Bacteria sulphur-utilizing

Best guesses suggest that life began in the oceans some 4.2-3.8 billion years ago, but there is no fossil record. The oldest known fossils are bacteria, some 3.5 billion years old. In rocks of this age there is fossil evidence of quite advanced metabolisms which utilized solar energy to synthesize organic material. The very earliest of autotrophic (self-feeding) reactions were probably based on sulphur (S), supplied from volcanic vents. 

The Sweet Process or Alkaline Process is an older method of steeping than the sulphurous acid method. The nature of this process is indicated by the name. This method was in use for many years and is in use to some extent to-day. By this process the com was placed in large tanks of lukewarm water to Which alkali had been added. The com in these tanks of alkali was allowed to rot for several days. The putrefaction became very foul and only the starch was used as a commercial product. The remainder of the constituents of com were made useless by the alkali or were destroyed by the putrefaction. A starch of high purity was made by this process but the process was too foul and wasteful to be practiced to any extent. It should be noted that this process utilized a combination of the actions of alkali and of bacteria. Little starch was lost in this form of steeping due to the fact that bacteria are practically helpless in their attack upon the starch granule so long as the starch cellulose wall remains intact. 

Serine and Cysteme Derivatives.-—L-Cysteine (1) is derived from L-serine (2) via O-acctyl-L-serine (3) in bacteria. Recent data indicate that the same pathway is utilized for the production of cysteine in plants. Thus, though never encountered in natural material, O-acetylserine is synthesized fi om serine and acetyl-CoA by enzyme preparations from kidney beans, lupin, barley, pea seedlings, leaves of swiss chard, turnip, and radishes. The transformation of O-acetylserine and sulphide into cysteine has been accomplished with enzyme systems from spinach, turnip, and kidney bean. Tracer experiments in turnip with [ S]sulphide and [ C]homoserine indicate that the reaction between O-acetylserine and sulphide constitutes the main entrance for sulphur into organic compounds in plants. ... 

The capture of sunlight releases electrons and protons from water in green plants, algae and cyanobacteria so that oxygen is produced as a byproduct. Certain sulphur bacteria utilize various sulphur substrates, e.g. HjS, as the electron donor and therefore make no contribution to the replenishment of atmospheric oxygen. 

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