The dynamics of iron (Fe)-bound organic carbon (OC) during dissimilatory microbial Fe(III) reduction can potentially play an important regulatory role in carbon (C) biogeochemical cycling in permanently or transiently anoxic soils and sediments. In this study, we investigated the release and transformation of ferrihydrite (Fh)-bound OC during microbial Fe reduction by <i>Shewanella</i> <i>putrefaciens</i> strain CN32 under a fixed Fe concentration of 13 mM and varying C/Fe molar ratios. We found that Fe reduction and OC reductive release was dependent on the C/Fe molar ratio, with high C/Fe ratio enhancing both Fe reduction and OC release. For Fh-OC co-precipitates with C/Fe of 3.7, 54.7% of Fh-bound OC was released to solution phase when 25.1% of Fe was reduced. The presence of OC inhibited the transformation of Fh to crystalline Fe phases both in the bulk and on the surface. Upon reduction, Fh-bound OC became more concentrated on the surface of Fh-OC co-precipitates, and surface components were enriched with carboxylic functional groups. Reduction likely increased the lability of Fh-bound OC for co-precipitate with highest C/Fe ratio, with aromatic OC preferentially retained within the co-precipitates. Our results indicate that microbial reduction altered the quantity and composition of OC released from Fh-OC co-precipitates., depending on the C/Fe ratio and associations between Fh and OC. Assuming higher availability of released OC compared to original Fh-bound OC, reduction of Fh can lead to enhanced degradation of OC and result in a shorter residence time for OC in soils and sediments.

Fate of ferrihydrite-bound organic carbon during microbial reduction

253rd National Meeting (2017)

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