Chemoautotrophic

Chemoautotroph An organism that obtains its energy from the oxidation of chemical compounds and uses only organic compounds as a source of carbon. Example nitrifiers. 

H2S- S-S20i- ->SO ) bacteria, some cyanobacteria Chemoautotrophic sulfur oxidizers... 

None of the biogenesis hypotheses previously discussed differs so clearly from all the other models as the chemoautotrophic theory proposed by the Munich patent attorney Dr. Gunter Wachtershauser. 

The first experiments on chemoautotrophic theory were carried out by Stetter at the University of Regensburg. It was found that synergy in the FeS/H2S system determined the reductive effect, for example, in the conversion of nitrate to ammonia or of alkynes to alkenes. The conditions used corresponded to those present in hydrothermal systems aqueous phase, 373 K, almost neutral pH and anaerobic conditions (Blochl et al 1992). Two years later, the formation of an amide bond without the use of a condensation agent was successfully demonstrated in the same laboratory (Keller et al 1994). 

About three years after Wachtershauser s first publication appeared, an article by Christian de Duve and Stanley Miller was published in the Proceedings of the National Academy of Sciences under the title Two-Dimensional Life the title alluded to the theory of reactions at positively charged pyrite surfaces (de Duve and Miller, 1991). Their criticisms of the chemoautotrophic theory were directed particularly towards certain kinetic and thermodynamic aspects, but also to theoretical statements for which no experimental support was available. 

Photoelectrochemical experiments on the pyrite/H2S system, as well as theoretical considerations, led Tributsch et al. (2003) to the conclusion that CO2 fixation at pyrite probably could not have led to the syntheses proposed by Wachtershauser. The reaction mechanism involved in such reactions is likely to be much more complex than had previously been assumed. The Berlin group supports the objection of Schoonen et al. (1999) that, apart from other points, the electron transfer from pyrrhotine to CO2 is hindered by an activation energy which is too high. There is, thus, no lack of different opinions on the model of chemoautotrophic biogenesis hopefully future studies will shed more light on the situation ... 

Further experiments by Huber and Wachtershauser on chemoautotrophic biogenesis under hydrothermal conditions have shown that a number of a-amino acids and a-hydroxyacids could have been formed, subsequent to the binding of carbon (in the form of CO and CN ) to catalytically active transition metal precipitates. The general structure of such compounds is R-CHA-COOH, with R = H, CH3, C2H5 or HOCH2 and A = OH or NH2. 

When the Fe2+/Fe3+ system is included, the thioester hypothesis, with its roots in sulphur chemistry, shows clear links with the iron-sulphur world of Wachtershauser s chemoautotrophic biogenesis model (see Sect. 7.3). 

A microbial contacting process for the oxidation of H2S was disclosed [22], in which a chemoautotrophic bacterium T. thiooxidants or T. ferroxidans) is used to remove sulfides from gaseous streams, at aerobic conditions and low pH. The low pH is preferred since the optimum pH for growth of the bacteria is below 4.0. and for the elimination of undesired contaminant bacterial strains. A contactor is employed, the flow of the sulfur-containing stream is contacted counter-currently with the biocatalytic aqueous solution. The sulfate is recovered from the aqueous solution, which contains the biocatalyst, as well. 

A sour natural gas stream can be anaerobically desulfurized by a process, which employs a consortium of chemoautotrophic bacteria (ATCC 202177). The H2S and other sulfur species are converted into elemental sulfur, which is recovered as a product [287], The process conditions involve pressures lower than 1000 psi and temperatures up to 60°C. Sulfur content might be diminished from 10,000 ppm H2S to pipeline standards of <4ppm. Further, C02 content can be reduced as well from levels as high as 10% to <2%. 

Prokaryotes Autotrophs Chemoautotrophs Photoautotrophs Aerobes Energy from energised minerals Energy from oxidised sources, Fe3+, S()42, NO s Energy from light, Mg, Mn Tolerate and use 02 from moderate to high atmospheric levels Use of Mg2+, Fe2+, Mo(W)... 

Martin, W. and Russell, M.J. (2003). On the origin of cells a hypothesis for the evolutionary transition from abiotic chemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells. Philos. Trans. R. Soc. London, B 358, 27-85... 

Oxidation of Fe(ll) occurs rapidly at low pH but at measureable rates of about 1-5 mmol/L/h in surface waters by chemoautotrophic bacteria and archaea (Nordstrom 2003). 

Chemoautotrophic Inorganic compound O, or another inorganic compound Oxidized inorganic compound... 

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