Abstract
Dam, the most described bacterial DNA-methyltransferase, is widespread in gamma-proteobacteria. Dam DNA methylation can play a role in various genes expression and is involved in pathogenicity of several bacterial species. The purpose of this study was to determine the role played by the dam ortholog identified in the entomopathogenic bacterium Photorhabdus luminescens. Complementation assays of an Escherichia coli dam mutant showed the restoration of the DNA methylation state of the parental strain. Overexpression of dam in P. luminescens did not impair growth ability in vitro. In contrast, compared to a control strain harboring an empty plasmid, a significant decrease in motility was observed in the dam-overexpressing strain. A transcriptome analysis revealed the differential expression of 208 genes between the two strains. In particular, the downregulation of flagellar genes was observed in the dam-overexpressing strain. In the closely related bacterium Xenorhabdus nematophila, dam overexpression also impaired motility. In addition, the dam-overexpressing P. luminescens strain showed a delayed virulence compared to that of the control strain after injection in larvae of the lepidopteran Spodoptera littoralis. These results reveal that Dam plays a major role during P. luminescens insect infection.
Highlights
Enterobacteria of the genus Photorhabdus are highly pathogenic to insects and are symbiotically associated to nematodes of the family Heterorhabditidae
The DNA extracted from the E. coli dam mutant harboring the control empty plasmid was digested by MboI, but not by DpnI, confirming that the GATC sites are not methylated in this mutant strain
The DNA extracted from the E. coli dam mutant harboring the pBB-Dam was digested by DpnI, but not by MboI, revealing a methylation on GATC sites
Summary
During the final stages of development, the bacteria and the nematode reassociate and subsequently leave the insect carcass in search of a new insect host (Nielsen-LeRoux et al, 2012). As described for many other microbial pathogens, which constantly alternate between their host and the compartment they disperse in Avery (2006), Photorhabdus displays phenotypic heterogeneity (Boemare and Akhurst, 1988; Somvanshi et al, 2012).
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