Metabolic versatility in Haemophilus influenzae: a metabolomic and genomic analysis

Abstract

Haemophilus influenzae is a host adapted human pathogen known to contribute to a variety of acute and chronic diseases of the upper and lower respiratory tract as well as the middle ear. At the sites of infection as well as during growth as a commensal the environmental conditions encountered by H. influenzae will vary significantly, especially in terms of oxygen availability, however, the mechanisms by which the bacteria can adapt their metabolism to cope with such changes have not been studied in detail. Using targeted metabolomics the spectrum of metabolites produced during growth of H. influenzae on glucose in RPMI-based medium was found to change from acetate as the main product during aerobic growth to formate as the major product during anaerobic growth. This change in end-product is likely caused by a switch in the major route of pyruvate degradation. Neither lactate nor succinate or fumarate were major products of H. influenzae growth under any condition studied. Gene expression studies and enzyme activity data revealed that despite an identical genetic makeup and very similar metabolite production profiles, H. influenzae strain Rd appeared to favor glucose degradation via the pentose phosphate pathway, while strain 2019, a clinical isolate, showed higher expression of enzymes involved in glycolysis. Components of the respiratory chain were most highly expressed during microaerophilic and anaerobic growth in both strains, but again clear differences existed in the expression of genes associated e.g., with NADH oxidation, nitrate and nitrite reduction in the two strains studied. Together our results indicate that H. influenzae uses a specialized type of metabolism that could be termed “respiration assisted fermentation” where the respiratory chain likely serves to alleviate redox imbalances caused by incomplete glucose oxidation, and at the same time provides a means of converting a variety of compounds including nitrite and nitrate that arise as part of the host defence mechanisms.

Haemophilus ducreyi Seeks Alternative Carbon Sources and Adapts to Nutrient Stress and Anaerobiosis during Experimental Infection of Human Volunteers

“…H. ducreyi upregulated three genes encoding different components of citrate lyase (citC, citD, and citE) and a gene encoding the formate transporter (focA) in vivo (Table 3). In an alternative pathway, oxaloacetate is converted by malate dehydrogenase to L-malate and L-malate is converted by fumarate hydratase to fumarate, which is metabolized by fumarate reductase to succinate during fumarate respiration (31,32,40). H. ducreyi also upregulated a gene encoding malate dehydrogenase (mdh) ( Another hallmark of the transcriptional response of H. ducreyi to the in vivo environment is the upregulation of genes involved in nutrient transport.…”

A Novel, Molybdenum-Containing Methionine Sulfoxide Reductase Supports Survival of Haemophilus influenzae in an In vivo Model of Infection

“…An emerging aspect of bacterial pathogenesis that is receiving increased attention is the role of metabolic interactions between the host and pathogen (Rhee et al, 2011; Bliska and Van Der Velden, 2012; Grubmüller et al, 2014; Heroven and Dersch, 2014; Hofreuter, 2014; Othman et al, 2014). We have previously analyzed the metabolic properties of Haemophilus influenzae (HI), a host adapted human pathogen of the family Pasteurellaceae that causes or contributes to a diverse array of upper and lower respiratory tract infections (Eldere et al, 2014; Othman et al, 2014).…”

“…We have previously analyzed the metabolic properties of Haemophilus influenzae (HI), a host adapted human pathogen of the family Pasteurellaceae that causes or contributes to a diverse array of upper and lower respiratory tract infections (Eldere et al, 2014; Othman et al, 2014). As is typical for a host-adapted pathogen, about 60–80% of healthy children and a high percentage of adults are asymptomatic carriers of HI (Mukundan et al, 2007).…”

“…Our previous analyses indicated that strain- as well as niche-specific factors including varying oxygen tension influence the metabolite profile of HI strains and also alter gene expression profiles, especially in genes involved in central carbon metabolism and the respiratory chain (Othman et al, 2014). These results suggested that the energy generation processes in HI provide the adaptability required for specific niches, e.g., during infection of the middle-ear or in biofilms, which would be mostly anaerobic, or for colonization of the more aerobic environment of the nasopharynx and respiratory tract, while specific, strain related adaptations may confer the ability to cause disease in these particular body niches.…”

Incorporating the airway microbiome into asthma phenotyping: Moving toward personalized medicine for noneosinophilic asthma

“…These include reactive oxygen and nitrogen species produced by neutrophils and other cell types that can be converted by members of the Gammaproteobacteria to support their anaerobic respiration in inflamed obstructed airways. 8 This reflects the versatility of microbes to adapt and even thrive under a variety of conditions, invoking mechanisms like those demonstrated in Gammaproteobacteria, such as Pseudomonas, Moraxella , 9 and Haemophilus 10 species.…”