Mechanisms of abiotic horizontal gene transfer. Comment on 'Lightning-triggered electroporation and electrofusion as possible contributors to natural horizontal gene transfer' by Tadej Kotnik.

摘要

Results suggestive of horizontal (lateral) gene transfer, attributed at the time to mutations, have been published since early 20th century [3]. Recent advances in gene sequencing technology have set on solid ground the idea that horizontal (lateral) gene transfer (HTG) is an important factor in evolution [10,11]. There is an increasing interest in this phenomenon [4,8,12], which is now thought to be largely responsible for the growing number of antibiotic resistant bacteria in the world [23]. In this issue, Kotnik, has developed a convincing hypothesis that lightning induced electroporation and electrofusion could be a mechanism for abiotic horizontal gene transfer [13]. Electroporation and electrofusion, described in detail in [13], are mechanisms that involve the application of certain electric fields across a cell and the consequent formation of defects in the cell membrane. These defects can be reversible or irreversible. Reversible electroporation is commonly used for gene transfection and cell fusion while irreversible electroporation is used for cell ablation [13]. Lightning produces a range of electric fields that include those for reversible electro-poration, irreversible electroporation and fusion. It is reasonable to assume that microorganisms and viruses exposed to lightning could be exposed to a combination of electric fields that will produce abiotic horizontal gene transfer, as suggested by Kotnik [13]. In fact, the group of Rafael Lee has shown that lightning can cause irreversible electropo-ration injury to tissue [1,14]. The idea that lighting can cause abiotic lateral gene transfer is somewhat reminiscent of the idea of abiogenesis and the classical experiment of Miller and Urey [17,18]. Could other mechanisms proposed for abiogenesis be also involved in abiotic gene transfer? The clay hypothesis for abiogenesis proposed by Cairns-Smith [2] or the W?chtersh?user [7] hypothesis for an iron sulfur world or Mulkidjanian’s [16] hypothesis of the Zn-world theory leads to thinking about micro and nano electroporation [5,6]. Clays and pyrite are structures with local electric charges. We have shown that when cells pass across surfaces with charges separated by nanometer distances the electric fields that are produced are sufficient to cause electroporation and electrolysis induced reversible and irreversible poration of the cell membrane [20,21]. We have also shown that it is sufficient for only part of the cell membrane to be exposed to electroporation fields for electroporation to occur [5,6]. Fig. 1 illustrates the electric field that would develop across a cell membrane when the cell flows across a substrate in which two small charges with a potential difference of 0.1 V are separated by a 100-nanometer gap. Even in the absence of native charges, an electrolytic process involving Zn and air can produce electric fields that can cause electroporation at the nanoscale [22]. It is interesting to note that these nanoscale electroporation processes may explain the observed abiotic gene transfer in bacteria gaining antibiotic resistance on surfaces [23].