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
What are the solutions to suphide toxicity for the host?
H2S reacts with O2 to produce less toxic compounds
Have no energetic value for symbionts
Must get sulphide to the trophosome without poisoning the worm’s aerobic respiration
What frms does the riftis take up and transport sulphide?
- H2S readily available in acidic vent water – strong diffusion gradient
Diffusion limited by an unknown mechanism
HS- is taken up and predominates in Riftia blood
- HS- binds rapidly with high affinity to haemoglobins in vascular blood and coelomic fluid
- Sulphide does not compete with the O2 binding site - unusual
- Exclude H2S as that is the toxic form that will block cytochrome-c oxidase
- Allows tubeworms to concentrate sulphide while maintaining low internal concentrations
What type of haempoglobon do riftia have?
- High affinity for sulphide
When bound it is stable – cannot react with O2 or cytochrome-c oxidase function
2 types of haemoglobin – large and small
- Large dominates in vascular blood – 3x binding capacity
Concentrate sulphide from the environment by 1-2 orders of magnitude
How are oxygen demands of riftia mnet?
High affinity for O2 = large take up and transport while maintaining low internal dissolved O2
Prevents spontaneous oxidation of free sulphide in the blood
Affinity decreases and O2 dissociation increase at elevated temperatures
Good for unloading O2 at the trophosome
Somero et al. (1989) proposed several mechanisms for protecting aerobic metabolic systems from sulphide poisoning
- Exclusion of H2S
- Symbiont consumption
- Sulphide binding
- Sulphide insensitive haemoglobins
Thermal adapttaions - what os the break point?
Arrhenius break point – “temperature above which respiration or enzyme activity drops off dramatically”
High correlation between break point and habitat temperature (Dahlhoff et al. 1991)
Enzyme kinetics of malate dehydrogenase can be used to predict maximal sustained body temperature (Dahlhoff and Somero, 1991)
Give an example of a thermally adapted species
Alvinellid polychaetes
Often exposed to 30-70oC, one measurement of 105oC!
Thermal gradient of up to 60oC over one body length
Haemoglobin of Alvinella pompejana is unstable at 50oC (1atm)
Thermal stability of enzymes indicates that species in ‘warmer’ habitats have thermally resistant enzymes compared to ‘cooler’ habitat species (Jollivet et al. 1995)
Membranes are more thermally stable – greater double bonding in fatty acids
Give a whale fall specialist
Osedax spp. – the ‘Zombie’ worm
Osedax spp. – the ‘Zombie’ worm
Describe the adaptations.
Genus of deep-sea siboglinid polychaete with 6 known species
Bore into the bone to reach the lipid energy source
Lacking stomach and mouth, Osedax rely on symbiotic bacteria to digest the bone lipids
Plumes act as gills for uptake of oxygen
Root-structure used to absorb nutrients from bacteria
50 - 100 microscopic dwarf males live inside a single female, and never develop past the larval stage
Summary
Specialist vent organisms obtain energy via chemosynthesis
Symbiotic and epibiotic bacteria
Symbionts make novel metabolic demands on the host
Tubeworms (Riftia pachyptila) and giant clams (Calyptogena magnifica) have adapted novel physiologies to survive
Uptake of CO2 by pH regulation (gradients) and transport as carboxylic acids
Sulphate uptake required as fuel – problems with toxicity
Uptake HS- instead of H2S (tubeworms)
Rapid binding to high affinity haemoglobins or non-protein binding factors
Temperature tolerances through resistant enzymes, more double bonds in cell membranes and rDNA with elevated guanine-cytosine
