Energy depletion and opportunistic microbial colonisation in white syndrome lesions from corals across the Indo-Pacific

Building living systematic reviews and reporting standards for comparative microscopic analysis of white diseases in hard corals

Over the last 4 decades, coral disease research has continued to provide reports of diseases, the occurrence and severity of disease outbreaks and associated disease signs. Histology using systematic protocols is a gold standard for the microscopic assessment of diseases in veterinary and medical research, while also providing valuable information on host condition. However, uptake of histological analysis for coral disease remains limited. Increasing disease outbreaks on coral reefs as human impacts intensify highlights a need to understand the use of histology to date in coral disease research. Here, we apply a systematic approach to collating, mapping and reviewing histological methods used to study coral diseases with 'white' signs (i.e., white diseases) in hard coral taxa and map research effort in this field spanning study design, sample processing and analysis in the 33 publications identified between 1984 and 2022. We find that studies to date have not uniformly detailed methodologies, and terminology associated with reporting and disease description is inconsistent between studies. Combined these limitations reduce study repeatability, limiting the capacity for researchers to compare disease reports. A primary outcome of this study is the provision of transparent and repeatable protocols for systematically reviewing literature associated with white diseases of hard coral taxa, and development of recommendations for standardised reporting procedures with the aim of increasing uptake of histology in addition to allowing for ongoing comparative analysis through living systematic reviews for the coral disease field.

Active prophages in coral-associated Halomonas capable of lateral transduction

Temperate phages can interact with bacterial hosts through lytic and lysogenic cycles via different mechanisms. Lysogeny has been identified as the major form of bacteria-phage interaction in the coral-associated microbiome. However, the lysogenic-to-lytic switch of temperate phages in ecologically important coral-associated bacteria and its ecological impact have not been extensively investigated. By studying the prophages in coral-associated Halomonas meridiana, we found that two prophages, Phm1 and Phm3, are inducible by the DNA-damaging agent mitomycin C and that Phm3 is spontaneously activated under normal cultivation conditions. Furthermore, Phm3 undergoes an atypical lytic pathway that can amplify and package adjacent host DNA, potentially resulting in lateral transduction. The induction of Phm3 triggered a process of cell lysis accompanied by the formation of outer membrane vesicles (OMVs) and Phm3 attached to OMVs. This unique cell-lysis process was controlled by a four-gene lytic module within Phm3. Further analysis of the Tara Ocean dataset revealed that Phm3 represents a new group of temperate phages that are widely distributed and transcriptionally active in the ocean. Therefore, the combination of lateral transduction mediated by temperate phages and OMV transmission offers a versatile strategy for host-phage coevolution in marine ecosystems.

Microbiomes and metabolomes of dominant coral reef primary producers illustrate a potential role for immunolipids in marine symbioses

The dominant benthic primary producers in coral reef ecosystems are complex holobionts with diverse microbiomes and metabolomes. In this study, we characterize the tissue metabolomes and microbiomes of corals, macroalgae, and crustose coralline algae via an intensive, replicated synoptic survey of a single coral reef system (Waimea Bay, O'ahu, Hawaii) and use these results to define associations between microbial taxa and metabolites specific to different hosts. Our results quantify and constrain the degree of host specificity of tissue metabolomes and microbiomes at both phylum and genus level. Both microbiome and metabolomes were distinct between calcifiers (corals and CCA) and erect macroalgae. Moreover, our multi-omics investigations highlight common lipid-based immune response pathways across host organisms. In addition, we observed strong covariation among several specific microbial taxa and metabolite classes, suggesting new metabolic roles of symbiosis to further explore.