Kl. Lowe et al., Microbiological and geochemical characterization of microbial Fe(III) reduction in salt marsh sediments, GEOMICROB J, 17(2), 2000, pp. 163-176
Population densities of anaerobic Fe(III)-reducing bacteria (FeRB) and aero
bic heterotrophs were inversely correlated in the surficial (0-2 cm) layers
of Sapelo Island, Georgia, salt marsh sediments. In surficial sediments wh
ere densities of aerobic heterotrophs were low, the density of culturable F
eRB correlated positively with the concentration of amorphous Fe(III) oxyhy
droxides extractable by ascorbate. High FeRB densities and a decrease with
depth of ascorbate-extractable Fe(III) were observed in the upper 6 cm of a
tidal creek core. Culturable sulfate-reducing bacteria (SRB) and SRB-targe
ted rRNA signals were also detected in the upper 6-cm depth. The disappeara
nce of FeRB below 6 cm, however, coincided with a large increase in the abu
ndance of SRB. Thus, when FeRB are not limited by the availability of readi
ly reducible amorphous Fe(III) oxyhydroxides, FeRB may outcompete SRB for g
rowth substrates. Shewanella putrefaciens- and Geobacteraceae-targeted rRNA
signals were at or below detection limits in all sediment samples, indicat
ing that these FeRB are not predominant members of the active FeRB populati
ons. The ubiquitous presence of FeRB at the sites studied challenges the tr
aditional view that dissimilatory Fe(III) reduction is not an important pat
hway of organic carbon oxidation in salt marsh sediments.