Determining the Contributions of Microorganisms to H2O2 Degradation and its Implications for the Success of Prochlorococcus in the Oligotrophic Ocean

Benjamin Carter Calfee, University of Tennessee, Microbiology, Knoxville, TN, United States, David Talmy, The University of Tennessee, Microbiology, Knoxville, TN, United States, Steven Wilhelm, University of Tennessee, Knoxville, TN, United States and Erik Zinser, University of Tennessee, Department of Microbiology, Knoxville, TN, United States
Abstract:
Cyanobacteria of the genus Prochlorococcus are one of the most abundant microorganisms throughout the oligotrophic ocean. Prochlorococcus, while being highly adapted to thrive in nutrient limited marine environments, are completely dependent upon other members of the microbial community for the detoxification of radical oxygen species (ROS), specifically hydrogen peroxide (H2O2). Prior research has demonstrated the ability of certain heterotrophic “helper” organisms to benefit the growth of Prochlorococcus both in the natural environment and in laboratory culture by mitigating concentrations of H2O2 in their surrounding environment. Organisms that perform this function are crucial to the success of Prochlorococcus, as H2O2 generated daily in marine surface waters reaches concentrations lethal to the cyanobacterium. While this “helping” phenotype has been observed with a small number of heterotrophic organisms, the diversity of microorganisms able to carry out this function in the oligotrophic ocean remains largely unknown. In order to address this knowledge gap, we performed both mono- and coculture experiments to determine the ability of strains of the marine Synechococcus, picoeukaryotic phytoplankton, and oligotrophic heterotrophs to degrade ecologically relevant concentrations of H2O2 and provide a benefit to Prochlorococcus. H2O2 exposure was carried out by either direct addition or artificial production by HEPES buffer over a diel. These laboratory studies improve our understanding of the contributions of microorganisms participating in H2O2 degradation and highlight the interdependencies of marine microbial communities.