Horizontal transfer of large plasmid with type IV secretion system and mosquitocidal genomic island with excision and integration capabilities in Lysinibacillus sphaericus

Abstract

Summary We identified a ~30‐kb genomic island (named GI8) carrying the binary toxin gene operon binA/binB on both the chromosome and large pBsph plasmid in the mosquitocidal Lysinibacillus sphaericus C3‐41 strain. We found that GI8 is related to the occurrence of binA/binB within L. sphaericus and displays excision and integration capability by recognizing the attB region, which consists of a 2‐nt target site (AT) flanked by an 11‐nt imperfect inverted repeat. pBsph and two pBsph‐like plasmids (p2362 and p1593) were found to carry a type IV secretion system (T4SS) and displayed transmissibility within a narrow host range specific to L. sphaericus . GI8 can be co‐transferred with pBsph as a composite element by integration into its attB site, then excised from pBsph and re‐integrated into the chromosomal attB site in the new host. The potential hosts of GI8, regardless of whether they are toxic or non‐toxic to mosquito larvae, share good collinearity at the chromosomal level. Data indicated that the appearance of the mosquitocidal L. sphaericus lineage was driven by horizontal transfer of the T4SS‐type conjugative plasmid and GI8 with excision and specific integration capability.

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