Marine Microbes
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.
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.
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.
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
• Viruses of marine eukaryotic hosts first
reported in the 1970s
• Reliable counts of marine viruses made in
the 1980s
Viral Characteristics
• Most authorities do not consider them to be alive
• 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
• Origin of viruses: two hypotheses
– highly reduced prokaryotic parasites
– renegade genes
• Viruses infect all groups of living organisms, but
may be specialized
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 a protective envelope, a membrane
derived from the host’s nuclear or cell
membrane
http://www.ncbi.nlm.nih.gov/ICTVdb/Images/
Viroscoop2005_07minPoster.jpg
Viral Characteristics
• Viral structure (con’t)
– 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
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
lysis (rupture) 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
Lytic Cycle
Infection
Replication
Lysis
Lysogenic Cycle
Stepped Art
Fig. 6-3, p. 128
•
•
•
•
Biodiversity and Distribution
of Marine Viruses
10 times more abundant than marine
prokaryotes, may reach 1010 virons per
liter of seawater, 1013 per kilogram of
sediment
Estimated 100 to 10,000 genotypes
Most planktonic viruses are icosahdral or
binal bacteriophages (“bacteria eaters”)
with lytic life cycles
Sediment viruses are typically helical and
lysogenic
Ecology of Marine Viruses
• Viruses kill host cells, and thus control populations
of bacteria and other microbes in plankton
communities
• Viruses also responsible for chronic infection and
mass mortality of populations of marine animals
• Bacterial lysis can alter biogeochemical cycles and
planktonic food webs
• Viral populations are probably controlled by several
biotic and abiotic factors
– e.g. alteration by light, adsorption onto suspended
particles, ingestion by microbes, failure to attach to
appropriate host cell
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
• Spirillum – cork screw shape
Aerobic
respiration
Oxygen
CONSUMERS
Zooplankton
Animals
Aerobic
respiration
Consumed by
Die
Cyanobacteria
Phytoplankton
Multicellular algae
Plants
Chemosynthetic
bacteria
Consumed by
DECOMPOSERS
PRIMARY PRODUCERS
Photosynthesizers
Wastes
Die
Aerobic bacteria
and fungi
Consumed by
Anaerobic
bacteria
Aerobic
metabolism Fermentation
Nutrients released
Nitrogen
Sulfur
Phosphorus
Carbon dioxide
Stepped Art
Fig. 6-6, p. 131
Nutritional Types
• Cyanobacteria (blue-green bacteria)
– 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
Light energy
Carbon dioxide
(CO2)
Water
(H2O)
Carbohydrates
(CH2O)x
Oxygen
(O2)
Carbohydrates
(CH2O)x
Sulfate
(SO42–)
(a) Cyanobacteria – Free oxygen produced
Light energy
Carbon dioxide
(CO2)
Hydrogen sulfide
(H2S)
(b) Purple and green bacteria – No free oxygen produced
Stepped Art
Fig. 6-8, p. 132
Nutritional Types (Cyanobacteria)
• Cyanobacteria (con’t)
– 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
• form associates called stromatolites—a coral-like
mound of microbes that trap sediment and
precipitate minerals in shallow tropical seas
Nutritional Types
• Other photosynthetic bacteria
– anaerobic green and purple sulfur and nonsulfur 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)
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
Chemosynthetic bacteria (in animal tissues, in water, and on rocks)
Carbon
dioxide (CO2)
Produce
Water
(H2O)
Carbohydrates
Hydrogen
sulfide (H2S)
Animal
community
Carbon
dioxide (CO2)
Hydrogen
sulfide (H2S)
Elemental
sulfur (S)
Carbon
dioxide (CO2)
Stepped Art
Magma (molten rock)
Fig. 6-10, p. 134
Nutritional Types
• 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
– populate the surface of organic particles
suspended in the water by secreting mucilage
(glue-like substance)
Nutritional Types (Heterotrophic Bacteria)
• 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
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
– only some cyanobacteria and a few
archaeons with nitrogenase (enzyme) are
capable of fixing nitrogen
Nitrogen Fixation and Nitrification
• Nitrification: process of bacterial
conversion of ammonium (NH4+) to nitrite
(NO2-) and nitrate (NO3-) ions
– bacterial nitrification converts ammonium into
a form of nitrogen usable by other primary
producers (autotrophs)
NITRIFICATION
NITROGEN FIXATION
Dissolved
nitrogen (N2)
Animal wastes
recycled by
microorganisms
Nitrogen-fixing
bacteria,
cyanobacteria
Ammonia (NH3)
+Hydrogen (H2)
Ammonium (NH4+)
2N
Bacteria +Oxygen (O2)
+Hydrogen (H2)
Nitrite (NO2–)
Ammonia (NH3)
Bacteria +Oxygen (O2)
Nitrate (NO3–)
Microorganisms
Marine
plants
Phytoplankton
Algae
Stepped Art
Fig. 6-11, p. 135
Symbiotic Bacteria
• 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
• General characteristics
– small (0.1 to 15 micrometers)
– prokaryotic
– adapted to extreme environmental conditions:
high and low temperatures, high salinities, low
pH, and high pressure
– formerly considered bacteria
– 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
Archaea
• Nutritional Types
– archaea includes photosynthesizers,
chemosynthesizers and heterotrophs
– most are methanogens: anaerobic organisms
that metabolize organic matter for energy,
producing methane as a waste product
– halobacteria (photosynthetic), thrive at high
salinities, trap light using bacteriorhodopsins,
