Development of a free radical scavenging probiotic to mitigate coral bleaching

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>Corals are colonized by symbiotic microorganisms that exert a profound influence on the animal’s health. One noted symbiont is a single-celled alga (from the family <jats:italic>Symbiodiniaceae</jats:italic>), which provides the coral with most of its carbon. During thermal stress, the algae’s photosystems are impaired, resulting in a toxic accumulation of reactive oxygen species (ROS) that cause cellular damage to both the host and symbiont. As a protective mechanism the coral host and algal symbiont disassociate; this process is known as bleaching. Our goal was to construct a probiotic comprised of host-associated bacteria able to neutralize free radicals such as ROS. Using the coral model, the anemone <jats:italic>Exaiptasia diaphana</jats:italic>, and pure bacterial cultures isolated from the model animal, we identified six strains with high free radical scavenging ability belonging to the families <jats:italic>Alteromonadaceae, Rhodobacteraceae, Flavobacteriaceae</jats:italic>, and <jats:italic>Micrococcaceae</jats:italic>. In parallel, we established a “negative” probiotic consisting of genetically related strains with poor free radical scavenging capacities. From their whole genome sequences, we explore genes of interest that may contribute to the potential beneficial roles of these putative probiotic members, which may help facilitate the therapeutic application of a bacterial probiotic. Probiotics is one of several interventions currently being developed with the aim of augmenting climate resilience in corals and increasing the likelihood of coral reef persistence into the future.</jats:p><jats:sec><jats:title>IMPORTANCE</jats:title><jats:p>Coral bleaching is tightly linked to the production of reactive oxygen species (ROS), whereby ROS accumulates to a toxic level in host-harboring algae cells leading to coral-algal dysbiosis. Interventions targeting toxic ROS accumulation, such as the application of exogenous antioxidants, have shown promise for maintaining the coral-algal partnership. With the feasibility of administering antioxidants directly to corals low, we have applied bioengineering strategies to develop a probiotic to neutralize toxic ROS during a thermal stress event. This probiotic can then be tested with corals or a coral model to assess its efficacy in improving coral resistance to environmental stress.</jats:p></jats:sec>

Short-Term Exposure to Sterile Seawater Reduces Bacterial Community Diversity in the Sea Anemone, Exaiptasia diaphana

“…Labrenzia is part of the core microbiome of the anemones' Symbiodiniaceae (Lawson et al, 2017) and may have a role in the production of antioxidants such as dimethylsulfoniopropionate (DMSP) and its breakdown products (Sunda et al, 2002). The DMSP biosynthesis (Curson et al, 2017) and degradation genes, were found in the whole genome sequences of E. diaphana-sourced Labrenzia isolates (Dungan et al, 2020a). Sphingobacteriales in soil systems are believed to be copiotrophic, referring to their ability to metabolize a wide array of carbon sources (Hester et al, 2018).…”

“…As an alternative approach to creating the MM, we have explored a community reduction strategy of the E. diaphana microbiome by manipulating the external environment (Clavel et al, 2017), instead of the application of antibiotics. Studies on the microbiome of E. diaphana indicate a similar phylum level diversity to corals (Blackall et al, 2015) for anemones sourced from the Great Barrier Reef (GBR) (Hartman et al, 2019(Hartman et al, , 2020Dungan et al, 2020a), Hawaii (Herrera et al, 2017), Pacific and Caribbean (Brown et al, 2017), Atlantic (Röthig et al, 2016), and Red Sea (Ahmed et al, 2019). We hypothesize that selective forces acting on E. diaphana and its microbiome, when placed in sterile seawater, will reduce the complexity of the microbiome with the loss of some (e.g., transient) members.…”

Exploring Microbial Diversity and Functional Potential along the Bay of Bengal Coastline in Bangladesh: Insights from Amplicon Sequencing and Shotgun Metagenomics

“…117 and Marinomonas ostreistagni 118 among others. Other microorganisms like Alteromonas portus 119,120 and Seonamhaeicola algicola 121,122 are known for production of antioxidants carotenoids, zeaxanthin; Alteromonas oceani 123 and Ruegeria sp. 115 for probiotics; Alteromonas portus 120 for anticancer activity;…”

Linking photoacclimation responses and microbiome shifts between depth-segregated sibling species of reef corals

“…Alteromonadaceae belong to a diverse group of heterotrophic gammaproteobacteria known to associate with marine hosts and nutrient rich environments. Members of this group tolerate relatively high temperatures and have been used in coral probiotic studies as coral-associated bacteria capable of scavenging free radicals (Dungan et al 2020), and therefore could provide similar benefits in shallow, high-light environments. Similarly, Acidimicrobiales are known to be planktonic free-living photoheterotrophs found in both temporal and tropical photic zones (Angly et al 2016) and are associated with DOM in marine environments (Osterholz et al 2018).…”