It has been shown that reactive soil minerals, specifically iron(III) (oxyhydr)oxides, can trap organic carbon in soils overlying intact permafrost, and may limit carbon mobilization and degradation ...as it is observed in other environments. However, the use of iron(III)-bearing minerals as terminal electron acceptors in permafrost environments, and thus their stability and capacity to prevent carbon mobilization during permafrost thaw, is poorly understood. We have followed the dynamic interactions between iron and carbon using a space-for-time approach across a thaw gradient in Abisko (Sweden), where wetlands are expanding rapidly due to permafrost thaw. We show through bulk (selective extractions, EXAFS) and nanoscale analysis (correlative SEM and nanoSIMS) that organic carbon is bound to reactive Fe primarily in the transition between organic and mineral horizons in palsa underlain by intact permafrost (41.8 ± 10.8 mg carbon per g soil, 9.9 to 14.8% of total soil organic carbon). During permafrost thaw, water-logging and O
limitation lead to reducing conditions and an increase in abundance of Fe(III)-reducing bacteria which favor mineral dissolution and drive mobilization of both iron and carbon along the thaw gradient. By providing a terminal electron acceptor, this rusty carbon sink is effectively destroyed along the thaw gradient and cannot prevent carbon release with thaw.
Anthropogenic activities are modifying the oceanic environment rapidly and are causing ocean warming and deoxygenation, affecting biodiversity, productivity, and biogeochemical cycling. In coastal ...sediments, anaerobic organic matter degradation essentially fuels the production of hydrogen sulfide and methane. The release of these compounds from sediments is detrimental for the (local) environment and entails socio-economic consequences. Therefore, it is vital to understand which microbes catalyze the re-oxidation of these compounds under environmental dynamics, thereby mitigating their release to the water column. Here we use the seasonally dynamic Boknis Eck study site (SW Baltic Sea), where bottom waters annually fall hypoxic or anoxic after the summer months, to extrapolate how the microbial community and its activity reflects rising temperatures and deoxygenation. During October 2018, hallmarked by warmer bottom water and following a hypoxic event, modeled sulfide and methane production and consumption rates are higher than in March at lower temperatures and under fully oxic bottom water conditions. The microbial populations catalyzing sulfide and methane metabolisms are found in shallower sediment zones in October 2018 than in March 2019. DNA-and RNA profiling of sediments indicate a shift from primarily organotrophic to (autotrophic) sulfide oxidizing Bacteria, respectively. Previous studies using data collected over decades demonstrate rising temperatures, decreasing eutrophication, lower primary production and thus less fresh organic matter transported to the Boknis Eck sediments. Elevated temperatures are known to stimulate methanogenesis, anaerobic oxidation of methane, sulfate reduction and essentially microbial sulfide consumption, likely explaining the shift to a phylogenetically more diverse sulfide oxidizing community based on RNA.
Abstract
Anoxygenic photoautotrophic bacteria which use light energy and electrons from Fe(II) for growth, so-called photoferrotrophs, are suggested to have been amongst the first phototrophic ...microorganisms on Earth and to have contributed to the deposition of sedimentary iron mineral deposits, i.e. banded iron formations. To date only two isolates of marine photoferrotrophic bacteria exist, both of which are closely related purple non-sulfur bacteria. Here we present a novel green-sulfur photoautotrophic Fe(II) oxidizer isolated from a marine coastal sediment, Chlorobium sp. strain N1, which is closely related to the freshwater green-sulfur bacterium Chlorobium luteolum DSM273 that is incapable of Fe(II) oxidation. Besides Fe(II), our isolated strain grew phototrophically with other inorganic and organic substrates such as sulfide, hydrogen, lactate or yeast extract. Highest Fe(II) oxidation rates were measured at pH 7.0–7.3, the temperature optimum was 25°C. Mössbauer spectroscopy identified ferrihydrite as the main Fe(III) mineral and fluorescence and helium-ion microscopy revealed cell-mineral aggregates without obvious cell encrustation. In summary, our study showed that the new isolate is physiologically adapted to the conditions of its natural habitat but also to conditions as proposed for early Earth and is thus a suitable model organism for further studies addressing phototrophic Fe(II) oxidation on early Earth.
This study presents the first green-sulfur photoautotrophic Fe(II)-oxidizer isolated from a marine coastal sediment.
