# Horizontal and vertical gene transfer shape the plasmid host range in surface-associated microbial systems

## TL;DR

This study shows how both vertical and horizontal gene transfer influence the spread of antibiotic resistance plasmids in microbial communities.

## Contribution

The study introduces a framework integrating vertical and horizontal gene transfer dynamics to predict plasmid host range.

## Key findings

- Fast-growth conditions increase transconjugant abundance but reduce diversity.
- Slow-growth conditions support fewer but more diverse transconjugants.
- Simulations show realized host range is shaped by initial HGT and subsequent VGT.

## Abstract

Broad-host-range plasmids drive the spread of antibiotic resistance, particularly in surface-associated microbial systems prevalent in natural and host-associated environments. Predicting their realized host range is challenging because both transconjugant proliferation (vertical gene transfer, VGT) and conjugation (horizontal gene transfer, HGT) contribute to transconjugant diversity. Here, we hypothesized that the realized host range is determined by the interplay between VGT and HGT. We experimentally tested this hypothesis by analyzing transconjugant diversity under conditions that differ in their ability to support bacterial growth. Fast-growth conditions increased transconjugant abundance but reduced diversity, whereas slow-growth conditions supported fewer but more diverse transconjugants. We complemented these experiments with individual-based simulations that explicitly incorporated both VGT and HGT. Our results demonstrate that the realized host range is jointly governed by initial HGT events and subsequent VGT-driven expansion, highlighting the importance of integrating transfer and post-transfer dynamics when predicting plasmid-mediated antibiotic resistance spread.

•Vertical and horizontal gene transfer jointly shape plasmid host range•Individual-based simulations quantify the interplay between VGT and HGT•Trait heterogeneity among recipients predicts realized host range contraction•Growth and conjugation dynamics define plasmid host range beyond molecular limits

Vertical and horizontal gene transfer jointly shape plasmid host range

Individual-based simulations quantify the interplay between VGT and HGT

Trait heterogeneity among recipients predicts realized host range contraction

Growth and conjugation dynamics define plasmid host range beyond molecular limits

Molecular biology; Microbiology