A decsription of The Sulfur Cycle

Sulfur cycle

   Despite nitrogen and carbon cycles in nature it is important to understand the role of the sulfur cycle.  The yellow, odorless, nonmetallic element plays an important role in plants and animals, forming methionine, cysteine and taurine amino acids. It is also a component of vitamin B1 and an antioxidant glutathione. Sulfur contributes to forming skin, nails and cartilage of joints and nose.

   The sulfur cycle is the sum of processes occurring in nature that moves sulfur through ecosystems. It encompasses both terrestrial and atmospheric processes. Stored in soil and rocks, sulfur is later released and comes in contact with air. Oxidation produces sulfate (SO4). Plants and microorganisms consume sulfate and convert it into organic forms. The food chain continues by animals eating organic food. Sulfur then returns back to soil as soon as animals die. Within atmospheric processes, sulfur is released into air by volcanoes, swamps and evaporation of water. It is inevitably comes back to Earth’s surface within rainfall. Within the ocean, sulfur moves through the food chain to the top layer. It is then released into atmosphere with water vapor. The remaining non-consumed sulfur resides at the bottom combined with iron (FeS) resulting in black color of the sediment. Moreover, humans have contributed to loss of sulfur into atmosphere by processing metals and burning fossil fuels. Reactions with other chemicals in the atmosphere create acid rains that can be damaging to environment. However, there is a positive effect of collection of sulfur dioxide in the atmosphere that acts as an offset of ultraviolet radiation.

   Winogradsky column is an intensified artificial model cultivating different microorganisms that can be observed in a lake ecosystem as well as under natural circumstances. The Winogradsky column may be viewed as a microcosm of the sulfur cycle as it relates to bodies of water. In the various layers of the column, sulfuric compounds undergo different reduction and oxidation states before finally reaching the top layer and releasing into the atmosphere. Different bacteria use sulfates or sulfides instead of water to gain energy or build their cells.

Beginning with the bottom layer such bacteria species as Desulfovibrio consume sulfate and reduce it to sulfide as follows:

2(CH2O) + SO4 =  HCO3 + H2S

Photoheterotrophic green sulfur bacteria of genus Chlorobium later oxidizes sulfide, produced by the previous bacteria and produces sulfur as follows:

CO2 + H2S = CH2O + S

Purple sulfur bacteria of genus Chromatium (photohetertrophic) use sulfates and reduce it to produce elemental sulfur.

Purple non-S bacteria ( Rhodospirilum, Rhodopseudomonas) are photoheterotrophs and exhibit the same nutritional mode as Green Sulfur Bacteria

   Bacteria in the bottom area of the column, such as Desulfovibrio, Desulfotomaculum and Desulfobacter, consume sulfates in large amounts, use it as an energy source and release toxic H2S as a waste product (dissimilatory sulfate reduction). By contrast, assimilatory sulfate reduction occurs when bacteria uses sulfates to build cell content and produce organic sulfur but do not resquire it as an energy source.

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Abstract

Light occlusions were placed in  strategic locations on three different Winogradsky columns composed of the same materials. They were hypothesized to disrupt the development of the oxygen-hydrogen sulfide and aerobic-anaerobic gradients of the column in the area of the occlusion and in the layers unoccluded. The result of eight weeks of bacterial development showed that the site of occlusion showed the most dramatic effects, halting the bacterial development of phototrophic bacteria and promoting the growth of obligate anaerobic bacteria depending on the site of the occlusion.

Hypothesis

The hypothesis was that light occlusion should have marked effects on the development of the hydrogen-sulfide/oxygen and aerobic/anaerobic gradients of the column. In particular, the top occlusion was expected to create a more abundant levels of  sulfuric anearobes and sulfuric aerobes and a reduced aerobic bacteria layer. The middle occlusion was expected to  disrupt the development of the sulfur based bacteria  and non-sulfur based (purple-s bacteria, green s bacteria, and purple non-S bacteria, respectively) as well as the aerobic layers at the top of the column.

The bottom occlusion was hypothesized not to effect the development of the other layers mainly because the bottom layer does not require sunlight to develop effectively, much like the bottom of the pond at Prospect Park, the source of our dirt and water.

Results

Top Occlusion: The occlusion termed “top” saw no significant bacterial development in the area covered by the light occlusion. The phototrophic aerobic layer developed above it and the area covered by the occlusion was in an underdeveloped state of bacterial development comprised of water and organic matter. Note this layer of undeveloped bacteria matched the dimensions of the occlusion.  The layer resembled the appearance of the columns several days after they were created. A very small rim of Green Sulfur Bacteria was detected above and below the area of the occlusion, suggesting that a larger amount of Hydrogen sulfide was available higher up in the column than in a non-occluded column.

