Bacterial spores survived being heated to 420 degrees Celsius
Microbes turn up in sediment at 120 degrees Celsius more than a kilometre beneath the seabed, in a lake sealed half a mile under Antarctic ice, and at the bottom of the Mariana Trench. Researchers at Ghent University even revived Bacillus spores after heating them to 420 degrees. Extremophiles redraw the boundaries of where life can exist.
The name joins Latin extremus with Greek philia, love: organisms that do well under extreme heat, cold, pressure, radiation, salt or acidity. Most are microbes, especially archaea, though some fungi qualify too. What counts as extreme is measured against a human-centred baseline, so from the planet's long view these organisms are among its most abundant and successful inhabitants.
Biologists grasped their range in the 1980s and 1990s, finding microbial life in places far too acidic, hot or pressurised for complex organisms. Some concluded life might have begun at hydrothermal vents deep in the ocean. Drilling by the International Ocean Discovery Program found microbes in hot sediment in the Nankai Trough subduction zone, and others live inside rock about 580 metres below the seafloor off the northwestern United States. The astrophysicist Steinn Sigurdsson notes that viable bacterial spores 40 million years old have been found, highly resistant to radiation. One key adaptation lies in amino acid makeup, which lets their proteins fold properly under harsh conditions.
Scientists sort them by their preferred extreme. Thermophiles grow best above 45 degrees Celsius and hyperthermophiles above 80; psychrophiles prefer 15 degrees or below. Halophiles need at least 50 grams of dissolved salt per litre, compared with about 35 in a coral reef. Acidophiles thrive at pH 3 or lower. Metal-tolerant species such as Cupriavidus metallidurans cope with copper, cadmium and arsenic. Many are polyextremophiles; a microbe on an Atacama Desert summit might be cold-loving, radiation-resistant, drought-adapted and starved of nutrients all at once.
Surviving is not the same as thriving. Tardigrades endure remarkable stresses, yet strictly speaking they are not extremophiles, because they tolerate harsh conditions rather than preferring them. The study of these organisms informs the search for life on other worlds and suggests ways to clean up polluted sites.
Source: Extremophile
