The allelopathic effects of Heterosigma akashiwo on Skeletonema costatum: Insights from gene expression and metabolomics analysis

The globally distributed harmful algal blooms (HAB) species, Heterosigma akashiwo, has been found to exhibit ichthyotoxicity. Previous studies have shown that H. akashiwo achieves a competitive edge during bloom occurrences by inhibiting the growth of a coexisting diatom, Skeletonema costatum, through allelopathy. However, the specific allelopathic mechanisms underlying the allelopathic effects of H. akashiwo on S. costatum remain unknown. To bridge this gap, our study utilized a combination of quantitative real-time PCR and metabolomics to examine the allelopathic processes of H. akashiwo on S. costatum. Our results demonstrate that the growth of S. costatum is hindered when co-cultured with H. akashiwo (initial cell concentration, 2 × 104 cell/mL). Gene expression investigation showed a substantial reduction in the mRNA levels of cytochrome b6, ribulose bisphosphate carboxylase large chain, and silicon transporter in S. costatum when grown in co-culture conditions. Furthermore, metabolic pathway analysis suggested that the allelopathic effects of H. akashiwo disrupted several vital metabolic pathways in S. costatum, including a reduction in purine and pyrimidine metabolism and an increase in fatty acid biosynthesis. Our investigation has revealed the intricate and substantial involvement of allelopathy in the formation of H. akashiwo blooms, demonstrating the complexity of the allelopathic interaction between H. akashiwo and S. costatum. These insights also contribute significantly to our understanding of the dynamics within HAB species.