Middle Occlusion: The occlusion termed “middle” blocked the normal development of Purple Non-S bacteria and created a gap between Purple Non-S bacteria and Purple S Bacteria which developed under the occlusion. The Purple Non-S layer was far smaller than in the control as a result of the occlusion. Green Sulfur Bacteria was also not produced in this column. The area covered by the occlusion produced a mud-colored layer. It can be safely assumed that there was a greater presence of hydrogen sulfide in this gap layer as it was not consumed by the Purple Non-Sulfur bacteria that would have developed in this area.

Bottom Occusion: The occlusion termed “bottom” blocked the development of the phototrophic Purple Non-S Bacteria as it occurred in the control column and bolstered the development of the obligate anerobic layer. Blocking light allowed these chemotropic bacteria to thrive.

Bacterial development of the phototrophic layers was confirmed by pipetting samples from the top aerobic layer and the Purple Non-S layer. Bacteria indigenous to this layer were then identified with a compound light microscope. The presence of the bacterial layers beneath Purple Non-S can be deduced by the confirmation of the presence of Purple Non-S bacteria. H2S would need to be present for this layer to exist and therefore the obligate anaerobes must be present to produce this essential compound.

Analysis

There are a number of practical applications to light occlusions as they disrupt thenormal bacterial development.

One can imagine if there is a desire to increase the anaerobic content of a body of water one can imagine the reduction of light absorption at the top layer of a freshwater pond or river becoming a viable method for spurring such microbial activity. Perhaps a sulfur source can be provided to such a body of water along with the light occlusion, a desired microbial environment could be created. This light deprivation to produce desired bacteria may be useful in bacteria based environmental remediation efforts. Light occlusions may also be used when attemping to create viable ecosytems in artificial bodies of water i.e. for fish farming, etc.

For examble, desulfovibrio has the potential to break down certain metals (Uranium, Chromium, and Iron) and radionucleotides. Clostridium, another anaerobic bacteria that develops in the anaerobic zone is being explored in the treatment of tumors. The bottom occlusion,as performed in this experiment, is a viable means to create a healthy allotment of these obligate anaerobes for the use of research.

Purple Non-S bacteria, along with infra-red light has been shown to breakdown organic material so controlled growth of this useful bacteria may be useful for efforts to reduce accumulations of organic waste in bodies of water.

Light occlusions of the  corresponding layers in artificial ponds and natural bodies is not plausible but large scale winogradsky columns with occlusions can be used to create accumulations of desired bacteria for cultures.

Resources: Toxic effects of dissolved heavy metals on Desulfovibrio vulgaris and Desulfovibrio sp. strains.

Cabrera G, Pérez R, Gómez JM, Abalos A, Cantero DSource

Department of Chemical Engineering, Food Technology and Environmental Technologies, Faculty of Sciences, University of Cadiz, 11510 Puerto Real, Cadiz, Spain. gema.cabrera@uca.es

Combination bacteriolytic therapy for the treatment of experimental tumors

Long H. Dang, Chetan Bettegowda, David L. Huso, Kenneth W. Kinzler, and Bert Vogelstein*

Source

Howard Hughes Medical Institute

Errors

As the experiment proceeded, a few errors were identified. Most importantly, the top occlusion did not serve properly as an occlusion of the uppermost phototrophic layer. While the location of the phototrophic layer could not have been predicted, a larger occlusion that blocked the entry of light through the top of the bottle would have gone further in testing the effect of light deprivation on the more oxygenated areas of the column.

BY using plastic containers with a smaller width, the 8 week period would have allowed more pronounced development of bacterial layers, especially Green Sulfuric Bacteria.

Future Experimentation

The results showed promise for using  occlusions as a method of producing desired bacteria. However, further experimentation is necessary to develop this method. In a future experiment, a top occlusion that covers the entire top of the column would be used to determine how the deprivation of the topmost phototrophic layer would impact the layers beneath it. This time, to increase the speed of bacterial development, a bottle with a smaller diameter would be used. Furthermore, an attempt would be made to count the bacteria of each layer using volume dilutions.

Another path for further development is to allow Winogradsky columns to develop without any occlusions until all the layers of bacteria become well developed and to then place occlusions and observe there development. Such an experiment would shed light on whether light occlusions can reverse bacterial development--a useful line of inquiry for scientists interested in bioremediation of bodies of water with unbalanced bacterial ecosytems.

Finally, the columns produced for this experiment can be allowed to develop with the occlusions removed.