Iron‐mediated suppression of bloom‐forming cyanobacteria by oxine in a eutrophic lake

Abstract

1. Published studies show that cyanobacteria have higher Fe requirements than eukaryotic algae. To test whether Fe availability can affect formation of a cyanobacterial bloom, a strong Fe chelator, oxine (8-hydroxyquinoline, C 9 H 7 NO), was added to enclosures in eutrophic Lake 227 in the Experimental Lakes Area (ELA) (northwestern Ontario). 2. Aphanizomenon schindlerii growth was suppressed, and growth of eukaryotic chlorophytes significantly promoted in enclosures to which oxine had been added. Significant eukaryotic growth did not occur in enclosures treated with ammonium, suggesting that N supplied by degradation of oxine was not responsible for eukaryotic success in the oxine enclosures. 3. In situ Fe 2+ measurements were unreliable because of interference from high concentrations of dissolved organic compounds. However, oxine rapidly promoted oxidation of Fe 2+ to Fe 3+ in deionised water, suggesting that rapid removal of Fe 2+ also occurred in the oxine-treated enclosures. 4. In batch cultures, 10 lM M Fe and 10 lM M oxine (a 1 : 1 ratio) completely inhibited the growth of the cyanobacteria Synechococcus sp. and Anabaena flos-aquae and the chlorophytes Pseudokirchneriella subcapitata and Scenedesmus quadricauda. Increasing Fe 10-fold to 100 lM M Fe completely and partially reversed oxine inhibition in the two chlorophytes but could not overcome inhibition of the cyanobacteria, indicating that inhibition was Fe-mediated at least in the eukaryotes. Since oxine binds Fe 3+ in a 1 : 3 ratio (Fe : oxine), inhibition at a 1 : 1 ratio indicates that not all of the Fe is bound, and a mechanism involving Fe other than chelation was at least partly responsible for inhibition. 5. Collectively, the enclosure and laboratory results suggest that the outcome of competition between cyanobacteria and eukaryotic algae in the oxine-treated enclosures in Lake 227 was likely a result of decreased availability of Fe, especially Fe 2+ . 6. The results suggest that remediation methods that dramatically restrict the supply rate of Fe 2+ could reduce the relative abundance of cyanobacteria in eutrophic systems.

Dynamics of phosphorus–iron–sulfur at the sediment–water interface influenced by algae blooms decomposition

“…P has attracted great attention for its significant contribution to eutrophication and algae blooms in aquatic ecosystems [8,9]. Fe is the most prevalent redox-sensitive metal, which has a paramount importance in the oxidation of organic matter [10] and the formation of phytoplankton blooms [11]. Soluble sulfide is highly toxic, and may have relevant impacts at the ecosystem level [12,13].…”

Harmful Algal Blooms

“…Many cyanobacteria, most notably diazotrophs, have high trace metal requirements (Raven, 1990;Wilhelm, 1995), and their growth can be limited by the availability of these micronutrients (Molot et al, 2010). Many cyanobacteria, most notably diazotrophs, have high trace metal requirements (Raven, 1990;Wilhelm, 1995), and their growth can be limited by the availability of these micronutrients (Molot et al, 2010).…”

Two cyanobacterial strains can be distinguished from each other and other eukaryotic algae by spectral absorption method

“…When cyanobacteria become limited by iron or due to lack of isiA gene, phycobilisomes (PBSs) especially PC may be degraded. Those kinds of cyanobacterial species are difficult to differentiate from their common companions i.e., PC containing cyanobacteria and can affect fluorometric method (Beutler et al 2003;Lewis et al 2010). However, fluorescence method does not have enough information for species/strains level identification of cyanobacteria.…”