Impact of temperature on the temporal dynamics of microcystin in Microcystis aeruginosa PCC7806

Cyanobacterial blooms pose a serious threat to water quality and human health due to the production of the potent hepatotoxin microcystin. In microcystinproducing strains of the widespread genus Microcystis, the toxin is largely constitutively produced, but there are fluctuations between the cellular and extracellular pool and between free microcystin and protein-bound microcystin. Here we addressed the question of how different temperatures affect the growth and temporal dynamics of secondary metabolite production in the strain Microcystis aeruginosa PCC7806 and its microcystin-deficient Delta mcyB mutant. While the wild-type strain showed pronounced growth advantages at 20 degrees C, 30 degrees C, and 35 degrees C, respectively, the Delta mcyB mutant was superior at 25 degrees C. We further show that short-term incubations at 25 degrees C-35 degrees C result in lower amounts of freely soluble microcystin than incubations at 20 degrees C and that microcystin congener ratios differ at the different temperatures. Subsequent assessment of the protein-bound microcystin pool by dot blot analysis and subcellular localization of microcystin using immunofluorescence microscopy showed re-localization of microcystin into the protein-bound pool combined with an enhanced condensation at the cytoplasmic membrane at temperatures above 25 degrees C. This temperature threshold also applies to the condensate formation of the carbon-fixing enzyme RubisCO thereby likely contributing to reciprocal growth advantages of wild type and Delta mcyB mutant at 20 degrees C and 25 degrees C. We discuss these findings in the context of the environmental success of Microcystis at higher temperatures.

Automated summary

Cyanobacterial blooms, which produce hepatotoxin microcystin, pose a serious threat to water quality and human health. This study explores how different temperatures affect the growth and secondary metabolite production in the cyanobacterium Microcystis aeruginosa. It is found that temperature fluctuations impact the production and localization of microcystin in the cells. Additionally, the wild-type strain of Microcystis shows better adaptation at higher temperatures, while the microcystin-deficient mutant performs better at lower temperatures.