers.
Certain cyanobacteria can also end up secreting
calcium carbonate, and these form structures
known as stromatolites.
Stromatolites make up some of the oldest fossils
we have of life here on planet Earth, and
they're still around today.
They are still being formed in certain marine
environments, here we see a scuba diver scuba
diving next to some of these stromatolites.
Structures that are quite large, but are made
by cyanobacteria.
As had been mentioned several times, there's
great metabolic diversity in the archaea and
bacteria.
Some bacteria are photosynthetic, meaning
they derive their energy from sunlight.
Some bacteria are chemosynthetic, and they
get their energy from inorganic chemical compounds
like hydrogen sulfide, and some are heterotrophic,
meaning that they break down organic molecules
for energy.
Prokaryotes with all three of these energy
gathering methods are important in marine
environments.
So that takes us to the end of our discussion
of viruses and prokaryotes.
Now, before our next video, I want you to
think “What does it take for something to
be a plant or an animal?”
We'll talk about that in our next video.
