LPS-mediated bacteriophage and Pseudomonas interaction

Pseudomonas protegens CHA0, a bacterial strain able to suppress diseases caused by plant pathogens as well as efficiently kill lepidopteran pest insects, has been studied as biocontrol agent to prevent ensuing agricultural damage. However, the success of this method is dependent on the efficient colonization of the bacterial inoculant that face competition against different root microbiota inhabitants as well as predators such as bacteriophages. One of these naturally occurring phages, FGP100, was found to drastically reduce the abundance of CHA0 once inoculated in soil, resulting in the loss of the plant protection effect in presence of a plant pathogen. Here, we investigated the molecular determinants implicated in the interaction between CHA0 and the phage FGP100 using a high-density transposon-sequencing approach. We show that lipopolysaccharide cell surface decorations, specifically the OBC3-type O-antigen of CHA0 is essential for the attachment and infection of the phage FGP100. Moreover, we looked at the distribution of the OBC3 cluster in bacterial genomes and identified several parts of this gene cluster that are conserved in phylogenetically distant bacteria. Through heterologous complementation, we integrated a gene copy from a bacterium that was phylogenetically distant and were able to restore the phage sensitivity of a CHA0 mutant which lacked the ability to form long O-PS. Finally, we evidence that the OBC3 gene cluster of CHA0 displays a high genomic plasticity and likely underwent several horizontal acquisitions and genomic rearrangements. Collectively, this study underlines the complexity of phage-bacteria interaction and the multifunctional aspect of bacterial cell surface decorations.