{"id":477618,"date":"2026-10-08T08:31:54","date_gmt":"2026-10-08T15:31:54","guid":{"rendered":"https:\/\/climatescience.press\/?p=477618"},"modified":"2026-10-08T08:31:56","modified_gmt":"2026-10-08T15:31:56","slug":"hidden-antarctic-microbe-forges-iron-minerals-in-total-darkness-and-may-rewrite-snowball-earth-history","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=477618","title":{"rendered":"Hidden Antarctic microbe forges iron minerals in total darkness \u2014 and may rewrite Snowball Earth history"},"content":{"rendered":"\n
AI generated by Grok<\/figcaption><\/figure>\n\n\n\n

A recent study by researchers from Yonsei University (led by Jaekyung Yoon and Jihyun F. Kim) and collaborators proposes that microbes capable of oxidizing iron in complete darkness and without oxygen could explain some banded iron formations (BIFs) from Snowball Earth periods.<\/strong><\/p>\n\n\n\n

The work centers on Holocene <\/strong>(roughly the last ~11,700 years) sediments recovered from beneath Antarctica\u2019s Larsen C Ice Shelf. A sediment core (GC16B) from ~324 m water depth provided a pristine, largely undisturbed archive sealed under ice since the Last Glacial Maximum<\/strong>. <\/p>\n\n\n\n

Microbial community profiling (16S rRNA amplicon sequencing across many layers) showed distinct phases that track geological facies: more diverse communities in shallower, occasionally open-marine intervals versus chemolithoautotroph-dominated assemblages in deeper anoxic, aphotic sub- ice- shelf layers.<\/p>\n\n\n\n

A keystone taxon in the sub- ice-shelf community is an uncultured member of the Thermodesulfovibrionia (phylum Nitrospirota). Metagenome -assembled genomes from these layers revealed a novel candidate order (Candidatus Mariimomonadales). The organism was provisionally named Candidatus Mariimomonas ferrooxydans<\/em>. <\/p>\n\n\n\n

Its genome encodes Cyc2<\/strong>, a fused porin\u2013 cytochrome outer -membrane protein previously linked to Fe (II) oxidation<\/strong> in other bacteria, along with other cytochromes, iron- sulfur proteins<\/strong>, and nitrate- related machinery that could support anaerobic iron oxidation coupled (directly or indirectly) to nitrate reduction.<\/p>\n\n\n\n

Functional confirmation came from expressing the cyc2<\/em> gene (codon- optimized) in Escherichia coli<\/em>: <\/strong>the protein incorporated heme, showed peroxidase activity, and significantly accelerated ferrous iron oxidation relative to controls. <\/p>\n\n\n\n

Fluorescence in situ<\/em> hybridization also visualized the cells in the sediment. Elevated iron- to- titanium ratios in the anoxic intervals roughly coincide with the distribution of these bacteria, consistent with in situ<\/em> iron mineralization.<\/p>\n\n\n\n

These dark, anoxic, oligotrophic, ice- covered sediments are presented as a modern analogue for synglacial BIFs deposited during Neoproterozoic Snowball Earth <\/strong>events (when ice reached low latitudes and iron- rich layers accumulated under or near ice). <\/p>\n\n\n\n

Classic models emphasize photosynthetic cyanobacteria or anoxygenic photoferrotrophs that require light. The Larsen C findings supply genomic and experimental evidence that chemolithotrophic iron oxidizers can drive substantial Fe (III) precipitation without sunlight or free oxygen, potentially resolving how iron formations could accumulate under global ice cover. <\/p>\n\n\n\n

The authors note this pathway may also have operated earlier in Earth\u2019s history and has implications for interpreting iron minerals on other worlds (e.g., Mars) or icy- ocean moons.<\/p>\n\n\n\n

The peer- reviewed paper is \u201cNovel Antarctic chemolithotroph drives iron biomineralization\u201d (Yoon et al., Microbiome<\/em>, 2026). <\/p>\n\n\n\n

A related preprint appeared earlier on bioRxiv under a similar title. Limitations include reliance on whole-genome amplification (due to very low DNA yields in deeper layers) and the still- open question of whether iron oxidation is directly coupled to nitrate reduction or involves abiotic steps. Overall, the work expands the known diversity of iron- cycling microbes and challenges purely phototroph- centered explanations for certain ancient iron deposits.<\/p>\n\n\n\n

\"A
Microbiota structure of the Holocene sediment beneath the Larsen C Ice Shelf.
Figure 1 | Novel Antarctic chemolithotroph drives iron biomineralization | Microbiome | Springer Nature Link<\/a><\/figcaption><\/figure>\n\n\n\n

<\/p>\n\n\n\n

Novel Antarctic chemolithotroph drives iron biomineralization<\/strong><\/p>\n\n\n\n

Background<\/strong><\/p>\n\n\n\n

Iron is the most abundant redox- active metal in Earth\u2019s crust and is tightly linked to many biogeochemical cycles, yet the organisms and mechanisms of iron oxidation are still incompletely understood. Banded iron formations (BIFs) <\/strong>are a major Precambrian iron- ore reservoir, but the biological contribution to their formation remains debated. Although large- scale BIF deposition largely stopped after the Proterozoic<\/strong>, modern Holocene sediments <\/strong>under fluctuating redox conditions offer analogues for studying similar iron-cycling processes.<\/p>\n\n\n\n

Results<\/strong><\/p>\n\n\n\n

Sediments from beneath the Larsen C Ice Shelf (LCIS),<\/strong> Antarctica<\/strong>, record microbial community shifts that closely track environmental changes through the Holocene. Metagenomic analyses identified three dominant microbial phases that align with geological facies boundaries:<\/p>\n\n\n\n