ORGANISMS OF THE WINOGRADSKY COLUMN
Review:
Carbon source:
heterotroph
autotroph
Energy source:
phototroph
chemotroph
chemoorganotroph
chemolithotroph
In the Winogradsky column, light is the incoming energy source (this is closed system, open o energy only).
Carbon subtrsate has been provided to start the process of anaerobiosis. Cellulose and other organic compounds support
the growth of Closteridia, an anaerobe that produces many fermentation products and consumes oxygen rapidly.
Sulfur plays an important role in the system. It acts as an electron donor for C-fixation in anaerobic PHS.
In the sediment, sulfate reducing bacteria (like Desulfovibrio) use organic compounds (made by the fermenters) , sulfate
as a terminal electron acceptor, and produce sulfide which diffuses upward. A redox gradient develops - with highly
reducing conditions in the mud, more oxidation towards the top of the water column - where traces of oxygen allow the
growth of cyanobacteria.
Sulfide produced by the sulfate reducers is available to sulfide oxidizers - like colorless sulfur bacteria (Beggiatoa or
Thiothrix , Thiobacilli). Of course, they make sulfate which can be used by sulfate reducers again.
The green sulfur bacteria (Chlorobium) form bright green bands in the sediment. They absorb at around 650nm. a little
higher are the purple sulfurs, like Thiocapsa. These absorb at around 830! The purple sulfurs have largish cells with sulfur
inclusions. Both like LOW light intensity since they grow in dim regions of lakes near the sediment interface. Greens and
purple sulfurs are more tolerant to sulfide than the purple nonsulfurs (like Rhodospirillum). The purple nonsulfurs make
very berry red blooms higher in water column, away from the sulfide. They will use organic acids as their carbon source.
The purple sulfurs deposit sulfur internally. Some purple nonsulfurs deposit sulfur externally. Green sulfurs deposit
externally. Greens have tiny cells. Once sulfur is made like this, sulfur oxidizers like Thiobacillus attach to the particles
and 'eat' them.
Sheathed bacteria are filamentous bacteria with fungal like growth cycle. They eat a variety of organic compounds, like
nutrient rich environments (like hay infusion) and form masses of fine filaments often encrusted with iron.
Note, Beggiatoa also makes filaments - usually white . Leptothrix and Sphaerotilus are representative species. IN iron rich
water, ferrous iron is kept in solution by chelation with organic matter. The sheathed bacteria take in the chelates, oxidize
the carbon compound, and release ferrous iron - which oxidizes on their surface.
SULFUR BACTERIA
A. NON-PHOTOSYNTHETIC:
1. Colorless sulfur bacteria use reduced sulfur compounds as energy sources. No pigments and do not do PHS.
2. Sulfate reducing bacteria: no pigments, reduce SO4 to H2S, anaerobic
B. PHOTOSYNTHETIC:
1. Purple and green sulfur bacteria use reduced sulfur for PHS
2. Purple and green non-sulfur bacteria have PHS pigment, but do not use H2S.
A. COLORLESS SULFUR BACTERIA: These would be found in high sulfide environments, not light-based, or, light niche
taken by cyanobacteria. Common sources of sulfur as energy: Hydrogen sulfide (-2 ox state); elemental sulfur (0)
thiosulfate (+2)
sulfate is final end product (+6)
H2S + 2O2 ------- SO4= + 2H+
HS- + 1/2 O2
+
H+ ------------
S0 + H2O + 2O2 ---------
S0 + H2O
2SO4=
+
2H+
Note some sulfide oxidizers stop at sulfur, and deposit inside cells, saving it for later use. (Beggiatoa, Thiothrix)
[Some purple sulfur bacteria that do PHS also deposit sulfur internally (Chromatium, Thiocapsa, Thiospirillum, Thiopedia, etc.)]

Some sulfide oxidizers deposit sulfur externally: do they? [Only the green sulfur bacteria (PHS) do this. ]

Organisms that oxidize elemental sulfur when it is provided externally must attach to the particle and solubilize it.
Sulfolubus acidocaldarius (an archaean) can do this. Thiobacilli are famous for their ability to oxidize elemental
sulfur, as well as sulfide or thiosulfate (or iron).

