Horizontal gene transfer (HGT) enables the spread of antimicrobial resistance, virulence, metabolic and other genes conferring an advantage to the organism. HGT is enhanced in biofilms because of increased cell-cell contact (conjugation), and eDNA in the biofilm matrix causing development of competence and providing material for transformation. Production of the Rhodobacter capsulatus gene transfer agent (RcGTA), another mechanism of HGT, could also increase in biofilm as high cell density increases the proportion of GTA particles produced that encounter a target cell. RcGTA is a phage-like particle that packages ∼4.5 kb pieces of random DNA from the producing cell’s genome and transfers it to a recipient cell. Five loci comprise the RcGTA genome: a 15kb cluster containing most of the RcGTA structural genes, a cell lysis locus, two structural loci encoding head spikes and tail fibres, and a maturation/regulation locus that includes that master regulator, gafA.

I assayed RcGTA production using gene transfer bioassays and biofilm using a 96 well plate assay. I will present data showing that deletion of four GTA-related genes, including gafA itself, all lead to reduced biofilm production. All four gene knock-outs also strongly reduce GTA-mediated gene transfer, suggesting GTA production and biofilm are co-regulated. I will also present work to characterize GTA production in biofilms, for example by monitoring the transfer of fluorescent protein genes through confocal microscopy, and assessing how specific regulators control this process. Biofilms are ubiquitous in the environment so studying the spread of antimicrobial resistance genes by GTAs is important.


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