BIODEGRADATION OF PHENOLS BY THE ALGA OCHROMONAS-DANICA

The eukaryotic alga Ochromonas danica, a nutritionally versatile, mixo trophic chrysophyte, grew on phenol as the sole carbon source in axeni c culture and removed the phenol carbon from the growth medium, Respir ometric studies confirmed that the enzymes involved in phenol cataboli sm were inducible and that the alga oxidized phenol; the amount of oxy gen consumed per mole of oxidized substrate was approximately 65% of t he theoretical value. [U-C-14]phenol was completely mineralized, with 65% of the C-14 label appearing as (CO2)-C-14, approximately 15% remai ning in the aqueous medium, and the rest accounted for in the biomass. Analysis of the biomass showed that C-14 label had been incorporated into the protein, nucleic acid, and lipid fractions; phenol carbon is thus unequivocally assimilated by the alga, Phenol-grown cultures of O . danica converted phenols to the corresponding catechols, which were further metabolized by the meta-cleavage pathway, This surprising resu lt was rigorously confirmed by taking the working stock culture throug h a variety of procedures to check that it was axenic and repeating th e experiments with algal extracts. This is, as far as is known, the fi rst definitive identification of the meta-cleavage pathway for aromati c ring degradation in a eukaryotic alga, though its incidence in other eukaryotes has been (infrequently) suggested.