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Chapter 6
Marine Microbes
© 2006 Thomson-Brooks Cole
Key Concepts
• Microbial life in the sea is extremely
diverse, including members of all three
domains of life as well as viruses.
• Marine virology is an emerging field of
study, due to recognition of the critical
role that viruses may play in
population control of other microbes,
in nutrient cycling, and in marine
pathology.
© 2006 Thomson-Brooks Cole
Key Concepts
• Photosynthetic and chemosynthetic
bacteria and archaeons are important
primary producers in marine
ecosystems.
• Heterotrophic bacteria, archaeons, and
fungi play essential roles in recycling
nutrients in the marine environment.
© 2006 Thomson-Brooks Cole
Key Concepts
• Marine eukaryotic microbes are
primary producers, decomposers, and
consumers, and some contribute
significantly to the accumulation of
deep-sea sediments.
• Populations of several kinds of
photosynthetic marine microbes may
form harmful blooms that affect other
marine and maritime organisms
directly and indirectly.
© 2006 Thomson-Brooks Cole
Marine Viruses
• Virology—the study of viruses
• Viruses are the more abundant than
any other organism in the sea, are
diverse, and participate in food webs
• But, most authorities do not consider
them to be alive
© 2006 Thomson-Brooks Cole
Viral Characteristics
• 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
• Viral replication must occur within a
host cell
• Viruses infect all groups of living
organisms, but may be specialized
© 2006 Thomson-Brooks Cole
Viral Characteristics
• Viral structure
– virus particle is called a virion when
outside the host cell
– virion composed of a nucleic acid core
surrounded by a coat of protein called a
capsid (together called a nucleocapsid)
– may have an envelope, a membrane
derived from the host’s nuclear or cell
membrane
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Viral Characteristics
– viral shapes:
• icosahedral viruses—capsid with 20 triangular
faces composed of protein subunits
• helical viruses—protein subunits of the capsid
spiral around the central core of nucleic acid
• binal viruses—those with icosahedral heads
and helical tails
– some virions have filaments and other
parts used to attach to and infect the host
cell
© 2006 Thomson-Brooks Cole
Viral Characteristics
• Viral life cycles
– lytic cycle—a rapid cycle of infection,
replication of viral nucleic acids and
proteins, assembly of virions, and release
of virions by rupture (lysis) of the cell
– lysogenic cycle—the viral nucleic acid is
inserted into the host genome and may
reside there through multiple cell divisions
before becoming lytic
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Biodiversity and Distribution
of Marine Viruses
• 10 times more abundant than marine
prokaryotes
• estimated 100 to 10,000 genotypes
• most planktonic viruses are icosahdral
or binal bacteriophages with lytic life
cycles
• sediment viruses are typically helical
and lysogenic
© 2006 Thomson-Brooks Cole
Ecology of Marine Viruses
• Viruses kill host cells, and thus control
populations of bacteria and other
microbes in plankton communities
• Lysis releases nutrients and facilitates
sedimentation
• Viral populations are probably
controlled by several factors
– e.g. alteration by light, adsorption onto
suspended particles, ingestion by
microbes, failure to attach to appropriate
host cell
© 2006 Thomson-Brooks Cole
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
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Nutritional Types
• Cyanobacteria
– photosynthetic bacteria which are found in
environments high in dissolved oxygen,
and produce free oxygen
– store excess photosynthetic products as
cyanophycean starch and oils
– primary photosynthetic pigments are
chlorophyll a and chlorophyll b
– accessory pigments include carotenoids
and phycobilins
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Nutritional Types
(Cyanobacteria)
– chromatic adaptation—response of
pigment composition to the quality of light
in the sea
– may exist as single cells or form dense
mats held together by mucilage
• stromatolites—a coral-like mound of microbes
that trap sediment and precipitate minerals in
shallow tropical seas
© 2006 Thomson-Brooks Cole
