Variation in type IV pilus stability modulates DNA uptake and biofilm formation

Area of Science:

• Microbiology
• Bacterial cell structures
• Molecular biology

Background:

• Type IV pili (T4P) are crucial for bacterial functions including motility and DNA uptake.
• Acinetobacter species exhibit varied T4P-dependent phenotypes.
• Previous studies have not fully elucidated the basis for these functional differences.

Purpose of the Study:

• To investigate the molecular basis for differential T4P-dependent functions in Acinetobacter.
• To characterize the subtypes of T4P based on the major pilin subunit, PilA.
• To correlate T4P subtype variation with functional outcomes like motility, DNA uptake, and biofilm formation.

Main Methods:

• Sequence analysis of PilA variants from Acinetobacter International Clone I (IC-I) and International Clone II (IC-II) strains.
• Functional assays measuring twitching motility and DNA uptake.
• Complementation experiments using isogenic Acinetobacter strains.
• Analysis of pilus stability and cell surface piliation levels.

Main Results:

• T4P subtypes in Acinetobacter are differentiated by PilA sequences, leading to variable retraction efficiencies.
• The IC-I pilus subtype enhances twitching motility and DNA uptake.
• The IC-II pilus subtype promotes biofilm formation with reduced motility and DNA uptake, consistent with impaired retraction and increased pilus stability.
• IC-II pilus complements showed higher surface PilA levels, indicating increased piliation.

Conclusions:

• T4P subtypes in Acinetobacter, specifically variations in PilA, dictate functional differences.
• Impaired pilus retraction in the IC-II subtype contributes to increased surface piliation and biofilm formation.
• Pilus stability is a key factor influencing retraction efficiency and overall T4P function.