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Marine Biology
Chapter 6
Marine Microbes
• Microbes
• Any living thing that is microscopic
• Can be one of the following:
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Viruses
Prokaryotes (Bacteria)
Unicellular Protists
Unicellular Fungi
Even very tiny animals
Marine Viruses
• Virology—the study of viruses
– Viruses are diverse and are more abundant than
any other organism in the sea
– Have significance for marine food webs,
population biology and diseases of marine
organisms
Viral Characteristics
• Are they “alive”? Most say no
• Remember you have to be made of at least one cell
to be alive, viruses are not cells
• Viruses consist of bits of DNA or RNA surrounded by
protein
• Have no metabolism, and rely entirely on host organism for
energy, material and organelles to reproduce themselves
– Viral replication must occur within a host cell
• Viruses infect all groups of living organisms, but may be
specialized
• Infect specific species
• Infect specific tissues of that species
– Influenza infects respiratory cells
– Hepatitis infects liver cells
Viral Characteristics
• Viral structure
– virus particle is called a virion when outside
the host cell
– Can’t do anything until it enters into a host cell
– virion composed of a nucleic acid core
surrounded by a coat of protein called a
capsid
– may have a protective envelope, a membrane
derived from the host’s nuclear or cell
membrane
Biodiversity and Distribution of Marine Viruses
• 10 times more abundant than marine
prokaryotes (bacteria)
• may reach 1010 virons per liter of seawater, 1013
per kilogram of sediment
• Bacteriophages – viruses that infect
bacteria
Ecology of Marine Viruses
• Viruses kill host cells, and thus control populations
of bacteria and other microbes in plankton
communities in the marine environment
• Viruses also responsible for chronic infection and
mass mortality of populations of marine animals
– Examples:
– Problems with shrimp aquaculture
– Papillomivirus and morbillivirus in marine mammal populations
• Now we will talk about bacteria
Marine Bacteria
• General characteristics
– simple, prokaryotic organization: no nuclei or
membrane-bound organelles, few genes,
nonliving cell wall
– reproduce asexually by binary fission
– many shapes and sizes
• bacillus—rod shape
• coccus—spherical shape
• Marine bacteria play many different roles
based on species
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Some photosynthesize
Some are important in the nitrogen cycle
Some cause disease
Some decompose
Some have symbiotic relationships with other
organisms
Nutritional Types of bacteria
• Cyanobacteria (blue-green bacteria)
– photosynthetic bacteria which are found in
environments high in dissolved oxygen, and produce
free oxygen
Photosynthesis
• Cyanobacteria
– may exist as single cells or form dense mats
held together by mucilage
• form associates called stromatolites—a coral-like
mound of microbes that trap sediment and
precipitate minerals in shallow tropical seas
Nutritional Types of Bacteria
• Heterotrophic bacteria
– decomposers that obtain energy and
materials from organic matter in their
surroundings
– return many chemicals to the marine
environment through respiration and
fermentation
Nutritional Types (Heterotrophic Bacteria)
• Heterotrophic bacteria
– marine snow: large, cobweb-like drifting structures formed by
mucus secreted by many kinds of plankton and bacteria, where
particles may accumulate
– Feces, dead material accumulate as marine snow
– Drops through the water column feeding other species that are deeper
Nitrogen Fixation and Nitrification
• Nitrogen cycle – nitrogen fixation and nitrification
• Why do we need nitrogen?
• Nitrogen is needed to make DNA and amino acids to make
proteins
• There is lots of nitrogen gas in the atmosphere, but most species
are not able to use it in that form
• Therefore, there are some bacteria that can convert the
atomospheric nitrogen into nitrogen they can use to make their DNA
and proteins
• That nitrogen then makes it’s way up the food chain
• There are bacteria that during the decomposition process
can convert the nitrogen back into nitrogen gas, therefore
continuing the nitrogen cycle
Symbiotic Bacteria
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Many bacteria have evolved symbiotic relationships with a variety of marine
organisms
Endosymbiotic theory
– mitochondria, plastids & hydrogenosomes evolved as symbionts within
other cells
Chemosynthetic bacteria live within tube worms and clams
Some deep-sea or nocturnal animals host helpful bioluminescent bacteria
– photophores
– embedded in the ink sacs of squid
Archaea Bacteria
• Archaeans are bacteria that include the “extremophile”
bacteria
• Example: Hyperthermophiles
– organisms that can survive at temperatures exceeding
100o C, such as near deep-sea vents
– Potential for biomedical and industrial application
Nutritional Types of Bacteria
• Chemosynthetic bacteria
– Chemosynthesize instead of photosynthesize
• Use sulfides and elemental sulfur, nitrites,
hydrogen, and ferrous ion that are coming up from
hydrothermal vents
– chemosynthesis is less efficient than
photosynthesis, so rates of cell growth and
division are slower
– found around hydrothermal vents and some
shallower habitats where needed materials
are available in abundance
• Now we will talk about Eukaryotes
Eukarya
• Eukarya includes all organisms with
eukaryotic cells
• Examples:
– plants
– animals
– fungi
– algae
– single-celled animal-like protozoa
• For this chapter, we are only going to talk
about Eukaryotes that are microscopic
• Within Eukarya, we will now talk about the
Fungi
Fungi
• General features of fungi
