Quantitative Detection of Active Vibrios Associated with White Plague Disease in Mussismilia braziliensis Corals

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.

Recent Insights into the Structure and Function of Mycobacterial Membrane Proteins Facilitated by Cryo-EM

Mycobacterium tuberculosis (Mtb) is one of the deadliest pathogens encountered by humanity. Over the decades, its characteristic membrane organization and composition have been understood. However, there is still limited structural information and mechanistic understanding of the constituent membrane proteins critical for drug discovery pipelines. Recent advances in single-particle cryo-electron microscopy and cryo-electron tomography have provided the much-needed impetus towards structure determination of several vital Mtb membrane proteins whose structures were inaccessible via X-ray crystallography and NMR. Important insights into membrane composition and organization have been gained via a combination of electron tomography and biochemical and biophysical assays. In addition, till the time of writing this review, 75 new structures of various Mtb proteins have been reported via single-particle cryo-EM. The information obtained from these structures has improved our understanding of the mechanisms of action of these proteins and the physiological pathways they are associated with. These structures have opened avenues for structure-based drug design and vaccine discovery programs that might help achieve global-TB control. This review describes the structural features of selected membrane proteins (type VII secretion systems, Rv1819c, Arabinosyltransferase, Fatty Acid Synthase, F-type ATP synthase, respiratory supercomplex, ClpP1P2 protease, ClpB disaggregase and SAM riboswitch), their involvement in physiological pathways, and possible use as a drug target. Tuberculosis is a deadly disease caused by Mycobacterium tuberculosis. The Cryo-EM and tomography have simplified the understanding of the mycobacterial membrane organization. Some proteins are located in the plasma membrane; some span the entire envelope, while some, like MspA, are located in the mycomembrane. Cryo-EM has made the study of such membrane proteins feasible.

Gene expression associated with disease resistance and long-term growth in a reef-building coral

Rampant coral disease, exacerbated by climate change and other anthropogenic stressors, threatens reefs worldwide, especially in the Caribbean. Physically isolated yet genetically connected reefs such as Flower Garden Banks National Marine Sanctuary (FGBNMS) may serve as potential refugia for degraded Caribbean reefs. However, little is known about the mechanisms and trade-offs of pathogen resistance in reef-building corals. Here, we measure pathogen resistance in Montastraea cavernosa from FGBNMS. We identified individual colonies that demonstrated resistance or susceptibility to Vibrio spp. in a controlled laboratory environment. Long-term growth patterns suggest no trade-off between disease resistance and calcification. Predictive (pre-exposure) gene expression highlights subtle differences between resistant and susceptible genets, encouraging future coral disease studies to investigate associations between resistance and replicative age and immune cell populations. Predictive gene expression associated with long-term growth underscores the role of transmembrane proteins involved in cell adhesion and cell-cell interactions, contributing to the growing body of knowledge surrounding genes that influence calcification in reef-building corals. Together these results demonstrate that coral genets from isolated sanctuaries such as FGBNMS can withstand pathogen challenges and potentially aid restoration efforts in degraded reefs. Furthermore, gene expression signatures associated with resistance and long-term growth help inform strategic assessment of coral health parameters.

Mussismilia braziliensis White Plague Disease Is Characterized by an Affected Coral Immune System and Dysbiosis

Infectious diseases are one of the major drivers of coral reef decline worldwide. White plague-like disease (WPL) is a widespread disease with a complex etiology that infects several coral species, including the Brazilian endemic species Mussismilia braziliensis. Gene expression profiles of healthy and WPL-affected M. braziliensis were analyzed in winter and summer seasons. The de novo assembly of the M. braziliensis transcriptome from healthy and white plague samples produced a reference transcriptome containing 119,088 transcripts. WPL-diseased samples were characterized by repression of immune system and cellular defense processes. Autophagy and cellular adhesion transcripts were also repressed in WPL samples, suggesting exhaustion of the coral host defenses. Seasonal variation leads to plasticity in transcription with upregulation of intracellular signal transduction, apoptosis regulation, and oocyte development in the summer. Analysis of the active bacterial rRNA indicated that Pantoea bacteria were more abundant in WPL corals, while Tistlia, Fulvivirga, and Gammaproteobacteria Ga0077536 were more abundant in healthy samples. Cyanobacteria proliferation was also observed in WPL, mostly in the winter. These results indicate a scenario of dysbiosis in WPL-affected M. braziliensis, with the loss of potentially symbiotic bacteria and proliferation of opportunistic microbes after the start of the infection process.