purple proteins
Archaea
• Hyperthermophiles
– organisms that can survive at temperatures
exceeding 100o C, such as near deep-sea vents
– Potential for biomedical and industrial
application
Eukarya
• Eukarya includes all organisms with
eukaryotic cells
• Examples:
– plants
– animals
– fungi
– algae
– single-celled animal-like protozoa
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
– important in marine ecosystems as
decomposers, prey, pathogens and symbionts
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
• General features of fungi (con’t)
– 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
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
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
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, general
structure, minerals, moisture
• The alga produces organic matter through
photosynthesis
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
Stramenophiles
• Heterokont: refers to the different form of
the 2 flagella
• Ochrophytes: photosynthetic type that are
usually golden brown
– e.g. diatoms, silicoflagellates and brown algae
Diatoms
• Extremely diverse and distinct members of
marine phytoplankton
• 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)
Diatoms
• Locomotion in diatoms
– some benthic diatoms move slowly 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)
Asexual Reproduction
Sexual Reproduction
New cell
Frustule formation
Growth of
the cell
(auxospore)
Zygote
Gamete
from another
Mitosis
Gametes
formed
Mitosis
Mitosis
Mitosis
Cells’ division
continues until
cells become too
small to divide
Gametes
released
Stepped Art
Fig. 6-19, p. 144
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
Other Ochrophytes
• Silicoflagellates
– abundant in cold marine waters
– basket-shaped external skeletons of silica
which the cell wraps around
– cell wraps around skeleton which appears
internal
Other Ochrophytes
• Pelagophyceans
– e.g. bloom-forming alga Aureococcus
anophagefferens (non-toxic, coastal)
responsible for “brown tides”
– can block light from sea grasses or clog filterfeeding structures of molluscs
Labyrinthomorphs
• Spindle-shaped, mucous secreting osmotrophic
cells
• Labyrinthulids
– e.g. Labyrinthula zosterae, causes devastating eelgrass
wasting disease
• Thraustochytrids
– planktonic and benthic decomposers
– some are pathogens of shellfish
– used to produce dietary supplements: oils extracted
from some species are high in polyunsaturated omega3 fatty acid docosahexaenoic acid (DHA)
Haptophytes
• Photosynthetic organisms with 2 simple
flagella both used for locomotion
• Have haptonema: a unique structure
arising from the cell surface between the 2
flagella, captures food
• Most are coccolithophores with a surface
coating of disc-shaped scales (coliths) of
calcium carbonate
– remains form calcereous oozes
Haptophytes
• Account for up to 40% of carbonate
production in modern seas
• High reflectance of chalky coccolithophores
and their production of dimethyl sulfide may
have impact on global climate change
Alveolates
• Recent re-grouping of several kinds of
marine microbes
• 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)
Alveolates
• Dinoflagellates
– globular, unicellular (sometimes colonial) with
2 flagella
– dinosporin: a unique chemical associated with
the cellulose plates within the alveoli of
dinoflagellates
– Most are planktonic, some are benthic and
others parasitic, also can be bioluminescent –
Bioluminescent Bay, Puerto Rico
Alveolates (Dinoflagellates)
• Dinoflagellate structure
– heterokont flagella
– simple flagellum encircles the cell in the cingulum (a
horizontal groove) and produces a spinning motion
– 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
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)
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
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 (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
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
– planktonic and benthic
– major links in marine food chains
– form symbiotic and parasitic relationships
– reproduce asexually by binary fission and
sexually by conjugation (nuclei transfer)
Alveolates (Ciliates)
• Types of marine ciliates
– scuticociliates (have a dense and 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
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
– cell often surrounded by a lorica of siliceous
rods; flagellum is surrounded by a funnelshaped collar of microvilli
• Highly efficient consumers of bacteria
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
• Most have a test—an externally secreted organic
membrane often covered with foreign particles or
strengthened by mineral secretions
Amoeboid Protozoans
• Two major phyla:
– foraminiferans (abundant, diverse)
– actinopods, which include:
• radiolarians (predominant type)
• acantharians
• heliozoans
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 (Foraminiferans)
• Foraminiferan test
– elaborate, multi-chambered tests of calcium
carbonate
– globigerina ooze: sediments of dead planktonic
forams, largely Globigerina
• Foraminiferans and zooxanthellae
– zooxanthellae live symbiotically within the
cytoplasm of many forams from nutrient-poor
waters
– photosynthetic zooxanthellae use foram waste
products (e.g. CO2, ammonia) as nutrients
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 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