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O-antigen modal chain length in Shigella flexneri 2a is growth-regulated through RfaH-mediated transcriptional control of the wzy gene

Javier A. Carter^1,

Carlos J. Blondel^1,

¹ Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, PO Box 174 Correo 22, Santiago, Chile
² Infectious Diseases Research Group, Siebens-Drake Research Institute, Department of Microbiology and Immunology, The University of Western Ontario, London, Ontario N6A 5C1, Canada

Correspondence
Inés Contreras
icontrer{at}uchile.cl

Shigella flexneri 2a 2457T produces lipopolysaccharide (LPS) with two O-antigen (OAg) chain lengths: a short (S-OAg) controlled by WzzB and a very long (VL-OAg) determined by Wzz_pHS-2. This study demonstrates that the synthesis and length distribution of the S. flexneri OAg are under growth-phase-dependent regulation. Quantitative electrophoretic analysis showed that the VL-OAg increased during growth while the S-OAg distribution remained constant. Increased production of VL-OAg correlated with the growth-phase-regulated expression of the transcription elongation factor RfaH, and was severely impaired in a rfaH mutant, which synthesized only low-molecular-mass OAg molecules and a small amount of S-OAg. Real-time RT-PCR revealed a drastic reduction of wzy polymerase gene expression in the rfaH mutant. Complementation of this mutant with the wzy gene cloned into a high-copy-number plasmid restored the bimodal OAg distribution, suggesting that cellular levels of Wzy influence not only OAg polymerization but also chain-length distribution. Accordingly, overexpression of wzy in the wild-type strain resulted in production of a large amount of high-molecular-mass OAg molecules. An increased dosage of either wzzB or wzz_pHS-2 also altered OAg chain-length distribution. Transcription of wzzB and wzz_pHS-2 genes was regulated during bacterial growth but in an RfaH-independent manner. Overall, these findings indicate that expression of the wzy, wzzB and wzz_pHS-2 genes is finely regulated to determine an appropriate balance between the proteins responsible for polymerization and chain-length distribution of S. flexneri OAg.

These authors contributed equally to this work.

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