With future long-term space exploration and life detection missions on Mars, understanding the
microbial survival beyond Earth as well as the identification of past life traces on other planetary
bodies becomes increasingly important. The series of the Tanpopo space mission experiments target
a long-term exposure (one to three years) of microorganisms on the KIBO Module of the
International Space Station (ISS) in the low Earth orbit (LEO) (Kawaguchi et al., 2020; Ott et al.,
2020). In the search for possible past and/or present microbial life on Mars, metallophilic archaeal
species are of a special interest due to their inherent extraordinary characteristics.
Chemolithotrophic archaea (e.g., from the order Sulfolobales) employ a number of ancient metabolic
pathways to extract energy from diverse inorganic electron donors and acceptors. Metallosphaera
sedula, an iron- and sulfur-oxidizing chemolithotrophic archaeon, which flourishes under hot and
acidic conditions (optimal growth at 74°C and pH 2.0), was cultivated on genuine extraterrestrial
minerals (Milojevic et al., 2019; Milojevic et al., 2021) as well as synthetic Martian materials (Kölbl
et al., 2017). In all cases, M. sedula cells were able to utilize given mineral materials as the sole
energy source for cellular growth and proliferation. During the growth of M. sedula cells on these
materials, a natural mineral impregnation and encrustation of microbial cells was achieved, followed
by their preservation under the conditions of desiccation (Kölbl et al. 2020). Our studies indicate
that this archaeon, when impregnated and encrusted with minerals, withstand long-term desiccation
and can be even recovered from the dried samples to the liquid cultures (Kölbl et al., 2020). The
achieved preservation of desiccated M. sedula cells facilitated our further survivability studies with
this desiccated microorganism under simulated Mars-like environmental conditions and during the
Tanpopo-4 space exposure experiment. [...
