Antitoxin CrlA of CrlTA Toxin–Antitoxin System in a Clinical Isolate Pseudomonas aeruginosa Inhibits Lytic Phage Infection

Abstract

Pseudomonas aeruginosa is an important opportunistic pathogen in cystic fibrosis patients and immunocompromised individuals, and the toxin–antitoxin (TA) system is involved in bacterial virulence and phage resistance. However, the roles of TA systems in P. aeruginosa are relatively less studied and no phage Cro-like regulators were identified as TA components. Here, we identified and characterized a chromosome-encoded prophage Cro-like antitoxin (CrlA) in the clinical isolate P. aeruginosa WK172. CrlA neutralized the toxicity of the toxin CrlA (CrlT) which cleaves mRNA, and they formed a type II TA system. Specifically, crlA and crlT are co-transcribed and their protein products interact with each other directly. The autorepression of CrlA is abolished by CrlT through the formation of the CrlTA complex. Furthermore, crlTA is induced in the stationary phase, and crlA is expressed at higher levels than crlT. The excess CrlA inhibits the infection of lytic Pseudomonas phages. CrlA is widely distributed among Pseudomonas and in other bacterial strains and may provide antiphage activities.

Molecular analysis of the interactions between phages and the bacterial host Klebsiella pneumoniae

“…This is a very interesting finding, as phage vB_KpnM-VAC36 did not successfully infect strain K3320. The fundamental role played by TA systems in the inhibition of phage infection has recently been demonstrated (20,(70)(71)(72). Interestingly, an inhibitor of the TA system (protein ID: QZE51102.1) was found in the genome of the phage vB_KpnP-VAC1.…”

Type II Toxin–Antitoxin Systems in Pseudomonas aeruginosa

“…Ten pairs of type II TA systems have been experimentally verified in P. aeruginosa ( Table 1 ), as follows: HigB/HigA [ 19 ], ParD/ParE [ 20 ], HicA/HicB [ 21 ], RelB/RelE [ 22 ], ResA/XreA [ 23 ], PrrT/PrrA [ 24 ], CrlT/CrlA [ 25 ], PacT/PacA [ 26 ], PumA/PumB [ 27 ], and PfiT/PfiA [ 28 ]. In type II TA systems, genes encoding the toxin and antitoxin are within a single operon ( Figure 1 ).…”

“…In P. aeruginosa , most type II TA systems are encoded on the chromosome [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ], the exceptions being PfiT/PfiA and PumA/PumB (phage and plasmid, respectively) [ 27 , 28 ]. These TA systems have diverse biological functions, such as virulence and biofilm formation [ 34 , 35 , 36 ], protection host against antibiotics [ 20 ], persistence [ 23 ], plasmid maintenance [ 27 ], and prophage production [ 25 , 37 ] ( Figure 2 ).…”

“…The chromosome-encoded CrlTA TA system in P. aeruginosa WK172 is involved in fighting against phage infection. In excess, the prophage Cro-like antitoxin CrlA inhibited infection by lytic Pseudomonas phages (PAP-L5, PAOP5, PAP8, and QDWS) because CrlA inhibited phage replication by binding to crlTA palindrome-like sequences in the phage genome [ 25 ]. The CrlTA complex confers phage resistance to lytic phages PAP8 and QDWS; however, the underlying molecular mechanism is unclear.…”

“…Dai et al found 16,963 TA gene hits in 5432 genomic sequences of P. aeruginosa from the NCBI Genome database, most of which were in chromosome sequences (94%) and belonged to type II TA systems (16,808 hits) [ 18 ]. To date, at least 10 pairs of type II TA systems have been experimentally characterised in P. aeruginosa , 8 of which are located on the chromosome [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ], whereas PumA/PumB and PfiT/PfiA were identified in plasmid pUM505 and prophage Pf4, respectively [ 27 , 28 ]. These TA systems have multiple biological functions and regulatory mechanisms, which makes TA research more interesting and attractive.…”