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Chapter 7

Chapter 7. Extreme environments. Deep-sea hydrothermal vents. Discovered in 1977 in Pacific Ocean off Central America Form at seafloor spreading centers First time that a food web was recognized to be supported through a chemosynthetic energy source. Plate tectonics.

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Chapter 7

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  1. Chapter 7 Extreme environments

  2. Deep-sea hydrothermal vents Discovered in 1977 in Pacific Ocean off Central America Form at seafloor spreading centers First time that a food web was recognized to be supported through a chemosynthetic energy source.

  3. Plate tectonics

  4. Volcanism and hydrothermal vents Sea floor spreading centers

  5. How to access these environments?

  6. Vent fluids Additional chemicals CH4, CO2 How can such high temperatures be achieved?

  7. Oasis for life Based on chemosynthesis rather than photosynthesis

  8. Organic matter Sulfide, CO2 Bacteria Riftia pachyptila Gills Heart Dorsal blood vessel Ventral blood vessel Trophosome Capillary Body cavity Trophosome Tube Tube

  9. Symbionts • Symbiotic relationship between: chemosynthetic bacteria and metazoans (tube worms, clams, mytilids, and other invertebrates) • Episymbionts – ε-Proteobacteria • Endosymbionts – γ-Proteobacteria (withinbacteriocytes) • Host: ingestive and digestive morphological features are lost • Host: supplies symbiont with H2S, CO2 and O2 • Endosymbiont: supplies host with fixed C and N • Episymbiont: acquires fixed location with respect to external nutrient pool

  10. HS-, NO3- transport O2, CO2 diffusion Host biomass HS-, O2 bind hemoglobin O2 Translocation Digestion HS -→ SO32- → SO42- S0 ATP ATP Organic C, symbiont biomass ADP ADP AMP → APS pathways ATP Calvin Benson Cycle APS reductase ATP sulfurylase NADPH NH3 CO2 fixation NADP+ NO3- → NO2- Ribulose 1,5-bisphosphate carboxylase/oxygenase gills gills Energy generation

  11. Free-living microbial mats at marine hydrothermal vent sites Epilithic microbes Positioned at the HS-/O2 interface http://www.ocean.udel.edu/deepsea/level-2/chemistry/chemo.html

  12. Sulfur Oxidation Reaction Thiothrix and Beggiatoa H2S + 1/2O2 So + H2O +50 kcal energy yield Overall Reaction O2 + CO2 + 4 H2S (CH2O)x + 4So + 3H2O Energy is used to fix CO2

  13. Attachment site Attachment site

  14. Calculating how much biomass is produced over time to support a food web Incubation Biomass Carbon Productiontime (days) pg C/filament/day mg C/m2/day*_________ ______________ __________ 1 0.3 3.0 2 35 350 3 10 100 6 231 2,310*based on 107 filaments/m2

  15. SampleSpecific growth rate (h-1)1-day 0.132-day 0.066-day 0.03Thermothrix thiopara S-enriched, 74oC 0.38(Brannon & Caldwell)

  16. Cell growth rate as a function of position in filament

  17. Terrestrial counterpart to deep-sea hydrothermal vents • Yellowstone National Park • Sulfur derivatives (SO2, H2S, S° vapor) are abundant components of volcanic gases, 2nd only to CO2 by weight. • Precipitation of S° is pervasive in thermal springs when source water contains >4 µM H2S • S° serves as an abundant e- donor and acceptor for microbial growth in Dragon Spring • Where do these chemicals come from? Dragon Springs – June 2006 [H2S] = 60-80 µM

  18. Yellowstone hydrogeology Snowmelt stopped Surface water drainage Runoff channels Recent sediments Hot springs Recharge Circulating hot freshwater in fractured, porous rock Solidified rhyolite lava flow Heat Circulating brine Magma chamber of spongy, partially molten granite Heat Basaltic magma source in upper mantle, 25 miles deep

  19. Biotic S° Reduction • S° reduction is widely distributed among members of bacteria and archaea • S° reduction is a prominent metabolic strategy in phyla Crenarchaea and Euryarchaea of the Archaeal domain of life • Order Desulfurococcales (Archaea: Crenarchaea) • Predominant metabolism is fermentation of complex polymeric carbon sources with enhanced growth in the presence of S° as a terminal electron acceptor for anaerobic respiration Presence of S° and organic carbon makes Dragon Spring an ideal habitat for enrichment isolation of Archaea involved in S° reduction

  20. Thermophiles • Organisms with optimal growth temperature >450C • Properties of thermophilic enzymes (bacteria and archaea) • Increased number of disulfide bridges • Increased interaction between aromatic peptides • Increased hydrogen bonding among peptides

  21. Unique properties of Archaea • Ether-linked lipids • Glycerol dialkyl glycerol tetraethers (GDGTs) Number of cyclopentyl rings associated with GDGTs increase with increasing surface water temperature.

  22. Other unique properties of Archaea DNA gyrase induces supercoiling of DNA High rates of uptake of foreign DNA from all domains of life

  23. Archaea associated with sulfur floc Chrenarchaea Peptone Cell biomass + CO2 Acidicoccus sulfurreducens Caldisphaera dracosis S0 H2S What physiological group does this fall into?

  24. Bacteria associated with sulfur floc CO2 Cell biomass Hydrogenobaculum spp. H2S So or 2H+ H2 What physiological group does this fall into?

  25. Desert environments • Atacama desert, Chile • Arid desert : years without precipitation • Limited water availability • High solar irradiation • Extremes in temperature • Low nutrient environment due to lack of plant life • Mojave: 0.7% Corganic • Sahara: 0.17% • Atacama: 0.02-0.09% • What physiological groups of bacteria would inhabit such a place and what strategy?

  26. Lithic microbial communities • Inhabit rock surfaces (hypolithic) and subsurface rock pores (endolithic) • Photoautotrophic N2-fixers dominate • Cyanobacteria: Chroococcidiopsis • Desiccation resistance • Mechanisms to repair and protect DNA from uv damage • Proteins remain stable in dehydrated state • Maintain membrane integrity

  27. Extracellular polysaccharides • Trap and bind water in polymer matrix • Contain oxygen-scavenging molecules • Contain water stress proteins

  28. Extensive capsule

  29. Acidic environments • Iron Mountain, California (pH=0.83, temp=42oC • Richmond mine: old copper mine that contains abundant deposits of pyrite (FeS2) • Mining activity exposes these minerals to atmosphere which contains O2 and CO2 • Iron and sulfur oxidizing bacteria are chemoautotrophs like Hydrogenobaculum • Fix CO2 using energy extracted from sulfide (HS-) and ferrous (Fe2+) iron in pyrite . • Product of metabolism is sulfuric acid

  30. Microbial iron oxidation CO2 Cell biomass Fe2+ Fe3+ HS1- SO4 or

  31. Fe(II)S2 Fe(II)S2 Fe(III)O3 Fe(III)O3 e- CH2O CO2 + Cell biomass CO2 Cell biomass Low-diversity microbial community Consortium interactions • Leptospirillium group II • Autotrophic growth • Ferroplasma type II • Heterotrophic growth • Each group of organisms contributes an essential metabolism for the other’s survival e- Sensitive to presence of organics Leptospirillium group II Ferroplasma type II

  32. Summary • Environments that seem extreme to humans are a preferred habitat for some microorganisms. • New extreme environments that harbor microorganisms await discovery by scientists willing to venture into and sample these habitats. • Microbial diversity generally is lower in extreme habitats than in less extreme systems. • Symbiosis and consortium interactions are examples of adaptations by microbes and higher life forms that permit habitation in extreme environments.

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