Selective utilization of phosphorus compounds by Chaetoceros tenuissimus (Bacillariophyceae): Approach using 31P nuclear magnetic resonance analysis

Abstract

Several diatom species can utilize various forms of organic phosphorus via enzymatic hydrolysis. The present study identified which phosphorus compounds are preferentially utilized by planktonic diatom Chaetoceros tenuissimus cultures using a 31P nuclear magnetic resonance (NMR)‐based method. Our 31P NMR analysis, which involves a sample extraction procedure using DIAION™ CR11, detected and quantified phosphorus compounds present at concentrations of at least 7.5 μM in the seawater‐based media, including orthophosphate, phosphate monoester, phosphate diester, phosphonate, and other compounds. Based on this analysis, we examined the temporal variations of phosphorus compounds in C. tenuissimus cultures in which orthophosphate, phosphate monoester, phosphate diester, and phosphonate compounds were present simultaneously. Cells pre‐grown under phosphorus‐replete conditions utilized orthophosphate as the preferential phosphorus source and switched to phosphate monoester after exhausting orthophosphate. Enzymatic activity for phosphate monoester hydrolysis, namely phosphomonoesterase (synonym to alkaline phosphatase) activity, appeared when C. tenuissimus began to utilize phosphate monoester. In contrast, C. tenuissimus pre‐grown on phosphorus‐depleted media simultaneously hydrolyzed phosphate monoester and phosphate diester compounds, released orthophosphate from these compounds, and utilized the released orthophosphate and original orthophosphate without discrimination. Overall, we demonstrated that 31P NMR‐based method can comprehensively analyze the variations of dissolved phosphorus compounds in diatom cultures. Our results showed selective utilization of phosphorus compounds by C. tenuissimus and suggested that phosphate monoester and phosphate diester compounds were important phosphorus sources for this diatom in orthophosphate‐depleted coastal waters.