Chemosynthetic pigments Flashcards
How does a hydrothermal event form?
- 1.fractures develop as the plates are pulled apart
2. Cold seawater (2-4oC) seeps into the fractures and is heated by the hot magma (1400oC)
3. superheated water is forced back up to the seafloor carrying dissolved minerals leached from the basalt ocean plate
4. a vent forms when the jet of water shoots through the sea floor and its dissolved minerals begin to precipitate out. The minerals grow into a chimney, or “black smoker“
5. diffuse vent, where lower temperature fluids exit the seafloor as shimmering water through cracks surrounding high-temperature smokers
What are the three main types of seepage?
- 3 main types of seepage: 1) hydrocarbon, 2) groundwater (brine) and 3) mantle materials
- Most common are seeps of CH4 rising up through sediments or exposed through erosion activity
- Percolating cool seawater contains H2S and other chemicals
What successional phases do we see at whale falls?
- Decaying whale carcasses undergo 3 (4?) successional phases
- 3rd phase is the sulphophilic (“or sulphur-loving”) stage lasting for decades
- Emits sulphide from anaerobic breakdown of bone lipids
- Chemoautotrophic component deriving nutrition from sulphur-oxidising bacteria
- Local species diversity on large whale skeletons during the sulphophilic stage (~185 species) is higher than in any other deep-sea hard substratum community
What is chemosynthesis?
the biological conversion of carbon molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic molecules (e.g. hydrogen gas, hydrogen sulphide) or methane as a source of energy
Thiotrophic
Describing an organism that oxidizes sulfur compounds as a major part of its metabolism
Thiotrophic
Sulphur chemoautotrophy is a 2-step process
Production of ATP by oxidation of Sulphide and fixation of inorganic carbon via the Calvin-Benson Cycle (light-independent reaction)
Where were chemoautotrophic symbioses first recognised?
Chemoautotrophic symbioses were first recognized in hydrothermal vent vestimentiferan tube worms (Felbeck, 1981; Cavanaugh et al, 1981) and shortly thereafter in vesicomyid clams (Cavanaugh, 1983)
Contain abundant intracellular chemoautotrophic sulphur bacteria that can use sulphide as an electron donor and can provide the bulk of their hosts’ organic carbon requirements (Childress and Fisher, 1992).
Bacteria can be _symbionts or _____symbionts.
Bacteria can be endosymbionts or episymbionts
Episymbionts tend to live on the surface of the bacteria
Novel metabolic demands
What requirements do internal symbionts have?
- Carbon - Autotrophic symbionts require a net uptake of CO2 into the host animal
- Sulphide - Demand for uptake and transport. Can poison aerobic metabolism and interfere with Haemoglobin O2 transport
- Oxygen - must supply the host, symbiont and provide for the oxidation of sulphide to sulphate
- Nitrogen - uptake of inorganic nitrogen is opposite to usual heterotrophic situation. Ammonium and nitrate from seawater contribute to symbiont requirements
Riftia pachyptila – the Giant Tubeworm
What are the main body regions of the tube worm?
Large, rapid growth rates
Lack MOUTH and DIGESTIVE SYSTEM
Specialised TROPHOSOME organ
Anatomy geared to substrate demands of symbionts
4 body regions
- Tentacular Plume – Obturaculum
- Muscular collar – Vestimentum
- Trunk
- Opisthosome – segmented, posterior
Tube sealed and attached to substratum
What are some adaptations of Riftia pachyptila – the Giant Tubeworm
- Found in areas of high vent fluid flow, 15-20oC
- [H2S]@15oC = 1-3mM, [O2] ~zero@11oC
- Trophosome, rich in blood vessels
- Inner layers lined with bacteriocyte cells (3-5µm)
- No cell is further than 10µm from a capillary
Inorganic Carbon Uptake and Transport
Majority of heterotrophs experience net outward flux of CO2
Tubeworms require net inward flux to support symbionts
where does this come from?
50% of fixed inorganic carbon is provide by respiratory CO2
Remainder comes from the environment
Problem! (Tubeworms require net inward flux to support symbionts)
Seawater = abundance of bicarbonate ions (HCO3-)
Not readily diffusible
CO2 is at low partial pressure @ambient seawater pH
Solution!
CO2 in enriched vent effluent elevated by reduced pH (~6.0)
Steep gradients facilitate diffusion
Uptake enhanced by more alkaline tubeworm blood (7.3-7.4) and carbonic anhydrase enzyme
How is carbon dioxide transported in tubeworms blood?
CO2 may be transported freely dissolved in the blood as CO2 or HCO3-
Not bound to haemoglobins
Some inorganic carbon is rapidly incorporated into 4-carbon organic acids (Felbeck 1985)
Initial fixation in the plume (releasing succinate into blood) and in the vestimentum (releasing malate)
Experimental evidence indicates that acid transport can match that of dissolved CO2 (Felbeck and Turner 1995)
Acids reaching the trophosome are decarboxylated releasing CO2 for symbionts
Tubeworm pH regulation
Regulation of tubeworm pH has been described as “unprecedented” (Goffredi et al. 1997a)
Maintains a large pH gradient
Erratic environmental fluctuations in pH
Metabolic processes releasing protons (CO2 to HCO3- and H2S oxidation to SO42-)
How?
Proposed high rate proton-pumping mechanism maintains internal, extracellular pH (7.3-7.4)
Alkaline pH then facilitates carbon uptake
H2S produces large amounts of energy when oxidised
Toxic at micromolar concentrations!
What are the problems to the host?
Binds to cytochrome-c oxidase – blocking function
Tubeworms have no special resistance and O2 consumption rates are comparable to other invertebrates
