Iron and sulfate reduction structure microbial communities in (sub-)Antarctic sediments

Abstract

Permanently cold marine sediments are heavily influenced by increased input of iron as a result of accelerated glacial melt, weathering, and erosion. The impact of such environmental changes on microbial communities in coastal sediments is poorly understood. We investigated geochemical parameters that shape microbial community compositions in anoxic surface sediments of four geochemically differing sites (Annenkov Trough, Church Trough, Cumberland Bay, Drygalski Trough) around South Georgia, Southern Ocean. Sulfate reduction prevails in Church Trough and iron reduction at the other sites, correlating with differing local microbial communities. Within the order Desulfuromonadales, the family Sva1033, not previously recognized for being capable of dissimilatory iron reduction, was detected at rather high relative abundances (up to 5%) while other members of Desulfuromonadales were less abundant (<0.6%). We propose that Sva1033 is capable of performing dissimilatory iron reduction in sediment incubations based on RNA stable isotope probing. Sulfate reducers, who maintain a high relative abundance of up to 30% of bacterial 16S rRNA genes at the iron reduction sites, were also active during iron reduction in the incubations. Thus, concurrent sulfate reduction is possibly masked by cryptic sulfur cycling, i.e., reoxidation or precipitation of produced sulfide at a small or undetectable pool size. Our results show the importance of iron and sulfate reduction, indicated by ferrous iron and sulfide, as processes that shape microbial communities and provide evidence for one of Sva1033’s metabolic capabilities in permanently cold marine sediments.

Soil metabolomics and bacterial functional traits revealed the responses of rhizosphere soil bacterial community to long-term continuous cropping of Tibetan barley

“…For example, Fibrobacteres is an important phylum of cellulose-degrading bacteria ( Ransom-Jones et al, 2012 ); the genus Devosia possesses bioremediation potential ( Talwar et al, 2020 ); and the denitrifying bacteria Noviherbaspirillum ( Wu et al, 2021 ) were significantly upregulated over time. The following significantly decreased over time: Firmicutes, which are plant growth-promoting bacilli ( Kumar, Khare & Dubey, 2012 ); Bacillales, which have effective biological control and biodegradation potential ( Barathi et al, 2020 ); Nitrosomonadales, which are related to sulfate and iron reduction; and Desulfuromonadales, which are an order capable of iron and sulfate reduction ( Wunder et al, 2021 ).…”

Benthic Carbon Remineralization and Iron Cycling in Relation to Sea Ice Cover Along the Eastern Continental Shelf of the Antarctic Peninsula

“…The molar DFe:PO 4 3− concentration ratios calculated from pore‐water profiles at the DFe peak position ranged between 2.1 and 4.8 (Table 3), a ratio which was reported to indicate that the majority of PO 4 3− release is closely associated with the reduction of iron (oxyhydr‐) oxides (Küster‐Heins, de Lange, et al., 2010; Küster‐Heins, Steinmetz, et al., 2010; Kraal et al., 2019, 2020; Noffke et al., 2012; Slomp et al., 1996; Voegelin et al., 2013). Below the iron reduction zone, lower DFe:PO 4 3− ratios were observed suggesting the presence of a DFe sink (FeS formation) and the continuing release of PO 4 3− from organic matter remineralization (Niewöhner et al., 1998; Schulz et al., 1994; Wunder et al., 2021) and/or desorption from Fe‐minerals. Similar trends of pore‐water profiles of PO 4 3− and DFe have previously been observed in the Arctic marginal sea ice zone (Tessin et al., 2020), in the Peruvian oxygen minimum zone (Noffke et al., 2012), in sediments off Namibia (Küster‐Heins, de Lange, et al., 2010; Küster‐Heins, Steinmetz, et al., 2010) and in shelf sediments of the sub‐Antarctic island of South Georgia (Wunder et al., 2021).…”

“…At the marginal sea ice stations, the steep concentration gradients of DFe close to the sediment surface indicate that more DFe might escape from shelf sediments into the water column. Further, the high availability of easily reducible Fe oxides at the marginal sea ice stations favor Fe-reduction over organoclastic sulfate reduction as found in other continental shelf environments (Henkel et al, 2018;Herbert et al, 2021;Oni et al, 2015;Schnakenberg et al, 2021;Wunder et al, 2021). We assume that the majority of easily reducible Fe is derived from re-oxidation/precipitation of upward diffusing DFe at the Fe(II)/Fe(III) redox boundary.…”

Ideas and perspectives: Sea-level change, anaerobic methane oxidation, and the glacial–interglacial phosphorus cycle

“…Hence, if the position of the SMT has been invariant for a while, despite a persistent methane flux and/or the presence of methane seeps, we would not expect a significant phosphate flux out of the sediment because phosphate-bearing oxides would either not accumulate in these sediments or have long been dissolved by the sulfidic pore waters, as observed by Niewöhner et al (1998) in sediments of the upwelling area off Namibia. In fact, porewater profiles would likely mirror those reported by Wunder et al (2021) in the Church Trough sediments of South Georgia where cold methane seeps are documented and where little phosphate escapes the sediment. In other words, one would not expect to observe strong phosphate fluxes across the SWI where persistent cold methane seeps are currently found.…”