Enrichment of anammox population has been established with an inoculum of sewage sludge, using a small-scale up-flow reactor (410 mL). Clone analyses revealed that most abundant anammox population was Ca. Brocadia sp., which was similar to those predominated in sediment at a station (KU3) in Lake Kitaura. Strong anammox activity has been persistently observed in this station. No pure culture of anammox microorganism has been isolated so far, suggesting that anammox microorganisms may not grow without any accompanying population. Complete genome of an anammox species has not been obtained, neither. This may suggest that catabolic and anabolic metabolisms of anammox microorganisms may not fully be elucidated with a complete genome of anammox species, if it will be obtained, but analyses on co-existing microorganisms with metagenomics could be useful. However, so far, metagenomics approach for analyzing whole community of enrichment culture of anammox population has not been conducted. This project is for metagenomic analyses of whole community of anammox enrichment culture to see which microorganisms co-existing with anammox population and to evaluate quantitatively such functions as nitrification, denitrification, anammox, and nitrogen fixation, which are responsible for nitrogen cycle, especially, not by specific genes for each function but by quantifying each of whole metabolic pathways using a newly developed analytical method called MAPLE. This approach could allow to elucidate interaction among microbial populations, including anammox population, in persistent anammox activity. MAPLE is for elucidating comprehensive potential functions from metagenome data. Potentials of each function evaluated by this metagenomics procedure would be compared with activity measurement data. Moreover, this project may possibly provide whole genome of an anammox species, as it is enriched.