Stuck on you

While bacterial conjugation, the horizontal transfer of genetic material, is traditionally viewed as a way for microbes to "swap" traits like antibiotic resistance, new research suggests it plays a much more physical role in shaping their environment. The Molecular Microbiology Group (Marc Erhardt) studied this and revealed that the process of horizontal gene transfer does more than that, it physically remodels the microbial environment. Using high-resolution 3D imaging, they found that the hair-like pili used for conjugation act as a structural "glue," pulling bacteria together into dense aggregates even when they lack the natural slime usually required to build biofilms. While this architectural makeover provides a significant survival advantage by creating a protective shield against antibiotics and predatory phages, it comes with a major evolutionary trade-off: the same adhesive forces that stabilize the community also trap the bacteria within it, significantly reducing their ability to disperse and colonize new locations. This discovery identifies a critical "biofilm-specific trade-off" where the benefits of local protection are balanced against the cost of reduced mobility. If you want to learn more about bacterial conjugation, read the Current Biology Article.

Abstract

Bacterial conjugation enables the horizontal transfer of plasmids that often carry genes influencing host physiology and behavior. In spatially structured biofilms, where many bacteria live in close proximity, conjugation can significantly alter both genetic and physical community composition. Here, we use a microfluidic system and fluorescence microscopy to track the transmission of the F-like plasmid pED208 within Escherichia coli biofilms, differentiating invading plasmid donors, transconjugants, and plasmid-free cells at high resolution. We find that conjugation within established resident biofilms is efficient until cell density reaches a threshold associated with high extracellular matrix secretion. Strikingly, plasmid-encoded conjugative pili also enable matrix-deficient cells to aggregate into dense biofilms, promoting the formation of multi-strain and multispecies cell clusters. This restoration of biofilm architecture increases antibiotic and phage tolerance but comes at the cost of altering dispersal dynamics: plasmid-bearing cells disperse less readily than plasmid-free cells, creating a trade-off between local advantage and distal spread. Our findings indicate that conjugative pilus-mediated adhesion incurs a fitness trade-off, compacting biofilm structure and thereby conferring enhanced antibiotic and phage tolerance while reducing the spread of plasmid carriers over larger spatial scales.