Impact of β-carotene transgenic rice with four synthetic genes on rhizosphere enzyme activities and bacterial communities at different growth stages

• β-carotene transgenic rice AH33 expressing four carotenoid biosynthetic genes.
• DGGE and 16S rRNA gene library used for analyzing bacterial community composition.
• No significant differences in activities of catalase, sucrase and protease.
• β-carotene transgenic rice AH33 has no detected effects on soils bacterial community.

A field experiment was carried out to assess the impact of β-carotene transgenic rice with four synthetic genes on bacterial communities and enzyme activities in the rhizosphere. Soil samples from two neighboring fields cultivated with transgenic rice AH33 and its parental non-transgenic variety Zhonghua 11 were taken at seedling, tillering, heading and maturing stages. There were no significant differences in activities of catalase, sucrase and protease between AH33 and Zhonghua 11 at the same growth stage. Although soil urease activities of AH33 showed significant differences (P < 0.05) compared with that of Zhonghua 11 at the heading stage, these differences were transient and disappeared at other stages, indicating that changes in soil enzyme activities were mainly related to plant age. Changes in the bacterial communities throughout different growth stages were monitored and analyzed using denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene clone library techniques. The resulting dendrograms of DGGE patterns showed four distinct clusters, which were identified to be correlating with the respective growth stages. No effect of the transgenic rice AH33 on dominant bacterial communities at the same growth stage was detectable. This indicated that the impact of crop growth stage outweighed possible alterations due to the genetic modifications. The analyses of DGGE and 16S rRNA gene clone libraries revealed that there were no significant differences (P < 0.05) in the Shannon–Wiener diversity index (H'), richness (R), and evenness (E) of rhizosphere soil between AH33 and Zhonghua 11 at any of the stages. Thus, there was no indication of altered overall bacterial diversity due to the genetic modification. Sequencing of PCR amplicons indicated that the DGGE profiles were mainly composed of Proteobacteria, Acidobacteria, Gemmatimonadetes, Chloroflexi and Verrucomicrobia, and in addition, the 16S rRNA gene clone libraries indicated the presence of Plantomycetes, Armatimonadetes, Actinobacteria, Chlorobi, Cyanobacteria and Fimicutes. In conclusion, our study based on the analysis of four different soil enzymes and the diversity of rhizosphere bacteria gives no indication that the genetic modification with the four synthetic genes and their expression in the transgenic rice AH33 has any specific effects, related to the genetic modification, on the soils in which they are cultivated.