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Cell-Surface Modifications Protect Pseudomonas aeruginosa from Certain Pilus-Specific Phages – and Others ‘Fight Back’.

Author: Christy Groves

An electron micrograph of the end of one Pseudomonas cell showing the single flagellum and multiple thin type IV pili. Photo credit: Dr. Driss Lajoie from U. de Montreal.

Bacteriophages – viruses that kill bacteria – are of great interest for their potential to kill antibiotic-resistant bacteria. However, how they infect specific hosts is not always well understood. In their recent publication in Nature Microbiology, McMaster researchers found that Pseudomonas aeruginosa bacteria glycosylate their type IV pili surface proteins to prevent the attachment of infectious phages. However, they have also discovered several phages that may have co-evolved to breach this defense.

Glycosylation – the process of adding sugar moieties to proteins – is an important and well-understood post-translational modification in eukaryotes that can affect the function, localization, and lifespan of proteins. However, the extent of glycosylation diversity and function in prokaryotes has remained unclear.

Dr. Alan Davidson’s lab at U. Toronto, in collaboration with Dr. Hélène Marquis, was studying the interaction between lysogenic phages and P. aeruginosa. Such phages often exploit the bacteria’s retractable pili as receptors. They noticed that P. aeruginosa strains expressing glycosylated pilins could not be infected by many of those phages. Dr. Lori Burrows’ lab than did a series of studies that led the groups to conclude that P. aeruginosa uses at least two different forms of pilus glycosylation to block the attachment of pilus-specific phages – an exciting observation providing a compelling rationale for post-translational modification of bacterial pilins as a defense mechanism against phage attack.

More variations on this fascinating, modern-day example of the ancient evolutionary battle between bacteria and phages were revealed by additional studies. Whilst screening various phages against a set of P. aeruginosa strains differing only in pilin type and modification status, the team found that some phages had evolved specific tail proteins that allowed for infection of bacterial strains with glycosylated pili. They identified one phage capable of dodging pilus glycosylation while still using the pilin proteins as receptors, and another that specifically exploited modified pilins for attachment – infecting only a strain expressing the glycosylated forms.

These studies clearly illustrate how bacterial hosts evolve modifications against predation, and how infectious phages can then evolve to circumvent these defenses. Their study provides a rationale for the prevalence of pilus glycosylation in nature, and provides insight into prokaryotic-phage co-evolution. Understanding how phage tails evolve to recognize new receptors on bacteria could help researchers to create designer phages directed against antibiotic-resistant pathogens.

Read the full publication in Nature Microbiology.


Christy Groves