HexR Controls Glucose-Responsive Genes and Central Carbon Metabolism in Neisseria meningitidis

Abstract

Neisseria meningitidis, an exclusively human pathogen and the leading cause of bacterial meningitis, must adapt to different host niches during human infection. N. meningitidis can utilize a restricted range of carbon sources, including lactate, glucose, and pyruvate, whose concentrations vary in host niches. Microarray analysis of N. meningitidis grown in a chemically defined medium in the presence or absence of glucose allowed us to identify genes regulated by carbon source availability. Most such genes are implicated in energy metabolism and transport, and some are implicated in virulence. In particular, genes involved in glucose catabolism were upregulated, whereas genes involved in the tricarboxylic acid cycle were downregulated. Several genes encoding surface-exposed proteins, including the MafA adhesins and Neisseria surface protein A, were upregulated in the presence of glucose. Our microarray analysis led to the identification of a glucose-responsive hexR-like transcriptional regulator that controls genes of the central carbon metabolism of N. meningitidis in response to glucose. We characterized the HexR regulon and showed that the hexR gene is accountable for some of the glucose-responsive regulation; in vitro assays with the purified protein showed that HexR binds to the promoters of the central metabolic operons of the bacterium. Based on DNA sequence alignment of the target sites, we propose a 17-bp pseudopalindromic consensus HexR binding motif. Furthermore, N. meningitidis strains lacking hexR expression were deficient in establishing successful bacteremia in an infant rat model of infection, indicating the importance of this regulator for the survival of this pathogen in vivo. IMPORTANCENeisseria meningitidis grows on a limited range of nutrients during infection. We analyzed the gene expression of N. meningitidis in response to glucose, the main energy source available in human blood, and we found that glucose regulates many genes implicated in energy metabolism and nutrient transport, as well as some implicated in virulence. We identified and characterized a transcriptional regulator (HexR) that controls metabolic genes of N. meningitidis in response to glucose. We generated a mutant lacking HexR and found that the mutant was impaired in causing systemic infection in animal models. Since N. meningitidis lacks known bacterial regulators of energy metabolism, our findings suggest that HexR plays a major role in its biology by regulating metabolism in response to environmental signals.

The Hfq regulon of Neisseria meningitidis

“…Crucially, aconitate hydratase B (AcnB) plays a dual role in catalyzing both the reaction 2‐methyl‐ cis ‐aconitate ↔ 2‐methylisocitrate of the methylcitrate cycle and the reaction cis ‐aconitate ↔ isocitrate of the TCA cycle. Proteins involved in the Entner–Doudoroff pathway, the preferred glucose breakdown route in N. meningitidis , show downregulation ( P ≤ 0.05) indicating a shift away from glucose catabolism . The lactate permease LctP that transports extracellular lactate into the cytosol is downregulated, impairing the use of lactate as a carbon source.…”

GlaR (YugA)—a novel RpiR‐family transcription activator of the Leloir pathway of galactose utilization in Lactococcus lactis IL1403

“…In other species distantly related to L. lactis , members of the RpiR family have been found to function as regulators targeting genes involved in the metabolism of diverse carbon sources. Thus, GlvR is a positive regulator of maltose metabolism in B. subtilis (Yamamoto, Serizawa, Thompson, & Sekiguchi, ), HexR, IolR, MurR, and RpiR act as repressors of glucose, inositol, N‐acetylmuramic acid, ribose or central carbon metabolism in several gram‐negative bacteria (Antunes et al., ; Jaeger & Mayer, ; Kohler, Choong, & Rossbach, ; Sørensen & Hove‐Jensen, ), and HexR is a dual‐mode pleiotropic regulator of the central carbohydrate metabolism in proteobacteria (Leyn et al., ). Thus far, none of the RpiR regulators has been implicated in modulating galactose metabolism.…”

Transport and Catabolism of Carbohydrates by Neisseria meningitidis

“…Interestingly, in two γ-proteobacteria, KDPG controls HexR by dissociating and thus inactivating the oligomeric regulator [Daddaoua et al, 2009;Leyn et al, 2011]. However, no such effect of KDPG was observed for N. meningitidis HexR [Antunes et al, 2015].…”

“…The operon also contains the gene for a P-glucose isomerase (NMV_1006), which interconverts glucose-6-P and fructose-6-P. A protein of unknown function is encoded by NMV_1007. The expression of the operon has recently been shown to be controlled by the RpiR-like repressor HexR, the gene of which, NMV_1005 , is also part of this operon [Antunes et al, 2015]. HexR was also reported to control the expression of the adjacent genes NMV_1000 and NMV_1001, which are divergently oriented to the NMV_1002 to NMV_1007…”

“…Meningococci catabolize glucose mainly via the Entner-Doudoroff (ED) pathway (70%) [Baart et al, 2007], and to a minor extent via the pentose phosphate pathway (PPP) [Schoen et al, 2014]. The transcription regulator HexR has recently been shown to control the expression of several genes presumed to encode enzymes of the PPP and the ED pathway [Antunes et al, 2015]. Part of the pyruvate formed via both pathways or from lactate utilization or taken up from the medium is either further metabolized via the tricarboxylic acid cycle or transformed into acetate, which is mostly secreted into the culture medium [Leighton et al, 2001].…”