Sulfate-reducing organisms

Recently, evidence for this microbial transformation initiation strategy has also been seen for alkanes incubated in anaerobic cultures (Kropp et al., 2000 Rabus et al., 2001). In one case, a denitrifying bacterium was involved, while in the other case, the alkane was metabolized by a sulfate-reducing organism. Consistent with the hydrogen abstraction-fumarate addition mechanism (Fig. 17.11), succinate was found attached to the subterminal carbons of alkanes like hexane and dodecane ... 

Sulfates are also involved in depassivation, especially with deposits or foulants. Sulfates can be reduced by selective microbial actions (sulfate-reducing organisms) that are almost always present in biofilms, producing deep pits of corroded steel. 

Location Sulfate (mg SO4 r ) Sulfide (mg H2SI-I) Sulfide production (mg HjSr d i) Sulfate-reducers (organisms X10"3 r ) Sulfide-oxidisers (organisms X10"3 1-1) S formation (mg S 1 1 d" )... 

Location Sulfate (mg SO4 ) Sulfide (mg H S) Reduction rate (mg H2S d ) Sulfate reducers (organisms 10 ) Organic matter... 

A protein named desulforedoxin was isolated from a sulfate reducer organism, Desulfovibrio gigas, by Moura et al.47) and which represents a variation on the basic rubredoxin type structure. Its spectroscopic features will be discussed in relation to those of rubredoxin isolated from D.gigas and Clpasteurianum. 

The sulfate reducers, mainly Desulfovibrio spp. and Desulfotomaculum spp., are heterotrophs and the amount of utilizable organic matter determines their activity. The activity of sulfate-reducing organisms is generally rather low and will vary with water depth as verified by investigations in the Black Sea (Sorokin, 1964). Sorokin found that in the shallow... 

Sulfite reductases contain siroheme and iron-sulfur centers. Siroheme, also present in some nitrite reductases, is an iron tetrahydroporphyrin of the isobacteriochlorin type with eight carboxylic acid side-chains (Fig. 1). Siroheme isolated from Desulfovibrio species was found to be a monoamide, heptamethyl ester derivative, rather than the usual octamethyl ester derivative, which suggests that in these organisms an amidated form of the siroheme may be the physiologically active prosthetic group [93]. Sulfite reductases are divided into two classes, the assimilatory and the dissimilatory enzymes. The assimilatory sulfite reductases produce sulfide for use in the cell biosynthetic pathways. The dissimilatory enzymes are present in the sulfate-reducing organisms, and reduce sulfite as a respiratory substrate in a process coupled to ATP formation. 

B) This figure com s the fractionations imparted by sulfate reduction (csr) with with depletion of into pyrite (o " Ssuifate - 8 " Spyrite) as a function of sulfate reduction rate (SRR). As sulfate reduction rates increase, the difference between the isotopic composition of pyrite and the fractionation imposed by sulfate-reducing organisms becomes smaller. This relationship probably reflects a higher proportion of sulfide oxidation through disproportionation pathways at low sulfate reduction rates, and more direct sulfide oxidation to sulfate at high rates of sulfate reduction. Replotted after Habicht and Canfield (2001). 

The reaction rates of dissimilatory sulfate reduction depend primarily on the interplay between several factors sulfate concentration, availability of organic matter and other nutrients, and the size and density of the bacterial population. Temperature can also affect sulfate reduction rates. Sulfate concentrations can have a greater effect on the sulfate reduction rate than on the available organic substrate concentration. In sulfate-deficient systems, the growth of the sulfate-reducing organism... 

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