Impact of seasonality on the phycosphere response to reactive oxygen stress during cyanobacterial blooms

Hydrogen peroxide is constantly produced by photo-oxidation in freshwater systems plagued by Microcystis blooms. However, unlike other cyanobacteria and aquatic microorganisms, Microcystis genomes do not contain catalase. Other cyanobacteria without catalase, such as Prochlorococcus, are known to benefit from the hydrogen peroxide degrading enzymes produced by heterotrophic bacteria. It has been shown previously that Microcystis may also benefit similarly from its phycosphere, improving the ability to tolerate hydrogen peroxide in the environment. Seasonality is known to shape the makeup of the phycosphere across marine and freshwater systems, and therefore its functional impact on the Microcystis host. In this study, we examined the effect of seasonality and bloom stage on the functional response of both Microcystis and the phycosphere when treated with 1 µM and 10 µM concentrations of hydrogen peroxide in field and synthetic bloom communities. Metatranscriptomic analysis was paired with growth metrics to determine the community composition of the phycosphere as well as the changes in gene expression for both the Microcystis and the bacterial community at different stages of bloom development. Analyzing the expression of genes related to hydrogen peroxide degradation continues to refine the interactome between Microcystis and its microbiome in the phycosphere