Despite all the benefits assigned to the genetically modified plants, there are still no sufficient data available in literature concerning the possible effects on the microbial communities associated with these plants. Therefore, this study was aimed at examining the effects of the genetic modifications of two transgenic maize genotypes (MON810 – expressing the insecticidal Bt-toxin and TC1507 – expressing the insecticidal Bt-toxin and the herbicide resistance PAT [phosphinothricin-N-acetyltransferase]) on their endophytic microbial communities, in comparison to the microbial community found in the near-isogenic non-transgenic maize (control). The structure of the endophytic communities (Bacteria, Archaea and fungi) and their composition (Bacteria) were evaluated by denaturing gradient gel electrophoresis (DGGE) and the construction of clone libraries, respectively. DGGE analysis and the clone libraries of the bacterial community showed that genotype TC1507 slightly differed from the other two genotypes. Genotype TC1507 showed a higher diversity within its endophytic bacterial community when compared to the other genotypes. Although some bacterial genera were found in all genotypes, such as the genera Burkholderia, Achromobacer and Stenotrophomonas, some were unique to genotype TC1507. Moreover, OTUs associated with Enterobacter predominated only in TC1507 clone libraries. The endophytic bacterial community of the maize genotype TC1507 differed from the communities of the maize genotype MON810 and of their near-isogenic parental genotypes (non-Bt or control). The differences observed among the maize genotypes studied may be associated with insertion of the gene coding for the protein PAT present only in the transgenic genotype TC1507.

The ecology of microbial communities associated with organic phosphorus (P) mineralization in soils is still understudied. Here, we assessed the abundance and diversity of bacteria harbouring genes encoding β-propeller phytases (BPP) in the rhizosphere of traditional and transgenic maize cultivated in two Brazilian soils. We found a soil-dependent effect towards a higher abundance of phytase genes in the rhizosphere, and an absence of any impact of plant genotype. Phylogenetic analyses indicated members of the genera Pseudomonas, Caulobacter, Idiomarina and Maricaulis, close to ‘uncultured bacteria’, to constitute the dominant bacteria hosting this gene. The results obtained validate a methodology to target bacteria that are involved in the organic P cycle, and depict the responsiveness of such bacteria to the rhizosphere, albeit in dependency of the soil in which maize is cultivated. The data also identified the major bacterial groups that are associated with the organic P mineralization function. Significance and Impact of the Study: Micro-organisms play a key role in nutrient balance in soil ecosystems that are essential to life on the planet. However, some processes such as organic phosphorus mineralization, an important source of phosphorus supply in soil, is poorly studied mainly due the absence of an efficient methodology to assess the phytase-producing micro-organisms. In this study, a method to assess beta-propeller phytase (BPP)-carrying bacteria in soil was validated. This method may contribute to the knowledge of how these micro-organisms behave in the environment and contribute for plant growth promotion.