Abstract
SummaryPf filamentous prophages are prevalent among clinical and environmental Pseudomonas aeruginosa isolates. Pf4 and Pf5 prophages are integrated into the host genomes of PAO1 and PA14, respectively, and play an important role in biofilm development. However, the genetic factors that directly control the lysis‐lysogeny switch in Pf prophages remain unclear. Here, we identified and characterized the excisionase genes in Pf4 and Pf5 (named xisF4 and xisF5, respectively). XisF4 and XisF5 represent two major subfamilies of functional excisionases and are commonly found in Pf prophages. While both of them can significantly promote prophage excision, only XisF5 is essential for Pf5 excision. XisF4 activates Pf4 phage replication by upregulating the phage initiator gene (PA0727). In addition, xisF4 and the neighboring phage repressor c gene pf4r are transcribed divergently and their 5′‐untranslated regions overlap. XisF4 and Pf4r not only auto‐activate their own expression but also repress each other. Furthermore, two H‐NS family proteins, MvaT and MvaU, coordinately repress Pf4 production by directly repressing xisF4. Collectively, we reveal that Pf prophage excisionases cooperate in controlling lysogeny and phage production.
Highlights
Filamentous phages, among the simplest biological entities known, were discovered over a half-century ago
Pf4 and Pf5 prophages are integrated into the host genomes of PAO1 and PA14, respectively, and play an important role in biofilm development
XisF4 and XisF5 represent two major subfamilies of functional excisionases and are commonly found in Pf prophages. While both of them can significantly promote prophage excision, only XisF5 is essential for Pf5 excision
Summary
Filamentous phages, among the simplest biological entities known, were discovered over a half-century ago. The filamentous phage CTXφ in Vibrio cholera carries genes encoding the cholera toxin and plays a critical role in the conversion of nontoxigenic strains into pathogens (Waldor and Mekalanos, 1996; Davis et al, 2002). Another filamentous phage, VPIφ in V. cholera, encodes the structural gene for a toxin-co-regulated pilus, which is the receptor for CTXφ and a colonization factor (Li et al, 2003). The filamentous phage φRSM3 in Ralstonia solanacearum encodes a transcriptional regulator that represses the expression of the host virulence genes (Addy et al, 2012)
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