Electron acceptors nitrate

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. 

Whether toluene metabolism was coupled to nitrate reduction was determined in several ways. Activity on toluene by the enrichment culture could be transferred and sustained in the transferred cultures. As shown in Table III, active enrichment cultures were provided with substrate toluene, with nitrate or with both. In the absence of the electron-acceptor nitrate with... 

How many moles of each of the electron acceptors (nitrate and sulfate) are required during oxidation of CHjCOOH to obtain same level of energy as would be generated during aerobic decomposition of 1 mol CH3COOH ... 

Apart from acetate, C. arsenatis will grow on pyruvate, L/D-lactate, ftimar-ate, succinate, and malate as electron donors (Table 1). However, in these cases, the electron acceptor arsenate is essential (10). When grown with acetate, nitrate and nitrite can serve as terminal electron acceptors. Nitrate is reduced to nitrite and then to ammonia. Yeast extract (0.1%) stimulates the rate and extent of growth on acetate plus in the presence of arsenate and/or nitrate (11). Moreover, the presence of hydrogen stimulates the rate and extent of growth with arsenate only (10). 

Sulfate reducers can use a wide range of terminal electron acceptors, and sulfate can be replaced by nitrate as a respiratory substrate. Molybdenum-containing enzymes have been discovered in SRB (also see later discussion) and, in particular, D. desulfuricans, grown in the presence of nitrate, generates a complex enzymatic system containing the following molybdenum enzymes (a) aldehyde oxidoreduc-tase (AOR), which reduces adehydes to carboxylic acids (b) formate dehydrogenase (FDH), which oxidizes formate to CO2 and (c) nitrate reductase (the first isolated from a SRB), which completes the enzy-... 

A facultative autotroph (lithotroph) strain MLHE-1 was able to oxidize arsenite under anaerobic conditions to arsenate using nitrate as electron acceptor (Oremland et al. 2002). 

Bacteria have been isolated using reduced anthraquinone-2,6-disulfonate (HjAQDS) as electron donor and nitrate as electron acceptor (Coates et al. 2002). The organisms belonged to the a-, p-, y-, and 5-subdivision of the Proteobacteria, and were able to couple the oxidation of H AQDS to the reduction of nitrate with acetate as the carbon source. In addition, a number of C2 and C3 substrates could be used including propionate, butyrate, fumarate, lactate, citrate, and pyruvate. 

Hutchins SR (1991) Biodegradation of monoaromatic hydrocarbons by aquifer microorganisms using oxygen, nitrate or nitrous oxide as the terminal electron acceptors. Appl Environ Microbiol 57 2403-2407. 

The selenate reductase from Enterobacter cloacae SLDla-1 functions only under aerobic conditions, and is not able to serve as an electron acceptor for anaerobic growth, in contrast to the periplasmic enzyme from Thauera selenatis (Schroder et al. 1997). In E. cloacae there are separate nitrate and selenate reductases, both of which are membrane-bound. The selenate reductase is able to reduce chlorate and bromate though not nitrate, contains Mo, heme and nonheme iron, and consists of three subunits in an a3p3y3 configuration. 

The chlorate reductase has been characterized in strain GR-1 where it was found in the periplasm, is oxygen-sensitive, and contains molybdenum, and both [3Fe-4S] and [4Fe-4S] clusters (Kengen et al. 1999). The arsenate reductase from Chrysiogenes arsenatis contains Mo, Fe, and acid-labile S (Krafft and Macy 1998), and the reductase from Thauera selenatis that is specific for selenate, is located in the periplasmic space, and contains Mo, Fe, acid-labile S, and cytochrome b (Schroeder et al. 1997). In contrast, the membrane-bound selenate reductase from Enterobacter cloacae SLDla-1 that cannot function as an electron acceptor under anaerobic conditions contains Mo and Fe and is distinct from nitrate reductase (Ridley et al. 2006). 

The growth of Bacillus subtilis may take place under a variety of conditions (a) aerobic conditions, (b) using nitrate as electron acceptor, and (c) fermentative conditions with glucose provided pyruvate is available as an electron acceptor since the organism lacks pyruvate formate hydrogen lyase (Nakano and Zuber 1998). 

A detailed investigation by Groenewegen et al. (1990) has examined the uptake of 4-chlorobenzoate by a coryneform bacterium that degraded this compound. The uptake was inducible and occurred in cells grown with 4-chlorobenzoate but not with glucose. A proton motive force (Ap)-driven mechanism was almost certainly involved, and uptake could not take place under anaerobic conditions unless an electron acceptor such as nitrate was present. 

Bacteria Using Nitrate Electron Acceptor under Anaerobic Conditions, and Anaerobic Phototrophs... 

In the absence of molecular oxygen, a nnmber of alternative electron acceptors may be used these include nitrate, sulfate, selenate, carbonate, chlorate, Fe(III), Cr(VI), and U(VI), and have already been discussed in Chapter 3, Part 2. In Chapter 14, which deals with applications, attention is directed primarily to the role of nitrate, sulfate, and Fe(III)— with only parenthetical remarks on Cr(VI) and U(VI). The role of nitrate and sulfate as electron acceptors for the degradation of monocyclic aromatic compounds is discnssed, and the particularly broad metabolic versatility of sulfate-reducing bacteria is worthy of notice. 

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