Effects of transgenic hybrid aspen over-expressing polyphenol oxidase on the diversity of rhizosphere bacteria and fungi

• Main Author: Oliver, Kathryn
• Other Authors: Hintz, William E.
• Language: English; en
• Published: 2010
• Subjects: transgenic plants; polyphenol oxidase; UVic Subject Index::Sciences and Engineering::Biology
• Online Access: http://hdl.handle.net/1828/2343

A greenhouse experiment was carried out to screen for potential effects of transgenic aspen over-expressing a hybrid poplar leaf polyphenol oxidase gene on rhizosphere communities. Heterotrophic plate counts and cultivation-independent methods were used to compare bacterial and fungal populations associated with transgenic PPO over-expressing and unmodified control trees. Total community DNA extracted from rhizosphere soils was used to establish Iibraries containing partial gene sequences that were PCR-amplified from community members, and putative taxonomy was assigned to clones based on similarity to reference sequences. Gene libraries for the bacterial component of the rhizosphere were established using partial 16S rRNA and chaperonin-60 gene sequences, and the fungal community was characterized based on partial 18S rRNA gene sequences. Phylogenetic analysis revealed that bacterial 16S gene libraries were dominated by Alphaproteobacterial sequences, and the CPN-60 gene libraries were dominated by members of the Bacteroidetes/Chlorobi group, illustrating the biases potentially incurred by using a single gene locus to profile microbial diversity. In both CPN-60 and 16S rRNA libraries, only minor components of the bacterial community differed between transgenic and unmodified trees. Comparisons based on library coverage indicated that changes in bacterial community structure between transgenic and unmodified trees were minor in comparison to differences observed between individual trees of the same type, and no significant differences in terms of bacterial species diversity were revealed by the calculated diversity, dominance and evenness indices. In comparison to the bacterial gene libraries, higher coverage of the underlying population was achieved in the fungal 18S libraries. Members of the Zygomycota, Chytridiomycota, Ascomycota, and Basidiomycota were recovered from both libraries. Dominant groups of fungi associated with each tree type were highly similar, although there were some qualitative differences in the recovery of less abundant fungi as a result of the underlying heterogeneity of the fungal population. No clear differences in terms of fungal species richness were associated with transgenic or unmodified trees, although control libraries were characterized by a slightly higher level of dominance. In general, the methods employed revealed only minor differences between the bacterial and fungal communities associated with transgenic and unmodified trees, suggesting that impacts of the transgenic plants on the rhizosphere community were minimal.