Information exchange among marine microbes via the reactive oxygen species hydrogen peroxide, with potential community reorganization effects

Chemical signaling is a mechanism potentially creating ocean ‘memory’, as short-term responses to environmental and biotic stimuli lead to altered microbial interactions with repercussions for (longer-lived) attributes of community structure and function. On even longer time scales, production and reception of defensive signals can promote co-evolution of predators and prey, a form of genetically embodied memory of past conditions and interactions. We present data on the production and decomposition of hydrogen peroxide by marine microbes in the context of its role as a potential signaling and defense compound, and hence a catalyst for physiological, ecological, and evolutionary change. Kinetic measurements using the Amplex Red assay showed that common marine phytoplankton from a range of taxonomic groups, as well as (in some cases) their associated bacteria, both produce and decompose H₂O₂ in nutrient-replete batch culture. Per-cell rates of phytoplankton H₂O₂ production were inversely proportional to cell density, suggesting a mechanism for the sensing of cell concentration by members of a population. Metabolic H₂O₂ production by the HAB species Heterosigma akashiwo, which can be toxic to protist predators, was stimulated by the presence of a ciliate grazer, while the ciliate culture showed a strong ability to decompose the HAB-produced H₂O₂. Consequences of these interactions for ‘memory’ in the form of persistent alterations to community structure will be discussed.