AUTHOR=Armoza-Zvuloni Rachel , Schneider Avi , Shaked Yeala 

TITLE=Rapid Hydrogen Peroxide Release during Coral-Bacteria Interactions

JOURNAL=Frontiers in Marine Science

VOLUME=3

YEAR=2016

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2016.00124

DOI=10.3389/fmars.2016.00124

ISSN=2296-7745

ABSTRACT=<p>Ocean warming has exacerbated the severity of coral diseases, many of which are mediated by pathogenic bacteria. In response to the presence of pathogens various organisms activate an oxidative burst response, involving strong and rapid generation of reactive oxygen species (ROS) that serve both as bactericides and as signals for other defense systems. While many components of the coral immune systems are being unveiled, an oxidative burst response, triggered by bacteria proximity, has not yet been reported. Hydrogen Peroxide (H<sub>2</sub>O<sub>2</sub>), one of the ROS produced during the oxidative burst, is often monitored as an indicator of this pathway. Here we report a yet undescribed release of H<sub>2</sub>O<sub>2</sub> from the coral <italic>Stylophora pistillata</italic> upon contact with bacteria. In a series of short term experiments we monitored H<sub>2</sub>O<sub>2</sub> concentrations in the vicinity of <italic>S. pistillata</italic> prior to and following local administration of five bacteria isolates belonging to the genus <italic>Vibrio</italic> (obtained from healthy <italic>S. pistillata</italic>). In most experiments, rapid H<sub>2</sub>O<sub>2</sub> release was recorded at the site of interaction within one min from <italic>Vibrio</italic> addition and persisted for the remaining 5 min of the experiment. In some experiments, discrete or continuous drop of H<sub>2</sub>O<sub>2</sub> to below background levels were seen following <italic>Vibrio</italic> addition. This H<sub>2</sub>O<sub>2</sub> loss was quantitatively accounted for by the bacterial antioxidants and implies that <italic>Vibrio</italic> may at times offset the coral released H<sub>2</sub>O<sub>2.</sub>The total H<sub>2</sub>O<sub>2</sub> released by the coral from the small interaction site (~10 mm<sup>2</sup>) was 200–600 pmol, which may build up to a concentration of ~20 μM in the coral diffusive boundary layer. H<sub>2</sub>O<sub>2</sub> concentrations above 10 μM resulted in significant mortality of the coral pathogen <italic>Vibrio coralliilyticus</italic>, suggesting that the released H<sub>2</sub>O<sub>2</sub> may act as a bactericide. It is thus far unclear if this H<sub>2</sub>O<sub>2</sub> release is part of an oxidative burst response, but it's occurrence strongly indicates that corals sense and chemically react toward bacteria.</p>