Whole genome sequencing of a novel Bacillus thuringiensis isolated from Assam soil

Background Bacillus thuringiensis (Bt) is a gram-positive ubiquitous saprophytic bacterium that produces proteins (Crystal protein, Vegetative insecticidal protein, and Secreted insecticidal protein) toxic to insects during its growth cycle.

In the present study, the whole genome of a locally isolated B. thuringiensis strain BA04 was sequenced to explore the genetic makeup and to identify the genes responsible to produce insecticidal proteins including the virulence factors.

The strain was isolated from the soil sample of the Kaziranga National Park, Assam, North-Eastern part of India (Latitude: 26°34′39.11''N and Longitude: 93°10′16.04''E).

Results The whole genome sequencing (WGS) of the BA04 strain revealed that it has a circular genome of size 6,113,005 bp with four numbers of plasmids.

A total of 6,111 genes including two novel crystal protein-encoding genes (MH753362.1 and MH753363.1) were identified.

The BLASTn analysis of MH753362.1 showed 84% similarities (maximum identity) with Cry1Ia (KJ710646.1) gene, whereas MH753363.1 exhibited 66% identity with Insecticidal Crystal Protein (ICP) - 6 gene (KM053257.1).

At the protein level, MH753362.1 and MH753363.1 shared 79% identity with Cry1Ia (AIW52613.1) and 40% identity with Insecticidal Crystal Protein (ICP)-6 (AJW76687.1) respectively.

Three-dimensional structures of these two novel protein sequences revealed that MH753362.1 have 48% structural similarity with Cry8ea1 protein, whereas MH753363.1 showed only 20% structural similarity with Cry4Aa protein.

Apart from these insecticidal genes, the strain was also found to contain virulence and virulence-associated factors including the antibiotic resistance genes and Clustered regularly interspaced short palindromic repeat (CRISPR) sequences.

Conclusion This is the first report on the whole genome sequence of Bt strain BA04 isolated from Assam, a North-Eastern state of India.

The WGS of strain BA04 unveils the presence of two novel types of insecticidal crystal protein-encoding genes which can be used for the development of insect-resistant transgenic crops.

Additionally, the strain could be used for the formulations of effective biopesticides.

The WGS provides the fastest and cheapest platform for a better understanding of the genetic makeup of a strain and helps to explore the role of virulence genes in pathogenicity against the insect host.