Characterization of allelochemicals from Nitzschia closterium and their allelopathic effects on Prorocentrum donghaiense

Abstract

This study explores the allelopathic interactions and chemical characterization of the diatom Nitzschia closterium and its impact on the harmful dinoflagellate Prorocentrum donghaiense. Using mixed culture and filtrate culture experiments, the allelochemicals released by N. closterium were shown to inhibit P. donghaiense growth in a concentration-dependent manner. These inhibitory effects were linked to disruptions in photosystem II efficiency. In addition, extracts from liquid-liquid extraction (LLE) including solvent of ethyl acetate, n-hexane, petroleum ether, dichloromethane and DMSO, and solid phase extraction (SPE) of filtrate of N. closterium cultures, were tested for their effects on P. donghaiense. Among these, only the n-hexane extracts from LLE significantly reduced algal growth, achieving a 78.1 % inhibition at the highest concentration (50 μL). Fractionation of the n-hexane extracts via HPLC yielded twelve fractions, with fraction F-IV showing the most potent inhibition. Further GC–MS analysis identified several compounds, especially of 3-acetoxy-7,8-epoxylanostan-11-ol, as a key allelopathic agent. These findings contribute to understand the ecological role of allelopathy in regulating harmful algal blooms and highlight the potential of N. closterium extracts for environmental management application.