Transcript Lecture23 S-cycling

Streams draining mine tailings are extremely acidic—the effect
of Thiobacillus ferrooxidans oxidizing sulfur and iron in pyrite
minerals. What kind of bacteria are these?
The Sulfur cycle has many important effects on Aquatic Ecosystems
Chemoheterotrophs (CH)
-2
-1
pyrites
(PA)
0
+4
CH
+6
PA
Photoautotrophs (PA)
Chemoautotrophs(CA)
Thiobacillus ferrooxidans
oxidizes both the iron,
Fe(+2) to Fe(+3)
and the sulphur in the pyrites,
S(-1) to S(+6) using
molecular oxygen.
This reaction splits water to
produce a great deal of acid.
How do you suggest that mine
tailings should be stored?
2FeS 2  7.5O2  4H 2O  4SO4 2  Fe2O3  8H   Energy
Hydrothermal vent fauna: a community founded on
Thiobacillus a chemoautotrophic bacteria
The pogonophoran tube worms harbour nodules of Thiobacillus
inside their body cavities as mutualistic symbionts
Desulfovibrio : Sulfate reducing bacteria
commonly found in anaerobic aquatic environments with high levels of organic material, such
as mud in lakes and ponds.
•have metal reductases which can precipitate metal sulfides from the water—
•bioremediation potentials for toxic radionuclides such as uranium by a reductive bioaccumulation process.
Sulfate reduction can absorb H+ and
counteract acid rain
They also contribute to methylation of
Mercury
Chemical equation for the oxidation of acetate by sulfate
CH 3COO   SO 4 2  H   S   H 2O  CO2  E

2


CH 3COO  SO 4  H  S  2 H 2O  2CO 2
( 6)
(0)
(-2)
( 4)
8 e - are accepted per S
-
4 e are donated per C
Where do sulphate reducing bacteria fit in the functional classification?
Purple Photosynthetic sulfur bacteria (eg Thiocapsa)
http://www.esf.edu/efb/schulz/Limnology/Laboratory/PurpleBacteriafromGreenLake.JPG
Thiocapsa are found most often in fresh water: lakes,
sulfur springs, and waste water ponds. Requires anoxic
conditions with light present. Under ideal conditions,
Thiocapsa can form dense blooms.
•use reduced sulfur as an electron donor during photosynthesis.
They are capable of oxidizing both sulfide and other reduced
sulfur compounds.
gas vacuoles. Why?
Chemical equation for anoxygenic photosynthesis in purple sulfur bacteria
H 2 S  CO2  light energy  S  CH 2O
12 H 2 S  6CO 2  12S  C 6 H 12O 6  6 H 2O
(-2)
( 4)
(0)
(0)
-
2 e are donated per S
-
4 e accepted per C
In aerobic photosynthesis O2 is produced. Why is no O2 produced here?
Redox profile at the earth’s surface
The earth is a 0.5 V battery
Photosynthesis
--a strong
photochemical
redox reaction-has produced a
strong redox
gradient across the
earth’s surface.
Atmosphere, oxidizing environment
This gradient
helps maintain
chemical diversity
at the boundary
Soil layer
Earth’s crust, a reducing environment
+0.25
0V
-0.25
Consider the
example of soil N