FAUNAL PHYSIOLOGICAL ADAPTATIONS IN HYDROTHERMAL VENT COMMUNITIES

1. FAUNAL PHYSIOLOGICAL ADAPTATIONS IN HYDROTHERMAL VENT COMMUNITIES 18 November 2009 Megan Vaughan, Megan Guest, Meade Humble

2. Introduction - Recap  Biomass trends in the deep sea – Biomass generally decreases with depth, until it is ~1% as that of the surface at 4km; Food intake – Most organisms in the deep sea depend on photosynthetically derived material from surface waters; Major divisions – Organisms divided into epifauna and infauna – deep sea dominated by Echinodermata and Arthropoda

3. ▫ discovery of hydrothermal vents (due to strange chemical and thermal readings) changes many of these assumptions - Vents have extreme environmental conditions – organisms must find ways to cope with drastic changes in temperature, pressure, lack of light, toxicity, dissolved oxygen

4. Fauna of Hydrothermal Vents - Molluscs  both very big compared to other deep-sea species; occupy crevices ▫ Calyptogenamagnifica ▫ Bathymodilusthermophilus can have densities of 10 kg/m2; influences names of vent sites (Mussel Bed and Clambake); has a mouth and gut, unlike most vent species, so may also get some nutrient flux from surface productivity; lower levels of enzymatic activity in gill tissues may mean more independence from symbiontsthan other species http://www.mbari.org/molecular/images/mussels.jpg http://www.ifm-geomar.de/fileadmin/ifm-geomar/allgemein/avillwock/meeresonline/calyptogena.jpg

5. - Worms ▫ Riftiapachyptila also anchored in crevices; placed within class Vestimentifera; gills not just for respiration, but also to collect food for symbionts; more tolerant of anoxia because of presence of haemoglobin (?); C.magnifica tends to avoid settling with Riftia, but other species use tube as extra habitat ▫ Alvinellapompejana a polychaete; tend to be found around hotter of vents (150-350°C); form ‘honeycomb-like tube masses’; seem to cultivate and eat bacteria more than use symbiosis ▫ Saxipendiumcoronatum draped over rocks on vents in Galapagos; could be suspension feeders http://www.bioweb.uncc.edu/biol2120/Images/Riftia.jpg

6. - Crustaceans ▫ Crabs (including Cyanograeapraedator, Bythograeathermydron)  live among Riftia tubes ▫ Shrimp (Alvinocarislusca) - Others  anemones, fish, larvae, copepods http://open.live.bbc.co.uk/dynamic_images/naturelibrary_626/downloads.bbc.co.uk/earth/naturelibrary/assets/b/by/bythograeidae/bythograeidae_1.jpg http://farm1.static.flickr.com/6/6488639_995a416072.jpg?v=0

7. Symbiosis -Whole vent community supported by chemoautotrophic bacteria – oxidize sulphur compounds from vent fluid – fix organic carbon from CO2 and CH4 - Can influence distribution of hosts around vents – depend on redox reactions to get energy/nutrition and therefore must lie between vent fluid and ambient water

8. - Both molluscs and worms contain huge numbers of symbionts within their tissues – C.magnifica’s gills are 75% bacteria, and so is a third of Riftia’s body weight! ▫ Belkinet al (1986) found that bacteria in Riftia can synthesize sulfide and not thiosulfate, but for Bathymodiolus, it was opposite. http://www.hydrothermalvent.com/php/symbiosis/174-424.html

9. Belkinet al, 1986

10. Chemosynthesis - “Chemosynthesis:The pathway by which bacteria in hydrothermal vent communities synthesize complex organic molecules from hydrogen sulphide gas and dissolved carbon dioxide:” 4H2S + CO2 + O2 → CH2O + 4S + 3H2O Allaby, A. and Allaby, M. (1999) “Chemosynthesis” The Dictionary of Earth Sciences, Acessed online 12 Nov 2009

11. - Cavanaugh et al (1981)  bacteria in Riftia mostly contained in an organ called a trophosome – contains sulphur granuoles; was previously found that APS reductase and ATP sulfurylase (enzymes that produce ATP from oxidizing sulphur) were in high concentrations in trophosomal tissue http://www.divediscover.whoi.edu/images/biology-anatomy.jpg

12. Hydrogen Sulfide • H2S, HS-, S2- • Oxidation produces high amounts of energy Hydrogen Sulfide Sulfate Elemental Sulfur Sulfite http://filebox.vt.edu/users/chagedor/biol_4684/Cycles/Soxidat.html

