Field study results on the probability and risk of a horizontal gene transfer from transgenic herbicide-resistant oilseed rape pollen to gut bacteria of bees

Bees are specifically subjected to intimate contacts with transgenic plants due to their feeding activities on pollen. In this study, the probability and ecological risk of a gene transfer from pollen to gut bacteria of bees was investigated with larvae of Apis mellifera (honeybee), Bombus terrestris (bumblebee), and Osmia bicornis (red mason bee), all collected at a flowering transgenic oilseed rape field. The plants were genetically engineered with the pat-gene, conferring resistance against glufosinate (syn. phosphinothricin), a glutamine-synthetase inhibitor in plants and microorganisms. Ninety-six bacterial strains were isolated and characterized by 16S rRNA gene sequencing, revealing that Firmicutes represented 58% of the isolates, Actinobacteria 31%, and Proteobacteria 11%, respectively. Of all isolates, 40% were resistant to 1 mM glufosinate, and 11% even to 10 mM. Resistant phenotypes were found in all phylogenetic groups. None of the resistant phenotypes carried the recombinant pat-gene in its genome. The threshold of detecting gene transfer in this field study was relatively insensitive due to the high background of natural glufosinate resistance. However, the broad occurrence of glufosinate-resistant bacteria from different phylogenetic groups suggests that rare events of horizontal gene transfer will not add significantly to natural bacterial glufosinate resistance.