Viruses are thought to be functionally inactive once they are outside and independent of their host cell¹. Here we describe an exceptional property of a newly discovered virus that infects a hyperthermophilic archaeon growing in acidic hot springs: the lemon-shaped viral particle develops a very long tail at each of its pointed ends after being released from its host cell. The process occurs only at the temperature of the host's habitat (75–90 °C) and it does not require the presence of the host cell, an exogenous energy source or any cofactors. This host-independent morphological development may be a strategy for viral survival in an environment that is unusually harsh and has limited host availability.

1. Molecular Biology of the Gene in Extremophiles Unit, Institut Pasteur, 75724 Paris Cedex 15, France
2. University of Regensburg, 93053 Regensburg, Germany
3. Danish Archaea Centre, Institute of Molecular Biology and Physiology, Copenhagen University, 1307 Copenhagen K, Denmark

Correspondence to: David Prangishvili^1,2 Email: prangish@pasteur.fr