Anaerobic, nitrate-dependent microbial oxidation of ferrous iron

SummaryMetal‐sulfides are wide‐spread in marine benthic habitats. At deep‐sea hydrothermal vents, they occur as massive sulfide chimneys formed by mineral precipitation upon mixing of reduced vent fluids with cold oxygenated sea water. Although microorganisms inhabiting actively venting chimneys and utilizing compounds supplied by the venting fluids are well studied, only little is known about microorganisms inhabiting inactive chimneys. In this study, we combined 16S rRNA gene‐based community profiling of sulfide chimneys from the Manus Basin (SW Pacific) with radiometric dating, metagenome (n = 4) and metaproteome (n = 1) analyses. Our results shed light on potential lifestyles of yet poorly characterized bacterial clades colonizing inactive chimneys. These include sulfate‐reducing Nitrospirae and sulfide‐oxidizing Gammaproteobacteria dominating most of the inactive chimney communities. Our phylogenetic analysis attributed the gammaproteobacterial clades to the recently described Woeseiaceae family and the SSr‐clade found in marine sediments around the world. Metaproteomic data identified these Gammaproteobacteria as autotrophic sulfide‐oxidizers potentially facilitating metal‐sulfide dissolution via extracellular electron transfer. Considering the wide distribution of these gammaproteobacterial clades in marine environments such as hydrothermal vents and sediments, microbially accelerated neutrophilic mineral oxidation might be a globally relevant process in benthic element cycling and a considerable energy source for carbon fixation in marine benthic habitats.

Section: Introductionmentioning

confidence: 99%

Microbial metal‐sulfide oxidation in inactive hydrothermal vent chimneys suggested by metagenomic and metaproteomic analyses

Meier

Pjevac

Bach

et al. 2019

“…These different biotic and abiotic Fe redox reactions cause the precipitation, transformation, and dissolution of different minerals and the biogeochemical Fe cycle is connected to many other elementary cycles, e.g. the carbon, nitrogen, sulfur and phosphorous cycle (Canfield, 1989;Martin et al, 1991;Widdel et al, 1993;Straub et al, 1996;Emerson and Moyer, 1997;Boyd et al, 2007). In nature Fe(II)-oxidizing and Fe(III)-reducing bacteria can be found in close proximity to each other, especially when biogeochemical gradients are steep e.g.…”

Section: Introductionmentioning

confidence: 99%

Anaerobic microbial Fe(II) oxidation and Fe(III) reduction in coastal marine sediments controlled by organic carbon content

Laufer

Byrne

Glombitza

et al. 2016

Coastal marine sediments contain varying concentrations of iron, oxygen, nitrate and organic carbon. It is unknown how organic carbon content influences the activity of nitrate-reducing and phototrophic Fe(II)-oxidizers and microbial Fe-redox cycling in such sediments. Therefore, microcosms were prepared with two coastal marine sediments (Kalø Vig and Norsminde Fjord at Aarhus Bay, Denmark) varying in TOC from 0.4 to 3.0 wt%. The microcosms were incubated under light/dark conditions with/without addition of nitrate and/or Fe(II). Although most probable number (MPN) counts of phototrophic Fe(II)-oxidizers were five times lower in the low-TOC sediment, phototrophic Fe(II) oxidation rates were higher compared with the high-TOC sediment. Fe(III)-amended microcosms showed that this lower net Fe(II) oxidation in the high-TOC sediment is caused by concurrent bacterial Fe(III) reduction. In contrast, MPN counts of nitrate-reducing Fe(II)-oxidizers and net rates of nitrate-reducing Fe(II) oxidation were comparable in low- and high-TOC sediments. However, the ratio of nitratereduced :iron(II)oxidized was higher in the high-TOC sediment, suggesting that a part of the nitrate was reduced by mixotrophic nitrate-reducing Fe(II)-oxidizers and chemoorganoheterotrophic nitrate-reducers. Our results demonstrate that dynamic microbial Fe cycling occurs in these sediments and that the extent of Fe cycling is dependent on organic carbon content.

“…1). In the anoxic sedimentary denitrification zone, nitrate can be utilized as an electron acceptor by many microbial processes, including Fe(II) oxidation (Straub et al, 1996;Hauck et al, 2001), anaerobic ammonium oxidation (anammox) (Thamdrup and Dalsgaard, 2002), organic matter oxidation (Hauck et al, 2001) and potentially even for pyrite oxidation (Bosch et al, 2012). The dissolved nitrogen concentration in the water column of (Upper) Lake Constance at more than 50 m depth has been fairly constant over the past 10 years with a concentration of approximately 70 μM (IGKB, 2001).…”

Section: Introductionmentioning

confidence: 99%

“…Deeper within the sediments, where oxygen is depleted, iron can be microbially oxidized and reduced through processes coupled to nitrogen species in the denitrification zone. Nitrate-reducing Fe(II) oxidizers require a source of ferrous iron, nitrate and an organic co-substrate (Straub et al, 1996). Enzymatic nitratereducing Fe(II) oxidation has not yet been conclusively demonstrated and it has been suggested that the oxidation of ferrous iron occurs chemically through the production of nitrite during microbial denitrification (Klueglein and Kappler, 2013).…”

Section: Introductionmentioning

confidence: 99%

High spatial resolution of distribution and interconnections between Fe‐ and N‐redox processes in profundal lake sediments

Melton

Stief

Behrens

et al. 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) oxidizers and chemically by NOx − species formed during denitrification, which can chemically oxidize Fe(II). This study combines high resolution chemical, molecular and microbiological data to pinpoint sedimentary redox zones in which Fe is cycled between Fe(II) and Fe(III) and where Fe and N-redox processes interact.