Phytoplankton-Mediated Redox Cycle of Iron in the Epilimnion of Lake Kinneret (original) (raw)
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Frontiers in microbiology, 2012
The distribution of neutrophilic microbial iron oxidation is mainly determined by local gradients of oxygen, light, nitrate and ferrous iron. In the anoxic top part of littoral freshwater lake sediment, nitrate-reducing and phototrophic Fe(II)-oxidizers compete for the same e(-) donor; reduced iron. It is not yet understood how these microbes co-exist in the sediment and what role they play in the Fe cycle. We show that both metabolic types of anaerobic Fe(II)-oxidizing microorganisms are present in the same sediment layer directly beneath the oxic-anoxic sediment interface. The photoferrotrophic most probable number counted 3.4·10(5) cells·g(-1) and the autotrophic and mixotrophic nitrate-reducing Fe(II)-oxidizers totaled 1.8·10(4) and 4.5·10(4) cells·g(-1) dry weight sediment, respectively. To distinguish between the two microbial Fe(II) oxidation processes and assess their individual contribution to the sedimentary Fe cycle, littoral lake sediment was incubated in microcosm exper...
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Environmental microbiology, 2014
The Fe and N biogeochemical cycles play key roles in freshwater environments. We aimed to determine the spatial positioning and interconnections of the N and Fe cycles in profundal lake sediments. The gradients of O2, NO3(-), NH4(+), pH, Eh, Fe(II) and Fe(III) were determined and the distribution of microorganisms was assessed by most probable numbers and quantitative polymerase chain reaction. The redox zones could be divided into an oxic zone (0-8 mm), where microaerophiles (Gallionellaceae) were most abundant at a depth of 7 mm. This was followed by a denitrification zone (6-12 mm), where NO3(-)-dependent Fe(II) oxidizers and organoheterotrophic denitrifiers both reduce nitrate. Lastly, an iron redox transition zone was identified at 12.5-22.5 mm. Fe(III) was most abundant above this zone while Fe(II) was most abundant beneath. The high abundance of poorly crystalline iron suggested iron cycling. The Fe and N cycles are biologically connected through nitrate-reducing Fe(II) oxidi...
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