Whole Genome DNA Methylation (Methylome) Analysis and Role of Dam DNA Methyltransferase in the life‐cycle of an Entomopathogenic Bacterium
Résumé
Background: DNA methylation is an epigenetic mechanism involved in the pathogenicity of several
major bacterial pathogens. It can decrease the affinity of some transcriptional regulators to their
binding site, leading to sub‐populations expressing or not various genes, depending on the DNA
methylation state. Dam DNA methyltransferase is widespread in Gammaproteobacteria and
methylates the adenine of GATC sites.
Objectives: The role of Dam was investigated in Photorhabdus luminescens during its symbiosis with
a soil nematode and during its pathogenic stage in insects.
Methods: SMRT sequencing (PacBio), which allows identification of the DNA methylation of the
whole genome (methylome), RNAseq and phenotypic analysis were performed in a P. luminescens
strain overexpressing Dam.
Results: Dam overexpression caused a decrease in motility whereas it increased biofilm formation.
While symbiosis ability of the Dam overexpressing strain was not significantly different from that of a
control strain, the nemato‐bacterial complex displayed an impaired pathogenicity in insect, as also
observed after direct insect injection of the bacteria alone. Transcriptomic analysis revealed that the
observed phenotypes were related to differences at the transcriptional level. More than 99% of the
GATC sites of the genome were found methylated and DNA methylation levels did not change over
growth kinetics. However, the Dam‐overexpressing strain displayed more methylated GATC sites
than the control and most of these sites were located in promoter regions. These sites may be
involved in the observed differences in phenotypes and gene expression and provide
Domaines
Biodiversité et Ecologie
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