Abstract
BackgroundAnaerobic ammonium oxidizing (anammox) bacteria may contribute up to 50% to the global nitrogen production, and are, thus, key players of the global nitrogen cycle. The molecular mechanism of anammox was recently elucidated and is suggested to proceed through a branched respiratory chain. This chain involves an exceptionally high number of c-type cytochrome proteins which are localized within the anammoxosome, a unique subcellular organelle. During transport into the organelle the c-type cytochrome apoproteins need to be post-translationally processed so that heme groups become covalently attached to them, resulting in mature c-type cytochrome proteins.ResultsIn this study, a comparative genome analysis was performed to identify the cytochrome c maturation system employed by anammox bacteria. Our results show that all available anammox genome assemblies contain a complete type II cytochrome c maturation system.ConclusionsOur working model suggests that this machinery is localized at the anammoxosome membrane which is assumed to be the locus of anammox catabolism. These findings will stimulate further studies in dissecting the molecular and cellular basis of cytochrome c biogenesis in anammox bacteria.
Highlights
Anaerobic ammonium oxidizing bacteria may contribute up to 50% to the global nitrogen production, and are, key players of the global nitrogen cycle
A dedicated membrane-anchored thiol-disulfide oxidoreductase (CcsX) reduces the apocytochrome c cysteines while reducing equivalents are transferred from a nonspecific cytoplasmic thioredoxin to the thiol-disulfide membrane transporter (DsbD or CcdA) [18]
In all four anammox species we studied, DsbD, a thioldisulfide membrane transporter involved in the aforementioned pathway, is annotated successfully and with high confidence by a similar comparative methodology adopted for canonical motif as known from the literature (CcsA) and CcsB (Table 2 and Additional file 6)
Summary
Anaerobic ammonium oxidizing (anammox) bacteria may contribute up to 50% to the global nitrogen production, and are, key players of the global nitrogen cycle. The molecular mechanism of anammox was recently elucidated and is suggested to proceed through a branched respiratory chain. This chain involves an exceptionally high number of c-type cytochrome proteins which are localized within the anammoxosome, a unique subcellular organelle. One of the most recent additions to the microbial nitrogen cycle is the anaerobic oxidation of ammonium (anammox), which utilizes nitrite as the electron acceptor and forms dinitrogen gas under anaerobic conditions. Anammox bacteria possess intracellular membrane systems, leading to a remarkable cell compartmentalization [1]. Three distinct cytochrome c maturation pathways (Systems I, II and III) have been described, each comprising system-specific assembly protein complexes; these biogenesis systems occur in a wide variety of organisms with a complex and unpredictable phylogenetic distribution [9]
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