SRA

The formation of endospores has always been considered as the unique mode of survival and transmission of sporulating Firmicutes due to the exceptional resistance and persistence of this bacterial cell form. In this study, we investigated the behavior of a bacterial population in the late stages of an infection as well as the characteristics of the Spo- bacterial form in the B. thuringiensis/Galleria mellonella infection model. Using fluorescent reporters coupled to flow cytometry as well as molecular markers, we demonstrated that the Spo- cells compose the majority of the population two weeks post-infection (pi) and that these bacteria present vitality signs. However, a protein synthesis and a growth recovery assay indicated that they are in a metabolically slowed-down state. Interestingly, they were found to be extremely resistant to the cadaver environment which proved deadly for in-vitro grown vegetative cells and, more strikingly, did not support the germination of spores. A transcriptomic analysis of this subpopulation at 7 days pi revealed a signature profile of this state. Analysis of the expression profile of individual genes at the cell level suggests that iron homeostasis is important at all stages of the infection, whereas the oxidative stress response seems of particular importance as the survival time increases. Altogether, these data indicate that non-sporulated bacteria engage in a profound adaptation process that leads to their persistence in the host cadaver. Overall design: RNA-seq data for 7 days post-infection (dpi) Bacillus thuringiensis cells extracted from Galleria mellonella cadavers (3 samples) versus 30°C LB in vitro-grown Bacillus thuringiensis cells in exponential (3 samples) and early stationnary growth-phase (3 samples)