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Anaerobic ammonium oxidation (anammox) is an important process for nitrogen removal in marine pelagic and benthic environments and represents a major sink in the global nitrogen cycle. We applied a suite of complementary methods for the detection and enumeration of anammox activity and anammox bacteria in marine sediments of the Gullmar Fjord, and compared the results obtained with each technique. 15N labelling experiments showed that nitrogen removal through N(2) production was essentially limited to the upper 2 cm of the sediment, where anammox contributed 23-47% of the total production. The presence of marine anammox bacteria belonging to the genus 'Candidatus Scalindua' was shown by 16S rRNA gene sequence comparison. FISH counts of anammox bacteria correlated well with anammox activity, while quantitative PCR may have underestimated the number of anammox bacterial 16S rRNA gene copies at this site. Potential nitrogen conversion by anammox ranged from 0.6 to 4.8 fmol N cell-1 day-1, in agreement with previous measurements in the marine environment and in bioreactors. Finally, intact ladderane glycerophospholipid concentrations better reflected anammox activity and abundance than ladderane core lipid concentrations, most likely because the core lipid fraction contained a substantial fossil component, especially deeper in the sediment.

Recently, two fresh water species, 'Candidatus Brocadia anammoxidans' and 'Candidatus Kuenenia stuttgartiensis', and one marine species, 'Candidatus Scalindua sorokinii', of planctomycete anammox bacteria have been identified. 'Candidatus Scalindua sorokinii' was discovered in the Black Sea, and contributed substantially to the loss of fixed nitrogen. All three species contain a unique organelle-the anammoxosome-in their cytoplasm. The anammoxosome contains the hydrazine/hydroxylamine oxidoreductase enzyme, and is thus the site of anammox catabolism. The anammoxosome is surrounded by a very dense membrane composed almost exclusively of linearly concatenated cyclobutane-containing lipids. These so-called 'ladderanes' are connected to the glycerol moiety via both ester and ether bonds. In natural and man-made ecosystems, anammox bacteria can cooperate with aerobic ammonium-oxidising bacteria, which protect them from harmful oxygen, and provide the necessary nitrite. The cooperation of these two groups of ammonium-oxidising bacteria is the microbial basis for a sustainable one reactor system, CANON (completely autotrophic nitrogen-removal over nitrite) to remove ammonia from high strength wastewater.