Abstract
Application of algicidal compounds secreted by bacteria is a promising and environmentally friendly strategy to control harmful algal blooms (HABs). Years ago prodigiosin was described as an efficient algicidal compound, but the details about the effect of prodigiosin on algal cells are still elusive. Prodigiosin shows high algicidal activity on Phaeocystis globosa, making it a potential algicide in HAB control. When P. globosa were treated with prodigiosin at 5 μg/mL, algae cells showed cytoplasmic hypervacuolization, chloroplast and nucleus rupture, flagella missing, and cell fracture, when observed by scanning electron microscope and transmission electron microscopy. Prodigiosin induced a reactive oxygen species (ROS) burst in P. globosa at 2 h, which could result in severe oxidative damage to algal cells. Chlorophyll a (Chl a) fluorescence decreased significantly after prodigiosin treatment; about 45.3 and 90.0% of algal cells lost Chl a fluorescence at 24 and 48 h. The Fv/Fm value, reflecting the status of the photosystem II electron flow also decreased after prodigiosin treatment. Quantitative polymerase chain reaction (PCR) analysis psbA and rbcS expression indicated that photosynthesis process was remarkably inhibited by prodigiosin. The results indicated that the inhibition of photosynthesis may produce excessive ROS causing cell necrosis. This study is the first report about algal lysis mechanism of prodigiosin on harmful algae. Our results could increase our knowledge on the interaction between algicidal compounds and harmful algae, which could lead to further studies in the microcosm.
Highlights
Harmful algal blooms (HABs), as the most severe consequence of eutrophication, occur worldwide causing irreversible damage to fisheries, tourism, public health, and the ecosystem (Heisler et al, 2008)
Prodigiosin continued to destroy cells and rbcS gene expression decreased again. These results indicate that the photodamage repair process was inhibited at 12 h, and that carbon fixation process was inhibited at 36 h. These results indicated that prodigiosin treatment induced photosynthesis inhibition at short time points, which may be related to algal cell death
We found that strain KA22 could secrete prodigiosin exhibiting effective algicidal activity on P. globosa (Zhang et al, 2016)
Summary
Harmful algal blooms (HABs), as the most severe consequence of eutrophication, occur worldwide causing irreversible damage to fisheries, tourism, public health, and the ecosystem (Heisler et al, 2008). HAB, caused by Phaeocystis globosa, are frequent blooms in coastal waters (Sheik et al, 2014), producing excessive foam when elimination, which would be a problem for socio-economic activities (Peperzak and Gäbler-Schwarz, 2012). There are Prodigiosin Induced Algal Cell Death several strategies to control HABs, including the use of physical methods (i.e., clay) and chemical algicides (Li and Pan, 2013; Guo et al, 2015). Some bacteria are able to secrete metabolic compounds killing harmful phytoplankton, suggesting that the algicide from bacteria might function as a harmful algae biological control agent in seawaters (Wang et al, 2010a). It has been proved that prodigiosin possesses algicidal activity on several specific dinoflagellates, including C. polykrikoides, Gyrodinium impudicum, and Heterosigma akashiwo, and raphidophyte Chattonella sp. The activity of prodigiosin has not been thoroughly examined and the algicidal mechanism on P. globosa remains elusive
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