Search for: All records

Abstract Conjugation is used by bacteria to propagate antimicrobial resistance (AMR) in the environment. Central to this process are widespread conjugative F-pili that establish the connection between donor and recipient cells, thereby facilitating the spread of IncF plasmids among enteropathogenic bacteria. Here, we show that the F-pilus is highly flexible but robust at the same time, properties that increase its resistance to thermochemical and mechanical stresses. By a combination of biophysical and molecular dynamics methods, we establish that the presence of phosphatidylglycerol molecules in the F-pilus contributes to the structural stability of the polymer. Moreover, this structural stability is important for successful delivery of DNA during conjugation and facilitates rapid formation of biofilms in harsh environmental conditions. Thus, our work highlights the importance of F-pilus structural adaptations for the efficient spread of AMR genes in a bacterial population and for the formation of biofilms that protect against the action of antibiotics. 

Escherichia coliexpress adhesion pili that mediate attachment to host cell surfaces and are exposed to body fluids in the urinary and gastrointestinal tracts. Pilin subunits are organized into helical polymers, with a tip adhesin for specific host binding. Pili can elastically unwind when exposed to fluid flow forces, reducing the adhesin load, thereby facilitating sustained attachment. Here we investigate biophysical and structural differences of pili commonly expressed on bacteria that inhabit the urinary and intestinal tracts. Optical tweezers measurements reveal that class 1a pili of uropathogenicE. coli(UPEC), as well as class 1b of enterotoxigenicE. coli(ETEC), undergo an additional conformational change beyond pilus unwinding, providing significantly more elasticity to their structure than ETEC class 5 pili. Examining structural and steered molecular dynamics simulation data, we find that this difference in class 1 pili subunit behavior originates from an α-helical motif that can unfold when exposed to force. A disulfide bond cross-linking β-strands in class 1 pili stabilizes subunits, allowing them to tolerate higher forces than class 5 pili that lack this covalent bond. We suggest that these extra contributions to pilus resiliency are relevant for the UPEC niche, since resident bacteria are exposed to stronger, more transient drag forces compared to those experienced by ETEC bacteria in the mucosa of the intestinal tract. Interestingly, class 1b ETEC pili include the same structural features seen in UPEC pili, while requiring lower unwinding forces that are more similar to those of class 5 ETEC pili.