Isolation of phylogenetically diverse nonylphenol ethoxylate-degrading bacteria and characterization of their corresponding biotransformation pathways

Most nonylphenol ethoxylate (NPEO)-degrading isolates have been assigned to gamma-Proteobacteria, which is different from the results acquired by using molecular ecological techniques. To better understand the environmental fate of NPEOs, bacterial isolation strategy characterized by the use of gellan gum as a gelling reagent and a low concentration of target carbon source were used to isolate phylogenetically diverse NPEO-degrading bacteria from activated sludge, and the biotransformation pathways of the isolates were investigated. Eight NPEO-degrading isolates with high diversity were acquired, which were distributed among seven different genera: Pseudomonas, Sphingomonas, Sphingobium, Cupriavidus, Ralstonia, Achromobacter and Staphylococcus. The latter five genera have never been reported to be able to degrade NPEOs. Three biotransformation pathways of NPEOs were observed in the eight stains. Six strains belonging to alpha, beta and gamma classes of Proteobacteria and Firmicutes phylum degraded NPEOs by initially shortening the EO chain and then oxidizing the terminal alcohol of the shortened NPEOs to the corresponding nonylphenoxy carboxylates (NPECs), which could explain most of the reported observations for the degradation of NPEOs in environment. An isolate (NP42a) belonging to the genus Sphingomonas degraded NPEOs through a non-oxidative pathway, with nonylphenol monoethoxylate (NP(1)EO) as the dominant product. Another isolate (NP47a) belonging to the genus Ralstonia degraded NPEOs by oxidizing the EO chain directly without the formation of short chain products.