A sulphite respiration system in the chemoheterotrophic human pathogen Campylobacter jejuni

Abstract

The ability to use sulphite as a respiratory electron donor is usually associated with free-living chemolithotrophic sulphur-oxidizing bacteria. However, this paper shows that the chemoheterotrophic human pathogen Campylobacter jejuni has the ability to respire sulphite, with oxygen uptake rates of 23±8 and 28±15 nmol O2 min−1 (mg cell protein)−1 after the addition of 0·5 mM sodium sulphite or metabisulphite, respectively, to intact cells. The C. jejuni NCTC 11168 Cj0004c and Cj0005c genes encode a monohaem cytochrome c and molybdopterin oxidoreductase, respectively, homologous to the sulphite : cytochrome c oxidoreductase (SOR) of Starkeya novella. Western blots of C. jejuni periplasm probed with a SorA antibody demonstrated cross-reaction of a 45 kDa band, consistent with the size of Cj0005. The Cj0004c gene was inactivated by insertion of a kanamycin-resistance cassette. The resulting mutant showed wild-type rates of formate-dependent respiration but was unable to respire with sulphite or metabisulphite as electron donors. 2-Heptyl-4-hydroxyquinoline-N-oxide (HQNO), a cytochrome bc 1 complex inhibitor, did not affect sulphite respiration at concentrations up to 25 μM, whereas formate respiration (which occurs partly via a bc 1 dependent route) was inhibited 50 %, thus suggesting that electrons from sulphite enter the respiratory chain after the bc 1 complex at the level of cytochrome c. Periplasmic extracts of wild-type C. jejuni 11168 showed a symmetrical absorption peak at 552 nm after the addition of sulphite, demonstrating the reduction of cytochrome c. No cytochrome c reduction was observed after addition of sulphite to periplasmic extracts of the Cj0004c mutant. A fractionation study confirmed that the majority of the SOR activity is located in the periplasm in C. jejuni, and this activity was partially purified by ion-exchange chromatography. The presence of a sulphite respiration system in C. jejuni is another example of the surprising diversity of the electron-transport chain in this small-genome pathogen. Sulphite respiration may be of importance for survival in environmental microaerobic niches and some foods, and may also provide a detoxification mechanism for this normally growth-inhibitory compound.

Energy Taxis Drives Campylobacter jejuni toward the Most Favorable Conditions for Growth

“…However, this taxis navigation is most likely not mediated through transmembrane MCP-like proteins in a classical and metabolism-independent chemotaxis response, since the MCP-like proteins of this study did not mediate a detectable chemotaxis response. C. jejuni solely employs oxidative phosphorylation to generate energy (46), and this organism carries a complex and highly branched electron transport system that allows the use of a wide variety of both electron donors and acceptors (36,40). Interestingly, we observed that the attractants of C. jejuni are all electron donors, electron acceptors, or carbon sources of this bacterium, which indicates that energy taxis could be the primary driving force in environmental navigation.…”

“…Interestingly, we observed that substances promoting attraction of C. jejuni NCTC11168 are all known to support the growth of C. jejuni and can be categorized as (i) metabolic substrates, including ␣-ketoglutamate, L-aspartate, L-aspargine, L-cysteine, L-glutamate, pyvuvate, and L-serine (17,34,45,48); (ii) electron donors, including formate, L-malate, Dlactate, and succinate; and (iii) electron acceptors, including fumarate, DMSO, nitrite, nitrate, and hydrogen peroxide (36,47). We observed a correlation between an attractant's potency and its efficiency as an energy source, since the preferred growth substrates L-serine and pyruvate (45) were the strongest attractants under microaerophilic conditions.…”

“…Oxygen is the preferred terminal electron acceptor for C. jejuni under microaerophilic conditions (41,47), and a considerable reduction of the electron flow can therefore be obtained by blocking central enzymes of the oxygen-linked respiration. The tactic assay was consequently carried out in the presence of 37 M HQNO or 500 M sodium azide that are inhibitors of the cytochrome bc 1 complex and the primary terminal cytochrome c oxidase, respectively (25,36,43). As illustrated in Fig.…”

Functional analysis of a Campylobacter jejuni alkaline phosphatase secreted via the Tat export machinery

“…A 10 ml C. jejuni culture grown with 0.08 mM P i was subjected to cellular fractionation as described by Myers & Kelly (2005).…”

Inactivation of the LysR regulator Cj1000 of Campylobacter jejuni affects host colonization and respiration

“…jejuni is able to adapt to changes in environmental oxygen levels due to a complex branched electron transport system. Specifically, C. jejuni is capable of utilizing various organic or inorganic electron donors (such as formate, hydrogen, lactate, sulfite) (Myers & Kelly, 2005;Thomas et al, 2011) as well as electron acceptors such as fumarate, Trimethylamine N-oxide, DMSO, nitrite and nitrate. Under microaerobic conditions, oxygen is reduced by either a low-O 2 -affinity CioAB oxidase or by a cytochrome cb9 oxidase (Jackson et al, 2007).…”