On sialic acid transport and utilization by Vibrio cholerae

The scavenging of host-derived sialic acid is important for a number of human pathogens during colonization of mammalian mucous membranes (Severi et al., 2007). This has been demonstrated for Vibrio cholerae (Almagro-Moreno & Boyd, 2009), where the genes for catabolism are encoded on vibrio pathogenicity island 2 (VPI-2) (Jermyn & Boyd, 2002). This genomic element is found only in pathogenic strains of V. cholerae and its presence correlates with the ability of vibrio species to utilize sialic acid (Almagro-Moreno & Boyd, 2009). As well as containing the catabolic genes (the nan cluster), VPI-2 also contains genes for a tripartite ATP-independent periplasmic (TRAP) transporter, siaPQM (VC1777-9), orthologous to the well-characterized sialic acid TRAP transporter from Haemophilus influenzae (Severi et al., 2005; Allen et al., 2005; Müller et al., 2006; Johnston et al., 2008; Mulligan et al., 2009). Indeed we have demonstrated that SiaP from V. cholerae (VC1779) is a high-affinity sialicacid-binding protein (Mulligan et al., 2009) and have functionally reconstituted the whole transporter which is active for sialic acid uptake into proteoliposomes (unpublished data).