Almost all Sulfolobales contain an type IV pili operon named the UV inducible pilus operon (ups). This operon is highly induced after UV treatment of Sulfolobus cells or the occurence of DNA double strand breakages. As a result the cells express multiple pili all around the cell surface and start to aggregate (see image). In these aggregates the cells exchange DNA which is subsequently used to repair their genomic DNA by homologous recombination.
Recently, we have have identified the DNA importer, the Ced system (Crenarhcaeal exchange of DNA), which takes up the DNA during the aggregation process and is depending on an ATPase (Van Wolferen et al., PNAS, 2016). We are now trying to understand how the cells aggregate and how the cell-cell-connection is established.