Interspecific protection against oxidative stress: green algae protect harmful cyanobacteria against hydrogen peroxide

Abstract

Summary Oceanographic studies have shown that heterotrophic bacteria can protect marine cyanobacteria against oxidative stress caused by hydrogen peroxide (H 2 O 2 ). Could a similar interspecific protection play a role in freshwater ecosystems? In a series of laboratory experiments and two lake treatments, we demonstrate that freshwater cyanobacteria are sensitive to H 2 O 2 but can be protected by less‐sensitive species such as green algae. Our laboratory results show that green algae degrade H 2 O 2 much faster than cyanobacteria. Consequently, the cyanobacterium Microcystis was able to survive at higher H 2 O 2 concentrations in mixtures with the green alga Chlorella than in monoculture. Interestingly, even the lysate of destructed Chlorella was capable to protect Microcystis , indicating a two‐component H 2 O 2 degradation system in which Chlorella provided antioxidant enzymes and Microcystis the reductants. The level of interspecific protection provided to Microcystis depended on the density of Chlorella . These findings have implications for the mitigation of toxic cyanobacterial blooms, which threaten the water quality of many eutrophic lakes and reservoirs worldwide. In several lakes, H 2 O 2 has been successfully applied to suppress cyanobacterial blooms. Our results demonstrate that high densities of green algae can interfere with these lake treatments, as they may rapidly degrade the added H 2 O 2 and thereby protect the bloom‐forming cyanobacteria.

Bibliographic Information