13. Hydrogen Sulfide • H2S extremely toxic • Inhibits cytochrome-c oxidase http://vcell.ndsu.edu/animations/etc/first.htm

14. Hydrogen Sulfide • Dissolved sulfide reacts spontaneously with oxygen and other oxidants to form less reduced compounds • Vent fauna must sequester and transport sulfide to the trophosome while preventing poisoning or oxidation

15. Sulfide Uptake and Transport • Acidic vent water  H2S • Physiological pH ~ 7.5 (H2S = HS-) Morel (1983)

16. Sulfide Uptake and Transport (R. pachyptila) • Diffusion of H2S limited (mechanism?) • HS- principal sulfure species at physiological pH • HS- taken up by the tubeworm binds rapidly to hemoglobin http://bugs.bio.usyd.edu.au/learning/resources/Polychaetes/riftia1.htm

17. Goffredi et al. (1997) HS- H2S

18. Hemoglobin • Hemoglobin transports HS- and O2 to the trophosome • Sulfide cannot react with O2 or inhibit aerobic respiration when bound to hemoglobin • High affinity for both HS- and O2 (no competition for O2 binding site) • High concentrations in the vascular blood • Three types: V1 (~3500 kDa), V2 (~400 kDa), and C1 (~400 kDa) • V1 can bind 3X more sulfide

19. Fisher et al. (1988)

20. Oxygen • Endosymbiotic bacteria require high concentrations of O2 • O2 binds to hemoglobin, maintaining a partial pressure gradient and reducing sulfide oxidation • Temperature Effects: • Hemoglobin affinity for O2 decreases at higher temperatures

21. R. pachyptila Wittenberg et al. (1981)

22. Temperature • Vent fauna are adapted to extreme temperatures • E.g. Alvinellid polychaetes are likely the most thermotolerant hydrothermal-vent metazoans A. pompejana http://absentmag.org/issue02/html/simon_dedeo.html

23. A. pompejana (Pompeii worm) Cary et al. (1998) Start Recording Recover Probes

24. A. pompejana (Pompeii worm) • Not possible to measure body temperature in situ • Methods obtain inaccurate results due to the nature of the worm and its tube Chevaldonne et al. (2000)

25. Thermal Adaptations Enzymes remain active at higher temperatures Dahloff et al. (1991)

26. Thermal Adaptations • High numbers of linker chains in hemoglobin • Thermostability of rDNA http://www.cadilapharma.com/cadila/business.htm

27. Dixon et al. (1992) Warmer Habitat Cooler Habitat

28. Growth Rates • Giant Tubeworm (Riftia) colonized new vents following volcanic eruption, 9˚N EPR • Tube length increased at rate > 85 cm yr during 1st year of growth • Sexually mature within 2 years • Smaller tubeworm (Tevnia jerichonana), colonized same site, with GR > 30 cm yr, reaching full size within one year (Lutz et al. 1994)

29. Growth Rates • Clayptogena Magnifica & Bathymodiolus thermophilus • Radiochronometry, direct measurement of shell growth and shell dissolution techniques • 0.5 to 4-6 cm y⁻1 depending on technique, size, and site

30. Energy Metabolism Hand & Somero 1983 • Non-vent organisms have low rates of metabolism, an adaptation to low food availability • Can rich food supply support high metabolism of vent species even in the presence of Hydrogen Sulfide? • HSˉ inhibitor of Cytochrome-c oxidase & aerobic respiration • Compared enzyme activity of energy metabolism pathways • Glycolysis • Citric Acid (Krebs) Cycle • Electron transport chain For Vent spp., and shallow-living marine spp.

31. Enzyme activity Hand and Somero (1983)

32. Hand & Somero (1983) Results: • Enzyme activity in vent tissues qualitatively and quantitatively similar to related shallow-living species • Types of metabolic pathways and flux rate through pathways are similar to non-vent organisms. • Rates of Primary production by chemolithotropic bacteria at vents may be high enough to sustain metabolic rates comparable to shallow water animals in food rich environments • Cytochrome c oxidase activity comparable, despite high HSˉ • Except clam which may rely on anaerobic metabolism Adaptation to HSˉ toxicity must depend on other physiological adaptations

33. Sulfide Detoxification • Sulfide insensitive systems • Exclusion of H2S • Symbiont Consumption • Sulfide binding • Amino Acid Metabolism • Peripheral & Internal Defense • Epibionts • Tubes & Cuticles

