Response of anaerobic ammonium-oxidizing bacteria to hydroxylamine

Anaerobic ammonium oxidation is a recent addition to the microbial nitrogen cycle, and its metabolic pathway, including the production and conversion of its intermediate hydrazine, is not well understood. Therefore, the effect of hydroxylamine addition on the hydrazine metabolism of anaerobic ammonium-oxidizing (anammox) bacteria was studied both experimentally and by mathematical modeling. It was observed that hydroxylamine was disproportionated biologically in the absence of nitrite into dinitrogen gas and ammonium. Little hydrazine accumulated during this process; however, rapid hydrazine production was observed when nearly all hydroxylamine was consumed. A mechanistic model is proposed in which hydrazine is suggested to be continuously produced from ammonium and hydroxylamine (possibly via nitric oxide) and subsequently oxidized to N(2). The electron acceptor for hydrazine oxidation is hydroxylamine, which is reduced to ammonium. A decrease in the hydroxylamine reduction rate, therefore, leads to a decrease in the hydrazine oxidation rate, resulting in the observed hydrazine accumulation. The proposed mechanism was verified by a mathematical model which could explain and predict most of the experimental data.

Anammox bacteria disguised as denitrifiers: nitrate reduction to dinitrogen gas via nitrite and ammonium

Anaerobic ammonium-oxidizing (anammox) bacteria oxidize ammonium with nitrite and produce N(2). They reside in many natural ecosystems and contribute significantly to the cycling of marine nitrogen. Anammox bacteria generally live under ammonium limitation, and it was assumed that in nature anammox bacteria depend on other biochemical processes for ammonium. In this study we investigated the possibility of dissimilatory nitrate reduction to ammonium by anammox bacteria. Physically purified Kuenenia stuttgartiensis cells reduced (15)NO(3) (-) to (15)NH(4) (+) via (15)NO(2) (-) as the intermediate. This was followed by the anaerobic oxidation of the produced ammonium and nitrite. The overall end-product of this metabolism of anammox bacteria was (15)N(15)N dinitrogen gas. The nitrate reduction to nitrite proceeds at a rate of 0.3 +/- 0.02 fmol cell(-1) day(-1) (10% of the 'normal' anammox rate). A calcium-dependent cytochrome c protein with a high (305 mumol min(-1) mg protein(-1)) rate of nitrite reduction to ammonium was partially purified. We present evidence that dissimilatory nitrate reduction to ammonium occurs in Benguela upwelling system at the same site where anammox bacteria were previously detected. This indicates that anammox bacteria could be mediating dissimilatory nitrate reduction to ammonium in natural ecosystems.

Candidatus “Anammoxoglobus propionicus” a new propionate oxidizing species of anaerobic ammonium oxidizing bacteria

The bacteria that mediate the anaerobic oxidation of ammonium (anammox) are detected worldwide in natural and man-made ecosystems, and contribute up to 50% to the loss of inorganic nitrogen in the oceans. Two different anammox species rarely live in a single habitat, suggesting that each species has a defined but yet unknown niche. Here we describe a new anaerobic ammonium oxidizing bacterium with a defined niche: the co-oxidation of propionate and ammonium. The new anammox species was enriched in a laboratory scale bioreactor in the presence of ammonium and propionate. Interestingly, this particular anammox species could out-compete other anammox bacteria and heterotrophic denitrifiers for the oxidation of propionate in the presence of ammonium, nitrite and nitrate. We provisionally named the new species Candidatus "Anammoxoglobus propionicus".

Adaptation of a freshwater anammox population to high salinity wastewater

For the successful application of anaerobic ammonium oxidation (anammox) in wastewater practice it is important to know how to seed new anammox reactors with biomass from existing reactors. In this study, a new high salinity anammox reactor was inoculated with biomass from a freshwater system. The changes in activity and population shifts were monitored. It was shown that freshwater anammox bacteria could adapt to salt concentrations as high as 30 gl(-1) provided the salt concentration was gradually increased. Higher salt concentrations reversibly inhibited anammox bacteria. The nitrogen removal efficiency and maximum anammox activity of the salt adapted sludge was very similar to the reference freshwater sludge. Fluorescence in situ hybridization analysis revealed that the freshwater anammox species Candidatus "Kuenenia stuttgartiensis" was the dominant in both salt adapted sludge and freshwater sludge. These results show that gradual adaptation may be the key to successful seeding of anammox bioreactors.

Deciphering the evolution and metabolism of an anammox bacterium from a community genome

Anaerobic ammonium oxidation (anammox) has become a main focus in oceanography and wastewater treatment. It is also the nitrogen cycle's major remaining biochemical enigma. Among its features, the occurrence of hydrazine as a free intermediate of catabolism, the biosynthesis of ladderane lipids and the role of cytoplasm differentiation are unique in biology. Here we use environmental genomics--the reconstruction of genomic data directly from the environment--to assemble the genome of the uncultured anammox bacterium Kuenenia stuttgartiensis from a complex bioreactor community. The genome data illuminate the evolutionary history of the Planctomycetes and allow us to expose the genetic blueprint of the organism's special properties. Most significantly, we identified candidate genes responsible for ladderane biosynthesis and biological hydrazine metabolism, and discovered unexpected metabolic versatility.

