Modular Genetic Architecture of the Toxigenic Plasmid pIS56-63 Harboring cry1Ab21 in Bacillus thuringiensis subsp. thuringiensis strain IS5056 

Emilia Murawska, Krzysztof Fiedoruk, Izabela Swiecicka
Pol J Microbiol
2014; 63 (2):
ICID: 1115549
Article type: Original article
IC™ Value: 10.00
Abstract provided by Publisher
Bacillus thuringiesis subsp.thuringinsis IS5056, a strain highly toxic to Trichoplusia ni larvae, produces the newly described Cry1Ab21 delta-endotoxin encoded by a gene located in the 63.8 kb plasmid. In this report we present structure and resemblance of this plasmid to other B. thuringiensis large toxienic plasmids.with particar interest focused on its modular architecture. The 61 open reading frames (ORFs) of the plasmid are contained in four functional modules: (i) M1-mic, the mobile insertion cassette harboring cry1Ab21; (ii) M2-tra, a putative conjugative element; (iii) M3-reg, regulation sequence, and (iv) M4-rep, the ori44 replicon. These modules display similarity to corresponding sequences in distinct B. thuringiensis plasmids, but in general, not to plamid of other Bacillus cereus sensu lato. The nucleotide sequence and organiazation of genes in pIS56-63 were highly similar (80-100%) to those in pHT73 of B. thuringiensis HT73, and in p03 of B. thuringiensis HD771particularly within the M3-reg and M4-rep modules, and slightly less in M2-tra, the letter of which is composed of two segments exhibiting homology to seqences in pBMB28, pAH187_45, pCT83, and pIS56-85 or to pCT72, pBMB67, p04, and pIS56-68. The tetrapartite of the toxigenic pIS56-63 plasmid strongly suggests that its hybrid nature is a result of recombination of various genetic elements originating from different extrachromosomal and chromosomal sources in B. thuringiensis. The presence of cry1Ab21 in the mobile cassette suggests that its occurrence on pIS56-63 resulted from recombination and transposition events during the evolution of the plasmid. 

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