Anammox Cell Biology, Metabolism, Growth, and Genetics

Abstract

One of the most recent contributions to the biogeochemical nitrogen cycle is anaerobic ammonium-oxidizing (anammox) bacteria. Anaerobic ammonium-oxidizing bacteria (anammox) obtain their energy for development by converting ammonium and nitrite into dinitrogen gas in the absence of oxygen. The species were thought to be extinct until around 15 years ago due to the believed inert nature of ammonium in anoxic circumstances. These slow-growing microorganisms are members of the Brocadiales order, which is related to the Planctomycetes. Membrane systems encircling the distinct cellular compartments are formed of unique “ladderane” lipid molecules. Anammox bacteria have a compartmentalized cell design with a central cell compartment, the “anammoxosome.” The intermediate production of hydrazine, a highly reactive and poisonous molecule, appears to be required for nitrogen generation. A metagenomics technique was used to assemble the genome of the anammox bacterium Kuenenia stuttgartiensis from a complex microbial community cultivated in a sequencing batch reactor (74% enriched in this bacterium). The anammox metabolism was in silico reconstructed using the assembled genome, and genes most likely involved in the process were identified. Anammox bacteria have been found in a variety of oxygen-depleted marine and freshwater environments, including oceans, seas, estuaries, marshes, rivers, and big lakes. Anammox bacteria may create more than half of the N2 gas discharged in the maritime environment. For the elimination of ammonia nitrogen, the anammox process is an appealing alternative to conventional wastewater treatment technologies.