The effect of root-released compounds of transplastomic tobacco
(Nicotiana tabacum) on the soil bacterial
community structure, and their potential to support horizontal gene transfer
(HGT) to bacteria have been studied. Soil microcosms were exposed to
root-released compounds collected from transplastomic and non-transgenic
tobacco cultivars. Cluster analysis of automated ribosomal intergenic spacer
analysis (ARISA) profiles of the soil bacterial community after 48 h
incubation grouped the transgenic cultivar apart from the non-transgenic,
indicating that it had a rhizodeposition pattern different from the parental
plants. However, these differences were less than between the two
non-transgenic tobacco cultivars studied. NMR characterization of the
root-released compounds showed some differences in chemical fingerprinting
pattern between the transplastomic and the parental cultivar. However, the
effect on bacterial community structure was transient, and tended to
disappear after 96 h of incubation. The potential of root-released
compounds as a source of transforming DNA for bacteria was investigated by
using four potential recipient species. No transformants were obtained
following exposure of all the recipients to the root-released compounds.
Root-released compounds amended to transgene donor DNA decreased the
transformation frequency of Acinetobacter baylyi
strain ADP1200, while Azospirillum,
Agrobacterium, and
Sinorhizobium strains failed to develop
competence also in the presence of an external added transgene source.
Detection of plastid sequences by PCR suggested that a very low amount of
fragmented plastid donor DNA was present in the root-released compounds.