title: Elevated pCO2 causes a shift towards more toxic microcystin variants in nitrogen-limited Microcystis aeruginosa.
abstract: Elevated pCO2 may promote phytoplankton growth, and potentially alleviate carbon limitation during dense blooms. Under nitrogen-limited conditions, elevated pCO2 may furthermore alter the phytoplankton carbon-nitrogen (C:N) balance and thereby the synthesis of secondary metabolites, such as cyanobacterial toxins. A common group of these toxins are the microcystins, with variants that differ not only in C:N stoichiometry, but also in toxicity. Here, we hypothesized that elevated pCO2 will increase the cellular C:N ratios of cyanobacteria, thereby promoting the more toxic microcystin variants with higher C:N ratios. To test this hypothesis, we performed chemostat experiments under nitrogen-limited conditions, exposing three Microcystis aeruginosa strains to two pCO2 treatments: 400 and 1200 μatm. Biomass, cellular C:N ratios and total microcystin contents at steady state remained largely unaltered in all three strains. Across strains and treatments, however, cellular microcystin content decreased with increasing cellular C:N ratios, suggesting a general stoichiometric regulation. Furthermore, as predicted, microcystin variants with higher C:N ratios generally increased with elevated pCO2, while the variant with a low C:N ratio decreased. Thus, elevated pCO2 under nitrogen-limited conditions may shift the cellular microcystin composition towards the more toxic variants. Such CO2-driven changes may have consequences for the toxicity of Microcystis blooms.
authors.affiliation: Institute of Hydrobiology, Jinan University, Guangzhou, 510632, China Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Droevendaalsesteeg 10, Wageningen 6708 PB, The Netherlands liu.jing198411@gmail.com.
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Droevendaalsesteeg 10, Wageningen 6708 PB, The Netherlands.
authors.forename: Elmer
authors.initials: E
authors.lastname: Van Oosterhout
authors.affiliation: Aquatic Ecology & Water Quality Management Group, Wageningen University, PO Box 47, Wageningen 6700 AA, The Netherlands.
authors.forename: Elisabeth J
authors.initials: EJ
authors.lastname: Faassen
authors.affiliation: Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Droevendaalsesteeg 10, Wageningen 6708 PB, The Netherlands Aquatic Ecology & Water Quality Management Group, Wageningen University, PO Box 47, Wageningen 6700 AA, The Netherlands.
authors.forename: Miquel
authors.initials: M
authors.lastname: Lürling
authors.affiliation: Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Droevendaalsesteeg 10, Wageningen 6708 PB, The Netherlands.
authors.forename: Nico R
authors.initials: NR
authors.lastname: Helmsing
authors.affiliation: Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Droevendaalsesteeg 10, Wageningen 6708 PB, The Netherlands.
authors.forename: Dedmer B
authors.initials: DB
authors.lastname: Van de Waal
mesh_terms: D001427:Bacterial Toxins / Q000096:biosynthesis*; D018533:Biomass; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D000087522:Cyanobacteria Toxins; D008387:Marine Toxins / Q000096:biosynthesis*; D052998:Microcystins / Q000096:biosynthesis*; D046931:Microcystis / Q000254:growth & development* / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D010839:Phytoplankton / Q000254:growth & development / Q000378:metabolism
chemical_list: D001427:Bacterial Toxins; D000087522:Cyanobacteria Toxins; D008387:Marine Toxins; D052998:Microcystins; D002245:Carbon Dioxide; D002244:Carbon; C078588:microcystin; D009584:Nitrogen
keywords: C:N ratio; Microcystis aeruginosa; amino acids; carbon dioxide; global change; microcystins