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The global rise of antimicrobial resistance has intensified efforts in bioprospecting, with researchers increasingly exploring unique marine environments for novel antimicrobials. In line with this trend, our study focused on bacteria isolated from the unique microbiome of crustose coralline algae (CCA), which has yet to be investigated for antimicrobial discovery. In the present work, bacteria were isolated from a CCA collected from Varadero Reef located in Cartagena Bay, Colombia. After performing antimicrobial assays against antibiotic-resistant human and marine pathogens, three isolates were selected for genome sequencing using the Oxford Nanopore technology. Genome mining of the high-quality assemblies revealed 115 putative biosynthetic gene clusters (BGCs) and identified genes in relevant biosynthetic pathways across the three genomes. Nonetheless, we hypothesize that the biosynthesis of antimicrobial compounds results from the expression of undescribed BGCs. Further analysis revealed the absence of genes pertaining to the synthesis of coral larvae settling molecule tetrabromopyrrole, commonly produced by CCA-associated bacteria. We also discuss how differential representation of gene functions between the three isolates may be attributed to the distinct ecological niches they occupy within the CCA. This study provides valuable resources for future research aimed at the discovery of novel antimicrobials, particularly in the face of the antibiotic-resistance global crisis, and highlights the potential of specialized marine environments like CCA. 

The upside-down jellyfish holobiont,Cassiopea xamachana, is a useful model system for tri-partite interactions between the cnidarian host, the photosymbiont, and the bacterial microbiome. While the interaction between the host and photosymbiont has been well studied, less is understood of the associated bacterial community. To date, the bacterial microbiome of wildC. xamachanahas remained largely uncharacterized. Thus, wild medusae (n=6) and larvae (n=3) were collected from two sites in the Florida Keys. Bacterial community composition was characterized via amplicon sequencing of the 16S rRNA gene V4 region. The medusa bacterial community was dominated by members of the Alphaproteobacteria and Gammaproteobacteria, while Planctomycetota, Actinomycetota, Bacteroidota, and Bacillota were also present, among others. Community composition was consistent between locations and across medusa structures (oral arm, bell, and gonad). The larval bacterial community clustered apart from the medusa community in beta diversity analysis and was characterized by the presence of several Pseudomonadota taxa that were not present in the medusa, including theAlteromonas,Pseudoalteromonas, andThalassobiusgenera. A bacterial isolate library encompassing much of the amplicon sequencing diversity was also developed and tested via metabolic assays in a separate culture-dependent analysis of isolates from medusa bells, oral arms, and laplets. Most characteristics were not correlated with host sex or medusa structure, but gelatinase production was more common in laplet isolates, while lactose fermentation was more common in female oral arm isolates. TheEndozoicomonasgenus was dominant in both amplicon sequencing and in our isolate library, and was equally prevalent across all medusa structures and in both sexes. Understanding the bacterial component of theC. xamachanaholobiont will allow us to further develop this important model cnidarian holobiont. 

Coral resilience varies across species, with some exhibiting remarkable stability and adaptability, often mediated by their associated microbiomes. Given the species-specific nature of coral-microbiome interactions, investigating the microbiomes of urban-adapted corals provides critical insights into the health, dynamics, and functioning of coral holobionts. In this study, we examined the microbiome ofMadracis auretenra, a Caribbean coral from Santa Marta, Colombia, across contrasting environmental conditions. Over two years, we compared the microbiomes of healthy and stressed coral colonies from two distinct reef habitats—urban and protected—using 16S rRNA gene sequencing (V4 region) to assess microbial diversity. Our findings revealed microbial richness and diversity were primarily influenced by seasonal and local factors rather than host-specific traits such as interaction with algae, health status, or microhabitat. These variations were not substantial enough to disrupt the overall microbial community structure, which remained stable across temporal and spatial scales. Dominant taxa includedEndozoicomonas, along with Vibrionaceae and Rhodobacteraceae, which form dense ecological interaction networks. Notably, nutrient and oxygen levels emerged as key drivers of microbiome fluctuations, yet Vibrionaceae populations exhibited exceptional temporal stability. These findings highlight the presence of a well-structured and resilient coral microbiome with minimal seasonal variability, even in urban-influenced environments. We propose that the dominance ofEndozoicomonasand the stability of Vibrionaceae populations play a pivotal role in maintaining microbiome balance, ultimately contributing to the ecological resilience ofM. auretenrain dynamic reef habitats. 

The regenerative capacity of Scyphozoans (Phylum Cnidaria) has been relatively understudied. The model organism Cas- siopea xamachana hosts photosynthetic dinoflagellate symbionts in the host’s motile amoebocyte cells. A handful of studies have reported regeneration in the polyps of C. xamachana, but the mechanisms underlying regeneration have not been fully explored. Despite undergoing drastic developmental changes when symbiotic, the effect of symbiont presence and species on host regeneration has never been explored. C. xamachana polyps were decapitated when aposymbiotic, and symbiotic with both a homologous and a heterologous symbiont species. Regeneration and asexual budding were observed, and EdU labeling was performed to observe patterns of cell proliferation in regenerating polyps. The presence of symbionts increased likelihood to regenerate, yet symbiont species did not affect success of regeneration. No blastema or dividing cells were observed, implying cell proliferation is not the primary mechanism behind regeneration in polyps of C. xamachana.