Oxidation of Naphthalene by Cyanobacteria and Microalgae

This study investigated the ability of 18 algal cultures representing five major groups—nine cyanobacteria, five green algae, one red alga, one brown alga, and two diatoms—to metabolize naphthalene under photoautotrophic conditions. All organisms oxidized naphthalene and produced at least six metabolites, with 1-naphthol identified as a major product in all strains. Using radioactive [14C]naphthalene tracing, researchers quantified metabolite production, which ranged from 0.1 to 2.4% of total naphthalene. Additional metabolites were identified as 4-hydroxy-1-tetralone and cis-naphthalene dihydrodiol, with several unidentified products also detected. The relative proportions of metabolites varied by organism. Notably, naphthalene was not toxic at 78 μM concentrations for most organisms, though two heterotrophic cyanobacteria showed sensitivity above 10 μM. These findings demonstrate that naphthalene oxidation is widely distributed across the algal kingdom, suggesting important implications for understanding aromatic hydrocarbon fate in marine ecosystems.

Key findings

• All 18 algal strains tested oxidized naphthalene to at least six metabolites under light conditions, with 1-naphthol as a universal product
• Metabolism rates ranged from 0.1 to 2.4% of input naphthalene, converting it to organic-soluble derivatives
• Both prokaryotic cyanobacteria and eukaryotic algae produced identical metabolic profiles, suggesting convergent metabolic pathways for aromatic hydrocarbon degradation
• This represents the first demonstration that naphthalene oxidation ability is widespread across the algal kingdom, with potential environmental significance