Was Zeus responsible for horizontal gene transfer. A comment on 'Lightning-triggered electroporation and electrofusion as possible contributors to natural horizontal gene transfer' by Tadej Kotnik.

摘要

In the present issue, Kotnik describes the possibility of physical processes that may have played a role in horizontal gene transfer between prokaryots during the early evolution [7]. It is well known in the area of microbiology that an efficient and user friendly experimental approach for gene transfer in bacteria is to apply a calibrated electrical discharge on an aqueous mixture of bacteria and plasmid DNA. The strong electric field pulse is able to destabilize the cell envelope and to push the pDNA inside the cytoplasm. Kotnik suggests that similar processes may be present during the propagation of thunderbolt along the wet earth surface and support horizontal gene transfer. Along its propagation, the lightning is associated with an electric field, which intensity is position dependent. This means that in some parts of the earth surface, this intensity will be the critical one described to induce both plasmid release and plasmid uptake in bacteria. Preliminary results in Lyon strongly support the model [1,3]. Open questions remain present. Thunderbolts have a rather short life time while optimal gene transfer is observed under much longer electric discharges under routine conditions [5]. Thunderbolts are triggering a lot of physical and chemical effects. One of the most impressive effects is the associated shock wave linked to the energy that is dispersed very fast. Wet air is inducing the formation of highly reactive oxygen derivatives under the electric discharges and the associated plasma. Both parameters have been shown to affect the bacterial envelope even of the extremely resistant spores [6]. Controlled shock waves were recently developed as a unique bacterial transformation method, first optimized for the maximum efficiency in Escherichia coli but valid on Pseudomonas aeruginosa and Salmonella typhimurium [4]. Plasma jets are shown to be highly active on microbes [9] and can support gene transfer on eukaryotes [2]. Kotnik suggests another biophysical processes supporting gene transfer: electrofusion. It is well known and routinely used in Biotechnology that when pulsed electric fields are applied on cells in close contact, cell hybridation will result [10]. His suggestion is that wall-less bacteria may fuse under the effect of lightnings. The resulting hybrid will share the genes of the two partners. This was indeed already proposed 30 years ago [8,11].