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Monitoring and modeling horizontal gene transfer


Monitoring efforts have failed to identify horizontal gene transfer (HGT) events occurring from transgenic plants into bacterial communities in soil or intestinal environments. The lack of such observations is frequently cited in biosafety literature and by regulatory risk assessment. Our analysis of the sensitivity of current monitoring efforts shows that studies to date have examined potential HGT events occurring in less than 2 g of sample material, when combined. Moreover, a population genetic model predicts that rare bacterial transformants acquiring transgenes require years of growth to out-compete wild-type bacteria. Time of sampling is there-fore crucial to the useful implementation of monitoring. A population genetic approach is advocated for elucidating the necessary sample sizes and times of sampling for monitoring HGT into large bacterial populations. Major changes in current monitoring approaches are needed, including explicit consideration of the population size of exposed bacteria, the bacterial generation time, the strength of selection acting on the transgene-carrying bacteria, and the sample size necessary to verify or falsify the HGT hypotheses tested.

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Figure 1: Time to fixation (in bacterial generations) of a single HGT event occurring in a bacterial population of N = 1010.
Figure 2: The probability of detection of an HGT event into a bacterial population of 1010.


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K.M.N. received financial support from the Research Council of Norway. J.P.T. thanks the Miller Institute for Basic Research in Science for funding and administrative support. We thank M. Choi for comments on the manuscript.

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Correspondence to Kaare M Nielsen.

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Nielsen, K., Townsend, J. Monitoring and modeling horizontal gene transfer. Nat Biotechnol 22, 1110–1114 (2004).

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