Lightning-triggered electroporation and electrofusion as possible contributors to natural HGT among prokaryotes

摘要

Phylogenetic studies show that horizontal gene transfer (HGT) is asignificant contributor to genetic variability of prokaryotes, and was perhapseven more abundant during early evolution. Hitherto, research of natural HGThas mainly focused on three mechanisms: conjugation, natural competence, andviral transduction. This paper discusses the feasibility of a fourth suchmechanism - cell electroporation and/or electrofusion triggered by atmosphericelectrostatic discharges (lightnings). A description of electroporation as aphenomenon is followed by a review of experimental evidence thatelectroporation of prokaryotes in aqueous environments can result in release ofnon-denatured DNA, as well as uptake of DNA from the surroundings andtransformation. Similarly, a description of electrofusion is followed by areview of experiments showing that prokaryotes devoid of cell wall canelectrofuse into hybrids expressing the genes of their both precursors. Undersufficiently fine-tuned conditions, electroporation and electrofusion areefficient tools for artificial transformation and hybridization, respectively,but the quantitative analysis developed here shows that conditions forelectroporation-based DNA release, DNA uptake and transformation, as well asfor electrofusion are also present in many natural aqueous environments exposedto lightnings. Electroporation is thus a plausible contributor to natural HGTamong prokaryotes, and could have been particularly important during the earlyevolution, when the other mechanisms might have been scarcer or nonexistent. Inmodern prokaryotes, natural absence of the cell wall is rare, but it isreasonable to assume that the wall has formed during evolution, and at leastprior to this, electrofusion could also have contributed to HGT. The concludingsection outlines several guidelines for assessment of the feasibility oflightning-triggered HGT.