biostudies-literatureDi Cianni NDFGuqaf008https://www.ebi.ac.uk/biostudies/studies/S-EPMC12091111biostudies-literatureUnknown6<i>Haloferax volcanii</i> harbours four putative proviruses: Halfvol1, Halfvol2, Halfvol3, and Halfvol4. In this study, we successfully deleted all four provirus genomes, demonstrating, that they are not essential. Transcriptome comparison between this strain (∆Halfvol1-4) and a wild-type strain reveals an increase in archaella and chemotaxis gene expression, resulting in higher swarming motility in ∆Halfvol1-4. Furthermore, ∆Halfvol1-4 cells show an elongated cell shape and a higher resistance to H₂O₂ stress compared to the wild type. RNA-seq also revealed downregulation of CRISPR arrays in the provirus-free strain. Circularised genomes of Halfvol1, Halfvol2, and Halfvol3 were found in the culture supernatant of the wild-type strain. This confirms excision of the promicroLifeProvirus deletion from &lt;i&gt;Haloferax volcanii&lt;/i&gt; affects motility, stress resistance, and CRISPR RNA expression.PMC12091111SPP2141Ma1538/25-2Ma1538/27-1Walther PAllers TUrlaub HMarchfelder ADi Cianni NKonig SMitchell LRaabe MGrafenhan TErdmann SDyall-Smith MRead CBischler TBrendel JPfeiffer FBolsinger SfalseProvirus deletion from &lt;i&gt;Haloferax volcanii&lt;/i&gt; affects motility, stress resistance, and CRISPR RNA expression.<i>Haloferax volcanii</i> harbours four putative proviruses: Halfvol1, Halfvol2, Halfvol3, and Halfvol4. In this study, we successfully deleted all four provirus genomes, demonstrating, that they are not essential. Transcriptome comparison between this strain (∆Halfvol1-4) and a wild-type strain reveals an increase in archaella and chemotaxis gene expression, resulting in higher swarming motility in ∆Halfvol1-4. Furthermore, ∆Halfvol1-4 cells show an elongated cell shape and a higher resistance to H₂O₂ stress compared to the wild type. RNA-seq also revealed downregulation of CRISPR arrays in the provirus-free strain. Circularised genomes of Halfvol1, Halfvol2, and Halfvol3 were found in the culture supernatant of the wild-type strain. This confirms excision of the pro2025-01-01T00:00:00Z20252026-04-08T18:39:13.835Z2026-04-08T09:51:35.475ZS-EPMC120911114039599710.1093/femsml/uqaf008