Pseudolysogeny and sequential mutations build multiresistance to virulent bacteriophages in Pseudomonas aeruginosa

Abstract

Coevolution between bacteriophages (phages) and their prey is the result of mutualistic interactions. Here, we show that pseudolysogeny is a frequent outcome of infection by virulent phages of Pseudomonas aeruginosa and that selection of resistant bacterial mutants is favoured by continuous production of phages. We investigated the frequency and characteristics of P. aeruginosa strain PAO1 variants resisting infection by different combinations of virulent phages belonging to four genera. The frequency of resistant bacteria was 10 25 for single phage infection and 10 26 for infections with combinations of two or four phages. The genome of 27 variants was sequenced and the comparison with the genome of the parental PAO1 strain allowed the identification of point mutations or small indels. Four additional variants were characterized by a candidate gene approach. In total, 27 independent mutations were observed affecting 14 genes and a regulatory region. The mutations affected genes involved in biosynthesis of type IV pilus, alginate, LPS and O-antigen. Half of the variants possessed changes in homopolymer tracts responsible for frameshift mutations and these phase variation mutants were shown to be unstable. Eleven double mutants were detected. The presence of free phage DNA was observed in association with exclusion of superinfection in half of the variants and no chromosomal mutation could be found in three of them. Upon further growth of these pseudolysogens, some variants with new chromosomal mutations were recovered, presumably due to continuous evolutionary pressure.

Large Preferred Region for Packaging of Bacterial DNA by phiC725A, a Novel Pseudomonas aeruginosa F116-Like Bacteriophage

“…Upon treatment of planktonic cells with mitomycin C, bacterial growth was rapidly stopped and massive lysis was observed. A bacteriophage forming small clear plaques with a dark center was isolated from the culture supernatant and amplified on a reference strain PAO1 representative called PAO1 Or (the genome sequence of the PAO1 representative used in our laboratory in Orsay (Or) was previously reported [24]). Upon examination by EM, the phages displayed a large head (78nm), and what seemed to be a short thin tail (66nm) (Fig 1).…”

A Kayvirus Distant Homolog of Staphylococcal Virulence Determinants and VISA Biomarker Is a Phage Lytic Enzyme

“…Cui et al [17] wondered whether S. aureus cells infected with a Kayvirus genus phage and producing Tgl could be less sensitive to vancomycin than non-infected cells. While this danger is irrelevant to normal kayvirus development, which leads to cell lysis, it may be relevant to cases of temporal maintenance of lytic phage genome at a stage of multiplication inhibition in slowly growing or starved bacterial cells, commonly known as pseudolysogeny and associated with the expression of certain phage genes and the loss of phage DNA by some pseudolysogens (see [112,113] and references therein). Our preliminary results suggest that kayviruses can form a pseudolysogenic relationship with their bacterial host.…”

Pseudomonas aeruginosa PA5oct jumbo phage impacts planktonic and biofilm population and reduces its host virulence

“…An often neglected phenomenon is the occurrence of pseudolysogeny/carrier stage, generally regarded as a temporary stage of phage particle dormancy. However, it appears that the presence of a phage episome inside the host cell influences its phenotype and contributes the cross-resistance to other bacteriophages as well (Cenens et al, 2015; Latino et al , 2016; Argov et al , 2017). The jumbo phages are known to easily undergo episome formation as was previously reported for phiKZ phage (Krylov et al , 2012).…”