Phototrophic Fe(II)‐oxidizers use Fe(II) as electron donor for CO2 fixation thus linking Fe(II) oxidation, ATP formation, and growth directly to the availability of sunlight. We compared the effect ...of short (10 h light/14 h dark) and long (2–3 days light/2–3 days dark) light/dark cycles to constant light conditions for the phototrophic Fe(II)‐oxidizer Chlorobium ferrooxidans KoFox. Fe(II) oxidation was completed first in the setup with constant light (9 mM Fe(II) oxidised within 8.9 days) compared to the light/dark cycles but both short and long light/dark cycles showed faster maximum Fe(II) oxidation rates. In the short and long cycle, Fe(II) oxidation rates reached 3.5 ± 1.0 and 2.6 ± 0.3 mM/d, respectively, compared to 2.1 ± 0.3 mM/d in the constant light setup. Maximum Fe(II) oxidation was significantly faster in the short cycle compared to the constant light setup. Cell growth reached roughly equivalent cell numbers across all three light conditions (from 0.2–2.0 × 106 cells/mL to 1.1–1.4 × 108 cells/mL) and took place in both the light and dark phases of incubation. SEM images showed different mineral structures independent of the light setup and 57Fe Mössbauer spectroscopy confirmed the formation of poorly crystalline Fe(III) oxyhydroxides (such as ferrihydrite) in all three setups. Our results suggest that periods of darkness have a significant impact on phototrophic Fe(II)‐oxidizers and significantly influence rates of Fe(II) oxidation.
Light/dark periods happen daily in nature but are seldom included in experimental designs of phototrophic Fe(II)‐oxidizers like Chlorobium ferrooxidans KoFox. We investigated how different light/dark cycles impact Fe(II) oxidation rates, cell growth and Fe(III) mineral formation of these bacteria. We found that imitating a day/night cycle increased the maximum Fe(II) oxidation rates significantly and suggest that this could lead to an under estimation of anoxygenic Fe(II)‐oxidizers in the environment.
Rhodopseudomonas palustris TIE‐1 grows photoautotrophically with Fe(II) as an electron donor and photoheterotrophically with a variety of organic substrates. However, it is unclear whether R. ...palustris TIE‐1 conducts Fe(II) oxidation in conditions where organic substrates and Fe(II) are available simultaneously. In addition, the effect of organic co‐substrates on Fe(II) oxidation rates or the identity of Fe(III) minerals formed is unknown. We incubated R. palustris TIE‐1 with 2 mM Fe(II), amended with 0.6 mM organic co‐substrate, and in the presence/absence of CO2. We found that in the absence of CO2, only the organic co‐substrates acetate, lactate and pyruvate, but not Fe(II), were consumed. When CO2 was present, Fe(II) and all organic substrates were consumed. Acetate, butyrate and pyruvate were consumed before Fe(II) oxidation commenced, whereas lactate and glucose were consumed at the same time as Fe(II) oxidation proceeded. Lactate, pyruvate and glucose increased the Fe(II) oxidation rate significantly (by up to threefold in the case of lactate). 57Fe Mössbauer spectroscopy revealed that short‐range ordered Fe(III) oxyhydroxides were formed under all conditions. This study demonstrates phototrophic Fe(II) oxidation proceeds even in the presence of organic compounds, and that the simultaneous oxidation of organic substrates can stimulate Fe(II) oxidation.
Rhodopseudomonas palustris TIE‐1, a phototrophic Fe(II) oxidiser, is metabolically flexible and can use inorganic and organic substrates as an electron donor. This study investigated the use of different organic molecules as co‐substrates on Fe(II) oxidation rates in the presence and absence of CO2 and mineral formation at environmentally relevant concentrations. We observed simultaneous and sequential consumption of Fe(II) with different substrates and organics influenced Fe(II) oxidation.
Metabolic flexibility controls microbial survival and shapes ecological structures. Although the utilization of a variety of substrates has been studied for individual metabolically versatile ...microorganisms, only little is known about the response of microbial communities toward substrate fluctuation. Here, we exposed a phototrophic co-culture (Rhodopseudomonas sp. and Chlorobium sp.) that was isolated from a littoral freshwater sediment to a variety of substrates (acetate, Fe(II), or H
2
) and followed the abundance of individual microbial partners based on their characteristic light absorption pattern. Chlorobium sp. dominated the culture when Fe(II) was supplied, whereas Rhodopseudomonas sp. decreased below detection. Rhodopseudomonas sp. dominated when the co-culture was transferred onto acetate (Chlorobium sp. below detection). When grown on H
2
, the dominance pattern depended on pre-culture conditions. Pre-cultures on Fe(II) or acetate resulted in dominance of Chlorobium sp. or Rhodopseudomonas sp., respectively. Although the relative abundance of the two partner strains strictly relies on substrate availability, we were incapable of isolating Chlorobium sp. from the co-culture. Our study shows how substrate fluctuations shape microbial distribution and points toward potential community interactions that enable microbial survival.
PDF
