Conjugation-mediated transfer of pXO16, a large plasmid from Bacillus thuringiensis sv. israelensis, across the Bacillus cereus group and its impact on host phenotype

• Published in: Plasmid 2022-07, Vol.122, p.102639-102639, Article 102639
• Main Authors: Hinnekens, Pauline, Mahillon, Jacques
• Format: Article
• Language: English
• Subjects: Bacillus cereus; Bacillus cereus - genetics; Bacillus thuringiensis - genetics; Conjugation; Conjugation, Genetic; Fitness; Large plasmid; Phenotype; Plasmids - genetics; pXO16
• ISSN: 0147-619X; 1095-9890
• DOI: 10.1016/j.plasmid.2022.102639

pXO16, the 350 kb-conjugative plasmid from Bacillus thuringiensis sv. israelensis promotes its own transfer at high efficiency, triggers the transfer of mobilizable and non-mobilizable plasmids, as well as the transfer of host chromosomal loci. Naturally found in B. thuringiensis sv. israelensis, pXO16 transfers to various strains of Bacillus cereus sensu lato (s.l.) at a wide range of frequencies. Despite this host diversity, a paradox remains between the relatively large host spectrum and the natural occurrence of pXO16, so far restricted to B. thuringiensis sv. israelensis. Proposing first insights exploring this paradox, we investigated the behaviour of pXO16 amongst different members of the B. cereus group. We first looked at the transfer of pXO16 to two new host clusters of B. cereus s.l., Bacillus mycoides and Bacillus anthracis clusters. This examination brought to light the impairment of the characteristic rhizoidal phenotype of B. mycoides in presence of pXO16. We also explored the stability of pXO16 at different temperatures as some B. cereus group members are well-known for their psychro- or thermo-tolerance. This shed light on the thermo-sensitivity of the plasmid. The influence of pXO16 on its host cell growth and on swimming capacity also revealed no or limited impact on its natural host B. thuringiensis sv. israelensis. On the contrary, pXO16 affected more strongly both the growth and swimming capacity of other B. cereus s.l. hosts. This reinforced the running hypothesis of a co-evolution between pXO16 and B. thuringiensis sv. israelensis, enabling the plasmid maintenance without impairing the host strain development. •pXO16, the 350-kb conjugative plasmid from Bacillus thuringiensis sv. israelensis, promotes its own transfer to all members of Bacillus cereus group, including strains pertaining to the Bacillus mycoides and Bacillus anthracis clusters.•pXO16 transfer in B. mycoides results in the impairment of the characteristic rhizoidal phenotype.•The acquisition of pXO16 by members of the B. cereus group affects both their growth and swimming capacity.•Altogether, the collected data revealed a significant impact of pXO16 presence in the different B. cereus s.l. strains, but not in B. thuringiensis sv. israelensis, its original host.