Lightning-triggered electroporation and electrofusion as possible contributors to natural horizontal gene transfer

Abstract

Phylogenetic studies show that horizontal gene transfer (HGT) is a significant contributor to genetic variability of prokaryotes, and was perhaps even more abundant during the early evolution. Hitherto, research of natural HGT has mainly focused on three mechanisms of DNA transfer: conjugation, natural competence, and viral transduction. This paper discusses the feasibility of a fourth such mechanism--cell electroporation and/or electrofusion triggered by atmospheric electrostatic discharges (lightnings). A description of electroporation as a phenomenon is followed by a review of experimental evidence that electroporation of prokaryotes in aqueous environments can result in release of non-denatured DNA, as well as uptake of DNA from the surroundings and transformation. Similarly, a description of electrofusion is followed by a review of experiments showing that prokaryotes devoid of cell wall can electrofuse into hybrids expressing the genes of their both precursors. Under sufficiently fine-tuned conditions, electroporation and electrofusion are efficient tools for artificial transformation and hybridization, respectively, but the quantitative analysis developed here shows that conditions for electroporation-based DNA release, DNA uptake and transformation, as well as for electrofusion are also present in many natural aqueous environments exposed to lightnings. Electroporation is thus a plausible contributor to natural HGT among prokaryotes, and could have been particularly important during the early evolution, when the other mechanisms might have been scarcer or nonexistent. In modern prokaryotes, natural absence of the cell wall is rare, but it is reasonable to assume that the wall has formed during a certain stage of evolution, and at least prior to this, electrofusion could also have contributed to natural HGT. The concluding section outlines several guidelines for assessment of the feasibility of lightning-triggered HGT.

Review of Antimicrobial Resistance in the Environment and Its Relevance to Environmental Regulators

“…The SOS response can also trigger HGT of ARGs, thereby providing a mechanism for the spread of ARGs from exposure to antibiotics (Beaber et al, 2004). Many additional drivers (e.g., chemical and environmental) of HGT have been identified (Hastings et al, 2004; Antonova and Hammer, 2011), including abiotic sources (Warnes et al, 2012; Kotnik, 2013). The relative importance of each of these drivers of HGT has yet to be assessed at an ecologically relevant scale.…”

Abiotic Gene Transfer: Rare or Rampant?

“…pp. 362-363 in (Kotnik 2013a)). Similarly, an electric field of 30 kV/cm (sufficient for irreversible electroporation of most microorganisms) is induced at a radial distance of ~2 cm, so that within the abovementioned ~100 cm 3 where electroporation can occur, in the inner ~20 cm 3 it is predominantly irreversible (i.e., with high probability of cell death), and in the remaining ~80 cm 3 largely reversible.…”

“…We have recently suggested that lightning-triggered electroporation of organisms’ envelopes acts as a natural abiotic mechanism of HGT, causing both DNA release and uptake (Kotnik 2013a; Weaver 2013; Kotnik 2013b). In this paper, we approach the topic of abiotic HGT mechanisms more broadly, positing that three physical methods used for artificial genetic transformation – freeze-and-thaw, microbeads-agitation, and electroporation-based transformation – all have prominent analogues in nature: freeze-and-thaw cycles in polar waters, sand-agitation in waters at riverbeds and foreshores, and lightning-triggered electroporation in all aqueous habitats accessible to lightning strokes.…”

Genetic Transformation of Cells using Physical Methods

“…This is due to its quick-ness, low cost, and simplicity even when it has a low efficiency, requires laborious protocols for regeneration after genetic transformation, and can only be applied to protoplasts [1,2,[12][13][14][15]. Electroporation is based on the application of a strong electrical field to enhance the formation of pores on the cell membrane due to a polarity alteration, caused by the electrical field (alternated or pulsed) that induces a dipolar moment inside the cells, and a potential difference through the plasmatic membrane [15][16][17][18].…”

“…Electroporation is extremely used to transform yeast, especially Saccharomyces cerevisiae, but the frequency of transformation (up to 1x105 trans-formants per microgram of DNA) is low in comparison with that obtained for bacteria. Due to this, the cell wall of Saccharomyces cerevisiae has been manipulated by using chemical treatments or employing enzymatic cocktails to produce protoplasts before electroporation [30,31].When using protoplasts of plants, fungi or animals, the uptake of DNA can be achieved by electrofusion, i.e., two membranes located very close to each other can be fused by application of an electric field and the DNA present in the cell suspension is trapped in the cytoplasm of the joined cells [13,32]. market in 2001 [33,34].…”