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Today, Mg2+ 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 O2, high Fe2+, and high Mn2+) 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 Mg2+, Fe2+, and Mn2+ on the tertiary structure of rRNA. Then, we used in vitro translation reactions to test whether Fe2+ or Mn2+ could mediate protein production, and quantified ribosomal metal content. We found that (i) Mg2+, Fe2+, and Mn2+ had strikingly similar effects on rRNA folding; (ii) Fe2+ and Mn2+ can replace Mg2+ 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 Fe2+ and Mn2+ were abundant, these findings suggest that Fe2+ and Mn2+ played a role in early ribosomal evolution.

Summary: 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. [ABSTRACT FROM AUTHOR]