Coral mucus as a reservoir of bacteriophages targeting Vibrio pathogens

Abstract

The increasing trend in sea surface temperature promotes the spread of Vibrio species, which are known to cause diseases in a wide range of marine organisms. Among these pathogens, Vibrio mediterranei has emerged as a significant threat, leading to bleaching in the coral species Oculina patagonica. Bacteriophages, or phages, are viruses that infect bacteria, thereby regulating microbial communities and playing a crucial role in the coral's defense against pathogens. However, our understanding of phages that infect V. mediterranei is limited. In this study, we identified two phage species capable of infecting V. mediterranei by utilizing a combination of cultivation and metagenomic approaches. These phages are low-abundance specialists within the coral mucus layer that exhibit rapid proliferation in the presence of their hosts, suggesting a potential role in coral defense. Additionally, one of these phages possesses a conserved domain of a leucine-rich repeat protein, similar to those harbored in the coral genome, that plays a key role in pathogen recognition, hinting at potential coral-phage coevolution. Furthermore, our research suggests that lytic Vibrio infections could trigger prophage induction, which may disseminate genetic elements, including virulence factors, in the coral mucus layer. Overall, our findings underscore the importance of historical coral-phage interactions as a form of coral immunity against invasive Vibrio pathogens.

Keywords: Vibrio mediterranei; coral mucus layer; vibriophage.

Figure 1

Schematic representation of the viromes utilized in the present study; this figure was created using BioRender (https://biorender.com/).

Figure 2

Characterization of coral mucus viromes; (A) two-dimensional NMDS plot based on the MASH distance; (B) bar graph showing the number of total viral OTUs detected and number of vibriophages detected; the dotted line shows the Nonpareil diversity in each virome; (C) bar plot showing read depth data truncated to the middle 80% (TAD80) of depth values for the most abundant viral OTUs identified in each virome.

Figure 3

Characterization of V. mediterranei phages; (A) heatmap generated using VIRIDIC software to compare phage genomes and identify the closet contigs recovered from the viromes; in the right half, the numbers inside the map represent the nucleotide identity values for each genome pair, rounded to the first decimal; in the left half, the aligned genome length is indicated * indicates the representative phage for each species; (B) transmission electron microscopy images of P. adelos and P. lipares virions.

Figure 4

Easyfig homology diagram of isolated phages and the closest contigs recovered from viromes using BLASTn; functional gene groups are indicated in different colors (see the legend); the blue regions between the genome maps indicate the level of identity from 66% to 100% (see the legend on the right); genome labels with lowercase are from virome assemblies and labels in uppercase from isolated phages.

Figure 5

Fragment recruitment plot of virome reads against V. mediterranei lytic phages (P. adelos and P. lipares) and the prophage (M. evadens); the horizontal axis of each panel corresponds to one viral species from the indicated reference microbial genome; the vertical axis indicates the sequence identity of an alignment between a virome sequence read and the reference genomic sequence; identities range from 95% (bottom) to 100% (top).