Deciphering the rhizobacterial assemblages under the influence of genetically engineered maize carrying mcry genes

Genetically engineered (GE) maize has been thoroughly studied regarding its agro-environmental impact; however, its concerns for the soil environment remain. This work was aimed to decode rhizosphere microbe interactions and potential ecological hazards associated with GE maize. Rhizobacterial communities of field grown transgenic insect-resistant 2A5 maize carrying mcry1Ab and mcry2Ab genes were compared with control Z58 using PacBio sequencing platform. Also full-length 16S rDNA gene sequencing was used to verify the partial (V3-V4) sequencing results obtained in 2017. Measures of α-diversity displayed transgenic 2A5 to be significantly lower in species richness at the flowering stage; however, diversity remained undisturbed. β-diversity was least affected by genetic modifications where similar community profiles were shared by transgenic 2A5 and control Z58. In addition, root exudation patterns were found to drive variations in bacterial assemblages based on developmental stages. For example, genus Massilia successfully colonized the rhizosphere at jointing stage, while Mucilaginobacter showed higher relative abundance in flowering stages of both 2A5 and Z58. These members are known to possess attributes related to plant growth. The impact of dual-transgene insertion on nifH gene abundance was also analyzed where no apparent significant difference in nifH gene copy number was observed. Our results confirmed that full-length 16S rDNA sequencing was sufficient to provide higher taxonomic resolution. Also, results of our 2-year field trials confirmed that there is no significant impact of mcry gene integration on belowground biomasses. Therefore, GE insect-resistant 2A5 maize carrying mcry1Ab and mcry2Ab genes can continue to benefit human populations by increasing crop productivity. In future, further research needs to be catalyzed to analyze the impact of Bt-insertion on microbial community structure across the years for ecosystem sustainability.