Biochemistry and molecular biology of anammox bacteria

Abstract

Anaerobic ammonium-oxidizing (anammox) bacteria are one of the latest additions to the biogeochemical nitrogen cycle. These bacteria derive their energy for growth from the conversion of ammonium and nitrite into dinitrogen gas in the complete absence of oxygen. These slowly growing microorganisms belong to the order Brocadiales and are affiliated to the Planctomycetes. Anammox bacteria are characterized by a compartmentalized cell architecture featuring a central cell compartment, the "anammoxosome". Thus far unique "ladderane" lipid molecules have been identified as part of their membrane systems surrounding the different cellular compartments. Nitrogen formation seems to involve the intermediary formation of hydrazine, a very reactive and toxic compound. The genome of the anammox bacterium Kuenenia stuttgartiensis was assembled from a complex microbial community grown in a sequencing batch reactor (74% enriched in this bacterium) using a metagenomics approach. The assembled genome allowed the in silico reconstruction of the anammox metabolism and identification of genes most likely involved in the process. The present anammox pathway is the only one consistent with the available experimental data, thermodynamically and biochemically feasible, and consistent with Ockham's razor: it invokes minimum biochemical novelty and requires the fewest number of biochemical reactions. The worldwide presence of anammox bacteria has now been established in many oxygen-limited marine and freshwater systems, including oceans, seas, estuaries, marshes, rivers and large lakes. In the marine environment over 50% of the N(2) gas released may be produced by anammox bacteria. Application of the anammox process offers an attractive alternative to current wastewater treatment systems for the removal of ammonia-nitrogen. Currently, at least five full scale reactor systems are operational.

Size-fraction partitioning of community gene transcription and nitrogen metabolism in a marine oxygen minimum zone

“…In contrast, transcripts encoding nitrate reductase NarGH were among those most abundant and enriched in PA profiles. Nar likely acts in reverse in anammox bacteria, converting nitrite to nitrate and helping replenish electrons lost during CO 2 fixation via the acetyl-CoA pathway (Strous et al, 2006;Jetten et al, 2009). Here transcripts encoding key acetyl-CoA pathway genes (formate dehydrogenase and carbon monoxide dehydrogenase) were~10-fold less abundant than Nar transcripts, and did not differ appreciably between PA and FL fractions.…”

Microbial nitrate-dependent cyclohexane degradation coupled with anaerobic ammonium oxidation

“…Such strong ammonium depletion can be only explained by a dissimilatory process, the known anaerobic ammonium oxidation (anammox) with nitrite. This process is catalyzed by specialized members of the Planctomycetales (Mulder et al, 1995;Jetten et al, 2009). Attempts to purify cyclohexane-degrading nitrate reducers and anammox bacteria to further verify the assumed reactions in the enrichment culture were not successful.…”

Evidence of Exponential Growth of an Anammox Population in an Anaerobic Batch Culture

“…As anammox needs neither aeration for oxygen supply nor organic substances for enhancing denitrification, both of which have been major expenses in conventional wastewater treatment processes for nitrogen removal, anammox has drawn attention especially for the development of a novel energy-saving process (1,4,5,16). One of the obstacles to developing such a process has been the relatively slow growth of anammox populations with its unique manner of cell division (17).…”

“…Anaerobic ammonium oxidation (anammox) is a bacterial reaction carried out by anaerobic chemolithotrophs, in which NH4 + is oxidized to N2 by reducing NO2 − under strictly anaerobic conditions (4,5,10,11,14,15). As anammox needs neither aeration for oxygen supply nor organic substances for enhancing denitrification, both of which have been major expenses in conventional wastewater treatment processes for nitrogen removal, anammox has drawn attention especially for the development of a novel energy-saving process (1,4,5,16).…”