Impact of tectiviral lysogeny on Bacillus thuringiensis life traits

Bacillus thuringiensis is an entomopathogenic bacterium that has been used as an efficient ecofriendly biopesticide over the last 70 years. Despite the fact that this bacterium is usually described as an insect pathogen, its life cycle in the environment is still largely unknown and the potential contribution of bacteriophages (phages) to the adaptation of this bacterium into different environmental niches still poorly understood. B. thuringiensis belongs to the Bacillus cereus group of bacteria, which has been lately associated with many species-specific temperate or virulent phages. Temperate (lysogenic) phages are able to establish a long-term relationship with their host, accounting for a significant genetic variability of their host and providing, in some cases, novel properties, such as virulence traits or increased survival/ecological fitness to the bacterial lysogens. Particularly, tectiviruses in the B. cereus group are, so far, the only phages capable to reside as prophages that do not integrate into the host genome and remain as autonomous linear plasmids inside the cell during their lysogenic cycle. In this context, the question of whether or not temperate tectiviruses influence some life traits in B. thuringiensis was addressed in this work. For this purpose, the kinetics of growth, metabolic profiles, antibiotic susceptibility, biofilm formation, swarming motility, and sporulation rates were compared between a plasmid-cured B. thuringiensis serovar israelensis strain (non-lysogenic strain) and two isogenic lysogens, derived from the same strain, harboring either the tectiviruses GIL01 or GIL16. It was found that GIL01 and GIL16 lysogeny had a significant impact on the bacterial growth, sporulation rate, biofilm formation, and swarming motility of B. thuringiensis, all of which are traits involved in the survival and colonization of this bacterium in different environmental habitats. These findings provide evidence that tectiviruses have a putative role in the B. thuringiensis life cycle as adapters of life traits with ecological advantages