Work

Diverse H 2 O 2 -scavenging phenotypes of coral-associated bacteria reveal candidates for bleaching mitigation

Year: 2026

Type: preprint

Abstract: There is growing interest in manipulating coral-associated bacteria to enhance coral thermal bleaching tolerance. Reactive oxygen species (ROS), particularly hydrogen peroxide (H 2 O 2 ), are major drivers of coral bleaching, therefore, coral-associated bacteria capable of scavenging H 2 O 2 may help reduce bleaching. Bacterial candidates are commonly selected through genome inference and occasionally phenotypic assays, but how well these approaches predict H 2 O 2 -scavenging capacity is unknown. We screened 29 bacterial strains isolated from the scleractinian corals Acropora loripes and Galaxea fascicularis for genome-inferred H 2 O 2 -scavenging pathways and in vitro activity using an ABTS radical-scavenging assay, H 2 O 2 tolerance (the highest H 2 O 2 concentration that allows bacterial growth), H 2 O 2 removal from the medium, and qualitative catalase activity. Although all strains encoded at least two complete H 2 O 2 -scavenging pathways, genomic prediction did not consistently align with in vitro scavenging activity. Growth under H 2 O 2 exposure was strongly coupled with H 2 O 2 scavenging, but these traits showed no correlation with ABTS inhibition or catalase activity inferred from bubble formation. The top-ranked phenotypes, based on H 2 O 2 tolerance and scavenging, were observed in Roseovarius , Roseibium , Ruegeria , and Muricauda strains, which tolerated 5–50 mM H 2 O 2 . These genera are common associates of microalgae, including coral endosymbionts, which are key sources of excess ROS during thermal stress. Among these, Roseovarius and Muricauda also showed high ABTS inhibition (>97%), indicating broader antioxidant capacity that may be advantageous within the complex oxidative environment of thermally stressed corals. Strains combining strong H 2 O 2 scavenging with broad antioxidant activity may therefore represent the most promising candidates for subsequent validation within the coral holobiont.

Source: bioRxiv (Cold Spring Harbor Laboratory)

DOI: 10.64898/2026.09.14.751348

Authors: Luanny Martins Fernandes, Talisa Doering, Wing Yan Chan, Madeleine JH van Oppen

Institutions: The University of Melbourne, Australian Institute of Marine Science

Language: English

Topic: Coral and Marine Ecosystems Studies

Subfield: Ecology

Field: Environmental Science

Domain: Physical Sciences

SDG: Life below water

Open Access status: green

Funder: Australian Government