Effectiveness of Bacillus thuringiensis MPOB Bt-1 flubendiamide on Metisa plana walker (Lepidoptera: Psychidae) using gene- and genome-centric approach

Malaysia is the second largest producer of palm oil in the world. However, palm oil production is often affected by bagworm infestation. The overuse of chemical insecticides to control the oil palm pest can lead to more persistent problems such as pest resistance to treatment and an abundance of harmful chemical residues in the environment. Therefore, this study aims to analyse the genome of Bacillus thuringiensis MPOB Bt1 (MPOB Bt1) and the synergistic effect of the combination treatment of MPOB Bt1 and flubendiamide (Fbd), the microbial community shift and the functional responses of metagenome-assembled genomes (MAGs) to pesticide exposure for improved control of Metisa plana in oil palm plantations. Whole genome sequencing of MPOB Bt1 was performed using Illumina HiSeq and PacBio platforms. Comparative genomics and analysis of insecticidal genes with other closely related genomes of B. thuringiensis used in commercial biopesticide products were also performed. The laboratory test and synergistic response of MPOB Bt1 and Fbd against M. plana larvae were then optimised using different combination ratios. The details of the changes in the microbial community of M. plana towards the pesticide treatments at day zero (DAT0), day one post- treatment (DAT1) and day three post- treatment (DAT3) were analysed using a gene-centric metagenomic approach. The genome-centric approach was performed for an advanced high–resolution analysis of the functional responses of the M. plana microbiome to the pesticide treatments. The MPOB Bt1 genome size is approximately 6.9 Mbp with the highest average nucleotide value (ANI) of 0.9765 in B. thuringiensis subsp. aizawai strain ABTS-1857. The bioassay results showed a synergistic ratio of more than 1 for 48 and 72 hours after the treatments, confirming the presence of synergistic interactions between MPOB Bt1 and Fbd. Community succession analysis of larval microbiome showed an increase in richness (p-value: 0.012537) and rapid growth in the combined MPOB Bt1-Fbd treatment compared to the individual Fbd treatment. Pearson correlation coefficient analysis showed that the combined MPOB Bt1-Fbd treatment affected the growth of the microbiome that can coexist with Bacillus, based on the positive correlation between Bacillus and the genera Enterobacter and Pseudomonas in the combined MPOB Bt1-Fbd treatment. A total of 11 MAGs were successfully binned from the co-assembled shotgun metagenomics data, with genome completeness ranging from 70.42% to 98.59%, and the major genera were Pantoea, Bacillus, Acinetobacter, Pseudomonas, Stenotrophomonas, and Enterococcus. Time interval studies of MAGs and functional Kyoto Enclyclopedia of Genes and Genomes (KEGG) modules in response to MPOB Bt1-Fbd treatment showed that the community and function of MAGs that initiate the degradation of xenobiotics shifts to a more resilient MAGs community that can produce the nutrient itself by synthesising terpenoids and polyketides in a state of dysbiosis. The results demonstrate for the first time how the combined MPOB Bt1-Fbd synergistically kills M. plana larvae and is linked to microbiome responses. This suggests that the resilience and interactions of taxonomic groups and functional shifts during dysbiosis may be responsible for community selection and the rapid rise of new taxonomic groups to survive. The study highlights the potential of the MPOB Bt1-Fbd combination for the development of effective M. plana control and reduces dependence on harmful chemical pesticides.

Text 122784.pdf Download (1MB) Official URL or Download Paper: http://ethesis.upm.edu.my/id/eprint/18663

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