Phage-based pathogen control (i.e., phage therapy) has received increasing scientific attention to reduce and prevent the emergence, transmission, and detrimental effects of antibiotic resistance. In the current study, multidrug-resistant Vibrio natriegens strain AbY-1805 was isolated and tentatively identified as a pathogen causing the death of juvenile Pacific abalones (Haliotis discus hannai Ino). In order to apply phage therapy, instead of antibiotics, to treat and control V. natriegens infections in marine aquaculture environments, a lytic phage, vB_VnaS-L3, was isolated. It could effectively infect V. natriegens AbY-1805 with a short latent period (40 min) and high burst size (~890 PFU/cell). Treatment with vB_VnaS-L3 significantly reduced the mortality of juvenile abalones and maintained abalone feeding capacity over a 40-day V. natriegens challenge experiment. Comparative genomic and phylogenetic analyses suggested that vB_VnaS-L3 was a novel marine Siphoviridae-family phage. Furthermore, vB_VnaS-L3 had a narrow host range, possibly specific to the pathogenic V. natriegens strains. It also exhibited viability at a wide range of pH, temperature, and salinity. The short latent period, large burst size, high host specificity, and broad environmental adaptation suggest that phage vB_VnaS-L3 could potentially be developed as an alternative antimicrobial for the control and prevention of marine animal infections caused by pathogenic V. natriegens.

Marine microorganisms play a vital role in aquaculture by influencing water quality and the health of cultured species. Relative to conventional mono-species aquaculture, integrated multi-trophic aquaculture is more environmentally friendly and economically sustainable. However, the temporospatial dynamics of the microbial community in different aquaculture modes and their roles in the seasonal diseases of aquacultural organisms are largely unknown. Here, the seawater bacterial communities and potential pathogens were investigated over thirteen months in three different aquaculture types in Sanggou Bay, a typical maricultural area with nearly 60 years of history. Seasonality played a primary role, while aquaculture type played a subtle role in shaping the bacterioplankton community. Diverse potential pathogens were identified, and r-strategist bacteria, most of which were opportunistic pathogens and typified by Vibrio species, increased and dominated in late summer and autumn, a period of high-risk disease outbreaks in mariculture organisms. Network analyses indicated that the increase in r-strategist bacteria reduced the complexity of microbial interactions, and Vibrio halioticoli (OTU1389), a hub species with extensive positive correlations to other Vibrio OTUs, likely contributed to the increase of pathogenic vibrios due to its macroalgae degradation capability. The major potential pathogenic Vibrio OTUs were further corroborated by genome analyses and environmental simulation experiments using pathogenic Vibrio isolates, including two new species. Moreover, we found seawater dissolved oxygen, temperature, and transparency correlated significantly with the bacterioplankton temporospatial dynamics and the seasonal outbreaks of bacterial pathogens. Our results emphasize the necessity of synchronically monitoring the bacterial community, its pathogens-stimulating species, such as V. halioticoli and other macroalgae-degrading bacteria, and critical physicochemical parameters for predicting and preventing pathogen outbreaks in mariculture.

A novel vibriophage vB_VpaM_XM1 (XM1) was described in the present study. Morphological analysis revealed that phage XM1 had Myovirus morphology, with an oblate icosahedral head and a long contractile tail. The genome size of XM1 is 46,056 bp, with a G + C content of 42.51%, encoding 69 open reading frames (ORFs). Moreover, XM1 showed a narrow host range, only lysing Vibrio xuii LMG 21346 (T) JL2919, Vibrio parahaemolyticus 1.1997, and V. parahaemolyticus MCCC 1H00029 among the tested bacteria. One-step growth curves showed that XM1 has a 20-min latent period and a burst size of 398 plaque-forming units (PFU)/cell. In addition, XM1 exhibited broad pH, thermal, and salinity stability, as well as strong lytic activity, even at a multiplicity of infection (MOI) of 0.001. Multiple genome comparisons and phylogenetic analyses showed that phage XM1 is grouped in a clade with three other phages, including Vibrio phages Rostov 7, X29, and phi 2, and is distinct from all known viral families that have ratified by the standard genomic analysis of the International Committee on Taxonomy of Viruses (ICTV). Therefore, the above four phages might represent a new viral family, tentatively named Weiviridae. The broad physiological adaptability of phage XM1 and its high lytic activity and host specificity indicated that this novel phage is a good candidate for being used as a therapeutic bioagent against infections caused by certain V. parahaemolyticus strains.

A novel lytic bacteriophage, designated vB_ValS-L9, infecting the potential pathogenic bacterium Vibrio alginolyticus L4, was isolated from a coastal aquaculture area in Beihai, China. Transmission electron microscopy revealed that vB_ValS-L9 possesses an icosa-hedral head (56.50 ± 4.19 nm in diameter) and a long tail (143.03 ± 5.32 nm in length), ex-hibiting a typical siphovirus-like morphology within the class Caudoviricetes. The phage demonstrated wide stability across various temperatures, pH levels, and salinities. Genomic sequencing showed that vB_ValS-L9 has a circular double-stranded DNA genome of 43,884 bp with a G+C content of 43.55% and 61 predicted ORFs. No tRNA, virulence, or antibiotic resistance genes were identified. Genomic and phylogenetic analyses, including ANI, VICTOR, VIRIDIC, and conserved protein phylogenies, identified vB_ValS-L9 as a novel species that, together with Vibrio phages Artemius and VapS30, forms a new genus in the class Caudoviricetes, for which the name Artemiovirus is proposed. Furthermore, in vivo trials using juvenile pearl oysters (Pinctada martensii) revealed that vB_ValS-L9 pro-vides substantial prophylactic and therapeutic protection against V. alginolyticus L4 infec-tion, especially when the phage was administered before bacterial challenge. Collectively, these findings suggest that vB_ValS-L9 shows potential as a safe, environmentally robust, and promising biocontrol candidate for managing vibriosis in aquaculture.

A novel lytic bacteriophage, designated vB_ValS-L9, infecting the potentially pathogenic bacterium Vibrio alginolyticus L4, was isolated from a coastal aquaculture area in Beihai, China. Transmission electron microscopy revealed that vB_ValS-L9 possesses an icosahedral head (56.50 ± 4.19 nm in diameter) and a long tail (143.03 ± 5.32 nm in length), exhibiting a typical siphovirus-like morphology within the class Caudoviricetes. The phage demonstrated stability across various temperatures, pH levels, and salinities. Genomic sequencing showed that vB_ValS-L9 has a circular double-stranded DNA genome of 44,025 bp with a G + C content of 43.56% and 61 predicted ORFs. No tRNA, virulence, or antibiotic resistance genes were identified. Genomic and phylogenetic analyses, including ANI, VICTOR, VIRIDIC, and conserved protein phylogenies, identified vB_ValS-L9 as a novel species that, together with Vibrio phages Artemius and VapS30, forms a new genus in the class Caudoviricetes, for which the name Artemiovirus is proposed. Furthermore, in vivo trials using juvenile pearl oysters (Pinctada martensii) revealed that vB_ValS-L9 provides substantial prophylactic and therapeutic protection against V. alginolyticus L4 infection, especially when the phage was administered before bacterial challenge. Collectively, these findings suggest that vB_ValS-L9 shows potential as a safe, environmentally robust, and promising biocontrol candidate for managing vibriosis in aquaculture.