title: Inactivation of deoxyadenosine methyltransferase (dam) attenuates Haemophilus influenzae virulence.
abstract: Mutants in deoxyadenosine methyltransferase (dam) from many Gram-negative pathogens suggest multiple roles for Dam methylase: directing post-replicative DNA mismatch repair to the correct strand, guiding the temporal control of DNA replication and regulating the expression of multiple genes (including virulence factors) by differential promoter methylation. Dam methylase (HI0209) in strain Rd KW20 was inactivated in Haemophilus influenzae strains Rd KW20, Strain 12 and INT-1; restriction with Dam methylation-sensitive enzymes DpnI and DpnII confirmed the absence of Dam methylation, which was restored by complementation with a single copy of dam ectopically expressed in cis. Despite the lack of increased mutation frequency, the dam mutants had a 2-aminopurine-susceptible phenotype that could be suppressed by secondary mutations in mutS, suggesting a role for Dam in H. influenzae DNA mismatch repair. Invasion of human brain microvascular endothelial cells (HBMECs) and human respiratory epithelial cells (NCI-H292) by the dam mutants was significantly attenuated in all strains, suggesting the absence of a Dam-regulated event necessary for uptake or invasion of host cells. Intracellular replication was inhibited only in the Strain 12 dam mutant, whereas in the infant rat model of infection, the INT-1 dam mutant was less virulent. Dam activity appears to be necessary for both in vitro and in vivo virulence in a strain-dependent fashion and may function as a regulator of gene expression including virulence factors.
authors.affiliation: Seattle Biomedical Research Institute, 307 Westlake, Suite 500, Seattle, WA 98109-5219, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Watson
authors.forename: Justin
authors.initials: J
authors.lastname: Jarisch
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Smith
mesh_terms: D015075:2-Aminopurine / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000502:physiology; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D003593:Cytoplasm / Q000382:microbiology; D004260:DNA Repair; D004269:DNA, Bacterial / Q000302:isolation & purification / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D004195:Disease Models, Animal; D042783:Endothelial Cells / Q000382:microbiology; D004847:Epithelial Cells / Q000382:microbiology; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D006192:Haemophilus Infections / Q000382:microbiology; D006193:Haemophilus influenzae / Q000201:enzymology* / Q000472:pathogenicity*; D006801:Humans; D051719:MutS DNA Mismatch-Binding Protein; D016254:Mutagenesis, Insertional; D051381:Rats; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific) / Q000235:genetics* / Q000378:metabolism*; D014774:Virulence / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D015075:2-Aminopurine; C058693:Dam methyltransferase; D015265:Site-Specific DNA-Methyltransferase (Adenine-Specific); C020102:endodeoxyribonuclease DpnI; D015252:Deoxyribonucleases, Type II Site-Specific; C024405:GATC-specific type II deoxyribonucleases; D000251:Adenosine Triphosphatases; D051719:MutS DNA Mismatch-Binding Protein