Specific global responses to N and Fe nutrition in toxic and non‐toxic Microcystis aeruginosa
2016
Alexova, Ralitza | Dang, The Cuong | Fujii, Manabu | Raftery, Mark J. | Waite, T David | Ferrari, Belinda C. | Neilan, Brett A.
The bloom‐forming cyanobacteria species Microcystis aeruginosa includes toxic and non‐toxic (microcystin‐producing) strains. Certain stress conditions stimulate synthesis of microcystin (MCYST) and enhance the binding of the MCYST molecule to proteins. In this quantitative proteomic study, we compared the response of a wild‐type toxic strain PCC 7806, an mcyH⁻ knockout non‐toxic strain, and a naturally occurring non‐toxic strain, PCC 7005, after 8 days in low iron (Fe) and nitrogen (N) starvation in order to assess the benefit of MCYST synthesis in non‐optimal conditions. Fe limitation increased MCYST synthesis and caused an accumulation of phycobilisome proteins and the ferric iron transporter FutA only in the toxic PCC 7806 but not the non‐toxic strains. In N starvation, photosynthetic, C and N metabolism proteins were more abundant in the non‐toxic strains, as were chaperones and proteases. Significant interaction between nutrient availability and toxicity existed for thioredoxin peroxidase and several thioredoxin‐regulated proteins. We propose a competition of MCYST for binding sites in thioredoxin‐regulated proteins during oxidative stress (low Fe) but not in growth‐limiting conditions (low N). This then leads to differences in the regulation of C:N metabolism in toxic and non‐toxic M. aeruginosa in nutrient‐replete and nutrient‐limited conditions.
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