Dam methylation controls O-antigen chain length in Salmonella enterica serovar Enteritidis by regulating the expression of Wzz protein

SARNACKI; MAROLDA; NOTO LLANA; GIACOMODONATO MN; VALVANO; CERQUETTI

JOURNAL OF BACTERIOLOGY

AMER SOC MICROBIOLOGY

Año: 2009 p. 6694 - 6700

0021-9193

We reported previously that a Salmonella enterica serovar Enteritidis dam mutant expressing a truncatedDam protein does not agglutinate in the presence of specific antibodies against O9 polysaccharide. Here weinvestigate the participation of Dam in lipopolysaccharide (LPS) synthesis in Salmonella. The LPS O-antigenprofiles of a dam null mutant (SEdam) and the Salmonella serovar Enteritidis parental strain were examinedby using electrophoresis and silver staining. Compared to the parental strain, SEdam produced LPS withshorter O-antigen polysaccharide chains. Since Wzz is responsible for the chain length distribution of the Oantigen, we investigated whether Dam methylation is involved in regulating wzz expression. Densitometryanalysis showed that the amount of Wzz produced by SEdam is threefold lower than the amount of Wzzproduced by the parental strain. Concomitantly, the activity of the wzz promoter in SEdam was reduced nearly50% in logarithmic phase and 25% in stationary phase. These results were further confirmed by reversetranscription-PCR showing that wzz gene expression was threefold lower in the dam mutant than in theparental strain. Our results demonstrate that wzz gene expression is downregulated in a dam mutant, indicatingthat Dam methylation activates expression of this gene. This work indicates that wzz is a new targetregulated by Dam methylation and demonstrates that DNA methylation not only affects the production ofbacterial surface proteins but also the production of surface polysaccharides.