Cadmium Stress Enhances Allelopathic Effect of Chlorella Pyrenoidosa on Bloom-Causing Dinoflagellate Heterocapsa Bohaiensis: Evidence from Allelopachemicals Production and Transcriptomes Analyses

Abstract

Heterocapsa bohaiensis is a recently reported dinoflagellate in coastal areas around the Pacific, especially, caused harmful algal blooms (HABs) in aquaculture ponds in Liaodong Bay, China, and led to significant economic losses. Chlorella pyrenoidosa, also present in these ponds, has been shown allelopathic inhibition on the growth of H. bohaiensis. Allelopathy is considered an eco-friendly way to control HABs. Environmental stressor, like cadmium (Cd) pollution, a common hazardous metal in aquaculture ponds, could potentially affect the allelopathy. In this study, we investigated the growth and allelopathic effect of C. pyrenoidosa on H. bohaiensis when exposed to range of toxic and environmentally relevant concentrations of dissolved Cd. Allelochemicals produced by C. pyrenoidosa were quantified using high-performance liquid chromatography-mass spectrometry (HPLC-MS), and the metabolism pathways was elucidated by transcriptomes analyses. The results showed that Cd stress enhanced allelopathic effects and increased the production of fatty acid, a role that has been commonly recognized as C. pyrenoidosa allelochemicals. Cd-induced oxidative stress enhanced the synthesis pathways of long-chain fatty acids, especially genes AccA, AccB, and LpxC-FabZ, which support the observed increase in the culture experiments. Our findings provide new insights into how Cd-stress regulates the production of natural allelochemicals, and potentially improved their application for HABs control through biosynthesis.

Keywords: Allelopathy, Cadmium, oxidative stress, Fatty acids biosynthesis, Harmful algal blooms