# The Molecular Profile of Soil Microbial Communities Inhabiting a Cambrian Host Rock

## TL;DR

This paper explores the molecular profile of soil microbes in ancient Cambrian rocks, revealing how microbial and plant activity shaped early soil ecosystems.

## Contribution

The study identifies specific microbial and plant-derived molecules in a 520-million-year-old rock, offering insights into ancient soil ecosystems.

## Key findings

- Elevated bacterial and fungal lipids indicate heterotrophic activity in the ancient soil ecosystem.
- Long-chain alkanols and fatty acids confirm plant residue inputs into the microbial community.
- The study emphasizes the need for contamination controls when analyzing ancient or extraterrestrial materials.

## Abstract

The process of soil genesis unfolds as pioneering microbial communities colonize mineral substrates, enriching them with biomolecules released from bedrock. The resultant intricate surface units emerge from a complex interplay among microbiota and plant communities. Under these conditions, host rocks undergo initial weathering through microbial activity, rendering them far from pristine and challenging the quest for biomarkers in ancient sedimentary rocks. In addressing this challenge, a comprehensive analysis utilizing Gas Chromatography Mass Spectrometry (GC-MS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was conducted on a 520-Ma-old Cambrian rock. This investigation revealed a diverse molecular assemblage with comprising alkanols, sterols, fatty acids, glycerolipids, wax esters, and nitrogen-bearing compounds. Notably, elevated levels of bacterial C16, C18 and C14 fatty acids, iso and anteiso methyl-branched fatty acids, as well as fungal sterols, long-chained fatty acids, and alcohols, consistently align with a consortium of bacteria and fungi accessing complex organic matter within a soil-type ecosystem. The prominence of bacterial and fungal lipids alongside maturity indicators denotes derivation from heterotrophic activity rather than ancient preservation or marine sources. Moreover, the identification of long-chain (>C22) n-alkanols, even-carbon-numbered long chain (>C20) fatty acids, and campesterol, as well as stigmastanol, provides confirmation of plant residue inputs. Furthermore, findings highlight the ability of contemporary soil microbiota to inhabit rocky substrates actively, requiring strict contamination controls when evaluating ancient molecular biosignatures or extraterrestrial materials collected.