Comparative genomic analysis and mosquito larvicidal activity of four Bacillus thuringiensis serovar israelensis strains

Giselly B Alves,Raimundo W S Aguiar,Fabrício S Campos,Gil R Santos,Sergio D Ascêncio,Marcelo L Dias,Eliseu J G Pereira,Lara T M Costa,Guy Smagghe,Bergmann M Ribeiro,Fernando L Melo,Khalid Haddi,Eugenio E Oliveira,Roberto F T Corrêa

doi:10.1038/s41598-020-60670-7

Abstract

Bacillus thuringiensis serovar israelensis (Bti) is used to control insect vectors of human and animal diseases. In the present study, the toxicity of four strains of Bti, named T0124, T0131, T0137, and T0139, toward Aedes aegypti and Culex quinquefasciatus larvae was analyzed. The T0131 strain showed the highest larvicidal activity against A. aegypti (LC50 = 0.015 µg/ml) and C. quinquefasciatus larvae (LC50 = 0.035 µg/ml) when compared to the other strains. Furthermore, the genomic sequences of the four strains were obtained and compared. These Bti strains had chromosomes sizes of approximately 5.4 Mb with GC contents of ~35% and 5472–5477 putative coding regions. Three small plasmids (5.4, 6.8, and 7.6 kb) and three large plasmids (127, 235, and 359 kb) were found in the extrachromosomal content of all four strains. The SNP-based phylogeny revealed close relationship among isolates from this study and other Bti isolates, and SNPs analysis of the plasmids 127 kb did not reveal any mutations in δ-endotoxins genes. This newly acquired sequence data for these Bti strains may be useful in the search for novel insecticidal toxins to improve existing ones or develop new strategies for the biological control of important insect vectors of human and animal diseases.

Highlights

Bacillus thuringiensis serovar israelensis (Bti) is used to control insect vectors of human and animal diseases
One study reported the plasmid sequence of a Bacillus thuringiensis serovar israelensis (Bti) strain, and revealed that it may produce up to seven crystal-forming toxins, named Cry4A, Cry4B, Cry10A, Cry11A, Cyt1A, Cyt2Ba, and Cyt1Ca, which are all encoded by genes found in a single 127923 bp plasmid called pBtoxis[18]
We sequenced the genomes of four Bti strains, T0124, T0131, T0137, and T0139 that were collected from the soil of the Tocantins state in Brazil and determined their larvicidal activity against larvae of two important mosquito species of A. aegypti and C. quinquefasciatus

Summary

Introduction

Bacillus thuringiensis serovar israelensis (Bti) is used to control insect vectors of human and animal diseases. The SNP-based phylogeny revealed close relationship among isolates from this study and other Bti isolates, and SNPs analysis of the plasmids 127 kb did not reveal any mutations in δ-endotoxins genes This newly acquired sequence data for these Bti strains may be useful in the search for novel insecticidal toxins to improve existing ones or develop new strategies for the biological control of important insect vectors of human and animal diseases. In case we identify high anti-mosquito activity with these strains, we believe these new data are useful in the continuous search for new insecticidal toxins to improve the existing ones or develop new strategies for the biological control of important insect vectors of human and animal diseases

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Results

Conclusion