Metabolic potential of the imperfect denitrifier Candidatus Desulfobacillus denitrificans in an anammox bioreactor

Abstract

The imperfect denitrifier, Candidatus (Ca.) Desulfobacillus denitrificans, which lacks nitric oxide (NO) reductase, frequently appears in anammox bioreactors depending on the operating conditions. We used genomic and metatranscriptomic analyses to evaluate the metabolic potential of Ca. D. denitrificans and deduce its functional relationships to anammox bacteria (i.e., Ca. Brocadia pituitae). Although Ca. D. denitrificans is hypothesized to supply NO to Ca. B. pituitae as a byproduct of imperfect denitrification, this microbe also possesses hydroxylamine oxidoreductase, which catalyzes the oxidation of hydroxylamine to NO and potentially the reverse reaction. Ca. D. denitrificans can use a range of electron donors for denitrification, including aromatic compounds, glucose, sulfur compounds, and hydrogen, but metatranscriptomic analysis suggested that the major electron donors are aromatic compounds, which inhibit anammox activity. The interrelationship between Ca. D. denitirificans and Ca. B. pituitae via the metabolism of aromatic compounds may govern the population balance of both species. Ca. D. denitrificans also has the potential to fix CO2 via an irregular Calvin cycle and couple denitrification to the oxidation of hydrogen and sulfur compounds under chemolithoautotrophic conditions. This metabolic versatility, which suggests a mixotrophic lifestyle, would facilitate the growth of Ca. D. denitrificans in the anammox bioreactor.

Sulfuricystis multivorans gen. nov., sp. nov. and Sulfuricystis thermophila sp. nov., facultatively autotropic sulfur-oxidizing bacteria isolated from a hot spring, and emended description of the genus Rugosibacter

“…The genus Rugosibacter was not taken into consideration in the proposal of Sterolibacteriaceae, and it is still placed in the family Rhodocyclaceae as noted in the original description. The close relatedness between Rugosibacter and genera of Sterolibacteriaceae has also been indicated by a phylogenetic analysis of concatenated ribosomal proteins (Okubo & Takami, 2021).…”

A comprehensive catalog encompassing 1376 species-level genomes reveals the core community and functional diversity of anammox microbiota

“…Previous studies have elucidated the crucial functions of the phylum Chloro exota (e.g., the core genera UBA12294 and OLB14) in anammox microbiota [71][72][73]. However, previous studies underestimated the signi cance of several core taxa associated with the phylum Proteobacteria [20,74]. Here, we conducted a comparative genomic analysis to reveal the global pro les of the strict core genera Desulfobacillus and Zeimonas (Additional le 2: Tables S24-S25).…”

“…S18-S20). Importantly, six predominant species within the genus Desulfobacillus carried the hydroxylamine oxidoreductase gene (hao), whereas most lowabundance and reference species had lost this crucial gene responsible for NO and/or hydroxylamine production [74]. The absence of the nitric oxide reductase gene (norB) indicated that the genus Desulfobacillus may serve as a potential N 2 O sink in anammox microbiota.…”

“…5e). The presence of these differentiated species with functional plasticity likely enhanced the mixotrophic nutrition modes among anammox microbiota [74]. In addition, the signaling molecules AI-2 and AHLs could regulate the metabolic activities of the two genera due to the availability of receptor proteins (Additional le 1: Fig.…”