Physiological and Ecological Significance of the Chemical Instability of Uric Acid and Related Purines in Sea Water and Marine Algal Culture Medium

Abstract

The chemical instability of uric acid and related purine bases in a seawater phytoplankton culture medium was evaluated spectrophotometrically from concentration changes incurred on aseptic incubation at about 20 C under cool-white light or complete darkness. Uric acid showed slow degradation in darkness, which was increased severalfold by illumination. Xanthine showed a small degree of degradation only from illumination, but adenine, guanine, and hypoxanthine appeared to be stable under both test conditions. The degradation of uric acid was traced to three factors differing in intensity of effect: 1) pH of sea water (minor effect), 2) photolysis (additional minor effect), 3) trace-metal cation content of sea water (major effect), whereas that of xanthine could be traced only to photolysis.These results cast doubt on previous reports of utilization of uric acid as N-source for phototrophic growth of marine planktonic algae in that the compound actually utilized may be degradation product(s) rather than the intact purine. Ecologically, the results signify that uric acid could undergo rapid chemical turnover, without biological intervention, in the marine environment.