Type IV Pilin Post-Translational Modifications Modulate Material Properties of Bacterial Colonies

Abstract

Bacterial type 4 pili (T4P) are extracellular polymers that initiate the formation of microcolonies and biofilms. T4P continuously elongate and retract. These pilus dynamics crucially affect the local order, shape, and fluidity of microcolonies. The major pilin subunit of the T4P bears multiple post-translational modifications. By interfering with different steps of the pilin glycosylation and phosphoform modification pathways, we investigated the effect of pilin post-translational modification on the shape and dynamics of microcolonies formed by Neisseria gonorrhoeae. Deleting the phosphotransferase responsible for phosphoethanolamine modification at residue serine 68 inhibits shape relaxations of microcolonies after perturbation and causes bacteria carrying the phosphoform modification to segregate to the surface of mixed colonies. We relate these mesoscopic phenotypes to increased attractive forces generated by T4P between cells. Moreover, by deleting genes responsible for the pilin glycan structure, we show that the number of saccharides attached at residue serine 63 affects the ratio between surface tension and viscosity and cause sorting between bacteria carrying different pilin glycoforms. We conclude that different pilin post-translational modifications moderately affect the attractive forces between bacteria but have severe effects on the material properties of microcolonies.

Antibiotics modulate attractive interactions in bacterial colonies affecting survivability under combined treatment

“…Characterizing both the short-term cellular response investigated in this study and long-term viability will provide a more complete picture of how antibiotics affect colony-bound gonococci.Many bacterial species employ T4P for cell motility and aggregation[12]. In Neisseria species, T4P-T4P mediated attractive forces control the dynamics of bacteria within colonies[15][16][17]28]. Here, we show that treatment with the protein synthesis inhibitor azithromycin reduces T4P-dependent attraction and, conversely, ceftriaxone enhances the attraction.…”

“…Therefore, we wondered whether colony dynamics impacts on survivability and used bacterial strains that form less fluid colonies as revealed by characterizing the relaxation dynamics of colonies. Fluidity of gonococcal colonies can be affected by the motor activity of the T4P or by the binding strength between T4P [16, 17]. In particular, colony fluidity is strongly reduced in a strain expressing genes encoding for non-functional pilT WB T4P retraction ATPases in addition to the functional ones [16].…”

“…T4P polymers grow, bind, and retract continuously [18], enabling a tug-of-war between bacteria in a colony [14, 19]. For Neisseria species it was demonstrated that by modulating motor activity, T4P-T4P binding force, or T4P density, the dynamics of a colony transitions from gas-like to fluid-like to solid-like [15-17]. It is tempting to speculate that colony fluidity affects bacterial fitness.…”

“…As a consequence, the restoring forces from neighboring bacteria are reduced and bacteria become more mobile. Ceftriaxone has the opposite effect of enhancing the probability that neighboring cells are bound via T4P thus reducing within-colony motility.Increased single cell motility within colonies correlates with increased colony fluidity (or decreased viscosity)[15][16][17]. Fine-tuning T4P-T4P mediated attractive forces induces a transition between gas-like, liquid-like, and solid-like behavior of the colonies.…”

Biofilms 2018: a Diversity of Microbes and Mechanisms

“…Within N. gonorrhoeae colonies, cells show liquid-like order that is dependent on T4P and their retraction capability (48). Analysis using dual-laser-trap methods revealed that both motor activity and pilin posttranslational modification affect the fluidity of gonococcal colonies, with a small increase in pilus-pilus interaction strongly enhancing viscosity (48,49). This represents another striking observation expanding the role of T4P retraction beyond motility and highlighting the idea that they function in the organizational dynamics of a microcolony, with implications for resistance to various stresses.…”