Comparative genomics of extrachromosomal elements in Bacillus thuringiensis subsp. israelensis

Abstract

Bacillus thuringiensis subsp. israelensis is one of the most important microorganisms used against mosquitoes. It was intensively studied following its discovery and became a model bacterium of the B. thuringiensis species. Those studies focused on toxin genes, aggregation-associated conjugation, linear genome phages, etc. Recent announcements of genomic sequences of different strains have not been explicitly related to the biological properties studied. We report data on plasmid content analysis of four strains using ultra-high-throughput sequencing. The strains were commercial product isolates, with their putative ancestor and type B. thuringiensis subsp. israelensis strain sequenced earlier. The assembled contigs corresponding to published and novel data were assigned to plasmids described earlier in B. thuringiensis subsp. israelensis and other B. thuringiensis strains. A new 360 kb plasmid was identified, encoding multiple transporters, also found in most of the earlier sequenced strains. Our genomic data show the presence of two toxin-coding plasmids of 128 and 100 kb instead of the reported 225 kb plasmid, a co-integrate of the former two. In two of the sequenced strains, only a 100 kb plasmid was present. Some heterogeneity exists in the small plasmid content and structure between strains. These data support the perception of active plasmid exchange among B. thuringiensis subsp. israelensis strains in nature.

Bam35 Tectivirus Intraviral Interaction Map Unveils New Function and Localization of Phage ORFan Proteins

“…These mutations were detected in 3 out of 3 different clones analyzed, which may indicate either that mutations occurred at any step of amplification from the original isolate, that a sequencing error occurred in the original genome, or that mutations were introduced during the PCR and cloning procedures. The last possibility is favored by the fact that 4 out of 5 ORFs containing mutations (namely, those coding for P8, P10, P14, and P18) were identical in three independent isolates, Bam35, Gil01, and the recently sequenced plasmid pGil02 (49).…”

A novel T4SS‐mediated DNA transfer used by pXO16, a conjugative plasmid from Bacillus thuringiensis serovar israelensis

“…Bacillus thuringiensis sv. israelensis strains all display a complex array of plasmids, whose sizes vary from less than 4 to more than 350 kb (Bolotin et al, 2017). Among them, the giant conjugative plasmid pXO16 (350 kb) encodes an unusual conjugation mechanism that possesses interesting features.…”

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

“…With regard to plasmids sequences, the high number of copies of extrachromosomal elements per chromosome can explain the high coverage of the plasmids with sizes of 5.4, 6.8, and 7.6 kb in this study 24,34 . Although some studies reported the ability of Bti strains to harbor up to nine plasmids, the assembly generated here revealed the presence of only six plasmids in the genomes of the isolates, which have also been reported elsewhere 21,24 . The 235 kb plasmids are presented in all sequenced genomes of these Bti strains.…”

“…The assembled chromosomes of T0124, T0131, T0137, and T0139 did not show the presence of the two prophages present in the Bti reference HD-789 21 . Bolotin et al 24 also identified the sequences the two prophages in the Bti AM65-52 strain. Phage sequences, as well as plasmids, are said to be mobile genetic elements which also contribute to genetic diversity among species and are considered important tools in the divergence of strains and closely related bacterial species 31 .…”

“…The average size of the complete genome sequences of Bti is 6.1 Mb, with ~35% GC content of the chromosomal DNA and an average of 6132 coding sequences 19,20 . Genome sequences of seven Bti isolates have been reported so far 19,[21][22][23][24] .…”