Electrical fields and current can permeabilize bacterial membranes, allowing for the penetration of naked DNA. Given that the environment is subjected to regular thunderstorms and lightning discharges that induce enormous electrical perturbations, the possibility of natural electrotransformation of bacteria was investigated. We demonstrated with soil microcosm experiments that the transformation of added bacteria could be increased locally via lightning-mediated current injection. The incorporation of three genes coding for antibiotic resistance (plasmid pBR328) into the Escherichia coli strain DH10B recipient previously added to soil was observed only after the soil had been subjected to laboratory-scale lightning. Laboratory-scale lightning had an electrical field gradient (700 versus 600 kV m ؊1) and current density (2.5 versus 12.6 kA m ؊2 ) similar to those of full-scale lightning. Controls handled identically except for not being subjected to lightning produced no detectable antibiotic-resistant clones. In addition, simulated storm cloud electrical fields (in the absence of current) did not produce detectable clones (transformation detection limit, 10 ؊9). Natural electrotransformation might be a mechanism involved in bacterial evolution.Ongoing sequencing and comparison of bacterial genomes are gradually modifying our understanding of how bacteria evolved. Although earlier ideas included a point mutationbased evolution occurring slowly and regularly, new theories propose a more erratic evolution in which drastic changes in the genome are due to irregular acquisition of new genetic information by horizontal gene transfers (HGT) (13). However, the frequency of HGT would have had to be so high during bacterial evolution that some evolutionists are questioning the accuracy of the phylogenetic analyses (5). Moreover, these analyses underestimate the actual number of transfers by missing the oldest events. Their efficiency is also limited to the transferred genes, which were successfully fixed in a microbial population by increasing the overall fitness. These sequence-based tools also miss the great majority of transfer events that conferred neutral or deleterious traits and therefore were subsequently deleted. In addition, numerous microcosm-based investigations devoted to studying these events, and specifically natural genetic transformation in environments, such as soil, sediment, and water, conclude that HGT would occur at extremely low frequencies (10,15).Natural transformation of bacteria in soil by extracellular DNA is a multistep process, precluding its occurrence at high frequency (15). When released into the soil at the death of organisms (or more actively for some bacteria), naked DNA has to avoid both enzymatic degradation and irreversible adsorption onto soil particles (4). Moreover, when taken up into the cell, transforming DNA still has to resist the numerous restriction and modification mechanisms and to be integrated into the host genome via homologous or illegitimate recombination (or to repli...

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