Nutritional Types
• Other photosynthetic bacteria
– anaerobic green and purple sulfur and non-sulfur
bacteria do not produce oxygen
– the primary photosynthetic pigments are
bacteriochlorophylls
– sulfur bacteria are obligate anaerobes (tolerating
no oxygen)
– non-sulfur bacteria are facultative anaerobes
(respiring when in low oxygen or in the dark and
photosynthesizing anaerobically when in the
presence of light)
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Nutritional Types
• Chemosynthetic bacteria
– use energy derived from chemical
reactions that involve substances such as
ammonium ion, sulfides and elemental
sulfur, nitrites, hydrogen, and ferrous ion
– 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
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Nutritional Types
• Heterotrophic bacteria
– decomposers that obtain energy and
materials from organic matter
– return many chemicals to the marine
environment through respiration and
fermentation
– populate the surface of organic particles
suspended in the water
© 2006 Thomson-Brooks Cole
Nutritional Types
(Heterotrophic Bacteria)
– association of heterotrophic bacteria with
particles in the water column aids with:
• consolidation—adjacent particles adhere
• lithification—formation of mineral cement
between particles
• sedimentation—settling of particles
– marine snow—large, cobweb-like drifting
structures formed by mucus secreted by
many kinds of plankton, where particles
may accumulate
© 2006 Thomson-Brooks Cole
Nitrogen Fixation and
Nitrification
• Nitrogen fixation—process that
converts molecular nitrogen dissolved
in seawater to ammonium ion
– major process that adds new usable
nitrogen to the sea
– carried out by some cyanobacteria and a
few archaeons with nitrogenase (enzyme)
– anaerobic process often occurs in
heterocyst (thick-walled cell in which
photosynthesis is altered to prevent
oxygen release) in cyanobacteria
© 2006 Thomson-Brooks Cole
Nitrogen Fixation and
Nitrification
• Nitrification—process of bacterial
conversion of ammonium to nitrite and
nitrate ions
– bacterial nitrification converts ammonium
into a form of nitrogen usable by other
primary producers
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Symbiotic Bacteria
• Mitochondria and chloroplasts of
members of the domain Eukarya
• 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
© 2006 Thomson-Brooks Cole
Archaea
• General characteristics
– small (0.1 to 15 micrometers)
– prokaryotic
– adapted to high and low temperatures,
high salinities, low pH, and high pressure
– differences from bacteria
• cell walls lack special sugar-amino acid
compounds in bacterial cell walls
• cell membranes contain different lipids, which
help stabilize them under extreme conditions
© 2006 Thomson-Brooks Cole
Nutritional Types
• Archaea includes photosynthesizers,
chemosynthesizers and heterotrophs
• Most are methanogens—anaerobic
organisms that metabolize organic
matter, producing methane as a waste
product
• Halobacteria (photosynthetic) trap light
using bacteriorhodopsins, purple
proteins
© 2006 Thomson-Brooks Cole
Hyperthermophiles
• Hyperthermophiles—organisms that
can survive at temperatures exceeding
100o C, such as near deep-sea vents
• Examples:
– Pyrolobus fumarii (“fire lobe of the
chimney”) is chemosynthetic, and grows
at temperatures between 90o and 113o C
– “strain 121” survived 2 hours of
incubation at 130o C
© 2006 Thomson-Brooks Cole
Eukarya
• Eukarya includes all organisms with
eukaryotic cells
• Examples:
– plants
– animals
– fungi
– algae
– single-celled animal-like protozoa
© 2006 Thomson-Brooks Cole
Fungi
• History of marine mycology
– marine fungi first discovered in 1849
– marine fungi’s ecological role is difficult to
evaluate; biomass needs to be quantified
• General features of fungi
– eukaryotes with cell walls of chitin
– many are unicellular yeasts
– filamentous fungi grow into long, multicellular filaments called hyphae that can
branch to produce a tangled mass called a
mycelium
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Fungi
– heterotrohic decomposers that recycle
organic material
• can digest lignin (major component of wood)
– store energy as glycogen
– 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
© 2006 Thomson-Brooks Cole
