Identification and functional analysis of a bacteriocin, pyocin S6, with ribonuclease activity from a Pseudomonas aeruginosa cystic fibrosis clinical isolate

Abstract

S‐type pyocins are bacteriocins produced by Pseudomonas aeruginosa isolates to antagonize or kill other strains of the same species. They have a modular organization comprising a receptor‐binding domain recognizing a surface constituent of the target bacterium, a domain for translocation through the periplasm, and a killing or toxic domain with DNase, tRNase, or pore‐forming activity. Pyocins S2, S3, S4, and S5 recognize TonB‐dependent ferri‐siderophore receptors in the outer membrane. We here describe a new nuclease bacteriocin, pyocin S6, encoded in the genome of a P. aeruginosa cystic fibrosis (CF) clinical isolate, CF_PA39. Similarly to pyocins S1 and S2, the S6 toxin–immunity gene tandem was recruited to the genomic region encoding exotoxin A. The pyocin S6 receptor‐binding and translocation domains are identical to those of pyocin S1, whereas the killing domain is similar to the 16S ribonuclease domain of Escherichia coli colicin E3. The cytotoxic activity was abolished in pyocin S6 forms with a mutation in the colicin E3‐equivalent catalytic motif. The CF_PA39 S6 immunity gene displays a higher expression level than the gene encoding the killing protein, the latter being only detected when bacteria are grown under iron‐limiting conditions. In the S1‐pyocinogenic strain P. aeruginosa ATCC 25324 and pyocin S2 producer P. aeruginosa PAO1, a remnant of the pyocin S6 killing domain and an intact S6‐type immunity gene are located downstream of their respective pyocin operons. Strain PAO1 is insensitive for pyocin S6, and its S6‐type immunity gene provides protection against pyocin S6 activity. Purified pyocin S6 inhibits one‐fifth of 110 P. aeruginosa CF clinical isolates tested, showing clearer inhibition zones when the target cells are grown under iron limitation. In this panel, about half of the CF clinical isolates were found to host the S6 genes. The pyocin S6 locus is also present in the genome of some non‐CF clinical isolates.

Draft genome sequence of the strain 16-537536, isolated from a patient with bronchiectasis and its relationship to the Pseudomonas koreensis group of the Pseudomonas fluorescens complex

“…This has for example been shown for Salmonella typhimurium in an animal model [24]. Pyocins, microcins, and bacteriocins, which are antibacterial peptides, may also contribute to this process [25]. Finally, fimbriae and flagella may contribute to virulence by facilitating adhesion and providing mobility.…”

LlpB represents a second subclass of lectin‐like bacteriocins

“…If so, llpB genes are organized in tandem, whereas llpA genes in strains carrying two representatives usually appear at distant loci (Ghequire and De Mot, ). As noted for other (mid‐sized) bacteriocins (Ghequire et al ., , ,; Dingemans et al ., ; Sharp et al ., ), llpB genes are typified by a lower GC content than the genomic average (~47% versus ~60%), pointing towards foreign origin. Yet another similarity with llpA genes is that some of these llpB genes arise in prophage/tailocin clusters (Ghequire et al ., ), for example in a Rp3 tailocin gene cluster of Pseudomonas libanensis DSM 17149.…”

A Colicin M-Type Bacteriocin from Pseudomonas aeruginosa Targeting the HxuC Heme Receptor Requires a Novel Immunity Partner

“…Overall, pmiC genes coupled to paeM4 display a high degree of sequence conservation (Ͼ97% pairwise AA identity of the encoded proteins), whereas conservation with and among pmiC orphans is lower (ϳ76% AA identity with PmiC BL03 and Ͼ93% AA identity among PmiC orphans). Previously, it was noted that homologous orphan pyocin immunity genes with significant sequence similarity may offer immunity to noncognate toxins (15,49), suggesting the functionality of orphan pmiC genes. It should be emphasized that significant DNA sequence variation can be noted in the regions preceding the orphan pmiC genes, which may in turn exert transcriptional effects.…”