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

Abstract

Signaling mechanisms used by Haemophilus influenzae to adapt to conditions it encounters during stages of infection and pathogenesis are not well understood. The ArcAB two-component signal transduction system controls gene expression in response to respiratory conditions of growth and contributes to resistance to bactericidal effects of serum and to bloodstream infection by H. influenzae. We show that ArcA of nontypeable H. influenzae (NTHI) activates expression of a glycosyltransferase gene, lic2B. Structural comparison of the lipooligosaccharide (LOS) of a lic2B mutant to that of the wild-type strain NT127 revealed that lic2B is required for addition of a galactose residue to the LOS outer core. The lic2B gene was crucial for optimal survival of NTHI in a mouse model of bacteremia and for evasion of serum complement. The results demonstrate that ArcA, which controls cellular metabolism in response to environmental reduction and oxidation (redox) conditions, also coordinately controls genes that are critical for immune evasion, providing evidence that NTHI integrates redox signals to regulate specific countermeasures against host defense.

A Novel Zinc Binding System, ZevAB, Is Critical for Survival of Nontypeable Haemophilus influenzae in a Murine Lung Infection Model

“…However, an fnr mutant and a wild-type strain were equally sensitive to a range of toxic zinc concentrations during anaerobic growth, and defects in the growth of a zevB mutant in zinc-limiting medium were not significantly different under aerobic and anaerobic conditions (C. V. Rosadini, unpublished results). Ultimately, regulation of zevAB by FNR may serve as an important strategy for increasing this system's expression exclusively in sites of infection where the bacterium encounters zinc limitation, as is likely to occur at airway mucosal surfaces, and is consistent with other reports indicating that oxygen is an important signal for modulation of virulence factor expression in H. influenzae (69,71,72).…”

Outer Membrane Protein P5 Is Required for Resistance of Nontypeable Haemophilus influenzae to Both the Classical and Alternative Complement Pathways

“…NZ_ACSM00000000), a capsule-deficient serotype d derivative (47), and nontypeable H. influenzae strain NT127 (GenBank accession no. NZ_ACSL01000014.1), originally isolated from the blood of a child with meningitis (27,48,49), were grown in brain heart infusion (BHI) broth supplemented with 10 g/ml hemin and 10 g/ml NAD (sBHI) or on sBHI agar plates at 35°C. Development of competence for transformation of H. influenzae was accomplished as previously described (50).…”

“…Lipooligosaccharide (LOS) glycans are essential for mediating this function, as mutations that truncate the LOS lead to severe defects in complement resistance and virulence in animal models (27)(28)(29)(30). Surface proteins have also been shown to be involved, including P6, via an unknown mechanism, and proteins E and F, which were shown to bind the host complement regulator vitronectin (31,32).…”

Characterization of a Ferrous Iron-Responsive Two-Component System in Nontypeable Haemophilus influenzae

“…While over 31 TCST systems have been identified in Escherichia coli and 13 in Streptococcus pneumoniae (83,90), only four have been identified in H. influenzae genome sequences (27,39). The identified NTHI TCST systems are orthologs to ArcAB (senses redox conditions) (22,85,86), NarPQ (senses nitrate-nitrite levels) (76), PhoBR (senses phosphate levels), and QseBC (senses quorum-sensing signals). To date, there are no published reports on the role of PhoBR and QseBC in H. influenzae.…”