Micro - environmental protists

What are important environmental protists?

• Coccolithophores

• Diatoms

• Dinoflagellates

What is the structure of Coccolithophores?

• Enclosed by calcareous plates called coccoliths

• Each cell contains two brown chloroplasts that surround the nucleus

What function do the coccoliths provide to the protist?

• Protection: predators, osmotic changes, chemical/mechanical shock, short-wavelength light

• Energy production: precipitation of CaCO3 directly from bicarbonate to form CO2

• Weight: allows the organism to reach the nutrient rich layers of water without sinking to dangerous depths

How can Coccolithophores form algal blooms?

• Favourable conditions cause algal blooms

• Growth is not inhibited by high UV light like other phytoplankton species

• Water turns an opaque turquoise - ‘white waters’

How do Coccolithophores help with sediment production?

• Account for 30-50% of global CaCO3 production

• Important role in the sequestration of carbon into the deeper ocean via formation of marine snow

• Major component of the calcareous oozes

• Main component of the White Cliffs of Dover

How do Coccolithophores have ecological importance through their distribution?

• Occur throughout the world oceans associated with very low levels of nutrients - oligotrophic conditions

• Light and temperature are the strongest predictors of coccolithophore diversity

How does ocean acidification affect coccolithophores?

• Experiments showed marked reduction in CaCO3 skeletons and deformations under high CO2

• As acidity increases the coccoliths become more important as carbon sinks

• Recent CO2 increases have seen a sharp increase in the population of coccolithophores

• Effect is uncertain - undergoing active research

What is the importance of diatoms in an ecosystem?

• Contribute ~45% of the total oceanic primary production of organic material

• Generate around 20-50% of the oxygen produced on the planet every year

• Shells of dead diatoms can reach as far as half a mile deep on the ocean floor

• Fertilised the entirety of the Amazon basin due to transatlantic winds

How are diatoms distributed in ecosystems?

• Dominant in nutrient-rich coastal water

• During oceanic spring blooms can divide more rapidly than other groups of phytoplankton - ‘bloom and bust’ lifestyle

• Silica frustules require less energy to synthesise - significant saving on overall cell energy budget

How do diatoms respond to increasing ocean acidification?

• Diatoms under high CO2 conditions show increased resilience in stress tests - show increased resilience to future acidified ocean conditions

• Decreased Fe bioavailability in an acidified ocean would have an opposite effect - increases stress and inhibits growth

What are the main characteristics of dinoflagellates?

• Possess two flagella

• Dinoflagellates are mostly marine, but also common in freshwater

• Many are photosynthetic

• Large fraction are mixotrophic - some are parasitic

What causes red tides?

• Caused by dinoflagellate blooms

• Produce brevetoxins (brevetoxin A) which bind to voltage-gated sodium channels

• Cause neurotoxicity

How can dinoflagellates bioluminesce?

• More than 18 genera of dinoflagellates are bioluminescent

• Majority emit a blue-green light

• Bioluminescence comes from scintillons distributed in the cortical region of the cells as off-shoots of the main vacuole

• Bioluminescence is regulated by the protists’ circadian clock

• Dinoflagellate luciferase is the main enzyme involved in dinoflagellate bioluminescence

• Chlorophyll-derived tetrapyrrole ring that acts as a substrate to the light producing reaction

• Luminescence occurs as a brief flash when stimulates - usually due to mechanical disturbance

How do dinoflagellates live in a symbiotic form?

• The Symbiodinium genus of dinoflagellate

• Resides in the endoderm of cnidarians (coral, sea anemones, jellyfish) in tropical oligotrophic marine environments

• Once within the host the symbionts rapidly proliferate and dominate the cytoplasm of the host cell

• Provide 80% of the energy the coral needs via photosynthesis and take up nutrients released by the coral’s metabolism (nitrogen and carbon dioxide)

How does coral reef bleaching affect the symbiotic dinoflagellates?

• Caused by a variety of biotic and abiotic factors

• Increased/decreased water temperatures

• Oxygen starvation caused by an increase in zooplankton

• Increased sedimentation

• Bacterial and fungal infections

• Changes in salinity

• Herbicides

• Low tide and UV exposure

• Elevated sea levels due to global warming

• Sustained elevation of sea surface temperatures causes coral bleaching and reef degradation - corals can recover Symbiodinium from the environment

How do ruminants produce methane?

• Average ruminant produces 250-500 litres of methane a day

• Cellulose molecules are broken down into monosaccharides by cellulase enzymes - cellulases are produced by symbiotic microbes

• Rumen ciliates are major producers of hydrogen

• Produced by mitochondrion-derived organelles - hydrogenosomes

• The hydrogen is used by methanogens that produce methane

How do termites produce methane?

• Termites are responsible for 1-3% of global methane emissions

• Termites produce methane via decomposition of cellulose

• Cellulose is broken down in the hindgut of the termite by microbes into short-chain fatty acids

• Part of this cellulose breakdown takes place in the protists with hydrogenosomes

• Produce hydrogen that is used by methanogens that produce methane

How can protists be used as biocontrol agents?

• Used Kneallhazia solenopsae (microsporidia) to control fire ant species in the south of America

• Pathogen intracellular microsporidium that infects two invasive fire ant species in North and South America