Some researchers study extreme Earth environments to see what the bacterial tolerance limits really are:
Bacteria have adapted to survive the extreme conditions of a crater lake in the active Poás volcano in Costa Rica, known as Laguna Caliente. These microorganisms provide clues to how potential life may have existed under similar circumstances on Mars.
Situated at 2300 metres above sea level, Laguna Caliente is one of the harshest environments on Earth. It is extremely sulphurous and highly acidic, with pH values ranging between -0.87 and 1.5. The lake is also subject to widely fluctuating temperatures, ranging from 38°C to 90°C.
Laguna Caliente has similar mineral compositions to Gusev crater on Mars, which was explored by NASA’s Spirit rover when it landed there in 2004. This suggests that lakes that may have existed on Mars in the past would also have been acidic and hot, says Justin Wang at the University of Colorado Boulder.Chen Ly, “Bacteria survive extremes that may have existed in ancient Mars lakes” at New Scientist (January 28, 2022)
Most life forms the researchers found there were bacteria from a genus called, not surprisingly, Acidiphilium.
Apart from having the ability to metabolize energy from sulphur, the bacteria that cling to the fringes of the erupting lake create “bioplastics” to store energy.
A similar project at Poas:
The point of the research is to pinpoint areas on Mars (remains of crater lakes, for example) that might offer samples of fossil bacteria, if they ever existed. If even such spots show no life, we will at least have a means of determining the likely success of further searches.
The paper is open access.
You may also wish to read: Light carbon another faint hope for past life on Mars? At Science: On Earth the signal would be seen as strong evidence for ancient microbial life.