Conserved Pigment Profiles in Phylogenetically Diverse Symbiotic Bacteria Associated with the Corals Montastraea cavernosa and Mussismilia braziliensis

Environmental acclimatization of the relatively high latitude scleractinian coral Pavona decussata: integrative perspectives on seasonal subaerial exposure and temperature fluctuations

BACKGROUND

Coral reefs are being increasingly threatened due to global climate change. However, some coral species have shown strong tolerance despite living in marginal environments. The species Pavona decussata from Weizhou Island in the South China Sea experiences subaerial exposure in summer and winter due to extreme low tides, and their environmental acclimatization to this aerial exposure remains unexplored.

RESULTS

Here we aimed to explore the molecular mechanism of P. decussata under season or subaerial exposure background through physiological and multi-omics integrative analyses. Specifically, corals with a history of seasonal air exposure underwent comprehensive changes in energy metabolism and defense mechanisms compared to permanently submerged corals. In summer, corals experiencing subaerial exposure enhanced antioxidant defense by increasing the activities of the enzymes T-SOD and CAT, and the coral-associated bacterial community shifted toward the class Alphaproteobacteria that may have provided corals with resistance to environmental stresses. Moreover, the decrease in the transcript levels of the TCA cycle and the increase in metabolite content of ornithine suggested an alteration in energy metabolic pathways. Corals with an air-exposed background may have enhanced energy reserves in winter, as indicated by a higher content of Chl a and a rebound in coral-associated bacterial community toward the class Gammaproteobacteria. Furthermore, accumulation of the metabolite leukotriene D4 and activation of the TGF-beta signaling pathway suggested higher anti-inflammatory requirements and positive regulation by innate immunity.

CONCLUSIONS

This study provides insights into the acclimatization of P. decussata to seasonal environmental fluctuations and demonstrates that relatively high-latitude corals possess the plasticity and acclimatory capacity to adapt to marginal environments.

Phototrophic bacteria as potential probiotics for corals

Coral-associated microorganisms provide crucial nutritional, protective, and developmental benefits, yet many functional traits remain unexplored. Phototrophic bacteria may enhance coral nutrition and reduce oxidative stress during bleaching via photosynthesis and antioxidant production. Despite this potential, their role in the holobiont's energy budget and heat stress resilience is understudied. This review explores the functional traits and potential of phototrophic bacteria to enhance coral health and resilience under environmental stress.

Novel Insights and Genomic Characterization of Coral-Associated Microorganisms from Maldives Displaying Antimicrobial, Antioxidant, and UV-Protectant Activities

Coral reef survival is crucial for the socio-ecological interest of many countries, particularly for the Republic of Maldives, whose reef integrity influences the country's livelihoods and economy. These ecosystems are being severely impacted by multiple stressors, leading to declines in biodiversity. In the last few decades, researchers have focused on studying coral-associated microorganisms (CAMs) and their symbiotic role in coral health and resilience. Metabarcoding analysis has been widely utilized to study CAM diversity under various conditions but provides limited information on their functional roles. Therefore, cultivation of bacterial strains remains indispensable for validating ecological and biotechnological hypotheses. In this study, we investigated the microbial community associated with two abundant corals in Maldives, Porites lobata and Acropora gemmifera, and evaluated the antimicrobial, antioxidant, and UV-protectant properties of 10 promising isolated strains. The selected CAMs, Pseudoalteromonas piscicida 39, Streptomyces parvus 79, Microbacterium sp. 92 (a potential novel species), and Micromonospora arenicola 93, exhibited antibiotic activity against a panel of pathogenic strains (MIC from 0.01 to 500 µg/mL), antioxidant (comparable effect to that of Trolox and ascorbic acid), and UV-screen activities (protection of human keratinocytes at 200 µg/mL). Genomes revealed their dual potential in contributing to coral restoration and drug discovery strategies. These findings highlight the biotechnological relevance of CAMs, representing an important step toward the identification of novel and bioactive bacterial species beneficial for coral reef ecosystems and human health.

Recent advancements in coral health, microbiome interactions and climate change

Corals are the visible indicators of the disasters induced by global climate change and anthropogenic activities and have become a highly vulnerable ecosystem on the verge of extinction. Multiple stressors could act individually or synergistically which results in small to large scale tissue degradation, reduced coral covers, and makes the corals vulnerable to various diseases. The coralline diseases are like the Chicken pox in humans because they spread hastily throughout the coral ecosystem and can devastate the coral cover formed over centuries in an abbreviated time. The extinction of the entire reef ecosystem will alter the ocean and earth's amalgam of biogeochemical cycles causing a threat to the entire planet. The current manuscript provides an overview of the recent advancement in coral health, microbiome interactions and climate change. Culture dependent and independent approaches in studying the microbiome of corals, the diseases caused by microorganisms, and the reservoirs of coral pathogens are also discussed. Finally, we discuss the possibilities of protecting the coral reefs from diseases through microbiome transplantation and the capabilities of remote sensing in monitoring their health status.

The coral microbiome: towards an understanding of the molecular mechanisms of coral-microbiota interactions

Corals live in a complex, multipartite symbiosis with diverse microbes across kingdoms, some of which are implicated in vital functions, such as those related to resilience against climate change. However, knowledge gaps and technical challenges limit our understanding of the nature and functional significance of complex symbiotic relationships within corals. Here, we provide an overview of the complexity of the coral microbiome focusing on taxonomic diversity and functions of well-studied and cryptic microbes. Mining the coral literature indicate that while corals collectively harbour a third of all marine bacterial phyla, known bacterial symbionts and antagonists of corals represent a minute fraction of this diversity and that these taxa cluster into select genera, suggesting selective evolutionary mechanisms enabled these bacteria to gain a niche within the holobiont. Recent advances in coral microbiome research aimed at leveraging microbiome manipulation to increase coral's fitness to help mitigate heat stress-related mortality are discussed. Then, insights into the potential mechanisms through which microbiota can communicate with and modify host responses are examined by describing known recognition patterns, potential microbially derived coral epigenome effector proteins and coral gene regulation. Finally, the power of omics tools used to study corals are highlighted with emphasis on an integrated host-microbiota multiomics framework to understand the underlying mechanisms during symbiosis and climate change-driven dysbiosis.

Insights into the genomic repertoire of Aquimarina litoralis CCMR20, a symbiont of coral Mussismilia braziliensis

Aquimarina litoralis CCMR20 originated from the coral Mussismilia braziliensis (Sebastião Gomes Reef, Brazil, summer 2010). To gain new insights into the genomic repertoire associated with symbioses, we obtained the genome sequence of this strains using Illumina sequencing. CCMR20 has a genome size of 6.3 Mb, 32.6%GC, and 5513 genes (37 tRNA and 4 rRNA). A more fine-grained examination of the gene repertoire of CCMR20 disclosed genes engaged with symbiosis (heterotrophic carbon metabolism, CAZymes, B-vitamins group, carotenoid pigment and antioxidant molecules production). Genomic evidence further expand the possible relevance of this symbiont in the health of Mussismilia holobiont.Whole Genome Shotgun project has been deposited at DDBJ/ENA/GeneBank under the accession number WEKL00000000.