Phage nucleus counts and distance measurements.

The emergence of antibiotic resistance in bacteria has led to the investigation of alternative treatments, such as phage therapy. In this study, we examined the interactions between the nucleus-forming jumbo phage ФKZ and antibiotic treatment against Pseudomonas aeruginosa. Using the fluorescence microscopy technique of bacterial cytological profiling, we identified mechanism-of-action-specific interactions between antibiotics that target different biosynthetic pathways and ФKZ infection. We found that certain classes of antibiotics strongly inhibited phage replication, while others had no effect or only mildly affected progression through the lytic cycle. Antibiotics that caused an increase in host cell length, such as the cell wall active antibiotic ceftazidime, prevented proper centering of the ФKZ nucleus via the PhuZ spindle at midcell, leading us to hypothesize that the kinetic parameters of the PhuZ spindle evolved to match the average length of the host cell. To test this, we developed a computational model explaining how the dynamic properties of the PhuZ spindle contribute to phage nucleus centering and why some antibiotics affect nucleus positioning while others do not. These findings provide an understanding of the molecular mechanisms underlying the interactions between antibiotics and jumbo phage replication.