Abstract
Algicidal bacteria can lyse microalgal blooms and trigger shifts within plankton communities. Resistant algal species can escape lysis, and have the opportunity to dominate the phytoplankton after a bacterial infection. Despite their important function in ecosystem regulation, little is known about mechanisms of resistance. Here, we show that the diatom Chaetoceros didymus releases eicosanoid oxylipins into the medium, and that the lytic algicidal bacterium, Kordia algicida, induces the production of several wound-activated oxylipins in this resistant diatom. Neither releases nor an induction occurs in the susceptible diatom Skeletonema costatum that is lysed by the bacterium within a few days. Among the upregulated oxylipins, hydroxylated eicosapentaenoic acids (HEPEs) dominate. However, also, resolvins, known lipid mediators in mammals, increase upon exposure of the algae to the algicidal bacteria. The prevailing hydroxylated fatty acid, 15-HEPE, significantly inhibits growth of K. algicida at a concentration of approximately 1 µM. The oxylipin production may represent an independent line of defense of the resistant alga, acting in addition to the previously reported upregulation of proteases.
Highlights
Multiple processes govern the complex species succession in plankton
We identify an induced upregulation of a family of oxylipins in the wound-activated response of the resistant alga, as well as a release of these metabolites, that may the wound-activated response of theagainst resistant alga, as well as a release of these metabolites, that may contribute to the chemical defense bacteria
Growing algal cultures were incubated with a suspension of K. algicida at a final
Summary
Multiple processes govern the complex species succession in plankton. It has been recognized, early on, that nutrient availability and abiotic conditions favor certain species that can reach dominating abundance within the community [1]. Diatoms that frequently dominate phytoplankton communities have evolved mechanisms to counter predation by the wound-activated formation of polyunsaturated aldehydes that inhibit the proliferation of herbivorous copepods [6,7] These responses are triggered by cell disruption, that leads to rapid activation of lipases and lipoxygenases, building up massive local amounts of defensive aldehydes [8,9]. Further higher molecular weight oxylipins have been reported from diatoms, and are potentially involved in wound-activated defense, their ecological role is not yet fully understood [10,11]. Algicidal bacteria can substantially reduce native populations, and are utilized in biotechnology for cell lysis Their mode of action is as diverse as diatom and[16].
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