Co-Biodegradation of Naphthalene and Phenanthrene by Acinetobacter johnsonii

Naphthalene (NAP) and phenanthrene (PHE) are broadly and enduringly distributed in the environment. It is of great difficulty to degrade either of these due to their toxicity and mutually competitive inhibition. Currently, a pure culture of Acinetobacter johnsonii was confirmed to have the capacity to completely degrade 2,000 mg L-1 NAP and 600 mg L-1 PHE. In dual-substrate batch culture, 550 mg L-1 PHE was completely degraded with 50-750 mg L-1 NAP and compared to single-substrate PHE, higher degradation velocity was obtained at a concentration of 150 mg L-1 NAP. Low-concentration of NAP accelerates the PHE biodegradation potential. However, by addition of 35 mg L-1 NAP, 626 mg L-1 PHE could be just degraded to 203.82 mg L-1 within 223 h at a removal rate of 67.4%. The accumulation of metabolites, including ethers, carboxylic acids, ester, and anthraquinone may account for the incomplete biodegradation. By contrast, PHE always acts as a competitive inhibitor in co-biodegradation of NAP and PHE, while the peak biodegradation of 1,800 mg L-1 NAP with 80 mg L-1 PHE could still proceed with low overall cell yield, resulting from decreasing contribution of NAP consumption. By introducing an inhibition constant parameter to fit the inhibition on cells, modeling furthermore confirmed strong substrate inhibition for NAP and PHE over the concentrations of 174 and 76 mg L-1, respectively. To research the interplay of NAP and PHE is conducive to targeted decontamination.