Response Mechanisms Of Domoic Acid In Pseudo-nitzschia Multiseries Under Copper Stress

Domoic acid(DA)is produced as.a secondary metabolite by some Pseudo-nitzschia.When Pseudo-nitzschia,which produces toxins,is affected by the external environment(such as temperature,pH,heavy metal stress),the production of DA will increase significantly.Studies have shown that metal stress promotes the accumulation and release of DA in toxin-producing Pseudo-nitzschia cells,but the reason for this is unknown.To clarify the role of DA in this process,we exposed the toxin-producing P.multiseries and the non-toxin-producing P.pungens to copper stress(5 and 9 ?M)for 96 hours.Studies have found that P.multiseries grows better than P.pungens under these two copper concentrations.Adding DA to the medium reduced the malondialdehyde(MDA)content in the cells of P.multiseries during copper stress,and the addition of DA also reduced the activity of catalase,(CAT),peroxidase(POD),and superoxide dismutase(SOD).ICP-MS analyses of the copper content in different forms determined that DA and 9?M copper co-treatment reduced the copper content adsorbed in the cells and cell walls of P.multiseries,but did not change the free copper ion content in seawater.LC-MS analysis indicated that DA content in the cells of P.multiseries increased with increased copper stress,and the DA released by cells under the 9 ?M copper treatment increased by 100%.This suggests that DA does not alleviate copper stress by improving the antioxidant defense system of algae cells,nor by complexing with copper ions by algae cells released into seawater.Instead,we speculate that DA forms a complex with copper and is eliminated to reduce the copper content in the cell.Furthermore,the reactive oxygen species(ROS)scavenger N-tert-butyl-?-phenylnitrone(BPN)was used to study the function of the DA accumulated in cells.The addition of BPN significantly reduced the accumulation of DA in the cells,suggesting that DA had a ROS removal effect.Moreover,further experiments demonstrated that the presence of DA could alleviate hydrogen peroxide stress in P.multiseries.Our findings indicate that Pseudo-nitzschia can quench ROS with DA when exposed to environmental oxidative stress.