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Chapter 5
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 5
The Microbial World
• Non-cellular infectious agents that have
two basic characteristics:
– Not capable of reproduction without a host
– Structure:
• Nucleic acid core- can be DNA or RNA
• 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 (great at mimicry!!)
– Many glycoprotein spikes extend from coat-these spikes
mutate so frequently that our immune system cannot
keep up.
• Notable Types of
Retroviruses- store
genetic information in
the form of nucleic acid
known as RNA
Lysogenic viruses –
reproduce by inserting
their DNA into the DNA
of the host cell
Bacteriophages –
viruses that infect
• 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)
• Archaea and Bacteria
• Characteristics of Archaean and Bacterial Cells:
– Prokaryotic- no nucleus
– Single chromosome (normally circular)- some also
with plasmids
– Most with cell wall
– Great metabolic diversity
• Archaea –
– “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 (drying out)
– Can be found in many areas including near
hydrothermal vents and salt flats (two very
extreme environments)
• Special Features of Bacteria:
– A variety of shapes including
spirals, spheres, rods and
– Cell wall structure is semirigid, but permeable; most
with cell wall
– Size is normally microscopic,
but a few are large
– Wide variety of metabolic
– Very abundant worldwide
• Special Features of Bacteria:
– One of the most important jobs 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
– Stromalites, massive calcareous mounds
formed by cyanobacteria, have been found
that are billion years old
• Metabolic diversity:
• Photosynthesis – derive energy from light
• Chemosynthetic – derive energy from
chemical compounds
• Heterotrophs – derive energy from organic
matter by respiration
• Diatoms:
– Photosynthetic
– Yellow-brown color in life
is a result of
photosynthetic pigments,
chlorophyll A and C and
– Shell of silica called a
– Most important primary
producer on Earth
– Mostly solitary and
– Some can form colonies
• Diatoms
– Around half of the 12, 000 known species are marine
– Most are planktonic
– Store excess energy as an oil which also aids in
– Tiny pores in shell 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
• Diatoms
– Mainly reproduce by cellular division (a form of asexual
– 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)
– Due to this, diatoms get smaller each time they
– To restore normal size, they must either sexual
reproduce or cast off the frustule and secrete an entire
new frustule
• Dinoflagellates
– Most species live in marine
– Mostly photosynthetic, some
can ingest particles
– Each species has unique shape
reinforced by plates of cellulose
– Two flagella in grooves on body
that produce motion
– Also reproduce by cellular
– Some are bioluminescent (read
“Bay of Fire” on pg. 96)
• 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
• This is a result of high
levels of nutrients in the
• These blooms can be
harmful to marine
organisms and even
people at times
• Dinoflagellates
– A few species lack chloroplasts and live as parasites
in marine organisms
– Some species can reproduce in larger numbers and
produce “Red Tide” (read “Red Tides and Harmful
Algal Blooms, pg. 338)
– 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
• A few more species of phytosynthetic
– Silicoflagellates
• Star-shaped internal skeleton of silica
• Two flagella of varying lengths
– Coccolithophores
• Ornate shells of calcium carbonate
• Foraminiferans (forams)
– Exclusively found in marine community
– Found on sandy or rocky bottoms
– Shells of calcium carbonate
– Can be important contributors of calcareous
material on coral reefs or sandy beaches
– Pseudopods (false feet) extend through pores
in the shell where they are used to capture
minute food particles such as phytoplankton
• Radiolarians
– Planktonic, mostly microscopic, although a
few can reach large sizes
– Shell 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
• Ciliates
– Cilia present for locomotion
– Most live as solitary cells
– Some build shells made of organic
– May live on hard substrate
– Some are planktonic
• Eukaryotic and mostly multicellular
• Heterotrophic
• Most of the 1500 species of marine fungi
are microscopic
• Like bacteria, many fungus break down
dead organic matter into detritus
• Some fungus live in symbiosis with
cyanobacteria, these are known as lichens
• Marine lichens often live in wave-splashed
areas of rocky shorelines and other hard
Most Important Characteristics
of Marine Microbes