Meteorite-enriched cultures reveal novel single-stranded DNA elements
Shotgun metagenomic sequencing of meteorite-enriched microbial cultures, combined with a multi-tier decontamination pipeline, yielded 28 ultra-divergent single-stranded DNA (ssDNA) contigs (200–498 bp) lacking similarity to any known nucleotide, protein or viral database. Over 50% of raw reads remained unclassified, indicating a substantial dark-matter fraction. All contigs feature a conserved 30-bp C/T-rich motif and fold into low-enthalpy secondary structures (?G = –35 kcal mol?¹). No replication, capsid or mobile-element domains were detected, and rigorous negative controls excluded contamination. These unassigned, structurally stable elements were selectively enriched in meteorite-treated flasks and absent from matched environmental samples. We propose that they represent a previously uncharacterised class of environmental ssDNA, potentially native to mineral-rich microenvironments. Their divergence and physical properties suggest a stable genomic architecture distinct from known taxa. Our findings reveal a previously uncharacterised class of ssDNA elements selectively enriched in meteorite-enriched cultures, expanding the known landscape of environmental nucleic acid diversity.