DNA Binding: a Novel Function of Pseudomonas aeruginosa Type IV Pili

Abstract

The opportunistic pathogen Pseudomonas aeruginosa produces multifunctional, polar, filamentous appendages termed type IV pili. Type IV pili are involved in colonization during infection, twitching motility, biofilm formation, bacteriophage infection, and natural transformation. Electrostatic surface analysis of modeled pilus fibers generated from P. aeruginosa strain PAK, K122-4, and KB-7 pilin monomers suggested that a solventexposed band of positive charge may be a common feature of all type IV pili. Several functions of type IV pili, including natural transformation and biofilm formation, involve DNA. We investigated the ability of P. aeruginosa type IV pili to bind DNA. Purified PAK, K122-4, and KB-7 pili were observed to bind both bacterial plasmid and salmon sperm DNA in a concentration-dependent and saturable manner. PAK pili had the highest affinity for DNA, followed by K122-4 and KB-7 pili. DNA binding involved backbone interactions and preferential binding to pyrimidine residues even though there was no evidence of sequence-specific binding. Pilusmediated DNA binding was a function of the intact pilus and thus required elements present in the quaternary structure. However, binding also involved the pilus tip as tip-specific, but not base-specific, antibodies inhibited DNA binding. The conservation of a Thr residue in all type IV pilin monomers examined to date, along with the electrostatic data, implies that DNA binding is a conserved function of type IV pili. Pilus-mediated DNA binding could be important for biofilm formation both in vivo during an infection and ex vivo on abiotic surfaces.

Emergent pattern formation in an interstitial biofilm

“…1c. This general phenomenon is ubiquitous to a broad range of bacteria such as P. aeruginosa and M. xanthus that use Type IV Pili for movement while actively modifying the surface properties through substance excretion [14][15][16].…”

“…Instead, morphogenesis results from two basic forms of stigmergy arising from the formation of furrows in a viscous substratum and following of EPS trails deposited by the moving bacteria. EPS following is implemented as preferential binding of pili to the EPS [14,15], as shown in Fig. 1c.…”

“…Based on literature precedent [14][15][16], the proposed role of EPS in motility is modeled by making the local probability of pilus attachment to the substratum, P s , scale with the the fraction K of the local area covered by EPS binding sites K = C p (x, y)/[∆x] 2 , so that movement is biased along trails.…”

Functional Analysis of PilT from the Toxic Cyanobacterium Microcystis aeruginosa PCC 7806

“…Tfp genes, such as pilA1, pilB1, and pilT1, have been shown to be essential for both motility and transformation (32,51). Recent evidence has shown that the PilA subunit can bind to DNA (45). It is also postulated, therefore, that retraction of pili brings the cell into closer proximity to DNA, thereby increasing the chance of transformation.…”

Burkholderia cenocepacia J2315-mediated destruction of Staphylococcus aureus NRS77 biofilms.

“…This strain also expresses type IV pili that are involved in motility and cellular adhesion to host tissue. Additionally, these pili have DNA binding activity [87] suggesting they may play a role in biofilm formation, in which extracellular DNA is a critical component of the secreted matrix. Like S. aureus, the ability of this strain to bind to both host tissue and form biofilms contributes to its virulence as a CF pathogen.…”