The abundance and diversity of anaerobic ammonium oxidation (anammox) bacteria were assessed in 152 groundwater samples in the Kathmandu Valley, Nepal. Anammox bacterial 16S rRNA genes were detected in 54% (37/68) of samples collected in the dry season at 1.6×105-8.8×106 copies L-1, and in 60% (50/84) of samples collected in the wet season at 4.3×104-1.2×107 copies L-1. The 16S rRNA genes of "Candidatus Brocadia", "Candidatus Anammoxoglobus", and five new deduced anammox bacterial phylotypes were detected in the shallow groundwater samples. Diverse anammox bacteria were broadly distributed in the shallow groundwater aquifer of the Kathmandu Valley.
Keywords: Kathmandu Valley; anammox bacteria; distribution; groundwater.