R-type bacteriocins in related strains ofXenorhabdus bovienii: Xenorhabdicin tail fiber modularity and contribution to competitiveness

Abstract

R-type bacteriocins are contractile phage tail-like structures that are bactericidal towards related bacterial species. The C-terminal region of the phage tail fiber protein determines target-binding specificity. The mutualistic bacteria Xenorhabdus nematophila and X. bovienii produce R-type bacteriocins (xenorhabdicins) that are selectively active against different Xenorhabdus species. We analyzed the P2-type remnant prophage clusters in draft sequences of nine strains of X. bovienii The C-terminal tail fiber region in each of the respective strains was unique and consisted of mosaics of modular units. The region between the main tail fiber gene (xbpH1) and the sheath gene (xbpS1) contained a variable number of modules encoding tail fiber fragments. DNA inversion and module exchange between strains was involved in generating tail fiber diversity. Xenorhabdicin-enriched fractions from three different X. bovienii strains isolated from the same nematode species displayed distinct activities against each other. In one set of strains, the strain that produced highly active xenorhabdicin was able to eliminate a sensitive strain. In contrast, xenorhabdicin activity was not a determining factor in the competitive fitness of a second set of strains. These findings suggest that related strains of X. bovienii use xenorhabdicin and additional antagonistic molecules to compete against each other.

R-type bacteriocins of Xenorhabdus bovienii determine the outcome of interspecies competition in a natural host environment

“…Xb-Sj possesses two P2-like prophage loci: xbp1 and xbp2 [52]. shows the xbp1 remnant P2-like prophage of Xb-Sj that is required for xenorhabdicin production [49, 50, 52, 57]. The remnant xbp1 cluster contains tail and baseplate synthesis genes (dark blue and dark purple, respectively), including tail sheath ( xbpS1, FI in P2 phage), tail tube ( xbpT1, FII in P2 phage) and main tail fibre ( xbpH1, H in P2 phage) genes, but lacks genes for capsid synthesis (green).…”

“…Thus, the survival and fitness of the Xn-Sc nematode partner were dependent on suppressing the growth of a related competitor in the insect host. Xenorhabdicins of other Xenorhabdus species have been less well studied [49]. We recently showed that Xenorhabdus bovienii SS2004 (Xb- Sj ) possesses both remnant ( xbp1 ) and intact ( xbp2 ) P2-like phage clusters [52], and that the xbp1 cluster was required for mitomycin C-induced xenorhabdicin production [49, 50, 52].…”

“… X. nematophila also produce P2 phage tail-like R-type bacteriocins called xenorhabdicin [43–50]. The R-type bacteriocins are composed of conserved tail sheath and tube proteins and divergent tail fibre proteins that bind specifically to cell surface receptors on target strains.…”

“…Xenorhabdus antibiotics are usually active against unrelated bacteria and fungi, but one species, Xenorhabdus szentirmaii ( Xsz-Sr ) , was found to produce antibiotics that inhibit the growth of other Xenorhabdus species [49, 53, 54]. For example, antibiotics produced by Xsz-Sr were required to suppress the growth of Xn-Sc when the Manduca sexta insect host was co-injected with both bacteria [53].…”

PhANNs, a fast and accurate tool and web server to classify phage structural proteins

“…The bias could be biological and/or due to a sampling bias. An example of the former is the tail fiber class: the tail fiber is one of the determinants of the host range of the virus, and is under strong evolutionary selective pressure (22)(23)(24)(25)(26)(27). On the other hand, sampling bias may be introduced due to oversampling of certain types of phages, such as the thousands of mycobacterial phages isolated as part of the SEA-PHAGES project(28); many of which are highly related to each other.…”