Abstract
Bacterial biodegradation mechanisms of non-ionic surfactants under aerobic conditions were studied by means of matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). First, biodegradation intermediates of octylphenol polyethoxylate (OPEO) were characterized by MALDI-MS. Since the formation of carboxylated OPEO (OPEC) and the changes in molecular weight distribution during biodegradation test were observed, it was proposed that the biodegradation of OPEO was proceeded mainly according to the exo-scission of EO chain accompanied with oxidation of the hydroxyl terminal side. Then, to clarify the mechanisms of the oxidative biodegradation in detail, biodegradation test was carried out using 18O-labeled water as a incubation medium. The incorporation behavior of 18O into OPEC molecules suggested that the formation of an enzyme (or coenzyme)-substrate complex linked via a covalent bond might be formed as a reaction intermediate. Finally, biodegradation profiles of non-ionic surfactants with a variety of hydrophobic moieties were investigated using 18O-labeled water. The incorporation rates of 18O into corresponding carboxylated intermediates were correlated with the hydrophobicity of the surfactants.
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