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Many organisms reduce small amounts of sulfates in order to synthesize sulfur-containing cell components; this is known as assimilatory sulfate reduction. By contrast, the sulfate-reducing microorganisms considered here reduce sulfate in large amounts to obtain energy and expel the resulting sulfide as waste; this is known as dissimilatory ...
The term "dissimilatory" is used when hydrogen sulfide (H 2 S) is produced in an anaerobic respiration process. By contrast, the term "assimilatory" would be used in relation to the biosynthesis of organosulfur compounds, even though hydrogen sulfide may be an intermediate. Dissimilatory sulfate reduction occurs in four steps: [1]
Bacteria use APS reductases to engage in assimilatory and dissimilatory sulfate reduction, which make them prime candidates to appear in wastewater treatment environments. [8] Biofoulants can contain a number of sulfate reducing bacteria, and studies have shown that if wastewater plants are left untreated sulfate levels will decrease. [8]
The uptake of sulfate by the roots and its transport to the shoot is strictly controlled and it appears to be one of the primary regulatory sites of sulfur assimilation. [3] Sulfate is actively taken up across the plasma membrane of the root cells, subsequently loaded into the xylem vessels and transported to the shoot by the transpiration stream.
In assimilatory sulfate reduction the sulfate is assimilated, or incorporated into organic compounds such as cysteine, methionine, or iron-sulfur clusters and enzyme cofactors. [13] In bacteria, sulfate and thiosulfate are transported into the cell by sulfate permeases where it can then be reduced and incorporated into biomolecules. [14]
Dissimilatory sulfite reductase (EC 1.8.99.5) is an enzyme that participates in sulfur metabolism in dissimilatory sulfate reduction. [1] The enzyme is essential in prokaryotic sulfur-based energy metabolism, including sulfate/sulfite reducing organisms, sulfur-oxidizing bacteria, and organosulfonate reducers.
Both enzymes are required for PAPS (phosphoadenosine-phosphosulfate) synthesis from inorganic sulfate. [1] [2] Within the cell sulfate adenylyltransferase plays a key role in both assimilatory sulfur reduction and dissimilatory sulfur oxidation and reduction (DSR) and participates in the biogeochemically relevant sulfur cycle.
[5] [6] [7] They are grouped as either the assimilatory or the dissimilatory sulfite reductases depending on their function, their spectroscopic properties, and their catalytic properties. This enzyme participates in selenoamino acid metabolism and sulfur assimilation .