Abstract
SummaryPf prophages are ssDNA filamentous prophages that are prevalent among various Pseudomonas aeruginosa strains. The genomes of Pf prophages contain not only core genes encoding functions involved in phage replication, structure and assembly but also accessory genes. By studying the accessory genes in the Pf4 prophage in P. aeruginosa PAO1, we provided experimental evidence to demonstrate that PA0729 and the upstream ORF Rorf0727 near the right attachment site of Pf4 form a type II toxin/antitoxin (TA) pair. Importantly, we found that the deletion of the toxin gene PA0729 greatly increased Pf4 phage production. We thus suggest the toxin PA0729 be named PfiT for Pf4 inhibition toxin and Rorf0727 be named PfiA for PfiT antitoxin. The PfiT toxin directly binds to PfiA and functions as a corepressor of PfiA for the TA operon. The PfiAT complex exhibited autoregulation by binding to a palindrome (5′‐AATTCN5 GTTAA‐3′) overlapping the ‐35 region of the TA operon. The deletion of pfiT disrupted TA autoregulation and activated pfiA expression. Additionally, the deletion of pfiT also activated the expression of the replication initiation factor gene PA0727. Moreover, the Pf4 phage released from the pfiT deletion mutant overcame the immunity provided by the phage repressor Pf4r. Therefore, this study reveals that the TA systems in Pf prophages can regulate phage production and phage immunity, providing new insights into the function of TAs in mobile genetic elements.
Highlights
Toxin/antitoxin (TA) systems are genetic modules widely distributed in prokaryotes
Toxin and antitoxin genes are in the same operon, and the cognate toxins either work as repressors or activators of antitoxins to autoregulate the expression of the TA operon (Magnuson and Yarmolinsky, 1998; Afif et al, 2001; Overgaard et al, 2008; Winther and Gerdes, 2012; Turnbull and Gerdes, 2017)
Rorf0727 encodes a protein of 83 aa that belongs to the Phd antitoxin family, and PA0729 encodes a protein of 115 aa that belongs to the ParE toxin family
Summary
Toxin/antitoxin (TA) systems are genetic modules widely distributed in prokaryotes. TA genes usually encode a toxin that kills cells or inhibits cell growth and a cognate antitoxin that neutralizes the toxicity of the toxin. Toxin and antitoxin genes are in the same operon, and the cognate toxins either work as repressors or activators of antitoxins to autoregulate the expression of the TA operon (Magnuson and Yarmolinsky, 1998; Afif et al, 2001; Overgaard et al, 2008; Winther and Gerdes, 2012; Turnbull and Gerdes, 2017). These type II TA systems are found in both chromosomes and mobile genetic elements including plasmids and prophages (Wang and Wood, 2016; Harms et al, 2018). The studied plasmid-encoded TA systems include the first type II TA CcdB/CcdA characterized ‘addiction’ systems on the F sex factor plasmid (Ogura and Hiraga, 1983), ParE/ ParD, Hok/Doc, HigB/HigA and HicB/HicA (Lehnherr et al, 1993; Roberts et al, 1994; Hayes, 2003; Christensen-Dalsgaard and Gerdes, 2006; Kroll et al, 2010)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
