The impact of pulsed electric fields on cells and biomolecules: comment on "Lightning-triggered electroporation and electrofusion as possible contributors to natural horizontal gene transfer" by Tadej Kotnik.

The discovery of a horizontal gene transfer (HGT) revolutionized the evolutionary biology. Suddenly, a long developed concept of a phylogenetic tree, where all organisms share a common ancestor, could not describe the outcome of gene transfer between perceived unrelated organisms [1]. Consequently, a new concept – net of life – is emerging [1]. In the “net of life”, each organisms is a combination of shared ancestry and HGT [2]. T. Kotnik reviews the history of biological classification in the human history and positions the role of HGT in the transformation of “phylogenetic tree” to the “net of life” [3]. Although the most frequent mechanisms for HGT are biological: bacterial conjugation, bacterial competence for DNA uptake and viral transduction, T. Kotnik emphasized in this work the role of a physical phenomena – lightning – as a potential trigger of HGT. To answer the question, if HGT could happen before biological mechanisms had evolved, T. Kotnik analyzes the potential of lightening induced electroporation on HGT. Electroporation is the increase of biological cell membrane permeabilization by externally applied pulsed electric fields (PEF) [4], probably by the formation of aqueous pores in the cell membrane [5–7]. As described by T. Kotnik, the formation of pores leads to reversible electroporation (REP), electrofusion (EF), and irreversible electroporation (IEP). I would like to point out to two important properties of PEF: 1) heterogeneity of microbial population response to PEF and 2) the effects of PEF on biomolecules. In the natural marine and fresh water environments, more than two million bacteria species exist [8]. Research on food disinfection by PEF showed the tremendous variation in the different species resistance to PEF. Bacterial properties that affect the electroporation threshold are cell size and shape [9], membrane structure [10], membrane charge [11], cells concentration [12] and growth stage [13]. Given the large number of species of bacteria in marine environment it is likely that IEP, REP and EF happen simultaneously at the same depth. It appears that in nature, the number of species plays a significant role in the PEF induced effects in the population: increasing the number of species increases the probability of each of the IEP, REP and EF events. This is different from classical laboratory electroporation studies where PEF are applied on a single species to induce the desired single effect.