Fungi
• Ecology and physiology of marine fungi
– 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
© 2006 Thomson-Brooks Cole
Reproduction of Marine Fungi
• Marine yeasts reproduce asexually by
budding—mitosis that produces
daughter cells of unequal size
• Filamentous marine fungi reproduce
asexually by production of
conidiospores on the tips of hyphae
• Filamentous marine ascomycotes can
reproduce sexually by forming a
fruiting body called an ascocarp, a
structure which produces ascospores
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Maritime Lichens
• Lichens—mutualistic associations
between a fungus and an alga
– fungi are usually ascomycotes
– algae are usually green or blue-green
bacteria
• The fungus provides attachment, the
general structure, minerals, moisture
• The alga produces organic matter
through photosynthesis
© 2006 Thomson-Brooks Cole
Stramenophiles
• Stramenophiles—a diverse group of
eukaryotic organisms unified by the
nature of their cells’ 2 flagella
• The special flagella
– 1 flagellum is a simple form, usually with
a light-sensing body at the base; senses
light
– 2nd bears many mastigonemes (hair-like
filaments) with a thickened base and a
branching tip along the shaft; used for
swimming
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Stramenophiles
• Heterokont—refers to the different
form of the 2 flagella
• ochrophytes—photosynthetic type that
are usually golden brown
– e.g. diatoms, silicoflagellates
– most have chlorophyll a, chlorophill c,
beta-carotene and fucoxanthin
– end-product of photosynthesis is laminarin
(a complex carbohydrate)
© 2006 Thomson-Brooks Cole
Diatoms
• Diatom structure
– frustule—a two-part, box-shaped organic
cell wall impregnated with silica
– valve—one half of a frustule; 1 valve is
larger and fits over the other like a box lid
– 2 basic diatom shapes:
• radially symmetrical valves (generally
planktonic)
• bilaterally symmetrical valves (generally
benthic)
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Diatoms
• Locomotion in diatoms
– some benthic diatoms move by mucilage
secretion from pores and grooves
• Reproduction in diatoms
– asexual reproduction by fission
• each daughter cell gets 1 valve, and has to
grow a 2nd, smaller one to complete frustule
• auxospore—daughter cell which casts off the
small valve, increases in size, and secretes a
new frustule of normal size (occurs when cell
size reaches 50% of maximum)
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Diatoms
• Diatomaceous sediments
– frustules of dead diatoms sink and collect
on the seafloor to form silaceous 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
– diatom productivity and death is
responsible for most petroleum reserves
© 2006 Thomson-Brooks Cole
Other Ochrophytes
• Silicoflagellates
– abundant in cold marine waters
– basket-shaped external skeletons of silica
which the cell wraps around
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Other Ochrophytes
• Pelagophyceans
– e.g. bloom-forming alga Aureococcus
anophagefferens (non-toxic, coastal)
– can block light from sea grasses or clog
filter-feeding structures of molluscs
© 2006 Thomson-Brooks Cole
Labyrinthomorphs
• Spindle-shaped osmotrophic cells
• Labyrinthulids
– e.g. Labyrinthula zosterae, which caused
devastating eelgrass wasting disease
• Thraustochytrids
– planktonic and benthic decomposers
– some are pathogens of shellfish
– used to produce dietary supplements of
the polyunsaturated omega-3 fatty acid
docosahexaenoic acid (DHA)
© 2006 Thomson-Brooks Cole
Haptophytes
• Photosynthetic organisms with 2
simple flagella used for locomotion
• Have haptonema—a unique structure
arising from the cell surface between
the 2 flagella, which captures food
• Most are coccolithophores with a
surface coating of disc-shaped scales
(coliths) of calcium carbonate
– remains form calcereous oozes
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Alveolates
• Have membranous sacs (alveoli)
beneath their cell membranes
– pellicle—term for the cell surface if the
combination of cell membrane and alveoli
is complex (distinct from cell wall)
• Examples:
– dinoflagellates
– ciliates
– apicomplexans (strictly parasitic)
© 2006 Thomson-Brooks Cole
Alveolates
• Dinoflagellates
