Date Published: March 12, 2019
Publisher: Public Library of Science
Author(s): Susmita Das Nishu, Yunhee Kang, Il Han, Tae Young Jung, Tae Kwon Lee, Jean-François Humbert.
Algicidal bacteria have received broad acceptance as an ecofriendly tool for controlling harmful algal blooms. However, their practical application is still limited to the lab-scale tests due to the complex alga–bacterium interactions in different nutrient statuses. In this study, the Aeromonas sp. L23 that exhibit relatively wide-spectrum in algicidal activity was isolated from a eutrophic agricultural lake. The physiological response of cyanobacteria and green to the algicidal activity under varied nutritional status were studied in an alga-bacterial co-culture. The algicidal activities of L23 against Microcystis aeruginosa UTEX LB 2385, Microcystis aeruginosa NHSB, Anabaena variabilis AG10064, Scenedesmus quadricauda AG10003, and Chlorella vulgaris AG10034 were 88 ± 1.2%, 94 ± 2.6%, 93 ± 0.5%, 82 ± 1.1%, and 47 ± 0.9%, respectively. The L23 cells had low algicidal activity in cell pellet (3%–9%) compared with the cell-free supernatant (78%–93%), indicating that the activity is induced by extracellular substances. Adding glucose, NaNO3, NH4Cl, and KH2PO4 to the co-culture raised the algicidal activity of the L23 against green algae by 5%–50%. Conversely, a 10%–20% decrease in activity occurred against the target cyanobacteria except M. aeruginosa UTEX LB 2385. These results indicated that the interspecific algicidal activity changes according to the nutritional status, which means that the alga-bacterium interaction will be more complex in the field where the nutritional status changes from time to time.
Harmful algal blooms (HABs) involve the rapid proliferation of phytoplankton, such as cyanobacteria and green algae, which produces toxins harmful to the environment . Increases in HABs due to anthropogenic interference are not only damaging the environment  but also threatening water security and public health [1, 3].
This study demonstrated the ability of the Aeromonas strain L23, isolated from a lake at which HABs frequently occur, to inhibit the growth of different types of microalgae including three cyanobacteria and two green algae using their extracellular substances in a manner dependent on the nutritional status. Specifically, the algicidal activity for different types of microalgae varied depending on the nutrient loading. It becomes clear that alga-bacterium interactions are highly complex as the interactions between algal species and bacteria varies continuously with nutritional status in the field. These insights will now pave the way toward elaborate studies which contribute a better understanding of the role of algicidal bacteria within algal communities in the field.