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5-Aminohydroximoyl-2-hydroxytetrazole (3) was synthesized in a three-step synthesis from inexpensive starting materials. This novel tetrazole derivative contains two energetic moieties: an N-oxide as well as an aminohydroximoyl group. Various energetic nitrogen-rich salts such as hydroxylammonium (4), guanidinium (5), aminoguanidinium (6), ammonium (7), and triaminoguanidinium (8) were synthesized. Moreover, zwitterionic 5-amidrazonyl-tetrazole-2-oxide monohydrate (9) was synthesized. Compounds4,5,8,9, and10were structurally characterized using single-crystal X-ray diffraction. Additionally, all new compounds were characterized using nuclear magnetic resonance (NMR) and vibrational (infrared [IR], Raman) spectroscopy as well as mass spectrometry and elemental analysis. The thermal behavior was studied using differential thermal analysis (DTA) measurements and the sensitivities of the compounds toward shock, friction, and electrostatic discharge were determined. Finally, the enthalpies of formation were calculated (atomization method, CBS-4 M enthalpies) and several detonation/propulsion parameters computed with the EXPLO5 code. [ABSTRACT FROM AUTHOR]

Sodium 5-cyanotetrazolate sesquihydrate (1) is prepared from sodium azide and two equivalents of sodium cyanide under acidic conditions. 1 is then N-oxidized with Oxone to sodium 5-cyanotetrazolate monohydrate (2). Compound 2 is treated with sodium azide and a Lewis acid to form 5-(1H-tetrazolyl)-2-hydroxytetrazole monohydrate (3). Compound 3 can be deprotonated twice by various bases to give ionic derivatives such as the bis(hydroxylammonium) (4), bis(hydrazinium) (6), bis(-guanidinium) (7), bis(aminoguanidinium) (8), bis(ammonium) (9), and diaminouronium (11) salt. In addition, compound 3 can only be deprotonated once, as demonstrated by the hydroxylammonium (4) and triaminoguanidinium (10) salts. Compounds 2-5 and 10-11 are structurally characterized by singlecrystal X-ray diffraction. Additionally, compounds 2-11 are characterized by using NMR and vibrational (IR, Raman) spectroscopy as well as mass spectrometry and elemental analysis. Their thermal behaviors are studied from differential thermal analysis measurements, and the sensitivities of the compounds toward shock, friction, and electrostatic discharge are determined. In addition, the heats of formation are calculated (atomization method, CBS-4M enthalpies), and several detonation/ propulsion parameters are computed with the EXPLO5 code. [ABSTRACT FROM AUTHOR]

Bacterial aerobic ammonium oxidation and anaerobic ammonium oxidation (anammox) are important processes in the global nitrogen cycle. Key enzymes in both processes are the octahaem cytochrome c (OCC) proteins, hydroxylamine oxidoreductase (HAO) of aerobic ammonium-oxidizing bacteria (AOB), which catalyses the oxidation of hydroxylamine to nitrite, and hydrazine oxidoreductase (HZO) of anammox bacteria, which converts hydrazine to N2. While the genomes of AOB encode up to three nearly identical copies of hao operons, genome analysis of Candidatus‘Kuenenia stuttgartiensis’ showed eight highly divergent octahaem protein coding regions as possible candidates for the HZO. Based on their phylogenetic relationship and biochemical characteristics, the sequences of these eight gene products grouped in three clusters. Degenerate primers were designed on the basis of available gene sequences with the aim to detect hao and hzo genes in various ecosystems. The hao primer pairs amplified gene fragments from 738 to 1172 bp and the hzo primer pairs amplified gene fragments from 289 to 876 bp in length, when tested on genomic DNA isolated from a variety of AOB and anammox bacteria. A selection of these primer pairs was also used successfully to amplify and analyse the hao and hzo genes in community DNA isolated from different ecosystems harbouring both AOB and anammox bacteria. We propose that OCC protein-encoding genes are suitable targets for molecular ecological studies on both aerobic and anaerobic ammonium-oxidizing bacteria. [ABSTRACT FROM AUTHOR]