Products of sulfide oxidation are sulfate and acid conditions. The acid and sulfate can be consumed/neutralised
by sulfate reducers!
B1. PURPLE AND GREEN SULFUR BACTERIA: They have pigments absorbing at about 830 (the purples) and 650 (the
greens) They use sulfide as terminal electron acceptor in PHS.
Purple sulfurs: Chromatium, Thiocapsa, Thiospirillum, Thiopedia
Most deposit sulfur internally, only a few do so externally but are halophilic.
Conspicuous purple color, grow at sediment water interface, where H2S is being emitted, but not oxidized.
Green sulfurs: Chlorobium, Chloronema, Peledictyon.
Strictly anaerobic and phototrophic. those that live in lakes have gas vesicles; those in hot springs and sediments
don't; most can use organic compounds as carbon sources; Chlorobium deposits external sulfur.
B2. PURPLE AND GREEN NON- SULFUR BACTERIA:
Purple non-sulfurs: Rhodospirillum, Rhodopseudomonas, Rhodobacter
At first it was thought they could not use sulfide as electron donor. But in reality they can -it's just that higher
levels like those preferred by sulfur purples - is toxic to them. They can respire in the dark aerobically, using
organic carbon or hydrogen. They can also ferment. Interestingly , they can grow in light doing PHS with methanol
as carbon source -- using CO2 as the electron acceptor!
Green non-sulfurs: Chloroflexus
can use organic compounds in the dark (aerobically) or use organic compounds for carbon while growing
photosynthetically.
Note: In bacterial photosynthesis, electron flow is cyclic, but if CO2 is being reduced, an electron source is required -- usually H2S. but
can be hydrogen. If methane is used for carbon, oddly, CO2 must be used as an electron acceptor, since methane is more reduced
than cell material!
IRON OXIDIZERS:
Acid conditions: Best known iron oxidizer is Thiobacillus ferrooxidans . It can use reduced iron or sulfur as an energy
source. Sulfolobus also likes to oxidize iron - and grows at boiling temperatures.
These microbes make use of the proton gradient to help make ATP. Oxidation of reduced iron consumes protons and
helps keep cytoplasm neutral as protons are used to make ATP.
Note, iron oxidation initially creates an increase in pH , the further oxidation of ferric iron to hydroxyls makes protons - in
proportionally larger amounts. So overall, iron oxidation lowers pH.
pyrite oxidation: Thiobacillus ferrooxidans.
First, chemcial process converts FeS2 into SO4 and H+ and reduced iron.
Then, Thiobacillus ferrooxidans oxidizes the reduced iron to ferric iron which react with pyrite to form more ferrous iron
and acid. This acts as a propagation cycle (a positive feedback loop) which reuslts in rapid acidification. Oxygen in the
environment leads to ferric hydroxide precipitation. Oxidation would take place far more slowly if only chemcial rxn.
Ferrous to ferric iron only occurs at acid pH only with bacterial intervention.
At neutral pH Leptothrix and Galionella can use reduced iron at the anoxic/oxic interface - similar to use of H2S at the
sediment /water interface. like purple sulfurs or non sulfurs. Ferrous iron is oxidized to ferric oxides.
PHS bacteria (purples) can also use reduced iron as an electron donor, producing iron deposits in ancient seidments
before oxygenic PHS evolved.
IRON REDUCERS:
Oxidized iron can be used as an electron acceptor (anaerobic respiration) in a wide variety of bacteria.. If H 2S is also
present n the environment, FeS can be the product.
This is very common in bogs and waterlogged soils. Through the process of iron reduction, iron becomes solubilized and
moves about in the groundwater. It pops out at bogs and springs and chemically oxidized iron results.
Perhaps I saw this in the Sheldrake near Rockland? Reduced iron coming to the surface., and Beggiatoa filaments using the reduced sulfur? Since no
black ppt this would mean pH must be acidic….OR, no sulfur is present and the cloudy white floc is merely ferric hydroxide.