Biofilms: hot spots of horizontal gene transfer (HGT) in aquatic environments, with a focus on a new HGT mechanism

Abstract

Biofilms in water environments are thought to be hot spots for horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs). ARGs can be spread via HGT, though mechanisms are known and have been shown to depend on the environment, bacterial communities and mobile genetic elements. Classically, HGT mechanisms include conjugation, transformation and transduction; more recently, membrane vesicles (MVs) have been reported as DNA reservoirs implicated in interspecies HGT. Here, we review the current knowledge on the HGT mechanisms with a focus on the role of MVs and the methodological innovations in the HGT research.

Keywords: antibiotic resistance gene; biofilm; horizontal gene transfer; membrane vesicle; water environment.

Figure 1.

Biofilm life cycle and HGT. The typical life cycle of biofilms includes attachment to surfaces, microcolony formation, maturation and detachment. MGE-encoded factors and MVs enhance attachment and cell aggregation at the early stages of biofilm formation. Degradation of the biofilm matrix by phages facilitates cell detachment. ARGs can be distributed via three classical mechanisms: conjugation, natural transformation and phage transduction (and ASEN), and two candidates for new HGT mechanisms: MVs and nanotube (denoted as new candidate) in biofilms. Examples of ARGs transferred through each pathway are shown with the respective references. DNA is depicted by red lines and circles.