Protists in the environment

• how much CO2 emitted from human activites has the ocean absorbed in the last 200 years

  50%
• coccolithospores structure

  • Group: Haptophyta
  • Enclosed by calcareous plates called coccoliths
  • Each cell contains two brown chloroplasts, which surround the nucleus.

  
• coccolithospores function

  • Protection? From predators, osmotic changes, chemical or mechanical shock, and short-wavelength light.
  • Energy production? Precipitation of calcium carbonate from bicarbonate solution produces free carbon dioxide directly within the cellular body of the alga
  • Added weight? Allows the organism to sink to lower, more nutrient rich layers of the water and conversely, that coccoliths add buoyancy, stopping the cell from sinking to dangerous depths.
• algal blooms

  • Favourable conditions cause algal blooms - can cover over 100,000 km2
  • Growth is not inhibited by high UV light, like other phytoplankton species.
  • Water turns an opaque turquoise “white waters” - calcite plates reflect light, brightening the ocean e.g. the Great Calcite Belt in the southern oceans.
• sediments of coccolithospores

  • Account for 30-50% of global CaCO3 production.
  • Important role in the sequestration of carbon into the deeper ocean via formation of marine snow.
  • A major component of the calcareous oozes - cover up to 35% of the ocean floor and is kilometres thick in places.
  • Coccoliths are the main component of the Chalk Cliffs of Dover.
• ecological importance of coccolithospores

  • Occur throughout the world ocean associated with very low levels of nutrients = oligotrophic conditions.
  • Light and temperature are the strongest predictors of coccolithophore diversity.
• ocean acidification of coccolithospores

  • First experiments showed marked reduction in CaCO3 skeleton and deformations, under high CO2
  • However, as ocean acidity increases, their coccoliths may become even more important as a carbon sink.
  • Recent CO2 increases have seen a sharp increase in the population of coccolithophores.
• diatoms

  • Found in the oceans, waterways and soils of the world.
  • Contribute ~45% of the total oceanic primary production of organic material found in the oceans.
  • Generate about 20-50% percent of the oxygen produced on the planet each year.
  • The shells of dead diatoms can reach as much as a half mile deep on the ocean floor
• distribution of diatoms

  • Dominant in nutrient-rich coastal waters and during oceanic spring blooms, since they can divide more rapidly than other groups of phytoplankton. “bloom and bust" lifestyle.
  • Silica frustules require less energy to synthesize, potentially a significant saving on the overall cell energy budget.
• ocean acidification

  • Importantly, diatoms under elevated CO2 conditions show increased resilience in stress tests, demonstrating increased resilience to future acidified ocean conditions.
  • However, decreased Fe bioavailability in an acidified ocean could have an opposite effect by increasing stress and inhibiting growth
• ecological importance of diatoms

  The entire Amazon basin is fertilised annually by 27 million tons of diatom shell dust transported by east-to-west (easterly) transatlantic winds from the bed of a dried up lake once covering much of the African Sahara. In 5000 BC, mega-lake Chad was the largest of several Saharan freshwater lakes. Huge volumes of diatoms died and dropped through the water column to the lakebed. The mega-lake dried up rapidly, leaving behind the deep Bodélé Depression and today’s Lake Chad, now only 1,350 km2 (520 mi2).
• dinoflagellates

  • They possess two flagella.
  • Dinoflagellates are mostly marine, but they also are common in freshwater.
  • Many dinoflagellates are photosynthetic but a large fraction of these are mixotrophic and some are parasitic.
• red tides and dinoflagellates

  • Red tides are a result of high concentrations of Karenia brevis, a microscopic marine algae that occurs naturally but normally in lower concentrations.
  • In high concentrations, its toxin paralyzes the central nervous system of fish so they cannot breathe
  • The brevetoxins bind to voltage-gated sodium channels
  • Neurotoxic shellfish poisoning: Neurotoxins contaminating food chain after “Red Tides” lead to modelling of 2005 Red tide data by WHO. Predictions in 2008 altered shell fishery behaviour so fewer health issues
• bioluminescence of dinoflagellates

  • At least 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 circadian clock: peak at CT14-18 (CT12 = LD transition)
  • dinoflagellate luciferase is the main enzyme involved in dinoflagellate bioluminescence, with luciferin, a chlorophyll-derived tetrapyrrole ring acting as a substrate to the light-producing reaction. T
  • The luminescence occurs as a brief (0.1 sec) blue flash (max 476 nm) when stimulated, usually mechanical disturbance
• symbiodinium

  • Genus of dinoflagellate -resides in the endoderm of cnidarians such as corals, sea anemones and jellyfish in tropical oligotrophic (nutrient-poor), marine environments.
  • Once within the host, these symbionts rapidly proliferate in and in many cases dominate the cytoplasm of the host cell.
  • Provide 80% of coral energy needs via photosynthesis, and also take up nutrients released by the coral’s metabolism such as nitrogen and carbon dioxide.
• coral bleaching

  • biotic and abiotic factors, including:
  • increased or reduced water temperatures
  • oxygen starvation caused by an increase in zooplankton
  • increased sedimentation (due to silt runoff)
  • 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 coral reef degradation.
  • 3 global scale coral pan-tropical bleaching events:
  • 1998 (mostly coastal in Great Barrier Reef)
  • 2010 (more widespread)
  • 2015/2016 (extensive and severe)
• ruminants and methane

  • Rumen: first chamber in the alimentary canal of ruminant animals. Primary site for microbial fermentation of ingested feed.
  • The average ruminant produces 250-500 litres of methane a day.
  • Cellulose molecules are broken down into monosaccharides by enzymes called cellulases  (not present in most animals)
  • Cellulases are produced by symbiotic microbes
  • Rumen ciliates are major producers of H2, produced by mitochondrion-derived organelles known as hydrogenosomes
  • The hydrogen is used by methanogens that produce methane
  • Can we rear cows without ciliates?
  • Elimination of the ciliates increases microbial protein supply by up to 30% and reduces methane production by up to 11%.
  • No safe, economically viable method to do this (yet)
• termites

  • Methane is roughly 30 times more potent as a heat-trapping gas than carbon dioxide.
  • Termites are responsible for 1 to 3% of global methane (CH4) emissions.
  • Cellulose is a major sugar in wood and it is broken down in the hindgut of the termite by microbes into molecules called short-chain fatty acids.
  • Part of this cellulose breakdown takes place in the protists which have hydrogenosomes (modified mitochondria).
  • These produce hydrogen which is used by methanogens that produce methane
  • Examples: Trichonympha (an excavate) and some hydrogenosome-containing ciliates