Production of extracellular superoxide and hydrogen peroxide by five marine species of harmful bloom-forming algae.

Julia M Diaz,Catharina Alves-De-Souza,Carmelo Tomas,Sydney Plummer,Pia Moisander

doi:10.1093/plankt/fby043

Abstract

Harmful bloom-forming algae include some of the most prolific microbial producers of extracellular reactive oxygen species (ROS). However, the taxonomic diversity of ROS production, the underlying physiological mechanisms and ecophysiological roles of ROS cycling are not completely characterized among phytoplankton taxa that form harmful algal blooms (HABs). This study examines the extracellular production of the ROS superoxide and hydrogen peroxide by five marine HAB species: Chattonella marina, Heterosigma akashiwo, Karenia brevis, Pseudo-nitzschia sp. and Aureococcus anophagefferens. All species produced extracellular superoxide and hydrogen peroxide. Rates of ROS production per cell spanned several orders of magnitude and varied inversely with cell density, suggesting a potential signaling role for extracellular ROS. ROS production was also detected in the spent media of all cultures except K. brevis, indicating the presence of cell-free ROS-generating constituents, such as enzymes or metabolites, which could be further investigated as molecular targets for tracking ROS production in laboratory and field settings. Finally, ratios of superoxide to hydrogen peroxide production could not be accounted for by superoxide dismutation alone, except in the case of K. brevis, indicating a diversity of ROS production and degradation pathways that may ultimately help illuminate the functions of HAB-derived ROS.

Highlights

reactive oxygen species (ROS) contribute to the cycling of carbon (Pullin et al, 2004), transform vital trace metals such as iron (Rose, 2012) and regulate toxic elements like mercury (Siciliano et al, 2002)
Rates of extracellular superoxide production measured over a broad range of cell densities of C. marina, H. akashiwo, K. brevis, Pseudo-nitzschia sp. and A. anophagefferens were corrected for superoxide production rates in cellfree filtrates
All harmful algal blooms (HABs) species examined in this study produced extracellular superoxide and hydrogen peroxide, and cellassociated ROS production rates ranged several orders of magnitude within and between organisms

Summary

Introduction

ROS contribute to the cycling of carbon (Pullin et al, 2004), transform vital trace metals such as iron (Rose, 2012) and regulate toxic elements like mercury (Siciliano et al, 2002). Harmful bloom-forming algae exhibit the highest rates of extracellular ROS production observed among aquatic microorganisms. These ROS contribute to the toxic or noxious activity of several harmful algal bloom (HAB) taxa, such as raphidophytes (Oda et al, 1992, 1997; Yang et al, 1995; Kim et al, 1999b) and the dinoflagellates Margalefidinium polykrikoides (Kim et al, 1999a; Tang and Gobler, 2009b; Tang and Gobler, 2010) and Alexandrium spp. We explore the rates, cell densitydependent regulation and mechanisms of extracellular ROS production by five species of harmful bloomforming algae, including the key taxa Karenia brevis, Pseudo-nitzschia sp. We explore the rates, cell densitydependent regulation and mechanisms of extracellular ROS production by five species of harmful bloomforming algae, including the key taxa Karenia brevis, Pseudo-nitzschia sp. and Aureococcus anophagefferens, for which extracellular ROS production either has not been reported or not been quantified previously

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