Microbiome ecological memory and responses to repeated marine heatwaves clarify variation in coral bleaching and mortality.

Microbiomes are essential features of holobionts, providing their hosts with key metabolic and functional traits like resistance to environmental disturbances and diseases. In scleractinian corals, questions remain about the microbiome's role in resistance and resilience to factors contributing to the ongoing global coral decline and whether microbes serve as a form of holobiont ecological memory. To test if and how coral microbiomes affect host health outcomes during repeated disturbances, we conducted a large-scale (32 exclosures, 200 colonies, and 3 coral species sampled) and long-term (28 months, 2018-2020) manipulative experiment on the forereef of Mo'orea, French Polynesia. In 2019 and 2020, this reef experienced the two most severe marine heatwaves on record for the site. Our experiment and these events afforded us the opportunity to test microbiome dynamics and roles in the context of coral bleaching and mortality resulting from these successive and severe heatwaves. We report unique microbiome responses to repeated heatwaves in Acropora retusa, Porites lobata, and Pocillopora spp., which included: microbiome acclimatization in A. retusa, and both microbiome resilience to the first marine heatwave and microbiome resistance to the second marine heatwave in Pocillopora spp. Moreover, observed microbiome dynamics significantly correlated with coral species-specific phenotypes. For example, bleaching and mortality in A. retusa both significantly increased with greater microbiome beta dispersion and greater Shannon Diversity, while P. lobata colonies had different microbiomes across mortality prevalence. Compositional microbiome changes, such as changes to proportions of differentially abundant putatively beneficial to putatively detrimental taxa to coral health outcomes during repeated heat stress, also correlated with host mortality, with higher proportions of detrimental taxa yielding higher mortality in A. retusa. This study reveals evidence for coral species-specific microbial responses to repeated heatwaves and, importantly, suggests that host-dependent microbiome dynamics may provide a form of holobiont ecological memory to repeated heat stress.

cAbl Kinase Regulates Inflammasome Activation and Pyroptosis via ASC Phosphorylation.

Inflammasome activation is regulated in part by the posttranslational modification of inflammasome proteins. Tyrosine phosphorylation is one possible modification. Having previously shown that the protein tyrosine kinase (PTK) inhibitor AG126 greatly inhibits inflammasome activation, we sought to uncover the target kinase. To do this, we screened a commercial tyrosine kinase library for inhibition of inflammasome-dependent IL-18/IL-1ß release and pyroptosis. THP-1 cells (human monocyte cell line) were incubated with PTK inhibitors (0.1, 1, and 10 µM) before stimulation with LPS followed by ATP. The PTK inhibitors DCC-2036 (Rebastinib) and GZD824, specific for Bcr-Abl kinase, showed the most severe reduction of IL-18 and lactate dehydrogenase release at all concentrations used. The suggested kinase target, cAbl kinase, was then deleted in THP-1 cells by CRISPR/Cas9 editing and then tested for its role in inflammasome function and potential to phosphorylate the inflammasome adaptor ASC. The cABL knockout not only significantly inhibited inflammasome function but also decreased release of phosphorylated ASC after LPS/ATP stimulation. One predicted target of cAbl kinase is tyrosine 146 in ASC. Complementation of ASC knockout THP-1 cells with mutated Y146A ASC significantly abrogated inflammasome activation and ASC oligomerization as compared with wild-type ASC complementation. Thus, these findings support cAbl kinase as a positive regulator of inflammasome activity and pyroptosis, likely via phosphorylation of ASC.

High infectivity and waterborne transmission of seagrass wasting disease.

Pathogen transmission pathways are fundamental to understanding the epidemiology of infectious diseases yet are challenging to estimate in nature, particularly in the ocean. Seagrass wasting disease (SWD), caused by Labyrinthula zosterae, impacts seagrass beds worldwide and is thought to be a contributing factor to declines; however, little is known about natural transmission of SWD. In this study, we used field and laboratory experiments to test SWD transmission pathways and temperature sensitivity. To test transmission modes in nature, we conducted three field experiments out-planting sentinel Zostera marina shoots within and adjacent to natural Z. marina beds (20 ± 5 and 110 ± 5 m from bed edge). Infection rates and severity did not differ among outplant locations, implicating waterborne transmission. The infectious dose of L. zosterae through waterborne exposure was assessed in a controlled laboratory experiment. The dose to 50% disease was 6 cells ml-1 and did not differ with the temperatures tested (7.5°C and 15°C). Our results show L. zosterae is transmissible through water without direct contact with infected plants. Understanding the transmission dynamics of this disease in the context of changing ocean conditions will improve Z. marina protection and restoration in critical coastal habitats worldwide.