Isolation and algicidal characteristics of a specific algicidal bacterium on Skeletonema costatum

Abstract:

[Background] The frequent occurrence of harmful algae blooms causes serious marine ecological problems, which not only directly affects the stability of marine ecosystems, the sustainable use of marine biological resources, and the healthy development of marine aquaculture, but also lead to a serious threat to human health and even life. Efficient algae-lysing bacteria are one of the effective tools to control harmful algae blooms by biological methods. [Objective] Isolation and molecular identification of algae-lysing bacteria with high algicidal effect on Skeletonema costatum, and studying the algae-lysing mechanism of this strain and the characteristics of algae-lysing substances secreted by algae-lysing bacteria. [Methods] The 2216E plate dilution method was used to isolate and purify bacteria. The 16S rRNA gene sequence was determined to identify the bacterial species. The cell concentration was monitored using microscope for both control and treatment to calculate algicidal rate. The algicidal progress of challenged S. costatum was observed by scanning electron microscope. The algae-dissolving process of S. costatum was studied by using conventional physiological and biochemical methods to study the characteristics of algae-lysing substances. The molecular weight of algae-lysing substances was detected by dialysis bag retention method. [Results] A high-efficiency alginolytic bacterium FDHY-CJ for S. costatum was isolated, which belonged to the genus Alteromonas (Alteromonas sp. FDHY-CJ). The 72-hour treatment of red tide algae by this strain showed that the algae lysis rate was 95.45% against S. costatum and less than 40% for other common red tide algae. Algae-lysing FDHY-CJ lyses algae through extracellular secretions. The algae-lysing properties of algae-lysing substances are not affected by repeated freezing and thawing, but are sensitive to acidity, alkalinity and temperature. Scanning electron microscopy observations showed that the algae-lysing bacteria’s algae the substance directly dissolves the cell wall of S. costatum, causing the siliceous shell to open and the contents to flow out, then the algae was lysed. The algae-lysing active substance has the characteristics of being precipitated by ethanol and ethyl acetate. [Conclusion] The algae-lysing bacteria FDHY-CJ has specific algae-lysing effect on S. costatum. The bacterial algae-lysing was indirect algae-dissolving through secretion, and the molecular weight of this compound was between 3.5 kD and 10.0 kD.

Key words:Harmful algae, Skeletonema costatum, Specific algicidal bacterium, Algicidal characteristics