Tectiviruses preying on the Bacillus cereus group
(2015) 21st Evergreen International Phage Biology Meeting — Location: Evergreen, United States of America (2.August.2015)
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- Abstract
- Tectiviridae is a rare phage family comprising non-enveloped tail-less phages, with a linear dsDNA located within a lipid-containing membrane, covered by a rigid icosahedral protein capsid. GIL01/Bam35, GIL16, AP50 and Wip1 are representative tectiviruses preying on the Bacillus cereus group. This bacterial group includes several species displaying distinct virulence spectra as diverse as mammal anthrax caused by Bacillus anthracis, food toxi-infection due to B. cereus or the entomopathogen Bacillus thuringiensis. Many of the phenotypical characteristics displayed by the members of this bacterial group are associated with Mobile Genetic Elements, particularly plasmids. Since tectiviruses are, so far, the only phages infecting the B. cereus group able to behave as linear plasmids during their lysogenic cycle, it is important to assess the potential contribution of this type of phages to the genetic diversity of their hosts and to understand the selective pressures experienced by the bacteria when facing these phages. Therefore, this work addresses the potential contribution of tectiviruses to the bacterial genetic pool and to the emergence of different life traits in their host. To this end, the prevalence and genetic diversity of tectiviruses in a worldwide collection of B. cereus sensu lato strains was evaluated to define to what extent novel tectiviruses can contribute to the bacterial mobilome. The screening and propagation tests indicated that tectiviruses occurred in less than 3% of the bacterial isolates. Notwithstanding this limited distribution, several novel tectiviruses were found. Partial DNA sequencing of variable regions indicated that a greater diversity than previously observed exists within the Tectiviridae, with some tectiviruses displaying ORFans genes in regulatory regions, a fact that suggests that the acquisition of those ORFans may provide a source of genetic diversity (Jalasvuori et al. 2013). Analysis of the tectiviruses host range showed that no simple relationship can be established between the infection patterns of these phages and their diversity. However, the data revealed that tectiviruses in the B. cereus group can be clustered into two major groups: the ones infecting B. anthracis and those isolated from other B. cereus group members. The second part of this work addresses the question of whether or not temperate tectiviruses influence some life traits in B. thuringiensis. For this purpose, the kinetics of growth, metabolic profiles, antibiotics susceptibilities, biofilm formation, swarming motility, and sporulation rates were compared between a tectivirus-cured B. thuringiensis strain (non-lysogenic strain) and two isogenic lysogens, derived from the same strain, harboring either the tectiviruses GIL01 or GIL16. It was found that tectiviral lysogeny had a significant impact on several B. thuringiensis life traits. These findings provide evidence that not only tectiviruses are more diverse than previously thought, but they might also have ecological roles in the already complex life cycle of B. thuringiensis.
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Gillis, A., & Mahillon, J. (2015). Tectiviruses preying on the Bacillus cereus group. 21st Evergreen International Phage Biology Meeting, Evergreen, United States of America. https://hdl.handle.net/2078.5/120433