Transcriptome analysis of Sulfolobus solfataricus infected with two related fuselloviruses reveals novel insights into the regulation of CRISPR-Cas system

Fuselloviruses SSV1 and SSV2 are model systems to investigate virusehost relationships in stably infected cells thanks to their temperate nature. Although they are very similar in morphology, genome organization and gene synteny, their replication is induced by different stimuli, i.e.: by UV-light exposure (for SSV1) and by the growth progression of the host (for SSV2). In this study, we have analysed global gene expression in SSV1- and SSV2-lysogens of Sulfolobus solfataricus P2 in the absence of any stimuli. Additionally, the interplay among SSV1, SSV2 and the host has been investigated in a double-infected strain to explore both virusehost and virusevirus interactions. Whereas SSV1 did not induce major changes of the host gene expression, SSV2 elicited a strong host response, which includes the transcriptional activation of CRISPR loci and cas genes. As a consequence, a significant decrease of the SSV2 copy number has been observed, which in turn led to provirus-capture into the host chromosome. Results of this study have revealed novel aspects of the hosteviral interaction in the frame of the CRISPRresponse.