Unveiling bacterial communities linked with Alexandrium catenella, their impact and influential mechanism on paralytic shellfish toxin production

Alexandrium causes serious food safety and human death due to paralytic shellfish toxins (PSTs) production. The associated bacteria can affect PSTs production of Alexandrium. However, the influencing mechanism is still unclear. Here we firstly screened functional associated bacteria for affecting PSTs production of Alexandrium catenella in Yangtze Estuary and further studied their influence on physiological process and molecular regulation of A. catenella. Thirteen bacteria strains for affecting PSTs production of A. catenella were selected. The A. catenella strains co-cultured with different functional associated bacteria all produced more PSTs than axenic strain with antibiotic treatment. Compared with axenic A. catenella, the non-axenic A. catenella produced more algal cells, soluble sugar, soluble protein and neutral lipid. By RNA-seq, it was found that non-axenic A. catenella produced more upregulated functional genes than axenic A. catenella. The biosynthesis of cofactors and spliceosome were the dominant different pathways between axenic and non-axenic A. catenella strains. The sxtA expression was closely related with Arginine and proline metabolism, Arginine biosynthesis, Fatty acid biosynthesis, TCA cycle and Glutathione metabolism, which were all downregulated in axenic A. catenella. Meantime, the non-axenic A. catenella under nitrogen deprivation produced less PSTs and functional genes than non-axenic strain under common culture condition, indicating the nitrogen significance for PSTs production. The detailed signal molecular released by associated bacteria for regulating PSTs of A. catenella needs to be further studied.