Biofilm formation upon virus infection in Sulfolobus solfataricus.

The hyperthermophilic crenarchaeote Sulfolobus solfataricus is a facultative autotroph with the ability to grow under aerobic conditions. The genome of several Sulfolobus species has been sequenced making Sulfolobus spp. model organisms for studying molecular and physiological processes in Archaea. Information about biofilm formation in Archaea is still at the stage of infancy. Recently, it has been shown that S. solfataricus forms a biofilm mainly made of polysaccharides upon attachment to various surfaces, such as glass, mica etc. The genes possibly involved in the production of the extracellular polysaccharides have been identified (1). We have investigated the ability of S. solfataricus to form biofilm as a stress response to the infection with the Spindle-shaped virus 2 (SSV2) (2). After prolonged growth on solid medium of a lawn of S. solfataricus cells spotted with SSV2, production of a white and dense material was observed. Formation of a white matrix was also observed in cells non-infected but grown at high density. The protein fraction of the white matrix was found to be very low and, although not confirmed, it is likely that the white matrix is an exopolysaccharide. We therefore suggest that the formation of the white matrix could be controlled by quorum sensing and cellular stress responses in order to protect cells from external factors. The physiology of the process as well as the chemical composition of the biolfilm-like white matrix, is under way.