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Divalent metal cations are essential to the structure and function of the ribosome. Previous characterizations of the ribosome performed under standard laboratory conditions have implicated Mg2+ as a primary mediator of ribosomal structure and function. Possible contributions of Fe2+ as a ribosomal cofactor have been largely overlooked, despite the ribosome's early evolution in a high Fe2+ environment, and the continued use of Fe2+ by obligate anaerobes inhabiting high Fe2+ niches. Here, we show that (i) Fe2+ cleaves RNA by in-line cleavage, a non-oxidative mechanism that has not previously been shown experimentally for this metal, (ii) the first-order in-line rate constant with respect to divalent cations is >200 times greater with Fe2+ than with Mg2+, (iii) functional ribosomes are associated with Fe2+ after purification from cells grown under low O2 and high Fe2+ and (iv) a small fraction of Fe2+ that is associated with the ribosome is not exchangeable with surrounding divalent cations, presumably because those ions are tightly coordinated by rRNA and deeply buried in the ribosome. In total, these results expand the ancient role of iron in biochemistry and highlight a possible new mechanism of iron toxicity., (© The Author(s) 2020. Published by Oxford University Press on behalf of Nucleic Acids Research.)

Electroactive type IV pili, or e-pili, are used by some microbial species for extracellular electron transfer. Recent studies suggest that e-pili may be more phylogenetically and structurally diverse than previously assumed. Here, we used updated aromatic density thresholds (≥9.8% aromatic amino acids, ≤22-aa aromatic gaps and aromatic amino acids at residues 1, 24, 27, 50 and/or 51, and 32 and/or 57) to search for putative e-pilin genes in metagenomes from diverse ecosystems with active microbial metal cycling. Environmental putative e-pilins were diverse in length and phylogeny, and included truncated e-pilins in Geobacter spp., as well as longer putative e-pilins in Fe(II)-oxidizing Betaproteobacteria and Zetaproteobacteria., (© 2019 Society for Applied Microbiology and John Wiley & Sons Ltd.)

Today, Mg 2+ is an essential cofactor with diverse structural and functional roles in life's oldest macromolecular machine, the translation system. We tested whether ancient Earth conditions (low O 2 , high Fe 2+ , and high Mn 2+ ) can revert the ribosome to a functional ancestral state. First, SHAPE (selective 2'-hydroxyl acylation analyzed by primer extension) was used to compare the effect of Mg 2+ , Fe 2+ , and Mn 2+ on the tertiary structure of rRNA. Then, we used in vitro translation reactions to test whether Fe 2+ or Mn 2+ could mediate protein production, and quantified ribosomal metal content. We found that ( i ) Mg 2+ , Fe 2+ , and Mn 2+ had strikingly similar effects on rRNA folding; ( ii ) Fe 2+ and Mn 2+ can replace Mg 2+ as the dominant divalent cation during translation of mRNA to functional protein; and ( iii ) Fe and Mn associate extensively with the ribosome. Given that the translation system originated and matured when Fe 2+ and Mn 2+ were abundant, these findings suggest that Fe 2+ and Mn 2+ played a role in early ribosomal evolution., Competing Interests: The authors declare no conflict of interest., (Copyright © 2018 the Author(s). Published by PNAS.)