Horizontal Gene Transfer in Planktonic and Biofilm Modes - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 64

Horizontal Gene Transfer in Planktonic
and Biofilm Modes

Melanie Broszat and Elisabeth Grohmann

Abstract Horizontal gene transfer (HGT) is an important means to obtain and
maintain plasticity of microbial genomes. Basically, bacteria apply three different
modes to horizontally exchange genetic material: (1) conjugative transfer mediated
by mobile genetic elements (MGE), (2) DNA uptake via transformation, and
(3) transduction. The three modes rely on different prerequisites of the participating
cells: conjugative transfer depends on close cell to cell contact between a donor and
a recipient cell and is mediated through multi-protein complexes, denominated type
IV secretion systems (T4SS), and DNA transformation does not rely on cell-cell
contact but is the uptake of free DNA from the environment by a competent
bacterial cell. In some bacteria it is also mediated by a T4SS. The third mechanism
depends on the presence of a bacteriophage, which can transfer genomic DNA from
one host cell to another. Experimental evidence exists that all three modes occur in
planktonic cultures and recent data have also been provided for the occurrence of all
three ways in biofilms. Regulation of these HGT events and their consequences for
the acting microbes and the biofilms they live in are discussed in this chapter.
Additionally, we focus on modern techniques to visualize and to quantify HGT in
planktonic and biofilm modes.

1 Introduction

HGT is the most important means for the spread of antimicrobial resistance and
virulence genes between related but also among unrelated bacteria. If antimicrobial
resistance traits are taken up by pathogenic bacteria, multiple-resistant pathogens
can evolve which then can further disseminate their resistance factors among the
microbial population. Conjugative transfer mediated by MGEs is the most