HPLC quantification of guanine, hypoxanthine, xanthine, and uric acid in microalgae : the effects of different nitrogen sources on the purine profile of Cryptomonas maculata

Abstract

Microalgae are a substantial group of primary contributors to all aquatic reservoirs on earth. A recently observed strategy in their nitrogen metabolism is the ability to form purine-based crystalline inclusions that are often solid solutions. In microalgae, they are proposed to function as concentrated reservoirs of stable, nitrogen-containing, rapid-turnover metabolites or stress responses. Yet, many aspects in nitrogen-metabolization and compositional dynamics remain unclear. To address this issue, an HPLC method for the quantification of all relevant purines (guanine, hypoxanthine, xanthine and uric acid) was designed and applied to 14 taxonomically different microalgae. Cryptomonas maculata was selected as a model species to study the effects of different nitrogen sources (NaNO3 and urea) at lowered and increased concentrations on purine formation over time. This study is the first to address purine formation in a time-resolved manner and to analyze compositional dynamics. One of the main results of the study is the high variability in uric acid concentrations, while the concentrations of guanine, xanthine, and hypoxanthine remain constant. The type of nitrogen source is shown to be more impacting on these concentrations than the actual concentration of nitrogen. Further, a significant amount of uric acid was produced during the initial phase of cultivation, followed by its subsequent degradation after 2 to 4 weeks. These findings offer a first insight into the complex dynamics and responses of microalgae to environmental changes and hold considerable potential to elucidate a wide range of phenomena, including algae blooms and the dynamics of coral ecosystems.