Flagellar interference with plasmid uptake in biofilms: a joint experimental and modeling study

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Horizontal gene transfer (HGT) via plasmids drives bacterial evolution and the spread of antibiotic resistance.
• Bacteria in biofilms exhibit altered phenotypes compared to planktonic cells, yet HGT mechanisms in biofilms are not fully understood.
• Understanding plasmid transfer in biofilms is critical for controlling antibiotic resistance.

Purpose of the Study:

• To investigate the impact of biofilm adaptation on plasmid transfer in *Xanthomonas retroflexus* (XRw).
• To identify factors influencing plasmid uptake in XRw biofilms.
• To elucidate the role of flagella in bacterial conjugation within biofilms.

Main Methods:

• Comparative analysis of plasmid uptake in wild-type (WT) and biofilm-adapted mutant (XRw) *X. retroflexus*.
• Proteomic analysis to identify differences in protein expression between WT and XRw.
• Genetic manipulation to create non-flagellated mutants (*fliM*) in both WT and XRw strains.
• Experimental validation and individual-based modeling to test proposed mechanisms of flagellar influence.

Main Results:

• XRw biofilms exhibited significantly higher uptake of the IncP-1ϵ plasmid pKJK5 compared to WT biofilms.
• Proteomics revealed reduced levels of flagellar proteins in XRw, correlating with increased plasmid uptake.
• Non-flagellated mutants (*fliM*) of both WT and XRw showed enhanced plasmid uptake, confirming the inhibitory role of flagella.
• The study identified steric hindrance by flagella as a viable mechanism reducing pilus-mediated plasmid transfer.

Conclusions:

• Flagella play a significant, complex role in modulating plasmid conjugation within bacterial biofilms.
• The absence or reduced activity of flagella can enhance plasmid uptake and HGT in biofilms.
• Findings provide novel insights into HGT dynamics in biofilms and have implications for controlling antibiotic resistance spread.