Examining the Role of Type IV Pili in Surface Motility of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a rod-shaped, Gram-negative, environmental bacterium and an opportunistic human pathogen that utilizes flagellar or type IV pili (TFP) appendages to mediate motility in finding favorable environments for colonization and development of biofilms. P. aeruginosa is notable for multiple motility phenotypes including flagellar-mediated swarming that is observed in the laboratory using 0.4%-0.6% (w/vol) agar-air surfaces and TFP-mediated twitching that is traditionally observed using ≥ 1.0% (w/vol) agar between the interstitial space the interstitial space and petri dish or cover slip and judged over multiple hours to days.

In my research, I show that the behavior of P. aeruginosa swarming cells can vary substantially in the earliest phases of swarming. This work highlights the importance of understanding single cell behavior that can be important to macro-scale behavior.

Moving beyond traditional motility assays, my research investigated the behavior of P. aeruginosa on open-air 0.8% (w/vol) agar surfaces. I found that P. aeruginosa develops into small cell clusters that exhibit long-range motility phenotype term “snapping”. Cluster development and snapping is mediated by functional TFP and require 3-(3-hydroxyalkanoyloxy) alkanoic acids or rhamnolipid as a surfactant.

While investigating cluster development and TFP motility, I probed a lack of TFP activity in a rhlI mutant named (PDO100). Prior to my work, there was a discrepancy in the literature regarding TFP motility for this PDO100 strain. I determined that cell-free supernatant from the PDO100 mutant completely inhibits TFP function (and motility), and furthermore, inhibits growth and TFP function in other strains. My results implicated an extracellular product in PDO100 CFS, which I linked to the bacteriophage Pf4.

Lastly, in collaborative work, I helped show that three specific lytic transglycosylases (Slt, MltD, and MltG) of the 11 found in P. aeruginosa serve as targets in β-lactam-induced bulge formation in combination with the compound Bulgecin A. Combined treatment with β-lactam- Bulgecin A may represent an effective therapeutic strategy for some P. aeruginosa infections.