Applying Surfactin in the Removal of Blooms of Karlodinium veneficum Increases the Toxic Potential

Xiaoyu Tian,Chengxu Zhou,Ran Meng,Xiaojun Yan,Yuanbo Pan

doi:10.3390/jmse10020196

Abstract

Biosurfactant has potential application value in the removal of microalgal blooms, but the ecological risks require more research. In this paper, the effects of surfactin on the toxic dinoflagellate Karlodinium veneficum were studied. The coaction of surfactin and K. veneficum was also evaluated through toxicological experiments on Artemia and juvenile clams. The results showed that: (1) in the concentration range of 0–10 mg/L, surfactin significantly killed algal cells in a dose-dependent manner within 48 h; the 24 h EC50 was 3.065 mg/L; (2) K. veneficum had the ability to restore population growth after stress reduction and the restored proliferation was positively correlated with the initial surfactin concentration; (3) the ability to restore population growth was associated with protection afforded by the promotion of antioxidant enzymes, including catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD), whose increase was positively correlated with the surfactin concentration; (4) the toxicity of the coculture of surfactin and K. veneficum was significantly greater than that of the K. veneficum culture or surfactin alone and was dose and time dependent. The potential ecological risks should be considered when applying biosurfactants, such as surfactin, in the removal of harmful algal blooms.

Highlights

The small athecate dinoflagellate Karlodinum veneficum is a cosmopolitan toxic harmful algal bloom (HAB) species that is commonly distributed in coastal seawaters, and estuarine or mariculture ponds [1,2,3,4,5]
On the 2nd day, the algal cell number continued to decrease in the groups treated with surfactin concentrations of 2.5–10 mg/L
During the 7 days of the experimental period, the algal cell density in the 10 mg/L surfactin group remained at the lowest value (0.25 × 104 cell/mL) from the 1st day onward

Summary

Introduction

The small athecate dinoflagellate Karlodinum veneficum is a cosmopolitan toxic harmful algal bloom (HAB) species that is commonly distributed in coastal seawaters, and estuarine or mariculture ponds [1,2,3,4,5]. Karlotoxins participate in predation or in grazer deterrence [3,14,17] During predation, these toxins are produced and secreted into the water to immobilize the prey [18]. When environmental conditions do not favor the growth of K. veneficum, toxins may be released from senescent cells, and the cellular content of the toxins increases when population growth is halted [3,19]. These characteristics of K. veneficum raise questions regarding the fate of the cells when the dense blooms are terminated and regarding the changes in toxicity that occur when the cells are lysed or stressed

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