Objective: To investigate the midgut bacterial community of sensitive and resistant Helicoverpa armigera for the emergence of resistance to Bacillus thuringiensis.
Methods: Two culture-independent techniques (16S rDNA library and DGGE) were introduced. The genomic DNA of midgut bacteria was extracted. The full length gene of 16S rDNA was amplified by PCR and then cloned. The 16S rDNA library was analyzed with Alu I and Sac I. The V3 region of 16S rDNA was amplified by PCR. The intrapopulation variation and variation between resistant and sensitive Helicoverpa armigera were assayed by DGGE.
Results: Analysis of 16S rDNA library showed similar patterns of midgut bacterial structure and diversity in terms of the dominant bacteria, but the inferior bacteria were significant different. The resistant population harbored abundant phylotypes belonging to uncultured bacterium (56.4%), Enterococcus gallinarum (17.0%) and Enterococcus casseliflavus (17.0%). For the sensitive population, the dominant bacteria were uncultured bacterium (60.2%), Enterococcus casseliflavus (14.7%) and Enterococcus gallinarum (19.3%). The divergence of midgut bacteria community between resistant and sensitive populations detected by 16S rDNA library analysis was verified by PCR with specific primers, and the result showed that all those inferior bacteria presented in both varieties. DGGE profile revealed that the similarity of the two varieties was 92.3%.
Conclusion: The midgut bacterial community of resistant and sensitive H. armigera was similar, which had no direct effect on Bt-resistance of H. armigera.