Growth factors, kinetics and biodegradation mechanism associated with Pseudomonas nitroreducens TX1 grown on octylphenol polyethoxylates

The growth properties and biodegradation mechanism of a Gram-negative bacterium, Pseudomonas nitroreducens TX1 that was able to grow on branched octylphenol polyethoxylates (OPEO_n, average n=9.5) as the sole carbon source over a wide concentration range (1-100,000 mg l^-1) were studied. Analysis of growth factors indicated the highest specific growth rate (μ) of 0.53 h^-1 was obtained at an initial concentration of 5000 mg l^-1 OPEO_n. An optimal C/N ratio of 12 was obtained for (NH₄)₂SO₄ as the nitrogen source in a cultivated medium at pH 7. The kinetic analysis demonstrated that bacterial growth and OPEO_n degradation followed the Monod equation and were based on a substrate concentration inhibition model and pseudo-first-order reaction, respectively. The substrate inhibition coefficient was over 18,000 mg l^-1 and this indicates that the strain has an ability to sustain growth at high concentrations of OPEO_n and use it as the sole carbon source under such a stress condition. Furthermore, LC-MS analysis showed that the biodegradation mechanism of dodecyl octaethoxylate (AEO₈) by P. nitroreducens TX1 was the sequential cleavage of the ethoxylate chain.