The biogeochemical nitrogen cycle is mediated by many groups of microorganisms that harbour octahaem cytochromes c (OCC). In this study molecular evolutionary analyses and the conservation of predicted functional residues and secondary structure were employed to investigate the descent of OCC proteins related to hydroxylamine oxidoreductase (HAO) and hydrazine oxidoreductase (HZO) from pentahaem cytochrome c nitrite reductase (NrfA). An ctahaem cytochrome c itrite eductase (ONR) was shown to be a possible intermediate in the process. Analysis of genomic neighbourhoods of OCC protein-encoding genes revealed adjacent conserved genes whose products, together with HAO, provide a path of electron transfer to quinone and constitute a functional catabolic module. The latter has evolved more than once under a variety of functional pressures on the catabolic lifestyles of their bacterial hosts. Structurally, the archetypical long helices in the large C-terminal domain of the proteins as well as the distal axial ligands to most haems were highly conserved in NrfA and all descendents. Residues known to be involved in the nitrite reductase activity of NrfA including the ‘CxxCK’ motif at the catalytic haem, the substrate and Ca binding sites, and the nitrite and ammonium channels were conserved in the eight representatives of ONR. In the latter, a unique cysteine has been inserted above the active site. The 64 other OCC proteins differed from ONR by the absence of the ‘CxxCK’ motif, the channel residues and most of the Ca-binding residues and the conserved presence of an ‘Asp–His’ pair inserted above the active site as well as the tyrosine that forms an intersubunit cross-link to the catalytic haem of HAO. Our proposed scenario of evolution of OCC proteins in the HAO family from NrfA is supported by (i) homology based on sequence and structure, (ii) its wide distribution among bacterial taxa, (iii) the dedicated interaction with specific proteins, and it is (iv) congruent with geological history. [ABSTRACT FROM AUTHOR]

The Thiobacilli are an important group of autotrophic bacteria occurring in nature linking the biogeochemical cycles of sulfur and nitrogen. Betaproteobacterial Thiobacilli are very likely candidates for mediating the process of nitrate-dependent anoxic iron sulfide mineral oxidation in freshwater wetlands. A Thiobacillus denitrificans-like bacterium was present in an enrichment on thiosulfate and nitrate, derived from an iron-sulfide- and nitrate-rich freshwater environment. Preliminary FISH analysis showed that the 16S rRNA gene-based bacterial probe mix showed great variation in intensity under different culture conditions. Furthermore, the widely applied 23S rRNA gene-based probe set BET42a/GAM42a incorrectly identified the T. denitrificans-like bacterium as a member of the Gammaproteobacteria. To circumvent these problems, the 23S rRNA genes of two T. denitrificans strains were partially sequenced and a new 23S rRNA gene-based probe (Betthio 1001) specific for betaproteobacterial Thiobacilli was designed. Use of this new probe Betthio 1001, combined with field measurements, indicates the involvement of Thiobacilli in the process of nitrate-dependent iron sulfide mineral oxidation. [ABSTRACT FROM AUTHOR]

Stringent standards for nitrogen discharge necessitate the implementation of new systems for the sustainable removal of ammonium from wastewater. One of such systems is based on the process of anaerobic ammonium oxidation (Anammox), which is a new powerful tool especially for strong nitrogenous wastewaters. In this study, the Anammox process performance was tested with synthetic wastewater in a completely stirred tank reactor (CSTR). The reactor was operated for 511 days and fed with increasing amounts of ammonium and nitrite. In this period, an increase of ammonium and nitrite utilization rates were observed as a result of the increase of nitrogen loads in the influent. After 272 days, about 60% of the biomass was removed from the reactor and the system was restarted. Throughout 511 days 90% of the ammonium and more than 99% of the nitrite were converted mainly to dinitrogen (N2) and nitrate. The microbial community in the reactor was characterized with Fluorescence in situ Hybridization (FISH). The study showed that the population in the reactor was dominated by the deep-branching planctomycete Candidatus “Brocadia anammoxidans” strain Dokhaven 2. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) is a recently discovered microbial pathway and a cost-effective way to remove ammonium from wastewater. Anammox bacteria have been described as obligate chemolithoautotrophs. However, many chemolithoautotrophs (i.e., nitrifiers) can use organic compounds as a supplementary carbon source. In this study, the effect of organic compounds on anammox bacteria was investigated. It was shown that alcohols inhibited anammox bacteria, while organic acids were converted by them. Methanol was the most potent inhibitor, leading to complete and irreversible loss of activity at concentrations as low as 0.5 mM. Of the organic acids acetate and propionate, propionate was consumed at a higher rate (0.8 nmol min-1 mg of protein-1) by Percoll-purified anammox cells. Glucose, formate, and alanine had no effect on the anammox process. It was shown that propionate was oxidized mainly to CO2, with nitrate and/or nitrite as the electron acceptor. The anammox bacteria carried out propionate oxidation simultaneously with anaerobic ammonium oxidation. In an anammox enrichment culture fed with propionate for 150 days, the relative amounts of anammox cells and denitrifiers did not change significantly over time, indicating that anammox bacteria could compete successfully with heterotrophic denitrifiers for propionate. In conclusion, this study shows that anammox bacteria have a more versatile metabolism than previously assumed. [ABSTRACT FROM AUTHOR]