Lava tubes on Mars hold exciting potential for the preservation of
biosignatures, which may survive on geological timescales in these
isolated, stable environments. To support the development of future
astrobiological mission concepts, we turn to terrestrial lava tubes,
host to a variety of microbial communities and secondary minerals.
Following a multidisciplinary sampling protocol, we retrieved
biological, molecular, and mineralogical data from several lava tubes in
Iceland. We report on blue-colored copper-rich secondary minerals and
their associated bacterial communities using a multi-method approach,
and an amalgam of 16S rRNA gene sequencing, Raman spectroscopy, scanning
electron microscopy, and energy-dispersive X-ray spectroscopy data sets.
We found numerous bacterial genera known for their high metal resistance
and ability to survive in low-nutrient environments, both
characteristics to be expected for any potential life in Martian lava
tubes. Associated with them, we identified several types of copper-rich
secondary minerals as well as carotenoid signals. If found in Martian
lava tubes, blue copper-rich mineral precipitates would be deserving of
astrobiological investigation, as they have potential to preserve
biosignatures and harbor life.