Hyperthermophiles in the history of life

Abstract

Today, hyperthermophilic ('superheat-loving') bacteria and archaea are found within high-temperature environments, representing the upper temperature border of life. They grow optimally above 80 degrees C and exhibit an upper temperature border of growth up to 113 degrees C. Members of the genera, Pyrodictium and Pyrolobus, survive at least 1h of autoclaving. In their basically anaerobic environments, hyperthermophiles (HT) gain energy by inorganic redox reactions employing compounds like molecular hydrogen, carbon dioxide, sulphur and ferric and ferrous iron. Based on their growth requirements, HT could have existed already on the early Earth about 3.9Gyr ago. In agreement, within the phylogenetic tree of life, they occupy all the short deep branches closest to the root. The earliest archaeal phylogenetic lineage is represented by the extremely tiny members of the novel kingdom of Nanoarchaeota, which thrive in submarine hot vents. HT are very tough survivors, even in deep-freezing at -140 degrees C. Therefore, during impact ejecta, they could have been successfully transferred to other planets and moons through the coldness of space.

Figure 1

Small subunit ribosomal RNA-based phylogenetic tree. The thick lineages represent HT.

Figure 2

Schematic of main energy-yielding reactions in chemolithoautotrophic HT.

Figure 3

Krafla solfataric field (Iceland), 2 days before a volcanic fissure eruption. A huge fumarole throws up lumps of boiling mud that contained viable HT.

Figure 4

Antler-shaped cell of Thermoproteus, about 100 μm in length and 0.4 μm in diameter. Phase-contrast light micrograph.

Figure 5

Oil wells within the permafrost soil at Prudhoe Bay, North Alaska.

Figure 6

Sampling at the submarine hydrothermal vents at Porto di Levante, Vulcano (Italy). Hot water and gas escape from cracks within hot volcanic rocks.

Figure 7

Pyrodictium abyssi, disk-shaped cells within a network of ultrathin tubules. Scanning electron micrograph.

Figure 8

Sampling of hot rocks from a ‘Beehive Smoker’ at the Mid-Atlantic Ridge (TAG site; 21° N; depth approx. 4000 m).

Figure 9

Pyrolobus fumarii, lobed coccoid cell. Ultrathin section. Transmission electron micrograph. Scale bar, 0.5 μm.

Figure 10

Cells of N. equitans (small) attached to Ignicoccus strain Kin 4M (large). (a) Platinum-shadowing. (b) Freeze-etching. Transmission electron micrographs.