Over 20 years ago it was asserted that there should be an organism that can exploit the ‘anammox’ reaction which involves the anaerobic oxidation of ammonium by nitrite. The search has now succeeded, and the organism turns out to be relative of bacterial group called the planctomycetes. The finding is of practical as well as scientific interest, in that the bacterium might be used to tackle the environmental problem of high nitrogen content in waste water.