Role of an Inducible Single-Domain Hemoglobin in Mediating Resistance to Nitric Oxide and Nitrosative Stress in Campylobacter jejuni and Campylobacter coli

Abstract

Campylobacter jejuni expresses two hemoglobins, each of which exhibits a heme pocket and structural signatures in common with vertebrate and plant globins. One of these, designated Cgb, is homologous to Vgb from Vitreoscilla stercoraria and does not possess the reductase domain seen in the flavohemoglobins. A Cgb-deficient mutant of C. jejuni was hypersensitive to nitrosating agents (S-nitrosoglutathione [GSNO] or sodium nitroprusside) and a nitric oxide-releasing compound (spermine NONOate). The sensitivity of the Cgb-deficient mutant to methyl viologen, hydrogen peroxide, and organic peroxides, however, was the same as for the wild type. Consistent with the protective role of Cgb against NO-related stress, cgb expression was minimal in standard laboratory media but strongly and specifically induced after exposure to nitrosative stress. In contrast, the expression of Cgb was independent of aeration and the presence of superoxide. In the absence of preinduction by exposure to nitrosative stress, no difference was seen in the degree of respiratory inhibition by NO or the half-life of the NO signal when cells of the wild type and the cgb mutant were compared. However, cells expressing GSNO-upregulated levels of Cgb exhibited robust NO consumption and respiration that was relatively NO insensitive compared to the respiration of the cgb mutant. Based on similar studies in Campylobacter coli, we also propose an identical role for Cgb in this closely related species. We conclude that, unlike the archetypal single-domain globin Vgb, Cgb forms a specific and inducible defense against NO and nitrosating agents.

Contribution of the stereospecific methionine sulphoxide reductases MsrA and MsrB to oxidative and nitrosative stress resistance in the food-borne pathogen Campylobacter jejuni

“…Indeed, H. pylori Msr is upregulated upon addition of peroxynitrite (Alamuri & Maier, 2006), indicating an important role of Met-SO repair when cells experience nitrosative stress. Our results indicate a significant contribution of MsrA and MsrB to nitrosative stress resistance in C. jejuni, in addition to the previously established roles for the globin Cgb (Elvers et al, 2004) and the nitrite reductase NrfA (Pittman et al, 2007).…”

“…Bacteria have evolved a multi-layered defence against these stresses, including superoxide dismutase (Pesci et al, 1994), catalase (Storz & Imlay, 1999;Chelikani et al, 2004), cytochrome c peroxidases (Atack & Kelly, 2007), peroxiredoxins such as alkyl-hydroperoxide reductase and thiol peroxidase Bryk et al, 2000;Wood et al, 2003;Poole, 2005), and bacterial globins (Poole & Hughes, 2000). Inactivation of genes encoding catalase, superoxide dismutase or the peroxiredoxin AhpC in C. jejuni results in an increase in sensitivity to various oxidative stresses (Grant & Park, 1995;Purdy et al, 1999;Baillon et al, 1999), and loss of the globin Cgb or the periplasmic nitrite reductase NrfA results in an increased sensitivity to RNI (Elvers et al, 2004;Pittman et al, 2007). These studies underline the importance to the fitness of C. jejuni of combating both ROS and RNI.…”

Identification of Campylobacter jejuni Genes Contributing to Acid Adaptation by Transcriptional Profiling and Genome-Wide Mutagenesis

“…The cgb gene, encoding a single-domain hemoglobin, was up-regulated at pH 5.5 and in response to acid shock. Cgb is an important player in the nitrosative stress response, scavenging and detoxifying nitric oxide (27). The expression of cgb and other members of the nitrosative stress regulon is controlled by NssR (26).…”

Purification and Spectroscopic Characterization of Ctb, a Group III Truncated Hemoglobin Implicated in Oxygen Metabolism in the Food-Borne Pathogen Campylobacter jejuni

“…confers tolerance to NO (9) and is up-regulated by NO and its congeners by an NO-activated transcriptional regulator (10).…”

“…However, C. jejuni is commonly a gut commensal in many food-producing animals and birds and contamination of meat during processing is an important method of transfer (20). Cgb protects the bacterium from the toxic effects of NO (9), but the group III trHb has no clearly defined function. Its expression is, however, elevated in response to nitrosative stress, a response mediated by the NssR sensor/regulator (10).…”