Escherichia coli sulfate reduction

The conditions under which these function and their regulation depend on the organism. For example, in Escherichia coli, oxygen represses the synthesis of the other reductases, and under anaerobic conditions the reductases for fumarate, DMSO, and TMAO are repressed by nitrate. This does not apply to Wolinella succinogenes in which sulfur represses the synthesis of the more positive electron acceptors nitrate and fumarate (Lorenzen et al. 1993). The DMSO reductase from Escherichia coli (Weiner et al. 1988) has a broad substrate versatility, and is able to reduce a range of sulfoxides and A-oxides. Anaerobic sulfate reduction is not discussed here in detail. 

There is no current commercial biologic process for the production of succinic acid. In past laboratory systems, when succinic acid has been produced by fermentation, lime is added to the fermentation medium to neutralize the acid, yielding calcium succinate (2). The calcium succinate salt then precipitates out of the solution. Subsequently, sulfuric acid is added to the salt to produce the free soluble succinic acid and solid calcium sulfate (gypsum). The acid is then purified with several washings over a sorbent to remove impurities. The disposal of the solid waste is both a directly economic and an environmental concern, as is the cost of the raw materials. Some key process-related problems have been identified as follows (1) the separation of dilute product streams and the related costs of recovery, (2) the elimination of the salt waste from the current purification process, and (3) the reduction of inhibition to the product succinic acid on the fermentation itself. Acetic acid is also a byproduct of the fermentation of glucose by Anaerobiospirillium succiniciproducens almost 1 mol of acetate will be produced for every 2 mol of succinate (3). Under certain cultivation conditions by a mutant Escherichia coli, lesser amounts of acetate can be produced (4,5). This byproduct will also need to be separated. 

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