Global impact and application of the anaerobic ammonium-oxidizing (anammox) bacteria

In the anaerobic ammonium oxidation (anammox) process, ammonia is oxidized with nitrite as primary electron acceptor under strictly anoxic conditions. The reaction is catalysed by a specialized group of planctomycete-like bacteria. These anammox bacteria use a complex reaction mechanism involving hydrazine as an intermediate. The reactions are assumed to be carried out in a unique prokaryotic organelle, the anammoxosome. This organelle is surrounded by ladderane lipids, which make the organelle nearly impermeable to hydrazine and protons. The localization of the major anammox protein, hydrazine oxidoreductase, was determined via immunogold labelling to be inside the anammoxosome. The anammox bacteria have been detected in many marine and freshwater ecosystems and were estimated to contribute up to 50% of oceanic nitrogen loss. Furthermore, the anammox process is currently implemented in water treatment for the low-cost removal of ammonia from high-strength waste streams. Recent findings suggested that the anammox bacteria may also use organic acids to convert nitrate and nitrite into dinitrogen gas when ammonia is in short supply.

1994-2004: 10 years of research on the anaerobic oxidation of ammonium

The obligately anaerobic ammonium oxidation (anammox) reaction with nitrite as primary electron acceptor is catalysed by the planctomycete-like bacteria Brocadia anammoxidans, Kuenenia stuttgartiensis and Scalindua sorokinii. The anammox bacteria use a complex reaction mechanism involving hydrazine as an intermediate. They have a unique prokaryotic organelle, the anammoxosome, surrounded by ladderane lipids, which exclusively contains the hydrazine oxidoreductase as the major protein to combine nitrite and ammonia in a one-to-one fashion. In addition to the peculiar microbiology, anammox was shown to be very important in the oceanic nitrogen cycle, and proved to be a very good alternative for treatment of high-strength nitrogenous waste streams. With the assembly of the K. stuttgartiensis genome at Genoscope, Evry, France, the anammox reaction has entered the genomic and proteomic era, enabling the elucidation of many intriguing aspects of this fascinating microbial process.

Propionate oxidation by and methanol inhibition of anaerobic ammonium-oxidizing bacteria

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 CO(2), 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.

Serum biochemical changes associated with cystic ovarian degeneration in pigs after atrazine treatment

Biochemical and histopathological parameters of the ovarian function were observed to assess the toxic effect of low dose of atrazine, an s-triazine herbicide, in female pigs (gilts) undergoing intensive breeding. Female pigs (cross-bred between Swedish and German landrace) received 2 mg atrazine kg-1 body wt. in feed daily during 19 days of the oestrous cycle. The last treatment day corresponded to day -3 of the onset of the next expected oestrus. Blood samples were collected 3 times daily at 3-h intervals on the first 5 post-treatment days. Serum 17 beta-oestradiol (17 beta-E) and progesterone (P) concentrations were determined. A significantly higher (P < 0.05 and P < 0.001, respectively) serum 17 beta-E concentration was recorded 48 and 24 h before the onset of the next expected oestrus in atrazine-treated pigs, as compared to intact pigs. The onset of the next expected oestrus failed to occur, but no other adverse clinical reactions associated with the treatment were recorded. Histopathological examination of the ovaries of treated pigs indicated multiple ovarian follicular cysts and persistence of corpus luteum. Biochemical and histopathological findings showed that subacute exposure of female pigs to low dose of atrazine prolonged their oestrous cycle.

Seasonal atrazine contamination of drinking water in pig-breeding farm surroundings in agricultural and industrial areas of Croatia

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) a s-triazine herbicide, has been widely used in Croatian agriculture. Due to atrazine extensive use and its biodegradation in nature within at least one year (Klassen and Kodoum 1979), atrazine residues are found in ground, surface, drain and drinking water (Vidacek et al. 1994; Gojmerac et al. 1994). Groundwater downgradient from atrazine treated fields may show seasonal concentration peaks which could exceed the safe level (Wehtje et al. 1983). Therefore, the use of atrazine includes permanent control of its residues in water, particularly in relation to its use as a herbicidal chemical and groundwater contamination (Graham 1991). Furthermore, the presence of atrazine in the environment and its possible ingestion via the water, food and feed chain, may present a risk for the animal and human health. The analysis of atrazine residues in soil can be performed by either colorimetry or high performance liquid chromatography (HPLC) (Vickrey et al. 1980), and in water, soil and food by immunoassay in comparison with HPLC or gas chromatography/mass spectrometry (GS-MS) (Bushway et al. 1988; Bushway et al. 1989; Bushway et al. 1992; Thurman et al. 1990). We describe the use of enzyme-linked immunosorbent assay (ELISA) for one-year seasonal monitoring of atrazine residues in drinking water from two differently situated pig-breeding farms (agricultural and industrial areas) in Croatia. Results obtained by ELISA were compared to those produced by HPLC.

Serum biochemical and histopathological changes related to the hepatic function in pigs following atrazine treatment

Biochemical and histopathological parameters of the hepatic function were used to quantify the hepatotoxic effects of atrazine in female pigs (gilts) undergoing intensive breeding. Female pigs (cross-bred Swedish and German landrace) received 2 mg atrazine kg-1 body wt. in feed daily during 19 days of the oestrous cycle. The last treatment day corresponded to day -3 of the onset of the next expected oestrus. Blood samples were collected three times daily at 3-h intervals on the first four post-treatment days. Serum activities of gamma-glutamyltransferase (GGT), alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (AP) were determined. Serum activity of GGT was significantly increased throughout the four post-treatment days. In comparison with the control values, a slight but not significant decrease was observed in the serum activities of ALT, AST and AP. Histopathological examination of the liver of exposed pigs showed mild centrolobular parenchymatous degeneration. Interstitial connective tissue proliferation resulted in narrow and irregular bile canaliculi.