Abstract
Extremophilic prokaryotes live under harsh environmental conditions which require far-reaching cellular adaptations. The acquisition of novel genetic information via natural transformation plays an important role in bacterial adaptation. This mode of DNA transfer permits the transfer of genetic information between microorganisms of distant evolutionary lineages and even between members of different domains. This phenomenon, known as horizontal gene transfer (HGT), significantly contributes to genome plasticity over evolutionary history and is a driving force for the spread of fitness-enhancing functions including virulence genes and antibiotic resistances. In particular, HGT has played an important role for adaptation of bacteria to extreme environments. Here, we present a survey of the natural transformation systems in bacteria that live under extreme conditions: the thermophile Thermus thermophilus and two desiccation-resistant members of the genus Acinetobacter such as Acinetobacter baylyi and Acinetobacter baumannii. The latter is an opportunistic pathogen and has become a world-wide threat in health-care institutions. We highlight conserved and unique features of the DNA transporter in Thermus and Acinetobacter and present tentative models of both systems. The structure and function of both DNA transporter are described and the mechanism of DNA uptake is discussed.
Highlights
Microbial life has been detected in virtually every environment on earth, even in extreme environments such as hydrothermal vents, salt-saturated alkaline ponds, acidic hot springs, antarctic ice, aridic soils and in plant, animal and human hosts
This review summarizes the current knowledge on physiology, structure and function of the transformation machineries of members of the two phylogenetically distant genera Acinetobacter and Thermus
The finding that comP, comC, comE and comF mutants were unaffected in piliation but defective or impaired in natural transformation suggests that a short DNA translocator pseudopilus is important for DNA uptake of A. baylyi
Summary
Microbial life has been detected in virtually every environment on earth, even in extreme environments such as hydrothermal vents, salt-saturated alkaline ponds, acidic hot springs, antarctic ice, aridic soils and in plant, animal and human hosts. Components of the A. baylyi natural transformation machinery were identified by mutant studies and led to the identification of twenty one competence genes (Table 1).
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