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Chapter 5
The Microbial World
Viruses
• Non-cellular infectious agents that have
two basic characteristics:
– Not capable of reproduction without a host
cell
– Structure:
• Nucleic acid core- can be ____ or ____
• Capsid (Protein coat)- consists of numerous protein subunits
organized into rod-like or many sided shape. Protein coat
also contains specific proteins that bind with receptors on
host cells. Many glycoprotein spikes extend from coat-these
spikes mutate so frequently that our immune system cannot
keep up.
Viruses
• Notable Types of Viruses:
• Retroviruses- store genetic information in
the form of nucleic acid known as RNA
• Bacteriophages – viruses that infect
bacteria
• Bacteriophages are either lytic or
lysogenic
• Viruses in eukaryotes can similarly be
active or latent
Viruses
• Viruses in the Marine Community:
– They are common in marine waters
– They can infect bacteria, plankton, fish, sea
turtles and marine mammals
– Lysis (bursting) of viral infected cells spills
contents and releases large amounts of
organic matter that can be utilized by other
organisms (dissolved organic matter or DOM)
Prokaryotes
• Archea and Bacteria
• Characteristics of Archean and Bacterial Cells:
– ____- no nucleus
– Single chromosome (normally circular)- some also
with plasmids
– Most with cell wall
– Great metabolic diversity
– microscopic
Prokaryotes
• Archea –
– Ancient organisms – fossils found that date
back 3.8 billion years
– Some live in very extreme environments
– Variety of metabolic types
– Widely distributed in the marine community
– They can tolerate wide ranges in temperature,
salinity and even desiccation
– Can be found in many areas including near
hydrothermal vents and salt flats (two very
extreme environments)
Prokaryotes
• Special Features of Bacteria:
• A variety of shapes including ____, ____,
and ____
• Cell wall structure is semi-rigid, but
permeable; Made of polysaccharide called
peptidoglycan
• Wide variety of metabolic types
• Very abundant worldwide
Prokaryotes
• Special Features of Bacteria:
– One of the most important functions of bacteria in the
marine community is to break down dead organic
matter – this forms detritus, which are minute
particles of organic matter now available as nutrition
for other organisms
– Cyanobacteria are a group of photosynthetic bacteria
that are extremely important in food chains producing
glucose and fixing nitrogen
– Stromatolites, massive calcareous mounds formed by
cyanobacteria, have been found that are over a billion
years old
stromatolites
Prokaryotes
• Metabolic diversity:
• Photosynthesis – derive energy from light
• Chemosynthetic – derive energy from
chemical compounds
• Heterotrophs – derive energy from organic
matter by respiration
Diatoms
• Diatoms:
– Photosynthetic
– Yellow-brown color in life is a result of
photosynthetic pigments- chlorophyll (A and
C) and carotenoids
– Cell wall of silica called a frustule forms a
complete cover called theca
– When die, frustules accumulate forming
diatomaceous earth used as abrasive, for
filtering and as pesticide
– Most important primary producer on Earth
– Mostly unicellular but some form colonies
Diatoms
• Diatoms
– Around half of the 12,000 known species are marine
– Most are planktonic
– Store excess energy as an oil which also aids in
buoyancy
– Tiny pores in frustule used for gas/nutrient exchange.
– Some produce a toxin, known as domoic acid, that
can accumulate in the tissues or organisms that eat
diatoms such as shellfish and small fish
– Larger organisms that eat these shellfish or small fish
can become ill or die from this accumulated toxin =
Biomagnification or bioaccumulation
Diatoms
• Diatoms
– Mainly reproduce by cellular division (a form of
asexual reproduction)
– In this type of reproduction, the cell divides and each
result cell gets one-half of the frustule.
– This cell now must secrete the other half of the
frustule (smaller piece of epi- or hypotheca)
– Due to this, diatoms get smaller each time they
reproduce
– To restore normal size, they must either sexual
reproduce or cast off the frustule and secrete an
entire new frustule
Dinoflagellates
• Dinoflagellates
– Most species live in marine environment
– Mostly photosynthetic, some can ingest particles
– Each species has unique shape reinforced by plates of
a polysaccharide called cellulose to form theca
– Two flagella in grooves on body that produce motion
– Also reproduce by cellular division
– Some are ____ (Have you ever noticed the greenish
glow as you wade in the Gulf?)
Dinoflagellates
Dinoflagellates
• Dinoflagellates
– Zooxanthellae are important dinoflagellates
that live in a symbiotic relationship with
corals, sea anemones and other organisms
(many of these host organisms have little or
no growth without their symbiotic partner)
Algal Blooms
• Diatoms and dinoflagellates can go
through periods of rapid growth known as
“blooms”
• This is a result of high levels of nutrients
in the water
• These blooms can be harmful to marine
organisms and even people at times
Dinoflagellates
• Dinoflagellates
– A few species lack chloroplasts and live as parasites
in marine organisms
– Some species can reproduce in larger numbers and
produce a “Red Tide”
– Pfiesteria is a dinoflagellate that produces very
serious toxins that can cause massive fish kills, harm
shellfish and impair the nervous system in humans.
– Pfiesteria was discovered near the Outer Banks in
North Carolina
Dinoflagellates often cause red
tides
Protozoa
• Foraminiferans (forams)
– Exclusively found in marine community
– Found on sandy or rocky bottoms
– Tests (shell) of calcium carbonate
– Can be important contributors of calcareous
material on coral reefs or sandy beaches
– ____ (false feet) extend through pores in the
shell where they are used to capture minute
food particles such as phytoplankton
Foraminiferans thin pointed pseudopods in ___ tests.
Protozoa
• Radiolarians
– Planktonic, mostly microscopic, although a
few can reach large sizes
– test of silica
– Like forams, they use pseudopods that extend
through pores in the shell where they are
used to capture minute food particles such as
phytoplankton
Radiolarian
Protozoa
• Ciliates
– ____ present for locomotion
– Most live as solitary cells
– Some build tests made of organic debris
– May live on hard substrate
– Some are planktonic
Ciliate
Fungi
• Eukaryotic and mostly multicellular
• Heterotrophic with unique cell walls made
of polysaccharide called chitin
• Most of the 1500 species of marine fungi
are microscopic
Fungi
• Like bacteria, many fungi break down
dead organic matter into detritus
• Some fungi live in symbiosis with
cyanobacteria, these are known as lichens
• Marine lichens often live in wave-splashed
areas of rocky shorelines and other hard
substrate
Marine lichens
Most Important Characteristics
of Marine Microbes