Constitutive and inducible hydroxylase activities involved in the degradation of naphthalene by Cunninghamella elegans

The non-ligninolytic fungus Cunninghamella elegans was investigated for its ability to produce naphthalene hydroxylase (NAH) and naphthol hydroxylase (NOH) activities under various conditions. When the organism was cultivated on a rich growth medium, the mycelia exhibited significant constitutive NA H activity in the late exponential growth phase, but not in the early-expon ential-growth-phase. On incubating the early-exponential-growth-phase mycel ia with naphthalene, NAH activity was increased five-fold; however, this in crease did not occur in the presence of the protein synthesis inhibitor cyc loheximide. Since incubation of the late-phase mycelia with naphthalene did not lead to a higher degradation rate of naphthalene, mycelia in this phys iological state have apparently lost the ability to induce synthesis of the enzyme exhibiting NAH activity. This is not due to an overall inability to perform de novo protein synthesis, since NOH activity, non-constitutive at all growth phases, could be induced by incubating late-phase mycelia with naphthalene. Whether inducible and constitutive NAH activity originate from one and the same enzyme remains to be elucidated. It is suggested that nap hthalene oxidizing enzyme(s) may also oxidize pyrene, but not anthracene or benzo[a]pyrene, although the latter are degradable by C. elegnns.