Adaptation of Pseudomonas aeruginosa to Phage PaP1 Predation via O-Antigen Polymerase Mutation

Abstract

Adaptation of bacteria to phage predation poses a major obstacle for phage therapy. Bacteria adopt multiple mechanisms, such as inhibition of phage adsorption and CRISPR/Cas systems, to resist phage infection. Here, a phage-resistant mutant of <i>Pseudomonas aeruginosa</i> strain PA1 under the infection of lytic phage PaP1 was selected for further study. The PaP1-resistant variant, termed PA1RG, showed decreased adsorption to PaP1 and was devoid of long chain <i>O</i>-antigen on its cell envelope. Whole genome sequencing and comparative analysis revealed a single nucleotide mutation in the gene PA1S_08510, which encodes the <i>O</i>-antigen polymerase Wzy that is involved in lipopolysaccharide (LPS) biosynthesis. PA1_Wzy was classified into the O6 serotype based on sequence homology analysis and adopts a transmembrane topology similar to that seem with <i>P. aeruginosa</i> strain PAO1. Complementation of gene <i>wzy in trans</i> enabled the mutant PA1RG to produce the normal LPS pattern with long chain <i>O</i>-antigen and restored the susceptibility of PA1RG to phage PaP1 infection. While <i>wzy</i> mutation did not affect bacterial growth, mutant PA1RG exhibited decreased biofilm production, suggesting a fitness cost of PA1 associated with resistance of phage PaP1 predation. This study uncovered the mechanism responsible for PA1RG resistance to phage PaP1 via <i>wzy</i> mutation and revealed the role of phages in regulating bacterial behavior.