Antigenic variation impacts gonococcal lifestyle and antibiotic tolerance by modulating interbacterial forces

Abstract

Type 4 pili (T4P) are multifunctional filaments involved in adhesion, surface motility, colony formation, and horizontal gene transfer. These extracellular polymers are surface-exposed and, therefore, act as antigens. The human pathogen Neisseria gonorrhoeae uses pilin antigenic variation to escape immune surveillance, yet it is unclear how antigenic variation impacts other functions of T4P. Here, we addressed this question by replacing the major pilin of a laboratory strain of N. gonorrhoeae with pilins from clinical isolates. Structural predictions reveal filament features that vary from one strain to the next, with the potential to impact pilus:pilus interactions. Using a combination of laser tweezers, electron microscopy, and advanced image analysis, we explore the phenotypic consequences of these structural changes. We reveal that strains differing only in their major pilin sequence vary substantially in their attractive forces, which we attribute to variations in the stereochemistry of the T4P filament. In liquid culture, strongly interacting bacteria form colonies while weakly interacting bacteria retain a planktonic lifestyle. We show that lifestyle strongly affects growth kinetics and antibiotic tolerance. In the absence of external stresses, planktonic bacteria grow faster than colony-forming bacteria. In the presence of the antibiotics ceftriaxone and ciprofloxacin, the killing kinetics indicate strongly increased tolerance of colony-forming strains. We propose that pilin antigenic variation produces a mixed population containing variants optimized for growth, colonization, or survivability under external stress. Different environments select different variants, ensuring the survival and reproduction of the population as a whole.

Interactions between pili affect the outcome of bacterial competition driven by the type VI secretion system

“…This variability can influence the strength of attractive forces between bacterial cells, which can explain our results. Such an effect was seen in Neisseria gonorrhoeae [63].…”

“…This variability can influence the strength of attractive forces between bacterial cells, which can explain our results. Such an effect was seen in Neisseria gonorrhoeae [63]. Similarly, the diversity in PilA variants in Acinetobacter baumannii was shown to impact the level of T4P self-interaction and its functional specialization [54].…”