Chapter 5
Oxidation of Inorganic Sulfur Compounds by Thiobacilli
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Isamu Suzuki, C. W. Chan, and T. L. Takeuchi Department of Microbiology, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
Thiobacilli oxidize inorganic sulfur compounds to sulfuric acid and obtain energy for growth from the oxidation. Various species of thiobacilli have different oxidative capabilities, but most can oxidize sulfide, sulfur and thiosulfate. The mechanism of inorganic sulfur oxidation by thiobacilli has been studied for a number of years. It is becoming increasing clear that sulfur and sulfite oxidation are the key reactions in the oxidation of sulfide, elemental sulfur, thiosulfate and polythionates.
Thiobacilli are capable of oxidizing reduced inorganic sulfur compounds such as sulfide, sulfur and thiosulfate to sulfate and of using the energy of oxidation for growth on inorganic nutrients. The physiology and the role of these bacteria in biohydrometallurgy have been extensively reviewed Q). Sulfur Oxidation Scheme The mechanism of oxidation of these sulfur compounds was formulated in 1974 (2) essentially as shown in Figure 1. The scheme still satisfies most experimental results, particularly the accumulated knowledge of enzymes involved. Reaction 1 is the oxidation of sulfide to sulfur which will be discussed later. 2
S - -> S + 2e
(1)
The original proposal was based on the following series of evidence. The S°-grown Thiobacillus thiooxidans (3) and Thiobacillus ferrooxidans (4) and thiosulfate-grown
Thiobacillus thioparus (5) (accumulating sulfur as intermediate) and Thiobacillus novellus (6) had the sulfur-oxidizing enzyme (reaction 2 in the presence of reduced glutathione, GSH) (5).
0097-6156/94/0550-0060$06.00/0 © 1994 American Chemical Society Alpers and Blowes; Environmental Geochemistry of Sulfide Oxidation ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
Downloaded by UNIV OF MISSOURI COLUMBIA on April 22, 2018 | https://pubs.acs.org Publication Date: December 20, 1993 | doi: 10.1021/bk-1994-0550.ch005
5.
SUZUKI ET AL.
Oxidation of Inorganic Sulfur Compounds by Thiobacilli 6
2
s°
s-so " - — - *o s-s-s-so 3
3
3
5
2s -
2so/
- s 1
2
3
2so 3
4
4
Figure 1. Oxidation of inorganic sulfur compounds. Reactions 1 to 6 are discussed in detail in the text In the original assignment (2), the enzymes responsible for the reactions were identified as follows: reaction 1, sulfide oxidase; 2, sulfur-oxidizing enzyme; 3, sulfite oxidase or APS reductase; 4, rhodanese (thiosulfate-cleaving enzyme, sulfur transferase); and 5, thiosulfateoxidizing enzyme.
Alpers and Blowes; Environmental Geochemistry of Sulfide Oxidation ACS Symposium Series; American Chemical Society: Washington, DC, 1993.
62
ENVIRONMENTAL GEOCHEMISTRY OF SULFIDE OXIDATION
S° + 0 + H 0 -> H S0 2
2
2
(2)
3
Sulfite oxidase (reaction 3a) was present in T. thioparus, T. novellus, and Τ ferrooxidans (7-9) and APS(adenosine phosphosulfate) reductase (reaction 3b) in Thiobacillus denitrificans and T. thioparus (10.11).
S0
2 3
+ H 0 -> S0 2
Downloaded by UNIV OF MISSOURI COLUMBIA on April 22, 2018 | https://pubs.acs.org Publication Date: December 20, 1993 | doi: 10.1021/bk-1994-0550.ch005
S0
2
2
+ 2e + 2H
4
+
(3a)
+ AMP -» APS + 2e"
3
(3b)
Rhodanese (reaction 4) found in T. denitrificans and T. novellus (12,13) was considered as sulfur transferase. SS0
2
