Effects of Azospirillum brasilense with genetically modified auxin biosynthesis gene ipdC upon the diversity of the indigenous microbiota of the wheat rhizosphere

The phytostimulatory properties of Azospirdlum moculants, which entail production of the phytohormone mclole-3-acetic acid (IAA), can be enhanced by genetic means. However, it is not known whether this could affect their interactions with indigenous soil microbes Here, wheat seeds were inoculated with the wild-type strain Azosptrillum brasdense Sp245 or one of three genetically modified (GM) derivatives and grown for one month The GM derivatives contained a plasmid vector harboring the indole-3-pyruvate/phenylpyruvate decarboxylase gene tpdC (IAA production) controlled either by the constitutive promoter Pnptll or the root exudate-responsive promoter PsbpA, or by an empty vector (GM control) All moculants displayed equal rhizosphere population densities. Only inoculation with either ipdC construct increased shoot biomass compared with the non-inoculated control At one month after inoculation, automated ribosomal intergemc spacer analysis (ARISA) revealed that the effect of the PsbpA construct on bacterial community structure differed from that of the GM control, which was confirmed by 16S rDNA-based denaturing gradient gel electrophoresis (DOGE) The fungal community was sensitive to inoculation with the PsbpA construct and especially the GM control, based on ARISA data. Overall, fungal and bacterial communities displayed distinct responses to inoculation of GM A brastlense phytostimulators, whose effects could differ from those of the wild-type (C) 2010 Elsevier Masson SAS All rights reserved.