Algicidal activity of marine Alteromonas sp. KNS-16 and isolation of active compounds.

The KNS-16 algicidal strain was isolated from a harmful alga bloom (HAB) area and identified as Alteromonas sp. based on 16S rDNA sequencing. The KNS-16 strain was found to control HABs by producing algicidal compounds in an indirect interaction. Four active compounds were isolated from KNS-16 culture, and their structures were analyzed by interpreting nuclear magnetic resonance and mass spectroscopy data. The structures were identified as 2-undecen-1'-yl-4-quinolone (1), 2-undecyl-4-quinolone (2), 3-hexyl-6-pentyl-4-hydroxyl-2H-pyran-2-one (3), and 6-heptyl-3-hexyl-4-hydroxyl-2H-pyran-2-one (4). Compound 1 was most active against HABs such as Heterosigma akashiwo, Cochlodinium polykrikoides, and Alexandrium tamarense with LC(50) values of 0.5-1.1 µg/mL. The four compounds exhibited high LC(50) values against aquaculture algae such as Tetaselmis suecica, Isochrysis galbana, and Pavlova lutheri at 39-66 µg/mL. Based on toxicity tests on the brine shrimp Artemia salina and the rotifer Brachionus rotundiformis, the four compounds showed ranges of 409-608 and 189-224 µg/mL of LC(50) for the two organisms, respectively. The LC(50) values for juvenile fish of Sebastes schlegelii were 284-304 µg/mL.