– globular, unicellular (sometimes colonial)
– dinosporin—a unique chemical associated
with the cellulose plates within the alveoli
of dinoflagellates
– dinoflagellate structure
• heterokont flagella
• simple flagellum encircles the cell in the
cingulum (a horizontal groove) and produces a
spinning motion
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Alveolates (Dinoflagellates)
– dinoflagellate structure
• longer flagellum with hair-like filaments trails
down the sulcus (a longitudinal groove) and
imparts most of the forward motion to the cell
• unarmored dinoflagellates have few or no
cellulose plates in the pellicle; armored
dinoflagellates have multiple layers of them
• number, size and shapes of plates are used to
identify different species
© 2006 Thomson-Brooks Cole
Alveolates (Dinoflagellates)
– dinoflagellate nutrition
• photosynthetic ones have chlorophylls a and c,
beta-carotene and peridinin (a xanthophyll
which imparts a golden-brown color)
• mixotrophic photosynthetic ones supplement
photosynthesis by osmotrophy (absorbing
nutrients) or phagotrophy (engulfing nutrients)
– reproduction in dinoflagellates
• asexual reproduction by fission
• sexual reproduction by fusion and meiosis
• often have dormant stages (cyst formation)
© 2006 Thomson-Brooks Cole
Alveolates (Dinoflagellates)
– 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
© 2006 Thomson-Brooks Cole
Alveolates (Dinoflagellates)
– 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 occurs in humans who
consume shellfish contaminated with these toxins
• oxygen content of the water may be reduced
to deadly levels as bacteria decompose
animals killed by dinoflagellate toxins
© 2006 Thomson-Brooks Cole
Alveolates
• 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
– 10 micrometers-3 mm long members of
plankton and bethos
– reproduce asexually by binary fission and
sexually by conjugation
(nuclei transfer)
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Alveolates (Ciliates)
– types of marine ciliates
• scuticociliates (have a dense andn uniform
distribution of cilia on their body)
• oligotrichs (have few cilia)
• tintinnids (usually lack body cilia and secrete
an organic, loosely fitting shell, the lorica)
– ecological roles of marine ciliates
• most are heterotrophs; some harbor
autotrophic symbionts or chloroplasts
• link hetero- and autotrophic blue-green
bacteria to higher levels in the food chain
© 2006 Thomson-Brooks Cole
Choanoflagellates
• A 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
– cell often surrounded by a lorica of
siliceous rods; flagellum is surrounded by
a funnel-shaped collar of microvilli
• Highly efficient consumers of bacteria
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
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)
• Most have a test—an externally
secreted organic membrane often
covered with foreign particles or
strengthened by mineral secretions
© 2006 Thomson-Brooks Cole
Amoeboid Protozoans
• Two major phyla:
– foraminiferans (abundant, diverse)
– actinopods, which include:
• radiolarians (predominant type)
• acantharians
• heliozoans
© 2006 Thomson-Brooks Cole
Amoeboid Protozoans
• Foraminiferans (forams)
– have branched pseudopods that form
reticulopods (elaborate, net-like
structures) used to:
• snare prey
• crawl (benthic)
• reduce sinking rate (pelagic)
© 2006 Thomson-Brooks Cole
Amoeboid Protozoans
(Foraminiferans)
– foraminiferan test
• often have elaborate, multi-chambered tests of
calcium carbonate
• globigerina ooze—sediments of dead
planktonic forams, largely Globigerina
– foraminiferans and zooxanthellae
• zooxanthellae live within the cytoplasm of
many forams from nutrient-poor waters
• photosynthetic zooxanthellae use foram waste
products (e.g. CO2, ammonia) as nutrients
© 2006 Thomson-Brooks Cole
Amoeboid Protozoans
• Radiolarians
– named for long, needle-like pseudopods
• central nuclear region is surrounded by a
capsule—an external organic membrane
• pseudopods pass through pores in the capsule
and form a region called the calymma
• pseudopods capture food and slow sinking
– radiolarian oozes form from the internal
skeleton of silica of dead radiolarians
– live in the photic zone and prey on phytoand zooplankton,
sometimes copepods
© 2006 Thomson-Brooks Cole