Deciphering Coral Disease Dynamics: Integrating Host, Microbiome, and the Changing Environment

Diseases of tropical reef organisms is an intensive area of study, but despite significant advances in methodology and the global knowledge base, identifying the proximate causes of disease outbreaks remains difficult. The dynamics of infectious wildlife diseases are known to be influenced by shifting interactions among the host, pathogen, and other members of the microbiome, and a collective body of work clearly demonstrates that this is also the case for the main foundation species on reefs, corals. Yet, among wildlife, outbreaks of coral diseases stand out as being driven largely by a changing environment. These outbreaks contributed not only to significant losses of coral species but also to whole ecosystem regime shifts. Here we suggest that to better decipher the disease dynamics of corals, we must integrate more holistic and modern paradigms that consider multiple and variable interactions among the three major players in epizootics: the host, its associated microbiome, and the environment. In this perspective, we discuss how expanding the pathogen component of the classic host-pathogen-environment disease triad to incorporate shifts in the microbiome leading to dysbiosis provides a better model for understanding coral disease dynamics. We outline and discuss issues arising when evaluating each component of this trio and make suggestions for bridging gaps between them. We further suggest that to best tackle these challenges, researchers must adjust standard paradigms, like the classic one pathogen-one disease model, that, to date, have been ineffectual at uncovering many of the emergent properties of coral reef disease dynamics. Lastly, we make recommendations for ways forward in the fields of marine disease ecology and the future of coral reef conservation and restoration given these observations.

Vibrio communities along a salinity gradient within a marine saltern hypersaline environment (Saline di Tarquinia, Italy)

Vibrio species are ubiquitous in a number of different aquatic environments and promptly adapting to environmental changes due to high genome plasticity. The presence of these bacteria in marine salterns, in relation to a salinity gradient has been not investigated yet. Moreover, it is not clear if these hypersaline environments could represent a reservoir for Vibrio spp. This work investigated, through a metagenetic approach, the distribution of Vibrio (over 2 years) in different ponds along the salinity gradient within the 'Saline di Tarquinia' salterns, considering also the adjacent coastal waters and an isolated brine storage basin (BSB). Vibrio occurrence was higher in the sea than in the ponds and BSB, where it usually represented a rare taxon (abundance <1%). In the sea, it showed abundances in-between 1%-2.6% in 8 months out of 24. Four OTUs were assigned to the Vibrio genus; except for one that was more abundant in BSB, the others were much higher in the sea. Redundancy analysis (RDA) suggested a different distribution of the OTUs in relation to water temperature and salinity. Vibrio was found, even with low abundances, at the highest salinities also, suggesting the salterns as a possible reservoir for the bacterium.

Design of novel primer sets for easy detection of Ruegeria species from seawater

Some coral-associated bacteria show protective roles for corals against pathogens. However, the distribution of coral-protecting bacteria in seawater is not well known. In addition, compared with the methods for investigating coral pathogens, few methods have been developed to detect coral-protecting bacteria. Here we prepared a simple method for detecting Ruegeria spp., some strains of which inhibit growth of the coral pathogen Vibrio coralliilyticus. We successfully obtained two Ruegeria-targeting primer sets through in silico and in vitro screening. The primer sets r38F-r30R and r445F-r446R, in addition to the newly designed universal primer set U357'F-U515'R, were evaluated in vitro using environmental DNA extracted from seawater collected in Osaka. These methods and primers should contribute to revealing the distribution of Ruegeria spp. in marine environments.