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

SARNACKI SH; MAROLDA CL; NOTO LLANA M; GIACOMODONATO MN; VALVANO MA; MC CERQUETTI

JOURNAL OF BACTERIOLOGY

ASM Press

Lugar: Washington D.C.; Año: 2009 vol. 191 p. 6694 - 6700

0021-9193

We reported earlier that a Salmonella enterica serovarEnteritidis dam mutant expressing a truncated Dam fails to agglutinate in the presence of specific antibodies against O9 polysaccharide. Here we investigate the participation of Dam in the LPS synthesis of Salmonella. LPS O antigen profiles of a dam null mutant (SEDdam) and the parental strain of S. Enteritidis were examined by electrophoresis and silver staining. Compared to the parental strain, SEDdam produced LPS with shorter O antigen polysaccharide chains. Since Wzz is responsible for the chain length distribution of the O antigen we investigated whether Dam methylation is involved in regulating wzz expression. Densitometry analysis showed that the relative amount of Wzz produced by SEDdam is three-fold lower than that of the parental strain. Concomitantly, the activity of wzz promoter in SEDdam was reduced nearly 50 % in logarithmic phase and 25 % in stationary phase. These results were further confirmed by RT-PCR showing that wzz gene expression was three-fold lower in the dam mutant compared with the parental strain. Our results demonstrate that wzz gene expression is downregulated in dam mutant, indicating that Dam methylation activates its expression. This work uncovers wzz as new target regulated by Dam methylation, demonstrating that DNA methylation not only affects the production of bacterial surface proteins but also the production of surface polysaccharides.