A new perspective of copper-iron effects on bloom-forming algae in a highly impacted environment

Relatively little work has been done on the role of micronutrients in influencing development and progression of harmful algal blooms, yet micronutrients are ineluctably required for growth. Relatively small changes in micronutrient status have wide-ranging consequences. Here, we report results from mesocosm experiments with Microcystis and Desmodesmus spp., in mono- and mixed-cultures, to probe questions of how copper, iron, and copper-iron amendments affect growth, short-term assemblage progression, and production of siderophore, chalkophore, and microcystin in lake water from a large, hypereutrophic lake (Taihu, China). Our approach offers an entirely new perspective to understanding micronutrient dynamics in aqueous environments, as this is the first work to systematically screen for chalkophores and siderophores separately, as a function of copper/iron amendment, and using community trajectory analysis. Singular findings are summarized as follows: 1) unlike lab-based studies, in our work we observe neither dramatic copper-modulation of iron demand, nor evidence of an iron-protective effect from copper toxicity. 2) The interplay between chalkophore/siderophore production supports a concept model wherein Microcystis spp. varies behavior to individually and uniquely manage copper/iron requirements in a phased manner. In being able to specifically screen for chalkophores, we observe a previously unreported link between chalkophore and microcystin production that may relate to iron-limitation. 3) Regarding harmful algal bloom (HAB) persistance, the lake water itself influences mesocosm changes; differentiated effects for iron regarding growth indicators and/or reduction of Fe-limitation stress were found at an HAB-free field station (Xukou Bay), likely a consequence of low bioavailability of iron in this station as compared to HAB-impacted stations (half the initial dissolved iron concentration, persisting throughout experiments). The low dissolved iron accompanies more intense chalkophore/siderophore community trajectories. Relatively little work has been done on the role of micronutrients in influencing development and pro-gression of harmful algal blooms, yet micronutrients are ineluctably required for growth. Relatively small changes in micronutrient status have wide-ranging consequences. Here, we report results from meso-cosm experiments with Microcystis and Desmodesmus spp., in mono-and mixed-cultures, to probe ques-tions of how copper, iron, and copper-iron amendments affect growth, short-term assemblage progres-sion, and production of siderophore, chalkophore, and microcystin in lake water from a large, hypereu-trophic lake (Taihu, China). Our approach offers an entirely new perspective to understanding micronutri-ent dynamics in aqueous environments, as this is the first work to systematically screen for chalkophores and siderophores separately, as a function of copper/iron amendment, and using community trajectory analysis. Singular findings are summarized as follows: 1) unlike lab-based studies, in our work we ob-serve neither dramatic copper-modulation of iron demand, nor evidence of an iron-protective effect from copper toxicity. 2) The interplay between chalkophore/siderophore production supports a concept model wherein Microcystis spp. varies behavior to individually and uniquely manage copper/iron requirements in a phased manner. In being able to specifically screen for chalkophores, we observe a previously un-reported link between chalkophore and microcystin production that may relate to iron-limitation. 3) Re-garding harmful algal bloom (HAB) persistance, the lake water itself influences mesocosm changes; differ-entiated effects for iron regarding growth indicators and/or reduction of Fe-limitation stress were found at an HAB-free field station (Xukou Bay), likely a consequence of low bioavailability of iron in this station as compared to HAB-impacted stations (half the initial dissolved iron concentration, persisting through-out experiments). The low dissolved iron accompanies more intense chalkophore/siderophore community trajectories. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Little work has been done on the role of micronutrients in influencing harmful algal blooms, yet they are essential for growth. This study investigates the effects of copper, iron, and copper-iron amendments on algal growth and production of certain compounds, providing new insights into micronutrient dynamics in aquatic environments.