The role of heterotrophic bacteria in mediating hydrogen peroxide concentrations in the Western Basin of Lake Erie

Abstract

Hydrogen peroxide (H2O2) plays a role in numerous environmental processes. Its interactions with biology are complex because microorganisms can be both sources and sinks of H2O2, and it is a potent oxidative stressor for all organisms. A newly hypothesized impact of this compound is selection for toxic strains of Microcystis spp., a globally important bloom-forming cyanobacterium. This effect is relevant in the Western Basin of Lake Erie of the Laurentian Great Lakes, where Microcystis spp. often dominate cyanobacterial blooms during the warm summer months. Previous measurements in the lake have revealed a dynamic and recurrent trend in H2O2 concentration over the bloom season: in mid-July of 2014 and 2015, there was a rapid increase in concentration, followed closely by a sharp decrease. In the past, H2O2 production in aquatic ecosystems was thought to occur primarily through abiotic pathways, but a recent study in Lake Erie suggested that biological activity was the primary determining factor in both H2O2 production and degradation over the bloom season. The present study sought to elucidate the mechanisms of H2O2 production and decay in the Western Basin of Lake Erie by studying bacteria that may influence H2O2 concentrations in the lake. Heterotrophic bacteria were isolated from Lake Erie water samples and enrichment cultures of Microcystis and other phytoplankton, characterized by 16S rRNA gene sequencing, and evaluated in terms of their environmental abundance. Experiments were performed on selected isolates that quantified their ability to both produce and degrade H2O2 in liquid culture. Rates of H2O2 production and decay measured in culture under environmentally relevant conditions show that these bacteria could account for the H2O2 trend in the Western Basin of Lake Erie. The results support the idea that heterotrophic organisms play an important role in mediating H2O2 concentration in cyanobacterial bloom communities and other aquatic ecosystems.