Fig. 6. Naphthalene (Nap) concentrations in Nap-degrading communities in the presence of 9,10-phenanthrenequinone (PheQ) or phenanthrene (Phe). The Nap-containing cultures were amended as follows with Phe or PheQ: "Saturated PheQ," PheQ at saturation (4 mg/L); "Nap only," no PheQ or Phe; "Saturated Phe," Phe at saturation (0.25 mg/L); "Low PheQ," PheQ at 0.25 mg/L; "Sterile controls," two representatives of each previously mentioned treatment containing no inoculum. Error bars represent two standard errors.