Mechanism for Biotransformation of Nonylphenol Polyethoxylates to Xenoestrogens in Pseudomonas putida

Abstract

A strain of Pseudomonas putida isolated from activated sewage grew aerobically on the xenoestrogen precursor, nonylphenol polyethoxylate (NPEO x , where x is the number of ethoxylate units) as sole carbon source. Comparative growth yields on NPEOav6, NPEOav9, and NPEOav20 (mixtures with average ethoxylate numbers as indicated) were consistent with utilization of all but two ethoxylate units, and the final accumulating metabolite was identified by gas chromatography-mass spectroscopy as nonylphenol diethoxylate (NPEO2). There was no growth on nonylphenol or polyethylene glycols, and there was no evidence for production of carboxylic acid analogs of NPEO x . Biodegradation kinetics measured by high-pressure liquid chromatography (HPLC) for each component in NPEO x mixtures showed that biodegradation proceeded via successive exoscission of the ethoxylate chain and not by direct scission between the second and third ethoxylate residues. The NPEO x -degrading activity was inducible by substrate, and cell extracts of NPEOav9-induced cells were also active on the pure alcohol ethoxylate, dodecyl octaethoxylate (AEO8), producing sequentially, under either aerobic or anaerobic conditions, AEO7, AEO6, AEO5, etc., thus demonstrating that the pathway involved removal of single ethoxylate units. HPLC analysis of 2,4-dinitrophenylhydrazone derivatives revealed acetaldehyde (ethanal) as the sole aldehydic product from either NPEOav9 or AEO8 under either aerobic or anaerobic conditions. We propose a mechanism for biotransformation which involves an oxygen-independent hydroxyl shift from the terminal to the penultimate carbon of the terminal ethoxylate unit of NPEO x and dissociation of the resulting hemiacetal to release acetaldehyde and the next-lower homolog, NPEO x−1, which then undergoes further cycles of the same reaction until x = 2.

Biodegradation of nonylphenol ethoxylates byBacillussp. LY capable of heterotrophic nitrification

“…In this experiment, a stepwise ethoxyl chain shortening process from long-chain NPEOs to shorter chain polyethoxylates without the formation of related NPECs was observed, which suggested that NPEOs were biodegraded through a nonoxidative pathway. John & White (1998) proposed a hydroxyl shift mechanism for this nonoxidative ethoxyl chain removal process. According to the model, the hydroxyl shift leads to the formation of labile hemiacetal, which will subsequently release an acetaldehyde.…”

Replicability of dominant bacterial populations after long‐term surfactant‐enrichment in lab‐scale activated sludge

“…Because of their extensive use as detergents, emulsifiers, dispersing and wetting agents, non-ionic surfactants such as NPE are widely released in the environment, mostly after secondary biological treatment. As a consequence of biological wastewater treatment, partial degradation occurs with the formation of recalcitrant intermediates, which are considered important environmental pollutants attributed to their toxicity and endocrine disrupting activity (John and White, 1998;Ferguson et al ., 2001). As the primary source of these compounds is considered to be the breakdown of NPE during sewage treatment, many efforts were made to understand the fate of NPE in biological treatment (Gross et al ., 2004).…”

Environmental Fate of Nonylphenol Ethoxylates: Differential Adsorption of Homologs to Components of River Sediment

“…Across the complete homolog distribution, a strong positive linear correlation (r 2 ϭ 0.96) occurred between ethoxylate chain length and K d for the organic-free sediment. For the longer homologs (NPEO [8][9][10][11][12] ), the K d values for the organic-free sediment were very similar to corresponding values for native sediment (within 95% confidence limits). However, at shorter chain lengths (NPEO 3-7 ) the values for the two sediments diverged markedly beyond 95% confidence limits, with the difference increasing with decreasing chain length.…”

“…We have recently provided definitive evidence [12] that bacteria in pure culture achieve biodegradation of NPEO x by sequential removal of ethoxylate units from the terminus of the polyethylene glycol chain, that is, by sequential conversion of each component into its next lower homolog. In riverine environments, the additional presence of sediment particles will clearly have a marked impact on this process by differentially sequestering homologs of different chain lengths into the adsorbed state and thus restricting bioavailability to planktonic bacteria.…”

“…Thus, a typical commercial sample denoted NPEO av9 contains a mixture of homologs of different ethoxylate chain length (ethoxamers) from x ϭ 1 to 14, giving a weighted mean chain length of 9. Recent studies [11,12], using pure cultures of NPEO xdegrading bacteria isolated from activated sewage sludge, have shown for the first time that biodegradation proceeds via sequential removal of C 2 units (as ethanal) from the hydrophilic terminus, thus progressively eroding longer ethoxamers to shorter homologs. These results are consistent with the formation of short ethoxamers as end-products of bacterial metabolism in pure cultures [13], the presence of short ethoxamers * To whom correspondence may be addressed (whitegfl@cf.ac.uk).…”