Bio 230 - Microbiology - Spring 2010
Study Guide 09
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http://www.cbu.edu/~jvarrian/122/absspex.html
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TB View Spring Microbial Mats
The green material from
the center of the channel is
are a green sulfur
bacterium, Chlorobium
tepidum, which lives by
anoxygenic photosynthesis.
It produces elemental sulfur
as a waste product, and
(unlike Chromatium and
Thiothrix) deposits the
sulfur outside its cells.
Here, the water is 59°C, pH
= 6.5, and highly sulfurous.
http://www.lpi.usra.edu/education/EPO/yellowstone2002/workshop/tbvspring2/index.html
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Carboxysomes in
fixed bacterial cells
(top) and purified at
higher mag (bottom)
from Cannon et al.,
App. Environ.
Microbiol. 67:53515361 (2001).
http://www.jensenlab.caltech.edu/Projects/carboxysome.html
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Important Reactions of the Sulfur Cycle
Assimilative sulfate reduction - sulfate (SO42-) is
reduced to organic sulfhydryl groups (R-SH) by
plants, fungi and various prokaryotes. The
oxidation states of sulfur are +6 in sulfate and -2
in R-SH.
Desulfuration - organic molecules containing
sulfur can be desulfurated, producing hydrogen
sulfide gas (H2S), oxidation state = -2. Note the
similarity to deamination.
http://www.biosci.ohio-state.edu/~mgonzalez/Micro521/23.html
Oxidation of hydrogen sulfide produces elemental
sulfur (So), oxidation state = 0. This reaction is
done by the photosynthetic green and purple
sulfur bacteria and some chemolithotrophs.
Further oxidation of elemental sulfur by sulfur
oxidizers produces sulfate.
Dissimilative sulfur reduction - elemental sulfur
can be reduced to hydrogen sulfide.
Dissimilative sulfate reduction - sulfate reducers
generate hydrogen sulfide from sulfate.
http://www.biosci.ohio-state.edu/~mgonzalez/Micro521/23.html
Sulfur Oxidation
1. The light-induced oxidation of hydrogen sulfide for harvesting
electrons during photosynthesis by green and purple sulfur
bacteria.
H2S -----> So + 2 H++ 2 e2. Chemolithotrophic oxidation of hydrogen sulfide generates
energy:
a. Hydrogen sulfide can be oxidized to elemental sulfur:
H2S + 1/2 O2 -----> So + H2O + energy
b. Elemental sulfur in turn can be oxidized to sulfate:
So + 1 1/2 O2 + H2O ---> SO42- + 2 H+ + energy
http://www.biosci.ohio-state.edu/~mgonzalez/Micro521/23.html
Chemolithotrophic Sulfur Oxidation
(i) Beggiatoa - historically important because it was the first chemolithotroph
identified.
Gliding motility
Growth on acetate
Growth on O 2 is limited by the lack
of catalase in Beggiatoa species. The
lack of catalase is compensated for
by the organisms' ability to oxidize
sulfide, which detoxifies
metabolically-formed hydrogen
peroxide in the absence of oxygen.
http://microbewiki.kenyon.edu/images/thumb/0/08/Filament.jpg/400px-Filament.jpg
Chemolithotrophic Sulfur Oxidation
(ii) Thiobacillus - an obligate acidophile, very tolerant of low pH; in addition to
oxidizing hydrogen sulfide, this organism can extract iron from solid pyrite
(FeS2) in a two-step process in which sulfur atoms are oxidized.
First, the organism catalyzes the oxidation of ferrous iron, generating ferric iron
Fe2++ 1/2 O 2 + 2 H+ -----> Fe3++ H2O
Secondly, the ferric iron produced spontaneously reacts with pyrite
FeS2 + 14 Fe3+ + 8 H2O -----> 15 Fe2+ + 2 SO42- + 16 H +
A colony of Thiobacillus
ferrooxidans. The reddish
color is the result of iron
production
Some of the Reactions Undertaken by Thiobacillus
http://microbewiki.kenyon.edu/index.php/Thiobacillus
A marine sulfuretum is a
microbial mat in which the
total turnover of inorganic and
organic compounds is heavily
dominated by the sulfur cycle
http://www.stat.rice.edu/~siefert/Links/SulfurRedTBL.html
Diurnal cycle of oxygen and sulfide distribution and of microbial zonation in a marine
sulfuretum. The zero line in each box indicates the interface between the sediment and the
overlaying water phase. The dominant genera at each stratum are indicated in each box.
http://www.stat.rice.edu/~siefert/sulfuretum.gif
Model of a Marine Sulfuretum
http://www.stat.rice.edu/~siefert/Links/SulfurRedTBL.html
The End