Abstract

No previous study has revealed that Fe(III)-reducing bacteria (IRB), which can solubilize ferric iron Fe(III) (oxyhydr)oxide to ferrous Fe(II) and the formation of Fe(II)/Fe(III) (oxyhydr)oxide minerals, are capable to degrade lignin We hypothesized that in soils with high Fe content, IRB contribute substantially to the SOM degradation, in particular lignin-like compounds under anaerobic conditions. The aim of this study was to isolate IRB and to evaluate their importance as lignin degrader in soils from different climates (humid temperate, cold temperate and subpolar), vegetation (steppe to temperate rainforest) and parent materials (Granitic, Volcanic, Metamorphic, Fluvioglacial and Basaltic-Antarctic). The isolated IRB from the top mineral soil (Ah 5-15 cm) were tested for their Fe(III) reduction potential in an anthraquinone-2,6-disulfonate (AQDS). The contribution of IRB to anaerobic soil respiration for 36 h was assessed in a microcosm experiment in a sterilized-inoculated soil and their respiration were compared with sterilized (abiotic), non-sterilized (biotic) and induced Fenton reaction soils. Lignin degradation was examined by adding Kraft to isolated IRB. Other tests such as peroxidase activity, counting viable cells, ATP concentration and fluorescence intensity. The major microbial component in all studied soil was Geobacter spp was the most abundant cells found in all soils as indicated by phospholipid-derived fatty acids. CO2 released of inoculated soil was >140 % than that of the sterilized soil and represented 60% of the total biotic anaerobic respiration. The Fe (II) acid-extractable concentration increased 362% in Basaltic-Antarctic soil that exhibited the highest Fe content. Lignin Kraft degradation followed similar pattern as fluorescence intensity decrease in agreement with other tests in soils with different origin, climate and vegetation that contributed to explain the rapid turnover of SOM in these ecosystems.