Title: Hyperthermophiles in the History of Life

Presenter: Professor Karl O. Stetter

University: Lehrstuhl für Mikrobiologie, Universit？t Regensburg, Germany

Time: 10:00-11:00, December 7, 2015

Venue: Room A203, Institute of Microbiology, Chinese Academy of Sciences

Abstract:

To-day, hyperthermophilic (“super-heat-loving”) bacteria and archaea are found within high temperature environments, representing the upper temperature border of life. They grow optimally at above 80°C and exhibit an upper temperature border of growth of up to 113°C. Members of the genera Pyrodictium and Pyrolobus even survive at least one hour of autoclaving. In their basically anaerobic environments, hyperthermophiles gain energy mainly by inorganic redox reactions employing compounds like molecular hydrogen, carbon dioxide, sulphur, nitrate and ferric and ferrous iron. In addition, several are opportunistic or obligate heterotrophs. Based on their growth requirements, hyperthermophiles could have existed already on the Early Earth, about 3.9 billion years ago. In agreement, within the ss rRNA-based phylogenetic tree of life they occupy all the short deep-branching lineages closest to the root. The deepest- branching archaeal lineages are represented by the Nanoarchaeota and the Korarchaeota. Various members of both groups are world-wide distributed and so far hardly investigated. Cells of Nanoarchaeum equitans consist of minicocci, only 0.4 μm in diameter. Their cultivation requires specific cell-cell-contact with Ignicoccus hospitalis, a crenarchaeal host. The N. equitans genome is among the smallest known to date (490,885 bp). From the first member of the Korarchaeota, an enrichment culture and a complete genome sequence has been obtained recently. It revealed an unprecedented heterogeneous gene complement suggesting that the Korarchaeota had diverged very early in the history of the archaeal lineage.