34. Sulfide Detoxification • Sulfide insensitive hemoglobin & cytochrome-c oxidase systems • Only Riftiahave sulfide insensitive hemoglobin • Exclusion of H2S • Active exclusion through membrane (only in Riftia) • Symbiont Consumption • Endosymbiotic bacteria oxidize sulfide as an energy source • Sulfide binding • Binding of Sulfide to render it inactive • Tubeworms, bind sulfide to hemoglobin • Clam, sulfide binding factor (Arp et al. 1983)

35. Sulfide Detoxification • Amino Acid Metabolism (Brand et al. 2007) • Protection from and/or transport of Sulfide • Hypotaurine • high in all tissues • Thiotaurine = (Hypotaurine + Sulfide) • Vent mussels have unusually high concentrations of the amino acid thiotaurine compared to shallow-water, non-symbiont bearing mussels • Vent tubeworms and clams also have high levels of thiotaurine • Thiotaurine contents increase during sulfide exposure in symbiont-bearing tissues • Rxn is reversible, stores sulfide, released as endosymbionts deplete free sulfide

36. Amino Acid Metabolism • Varying levels of Thiotaurine represent differences in sulfide levels • Environmental sulfide levels • Dependency on amino acid detoxification (Brand et al. 2007)

37. Sulfide Detoxification • Peripheral & Internal Defence • Sulfide oxidizing activities in superficial cell layers of non-symbiotic species • Epibionts • Sulfide-oxidizing chemoautotrophic activity • Precipitate sulfide bound to minerals • Tubes & Cuticles • Act as Barriers to diffusion of sulfide http://oldsite.dri.edu/deesprojects/alison_VEEG.htm

38. Heavy Metal Detoxification • Metallothinein • Metal-binding protein • Common in specific tissues of vent organisms • Polychaetes store metals in membrane bound vesicles • Riftia • highest concentrations found in trophosome • A. Pompejana (Pompeii worm) • metallothinein associated with dorsal epidermis and digestive system • Paralvinella sp • mucus (Containing metallothionein-like proteins) sheds inorganic particles from surface

39. Heavy Metal Detoxification • C. magnifica (vent clam) • Intracellular granules in kidney cells, eventually excreted • Crustaceans • Incorporate trace elements in exoskeleton • Loose metals during molting

40. Additional References • Brand, G.L., Horak, R.V., Le Bris, N., Goffredi, S.K., Carney, S.L., Govenar, B., Yancey, P.H. 2006. Hypotaurine and thiotaurineas indicators of sulfide exposure in bivalves and vestimentiferans from hydrothermal vents and cold seeps. Marine Ecology. 28 (1): 206-216. • Dahloff, E., O’Brien, J., Somero, G. N., Vetter, R. D. 1991. Temperature effects on mitochondria from hydrothermal vent invertebrates: Evidence for adaptations to elevated and variable habitat temperatures. Physiol. Zool. 64:1490-1508 • Dahloff, E., J., Somero, G. N. 1991. Pressure and temperature effects on mitochondria dehydrogenase of shallow- and deep-living marine invertebrates: Evidence for high body temperatures in hydrothermal vent animals. J. Exp. Biol. 159: 473-487 • Dixon, D. R., Simpson-White, R., Dixon, L. R. J. 1992. Evidence for thermal stability of ribosomal DNA sequences in hydrothermal vent organisms. J. Mar. Biol. Assoc. U.K. 72: 519-527. • Fisher, C. R., Childress, J. J., Sanders, N. K. 1988. The role of vestimentiferan hemoglobin in providing an environment suitable for chemoautotrophic sulfide-oxidizing endosymbionts. Symbiosis 5: 229-246. • Godfredi, S. K., Childress, J. J., Desaulniers, N. T., Lallier, F. H. 1997. Sulfide acquisition by the vent worm Riftia pachyptila appears to be via uptake of HS- rather than H2S. J. Exp. Biol. 200: 2609-2616. • Morel, F. M. M. 1983. Principles of Aquatic Chemistry. John Wiley & Sons, New York, 446 p. • Van Dover, C. L. 2000. Physiological ecology. In: The Ecology of Deep-Sea Hydrothermal Vents. Princeton University Press, Princeton, pp. 183-208. • Wittenberg, J. B., Morris, R. J., Gibson, Q. H., Jones, M. L. 1981. Hemoglobin kinetics of the Galapagos rift vent worm, Riftia pachyptila Jones (Pogonophora: Vestimentifera). Science 213: 344-346.