Horizontal Gene Transfer in Thermus spp.

Alba Blesa,Beate Averhoff,José Berenguer

doi:10.21775/cimb.029.023

Alba Blesa, Beate Averhoff + Show 1 more

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https://doi.org/10.21775/cimb.029.023

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Abstract

The small amount of genetic content in thermophiles generally limits their adaptability to environmental changes. In Thermus spp., very active horizontal gene transfer (HGT) mechanisms allow the rapid spread of strain-specific adaptive gene modules among the entire population. Constitutive expression of a rather particular and highly efficient DNA transport apparatus (DTA) is at the center of this HGT-mediated enhanced adaptability. The function of the DTA is dependent on the integrity and longevity of the extracellular DNA (eDNA) being transformed, which can be improved by the production of extracellular vesicles (EV) through lysis of a fraction of the population. The DTA must also contend with the recipient cell's defensive barriers, namely restriction enzymes, a panoply of CRISPR-Cas systems, and the argonaute-like protein TtAgo, which may be bypassed by transjugation, a new class of bidirectional transformation-dependent conjugation. Efficient transjugation depends on the presence of the ICETh1, an integrative and conjugative element which promotes simultaneous, generalized DNA transfer from several points in the genome. Transjugation shows preference for genes located within a megaplasmid replicon, where the main strain-specific adaptive modules are located. Contribution of transformation, vesicle-mediated eDNAs, and transjugation to HGT in this genus is discussed.

Highlights

Horizontal gene transfer (HGT) and symbiosis constitute a basis to explain the explosive evolution and dramatic adaptability to new environments shown by both prokaryotes and eukaryotes
The function of the DNA transport apparatus (DTA) is dependent on the integrity and longevity of the extracellular DNA being transformed, which can be improved by the production of extracellular vesicles (EV) through lysis of a fraction of the population
The DTA is a highly complex and very dynamic system composed of several unique proteins, highlighting the features which might have been triggered by the extreme environment and/or the complex cell envelope

Summary

Introduction

Horizontal gene transfer (HGT) and symbiosis constitute a basis to explain the explosive evolution and dramatic adaptability to new environments shown by both prokaryotes and eukaryotes. The main HGT mechanisms in T. thermophilus involve a DTA that can act directly on free eDNA (Averhoff, 2009) as described in other bacteria, or uptake eDNA from extracellular vesicles (EV) (Blesa and Berenguer, 2015), or directly transfer from donor cells in intimate contact in a process called transjugation (Blesa et al, 2017).

Results

Conclusion