# Iron Sulfides Produced by Thermococcales: An Iron Detoxification Mechanism

## TL;DR

Thermococcales archaea survive in iron-rich hydrothermal vents by forming iron sulfides, with some cells dying to protect the rest of the population.

## Contribution

The study reveals a novel population-level iron detoxification mechanism involving biomineralization and gene expression in Thermococcales.

## Key findings

- Thermococcales induce faster iron precipitation compared to abiotic conditions.
- A subpopulation of cells becomes encrusted in pyrite and dies during mineralization.
- Surviving cells activate DNA repair and metal detoxification genes.

## Abstract

Thermococcales, sulfur‐reducing archaea inhabiting the hottest parts of hydrothermal vents, have evolved to thrive in environments rich in iron and sulfide species. In this study, using experimental analogues of sulfur‐rich hydrothermal chimneys, we confirm previous suggestions that the precipitation of iron sulfide minerals promoted by Thermococcales contributes to a population‐wide adaptation to reactive species induced by the presence of high levels of iron. In parallel with mineral phases identification, cellular metabolic activity was monitored during mineralization, revealing a mechanism in which a subpopulation of cells does not survive mineralization and becomes encrusted in pyrite, while the remaining living cells exhibit a gene expression profile focused on DNA repair and metal excess associated detoxification. Compared to abiotic conditions, Thermococcales induce a faster precipitation of dissolved iron, immobilising excess metal. Our results clarify the role of mineralizing cells in this survival mechanism, suggesting that this biomineralization process allows resilience to extreme chemical stress. Upon drastic levels of toxic dissolved iron, thanks to a population of mineralizing cells, the surviving Thermococcales are thus more likely to endure those still harsh environments. This complex mechanism is likely a key factor in the adaptation of microorganisms to the hottest environments of hydrothermal vents.

Thermococcales, archaea from hydrothermal vents, promote iron sulfide precipitation, enabling survival in iron‐rich environments. Some cells become encrusted in pyrite and do not survive mineralization, while surviving cells activate metal detoxification genes. This biomineralization process allows the population to withstand toxic iron concentrations, supporting adaptation to extreme, high‐temperature hydrothermal conditions.