Systematic Discovery of Pseudomonad Genetic Factors Involved in Sensitivity to Tailocins

Abstract

Tailocins are bactericidal protein complexes produced by a wide variety of bacteria to compete against closely related strains. Like tailed bacteriophages, with whom they share an evolutionary and morphological relationship, tailocins bind and kill a narrow spectrum of target cells. Thanks to their high specificity, tailocins have garnered recent attention for their potential as precision antibacterial agents. Nevertheless, the field currently lacks a systematic investigation of genetic determinants of tailocin sensitivity. Here, we employed barcoded transposon-insertion mutant libraries and comparative genomics to assess genetic contributions to tailocin sensitivity in pseudomonads. Our mutant screens identified O-specific antigen (OSA) composition and display as most important in defining sensitivity to our tailocins. Additionally, the screens suggest lipopolysaccharide (LPS) thinning as a mechanism by which resistant strains can become more sensitive to tailocins. Our comparative genomics analyses show a loose relationship between OSA biosynthetic genes and tailocin sensitivity, as well as sensitivity nuances that require further investigation. Overall, our data reinforces the model that LPS molecules can act as either a receptor for, or shield against, tailocin binding and killing. This work offers insight into the specificity of tailocins and tailocin-mediated competition, informing the potential use of tailocins in microbiome manipulation and antibacterial therapy.

A Pseudomonas plant pathogen uses distinct modes of stationary phase persistence to survive bacteriocin and streptomycin treatments

“…Colistin tolerance was associated with increased expression of Pmr proteins that modify LPS to reduce colistin a nity, meaning that only transcriptionally active cells avoid membrane destabilization (27,28,39). Tailocin sensitivity is also linked to the composition of LPS (40), which can vary according to changes in environment and gene expression (41). We recently found that an LPS cluster gene of unknown function affects the frequency of tailocin persisters without impacting tailocin susceptibility or host tness (30).…”

Variation at the common polysaccharide antigen locus drives lipopolysaccharide diversity within the Pseudomonas syringae species complex

“…While it is clear that LPS is a receptor for some tailocins ( Kutschera et al, 2019a;Kandal et al, 2020), a link between the sensitivity to tailocins and the structural variation in LPS has not been demonstrated until recently. Carim et al (2020) have shown within the genus Pseudomonas that OSA composition and display are the most important contributors to tailocin sensitivity. Our results also indicate a strong but not perfect relationship between tailocin sensitivity and CPA within P. syringae.…”

“…Carim et al . (2020) have shown within the genus Pseudomonas that OSA composition and display are the most important contributors to tailocin sensitivity. Our results also indicate a strong but not perfect relationship between tailocin sensitivity and CPA within P. syringae .…”

“…Furthermore, LPS was not observed in these mutants, suggesting CPA is the sole OPS in Psa (Hockett et al ., 2017). Other recent papers have shown a relationship between OSA and tailocin sensitivity among the Pseudomonads (Carim et al ., 2020), directly identified components of CPA biosynthesis in P. syringae through gene knockouts (Kutschera et al ., 2019a) and increased resistance to tailocins (Kandel et al ., 2020).…”

The Genetic Basis of phage susceptibility, cross-resistance and host-range in Salmonella

“…Compared to other antimicrobials, characterization of infectivity and cross-resistance between a panel of phages has been limited to a few model organisms and remained phenomenological until recently(Hudson et al, 1978; Lindberg and Hellerqvist, 1971; Marti et al, 2013; Samuel et al, 1999; Tu et al, 2017; Wright et al, 1980). The advent of genome-wide saturated transposon sequencing (Bohm et al, 2018; Chan and Turner, 2020; Christen et al, 2016; Cowley et al, 2018; Pickard et al, 2013) and the corresponding DNA bar-code based modifications has enabled the high-throughput and low cost genome-scale screening for the genetic determinants of these phenomena(Carim et al, 2020; Mutalik et al, 2019, 2020; Rousset et al, 2018; Wetmore et al, 2015). Since this economically permits the independent screening of many phages against a host library, it is now possible to determine and compare the genes that affect the successful infection of one or more phages.…”