Sialic acid mediated transcriptional modulation of a highly conserved sialometabolism gene cluster in Haemophilus influenzae and its effect on virulence

Abstract

BackgroundSialic acid has been shown to be a major virulence determinant in the pathogenesis of otitis media caused by the bacterium Haemophilus influenzae. This study aimed to characterise the expression of genes required for the metabolism of sialic acid and to investigate the role of these genes in virulence.ResultsUsing qRT-PCR, we observed decreased transcriptional activity of genes within a cluster that are required for uptake and catabolism of 5-acetyl neuraminic acid (Neu5Ac), when bacteria were cultured in the presence of the sugar. We show that these uptake and catabolic genes, including a sialic acid regulatory gene (siaR), are highly conserved in the H. influenzae natural population. Mutant strains were constructed for seven of the nine genes and their influence upon LPS sialylation and resistance of the bacteria to the killing effect of normal human serum were assessed. Mutations in the Neu5Ac uptake (TRAP transporter) genes decreased virulence in the chinchilla model of otitis media, but the attenuation was strain dependent. In contrast, mutations in catabolism genes and genes regulating sialic acid metabolism (siaR and crp) did not attenuate virulence.ConclusionThe commensal and pathogenic behaviour of H. influenzae involves LPS sialylation that can be influenced by a complex regulatory interplay of sialometabolism genes.

Degradation, Foraging, and Depletion of Mucus Sialoglycans by the Vagina-adapted Actinobacterium Gardnerella vaginalis

“…The machinery for bacterial sialic acid catabolism has been described in several other systems, mostly in aerobic Gramnegative Proteobacteria (72)(73)(74)(75)(76)(77). Sialic acid catabolism has also been recently demonstrated to support growth of the Grampositive bacterium Group B Streptococcus in a vaginal model of infection (78).…”

Gene Content and Diversity of the Loci Encoding Biosynthesis of Capsular Polysaccharides of the 15 Serovar Reference Strains of Haemophilus parasuis

“…Several polysaccharide modifications can be found in the structures that aid in this role, including sialyl groups and phosphorylcholine (25,(76)(77)(78). The presence of sialyl groups in the newly published structures may be an important factor for virulence of this bacterium, as has been suggested for H. parasuis and shown in H. influenzae (25,76,77). Homologues of lsgB and neuA have been predicted for the capsule loci of serovars 5 and 15, which would allow the modification and transfer of Neu5 in the capsule structures.…”

ArcA-Regulated Glycosyltransferase Lic2B Promotes Complement Evasion and Pathogenesis of Nontypeable Haemophilus influenzae

“…The structures that are regulated and their control mechanisms vary extensively between species (22). In H. influenzae, regulators have been identified for LOS sialic acid modification, which is controlled by the cyclic AMP (cAMP)-responsive cAMP receptor protein (CRP) in conjunction with a response to substrate availability by SiaR (34,35,36). Several studies have revealed regulation of LOS or LPS outer core glycosyltransferase activity in other species (27,69,70); however, connections between specific signaling proteins and the regulated glycosyltransferase genes are not well understood.…”