Impact of genetically modified herbicide-resistant maize on rhizosphere bacterial communities

Abstract

Rhizosphere bacterial community studies offer valuable insights into the environmental implications of genetically modified (GM) crops. This study compared the effects of a non-GM maize cultivar, namely Hi-IIA, with those of a herbicide-resistant maize cultivar containing the phosphinothricin N-acetyltransferase gene on the rhizosphere bacterial community across growth stages. 16s rRNA amplicon sequencing and data analysis tools revealed no significant differences in bacterial community composition or diversity between the cultivars. Principal component analysis revealed that differences in community structure were driven by plant growth stages rather than plant type. Polymerase chain reaction analysis was conducted to examine the potential horizontal transfer of the introduced gene from the GM maize to rhizosphere microorganisms; however, the introduced gene was not detected in the soil genomic DNA. Overall, the environmental impact of GM maize, particularly on soil microorganisms, is negligible, and the cultivation of GM maize does not alter significantly the rhizosphere bacterial community.

Keywords: Environmental risks; GM maize; horizontal gene transfer; soil microbial community.

Figure 1.

Genetic information of herbicide-resistant genetically modified (GM) maize. Schematic diagram of the T-DNA region used in the maize transformation in the Agrobacterium-mediated method (a). The presence of the pat gene was confirmed through polymerase chain reaction (PCR) (b). Additionally, the immunostrip results indicated proper expression of the PAT protein (c).

Figure 2.

Rarefaction curves of the number of operational taxonomic units (OTUs) of two maize cultivars at different growth stages (a), and box plots showing Good’s coverage for the bacterial community (b). 0 w, soil sample collected before maize cultivation; Non-gm, Hi-iia; GM, herbicide resistance transgenic maize.

Figure 3.

Comparison of the bacterial composition at the phylum level across all growth stages. 0 w, soil sample collected before maize cultivation; Non-gm, Hi-iia; GM, herbicide resistance transgenic maize.

Figure 4.

Species abundance and diversity indices of the maize rhizosphere. Chao1 index (a), Shannon index (b) and Simpson index (c). 0 w, soil sample collected before maize cultivation; Non-gm, Hi-iia; GM, herbicide resistance transgenic maize. There was no significant difference between the GM and non-gm maize (p < .05).

Figure 5.

Score (a) and loading plots (b) of the principle component analysis (PCA) results obtained from data in soil bacteria collected from two different genotypes (GM and non-gm) of maize cultivated in four growing stages. 0 w, soil sample collected before maize cultivation; Non-gm, Hi-iia; GM, herbicide resistance transgenic maize.

Figure 6.

Detection of the transgene (pat) in the rhizosphere soil samples (a) and use of 16s rRNA (1.4 kb) for the endogenous gene (b). 0 w, soil sample collected before maize cultivation; N/C, no DNA; P/C, genomic DNA of GM maize for positive control; Non-gm, Hi-iia; GM, herbicide resistance transgenic maize.