– eukaryotes with cell walls of chitin
– many are unicellular yeasts
– filamentous fungi grow into long, multi-cellular
filaments called hyphae that can branch to
produce a tangled mass called a mycelium
– heterotrohic decomposers that recycle organic
material
• can digest lignin (major component of wood)
Fungi
– Kingdom Fungi is divided into 4 phyla:
• Chytridiomycota (motile cells)
• Zygomycota (e.g. black bread mold)
• Basidiomycota (club fungi, e.g. mushrooms)
• Ascomycota (sac fungi)
– in the sea, ascomycotes are the most diverse and abundant fungi
Fungi
• Ecology and physiology of marine fungi
– can be either obligately marine, requiring ocean
or brakish water or facultatively marine (primarily
of terrestrial or fresh water origin)
– salinity is toxic to fungi, so they must devote
energy to removing sodium
– most marine fungi live on wood from land
– some live on grass in salt marshes
– others live on algae, mangroves or sand
– fungi decompose the chitinous remains of dead
crustaceans in open sea plankton communities
• Now we will talk about the protists
• Here we will talk mainly about the unicellular
protists
» Unicellular algae – Phytoplankton
» Unicellular heterotrophs - protozoans
• Later, we will talk about multicellular protists
» Algae - “seaweed”
Diatoms
• Extremely diverse and distinct members of
marine phytoplankton
• Diatom structure
– frustule—a two-part, box-shaped organic cell
wall impregnated with silica
Diatoms
• Diatomaceous sediments
– frustules of dead diatoms sink and collect on the seafloor to form
siliceous oozes
– accumulations form sedimentary rock
– these deposits, called diatomaceous earth, are mined for use as
filtering material, a mild abrasive, and for soundproofing and
insulation products
– nutrient reserves, stored as lipids, accumulate in siliceous oozes
accounting for most of the worlds petroleum reserves
– Ancient diatoms sank to the bottom of the ocean, were
covered by sediment before they decomposed, were
subjected to pressure and heat and turned into petroleum
Diatoms
Coccolithophores
• Photosynthetic organisms with 2 simple
flagella both used for locomotion
• Most are coccolithophores with a surface
coating of disc-shaped scales (coliths) of
calcium carbonate
– remains form calcereous oozes
Alveolates
• Examples:
– dinoflagellates
– ciliates
– apicomplexans (strictly parasitic)
• Dinoflagellates
– globular, unicellular (sometimes colonial) with
2 flagella
– Most are planktonic, some are benthic and
others parasitic, also can be bioluminescent –
Bioluminescent Bay, Puerto Rico
Dinoflagellates
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Ecological roles of dinoflagellates
– major component of phytoplankton
– some are parasites of copepods (crustaceans)
– zooxanthellae: species lacking flagella which are symbionts of jellyfish,
corals and molluscs
– photosynthetic zooxanthellae provide food for hosts
– hosts provide carbon dioxide, other nutrients, and shelter
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Harmful Algal Blooms (HABs)
• occur when photosynthetic dinoflagellates undergo a population explosion
• colors the water red, orange or brown
• dinoflagellates that cause HABs produce toxins
– paralytic shellfish poisoning (PSP) occurs in humans who consume shellfish
contaminated with these toxins
– toxins cannot be destroyed by cooking
• oxygen content of the water may be reduced to deadly levels as bacteria decompose
animals killed by dinoflagellate toxins
Red Tides
• Ciliates
– protozoans that bear cilia for locomotion and for
gathering food
• membranelles—tufts or long rows of fused adjacent
cilia
• cytostome—an organelle serving as a permanent site
for phagocytosis of food
– planktonic and benthic
– major links in marine food chains
– form symbiotic and parasitic relationships
Paramecium – a ciliate
Choanoflagellates
• Phylum of marine and freshwater flagellated
cells that are more closely related to animals
than any other group of one-celled microbes
• Unicellular or colonial
– colonies may be stalked or embedded in a
gelatinous mass
• Highly efficient consumers of bacteria
• Ancestors to the animals?
Choanoflagellate
Sponge
Amoeboid Protozoans
• All have an organelle called a pseudopod—an
extension of the cell surface that can change
shape and is used for locomotion (benthic species)
and food capture (benthic and pelagic)
• Are hererotrophs consuming bacteria and other
small organisms
Amoeboid Protozoans
• foraminiferans
• radiolarians
Amoeboid Protozoans
• Foraminiferans (forams)
– have branched pseudopods that form
reticulopods (elaborate, net-like structures)
used to:
• snare prey
• crawl (benthic)
• reduce sinking rate (pelagic)
– consume bacteria and diatoms
– some harbor symbiotic green and red algae
and zooxanthellae
Amoeboid Protozoans
• Radiolarians
– named for long, needle-like pseudopods
• pseudopods capture food and slow sinking
– radiolarian oozes form from the internal siliceous
skeleton of dead radiolarians
– live in the photic zone and capture phyto- and
zooplankton, sometimes copepods
– larger radiolarians prey on copepods and other
planktonic crustaceans
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So far, we have talked about:
– Viruses
– Infect bacteria, protists, plants and animals in the marine
environment
– Domain Archaea – prokaryotes, extremophiles
– Domain Bacteria
– Cyanobacteria – photosynthetic bacteria
– Heterotrophic bacteria – can be nitrogen fixers, can have
symbiotic relationship with other organisms, can infect other
organisms, can help with decay
– Domain Eukarya
– Fungi
– Protists
» Unicellular algae – diatoms, dinoflagellates,
coccolithophores (Phytoplankton)
» Protozoans – ciliates, choanoflagellates, amoeboids
(foraminiferans, radiolarians)