Ensifer sp. strain AS08 and Pseudomonas sp. strain AS90 degrading short ethoxy (EO) chain-nonylphenol (NP) [NPEOav2.0 containing NP mono-similar to tetraethoxylates (NP1EO similar to NP4EO); average 2.0 EO units] were isolated by enrichment cultures. Both strains grew on NP but not on octyl- and nonylphenol polyethoxylates (NPEOs) (average 10 EO units). Growth and degradation of NPEOav2.0 was increased with increased concentrations of yeast extract (0.02-0.5%) in a culture medium. Culture supernatants of both strains grown on NPEOav2.0 were analyzed by high-performance liquid chromatography, showing degradation of NP4EO-NP1EO. The metabolites from nonylphenol diethoxylate (NP2EO) by resting cells of both strains were identified by gas chromatography-mass spectrometry as nonylphenoxyethoxyacetic acid, NP1EO, nonylphenoxyacetic acid (NP1EC), and NP, while those from NP1EO were identified as NP1EC and NP. Cell-free extracts from strain AS08 grown on NPEOav2.0 dehydrogenated NPEOs, NPEOav2.0, NP2EO, NP1EO, and PEG 400, but the extracts were inactive toward di- similar to tetraethylene glycol. Aldehydes were formed in the reaction mixture of each substrate with cell-free extracts. From these results, the aerobic metabolic pathway for short EO chain-NP is proposed: A terminal alcohol group of the EO chain is oxidized to a carboxylic acid via an aldehyde, and then one EO unit is removed. This process is repeated until NP is produced.