Responses of Bloom-Forming Heterosigma akashiwo to Allelochemical Linoleic Acid: Growth Inhibition, Oxidative Stress and Apoptosis

Abstract

Algal blooms have been occurring in many regions worldwide, and allelochemicals are important algaecides used to control harmful algal blooms (HABs). The allelopathic effects of linoleic acid (LA) on the harmful raphidophyte Heterosigma akashiwo were studied, and the possible mechanisms were investigated through analyses of population growth dynamics, cellular ultrastructure and the physiological levels of H. akashiwo. The results showed that the inhibitory effect of LA on H. akashiwo cells increased with an increasing LA concentration. The levels of ROS and MDA were significantly elevated, indicating oxidative stress and lipid peroxidation due to LA exposure. At the same time, LA also activated the antioxidant system, including superoxide dismutase (SOD), catalase (CAT), and POD, and non-enzymatic antioxidants such as reduced AsA and glutathione (GSH). Transmission electron microscopy (TEM) revealed that the morphology of the algal cells was impaired in an LA-dependent manner. Annexin V-FITC/PI double staining and flow cytometric analysis revealed that LA exposure decreased the cellular mitochondrial membrane potential (MMP), increased the rate of apoptosis. LA modulated bcl-2/bax homeostasis and increased the expressions of cytochrome c and caspases-3 and -9, proving that LA induced cell death via the mitochondria-mediated apoptotic pathway. It was suggested that LA had allelopathic effects on H. akashiwo, inducing physiological and morphological changes and finally triggering the apoptosis of H. akashiwo. All of these results showed that LA might have the potential as an algaecide to control harmful algae.

Responses of Karenia mikimotoi to allelochemical linoleic acid: Growth inhibition, photosynthetic damage, oxidative stress and cell apoptosis

“…In recent years, HABs have received widespread attention as it drives great marine environmental crises and K. mikimotoi has been the main casual species of those HABs (Gentien et al, 2007;Griffith and Gobler, 2020). Biological approaches have potential for controlling HABs and some macroalgae have been confirmed to inhibit the growth of many red tide algae using allelochemicals, including LA, ALA and so on (Hirao et al, 2012;Wang and Liu, 2022). In this study, LA was selected as a stress factor to illustrate its effects on K. mikimotoi based on some physiological indicators, which explained the mechanism of algal mortality and revealed the action of ROS to cell cycle and cell apoptosis.…”

“…Annexin V-FITC and PI were added to stain algal cells and cells were incubated at 25°C for 20 min. FITC and PI fluorescence were monitored by the FL-1 channel and FL-2 channel in the FC 500 MPL flow cytometer (Novocyte2040R, ACEA, USA), respectively (Wang and Liu, 2022).…”

Effect of copper sulphate on Cryptocaryon irritans based on metabolome analysis

“…But when the cells are exposed to linoleate for a long time, the cells are obviously damaged, such as cell cavitation and organelle disintegration. This will inhibit the growth of cells, and the damage to mitochondria will aggravate oxidative stress (Wang & Liu, 2022). Studies have shown that linoleic acid destroys the cell membrane of Lactobacillus rhamnosus , then affects the bacterial metabolism and eventually leads to its death (Lv et al, 2020).…”

Efficient Inactivation and Removal of a Harmful Marine Algae—Heterosigma akashiwo—By UV-Assisted Permanganate Oxidation

“…The SOD and CAT activities of algal cells by UV/KMnO 4 treatment were increased remarkably during the first 20 min (Figure 6a,b), indicating that the antioxidant enzyme defense system was activated to resist the attack of ROSs induced by UV/KMnO 4 [52]. However, both the SOD and CAT levels declined subsequently (Figure 6b,c), which suggested that ROS induced by UV/KMnO 4 may exceed the antioxidant capacity and cause damage to the antioxidant enzyme defense system [25]. The significant increase in the MDA content also implied that algal cells were severely damaged by the UV/KMnO 4 treatment (Figure 7d), since MDA is a major product of lipid peroxidation in algal cell membranes [41].…”

“…There are considerable discrepancies between M. aeruginosa and H. akashiwo. The former belongs to prokaryotic algae, while the latter is classified as eukaryotic algae [24,25]. H. akashiwo cells generally have larger sizes (from 10 µm to 17 µm) than M. aeruginosa cells (from 2 µm to 7 µm) [26,27].…”