Extracellular Production of Reactive Oxygen Species by Marine Microbiota

The reactive oxygen species (ROS) superoxide (O₂^-) and hydrogen peroxide (H₂O₂) are important to the cycling of trace metals and carbon in marine systems. Previous studies have shown that biological ROS production in the ocean may be significant. We examined the ability of five common species of diatoms to produce and break down ROS in the presence and absence of light by suspending cells on filters and measuring downstream ROS concentrations using chemiluminescence probes. Results show a wide range of rates (undetectable to 7.3 x 10^-16 mol cell^-1 hr^-1) and suggest that extracellular ROS production occurs through a variety of pathways. H₂O₂ decay appears to be mediated primarily by active cell processes, while O₂^- appears to occur through a combination of active and passive cell processes. Extracellular H₂O₂ production and decay were also determined for twelve species of heterotrophic bacteria using two different methodologies. Measured decay rates were consistent despite methodological differences. By contrast, large variability of production rates was observed could vary significantly even among between replicates of the same species measured using the same methodology. Although production rates cannot be stated with certainty, it is likely that extracellular H₂O₂ production occurs in most bacterial species.