Bacterial Reduction of Ferric Iron in a Stratified Eutrophic Lake

Abstract

The rate of release of Fe(I1) from anoxic lake sediments was lower in the presence than in the absence of nitrate. The reduction of Fe(II1) by the sediments had a temperature optimum of 30 "C and was inhibited by HgC12, suggesting that the process was largely biological in nature.Of the iron sources tested with cultures of anaerobic iron-reducing bacteria, FeC13 was the most readily reduced and goethite the least. Reduction was faster in the presence of a chelating agent and was suppressed by the addition of NO,, C105, MnO,, Mn203 and 02. An iron-reducing chemoorganotroph, tentatively identified as a member of the genus Vibrio, was isolated. Physical contact between the bacterium and iron particles was essential to ensure maximum rates of Fe(II1) reduction but > 30% of the activity appeared to be associated with extracellular components. Although Fe(II1) reduction by whole cells and cell-free extracts was decreased in the presence of electron transport inhibitors, the molar growth yield of the organism was unaffected by the presence of Fe(II1). It is assumed that the organism used the Fe(II1) as a hydrogen sink. A second organism, an anaerobic facultative chemolithotroph, appeared to conserve energy by the reduction of Fe(II1). Biomass yield (measured as ATP) was greater in the presence of Fe(III), and the organism was able to use H2 as a source of reducing power.

Dissimilatory Fe(III) and Mn(IV) Reduction

“…Pasteurization of marine sediments inhibited the release of Fe(II) into the interstitial water even though the pasteurization process increased the concentration of dissolved organic carbon more than 10-fold (54). The finding that heat sterilization (46,54,158,189,286) (295). Reducing sugars such as glucose and xylose may also nonenzymatically reduce Mn(IV) oxides under some conditions (319).…”

“…A gram-negative, coccobacillus which might have the ability to couple the oxidation of H2 to the reduction of Fe(III) was also reported (158). However, growth and Fe(III) reduction were weak.…”

“…Starkey and Halverson (289) found that Fe(III) was reduced in anaerobic cultures of Clostridium sporogenes or E. coli growing in a glucose or peptone medium, and Roberts (272) found that Bacillus polymyxa reduced Fe(III) while fermenting glucose. Subsequent studies found that a wide variety of fermentative microorganisms reduced Fe(III) or Mn(IV) during anaerobic growth (45,46,128,158,159,226,245,246), and organisms capable of reducing Fe(III) and Mn(IV) under aerobic culture conditions have also been described (76,82,86,316).…”

“…Fe(III) reduction is invariably inhibited when microbial metabolism in aquatic sediments is inhibited (158,164,189,286). However, this result does not necessarily exclude the redox or direct-reduction mechanism.…”

“…Numerous studies have demonstrated that the more crystalline the Fe(III) oxide, the slower the rate of Fe(III) reduction and that soluble, chelated Fe(III) forms are reduced the fastest (11,13,76,155,158,193,194,198,224,225,242,256,319,334). The form of the Mn(IV) oxides is also likely to affect the rate and extent of Mn(IV) reduction, but this does not appear to have been investigated systematically.…”