Seaweed exposure modulates Escherichia coli plasmid conjugation rate

Seaweeds are a common and diverse component of coastal ecosystems and are known to be associated with Escherichia coli due to faecal pollution. As a biotic substrate, beach-cast seaweed may affect bacterial physiology and thereby horizontal gene transfer (HGT). Here, we test how the presence of three distinct senescing seaweed species affects E. coli plasmid conjugation. We allow the IncP plasmid pKJK5 to conjugate while supplying a substrate of Palmaria palmata (dulse), Ulva lactuca (sea lettuce) or Fucus serratus (serrated wrack). The three seaweed species induce distinct conjugative behaviours in E. coli: U. lactuca has no significant impact relative to a plastic control, the presence of F. serratus results in undetectable levels of conjugation and P. palmata promotes conjugation in a density-independent manner. This study highlights how biotic interactions can influence survival, HGT and antibiotic resistance in a human pathogen.