Chemoautotrophy

1
Chemoautotrophy

• They are autotrophs
• All are bacteria
• Fix their own carbon obtain carbon from the
  environment, and use it to make carbon-based
  molecules.
• Obtain energy by oxidation of substances from
  the environment, usually inorganic minerals.
• Unlike autotrophs and heterotrophs, the sources
  of Energy and electrons for chemoautotrophs vary
  greatly.
• The processes used by the various
  chemoautotrophs are generally less efficient than
  photosynthesis or heterotrophy. This may be a
  cause for all chemoautotrophs to be
  bacteria-sized.
• Not good in competition with more complex
  organisms. Generally grow best in habitats where
  photosynthesis is not possible, and where other
  organisms cant survive. (However, see special
  associations below)
• Some large heterotrophic animals live in
  symbiotic relationships with chemoautotrophic
  bacteria that supply some percentage of their
  carbon needs.

2
Sources of resources for Chemoautotrophs

• 1- Source of E Oxidation of inorganic
  substances in the environment. Vary greatly
  depending on type of bacteria. Some are
  facultative heterotrophs.
• 2- Source of Carbon Most fix carbon dioxide
  (CO2), usually with the Calvin Cycle. Some fix
  Carbon monoxide (CO), and some methane (CH4).
• 3- Source of electrons Oxidation of inorganic
  substances in the environment. Vary greatly
  depending on type of bacteria. Some may switch
  sources depending on availability.
• ______________________________________________
• Photoautotrophs - Energy from sunlight, C
  from CO2
• Heterotrophs - Energy and C from
  consuming other organisms.

3
Energy sources for Chemoautotrophs
4
More on sources of Energy and electrons

• Chemoautotrophs have e- transport systems.
• Use e- to generate ATP and NADPH, or NADH. Thus
  they are similar to photoautotrophs, except that
  they dont utilize light Energy.
• Some chemoautotrophs get their energy from
  compounds that are higher in Energy content, some
  from lower E compounds
• The more reduced the molecule that is used as
  source of E, the more Energy yield is obtained
  (ions will yield less Energy)
• H2 (hydrogen gas) higher E yield
• So (elemental sulfur) higher E yield
• H2S (hydrogen sulfide) higher E yield
• Fe2 (ferrous ion) lower E yield
• NO2- (nitrite ions) lower yield
• NH4 (ammonia) lower yield
• S2O3- (thiosulfate ion) lower yield
• Many chemoautotrophs may switch sources of E/e-,
  depending on what is available.

5
Where do Chemoautotrophs live ?

• Generally, chemoautotrophs live in places where
  no photoautotrophs can survive or do well.
• - deep in the ocean (dark, cold, high
  pressure, low nutrients)
• - deep underground in porous rocks
• - poles - high ultraviolet, dry and frigid
  conditions
• - in association with volcanic sites
  (sulfur-rich habitats)
• - in anoxic enviroments (no oxygen available)
• - hydrothermal vents (volcanic vents in deep
  ocean)
• - chemically unsuitable habitats (natural or
  polluted)
• However, not all live in such extreme
  environments. Chemoautotrophic bacteria that
  oxydize nitrogen live underground, moderate
  depths, in areas accessible to plants roots.
  There is no light there.

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Chemoautotrophs and the environment

• In deep ocean, the only Carbon-fixing organisms
  are chemo-autotrophic bacteria. Heterotrophs
  depend on them for Carbon.
• Around hydrothermal vents, chemoautotrophs exist
  by themselves, or in symbiotic association with
  animals (heterotrophs) that have developed
  adaptations to live there, as long as the
  symbiotic bacteria inside provide them with
  important nutrients.
• Below 1000 m in oceans, and below 500 m on land,
  chemo-autotrophs make up the majority of life. No
  photoautotrophs there, and very few heterotrophs.
• Some elements of interest to industry (Fe, S, Mn
  and others) are abundant in some places because
  of the activity (oxidation reactions) of
  chemoautotrophs. Some of these materials are
  mined for profit.
• Some bacteria mediate the natural purification of
  copper metal (Cu) from copper-rich ores. Under
  certain conditions, sulfuric acid (H2SO4) is
  produced, contaminating streams and killing
  organisms.
• N-oxidizing bacteria are the source of nitrogen,
  a most important element for plants, and play a
  major role in Earths Nitrogen Cycle. They
  oxidize ammonium ions (NH4) to nitrite ions
  (NO2-), and these they oxidize into nitrate ions
  (NO3-), which are preferred by plants as a
  nutrient.

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Some chemoautotrophs and their habitats
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Some chemoautotrophs and their habitats