Abstract
Vibrio mediterranei 117-T6 is extensively pathogenic to several Pyropia species, leading to the death of conchocelis. In this study, the first V. mediterranei phage (named Vibrio phage Yong-XC31, abbreviated as Yong-XC31) was isolated. Yong-XC31 is a giant phage containing an icosahedral head about 113 nm in diameter and a contractible tail about 219 nm in length. The latent period of Yong-XC31 is 30 min, and burst size is 64,227. Adsorption rate of Yong-XC31 to V. mediterranei 117-T6 can reach 93.8% in 2 min. The phage genome consisted of a linear, double-stranded 290,532 bp DNA molecule with a G + C content of 45.87%. Bioinformatic analyses predicted 318 open reading frames (ORFs), 80 of which had no similarity to protein sequences in current (26 January 2021) public databases. Yong-XC31 shared the highest pair-wise average nucleotide identity (ANI) value of 58.65% (below the ≥95% boundary to define a species) and the highest nucleotide sequence similarity of 11.71% (below the >50% boundary to define a genus) with the closest related phage. In the proteomic tree based on genome-wide sequence similarities, Yong-XC31 and three unclassified giant phages clustered in a monophyletic clade independently between the family Drexlerviridae and Herelleviridae. Results demonstrated Yong-XC31 as a new evolutionary lineage of phage. We propose a new phage family in Caudovirales order. This study provides new insights and fundamental data for the study and application of giant phages.
Highlights
Bacterium resistant to three or more antimicrobials was defined as multidrug resistant (MDR) [39,40]
Results of this study indicated that the temperature and pH stability of Yong-XC31 was good, which is conducive to its application to control V. mediterranei infections in complex environment
This study finds that Yong-XC31 contains five genes encoding virion-associated RNA polymerase (RNAP) (ORF34, ORF136, ORF140, ORF142, ORF153) and three early expressed RNAPs (ORF46, ORF47, ORF69)
Summary
Vibrio mediterranei is a potential emerging pathogen of marine animals such as corals and scallops [5,6]. V. mediterranei 117-T6 (CGMCC1.16311) was isolated from the bleached shell-born conchocelis of Pyropia yezoensis and was pathogenic to the conchocelis of several Pyropia species, including P. yezoensis [7,8]. Pyropia culture has a long history in China, but there are no effective prevention and control measures for bacterial diseases, which seriously affect the economic income of farmers and the healthy and sustainable development of Pyropia industry [8,9]. Global warming has caused an increase in sea surface temperature that has undoubtedly led to the unseasonal outbreaks of Vibrios as well as their increased abundance and virulence in marine environments and aquaculture [10,11]. There are a growing need for effective methods for managing bacterial infections
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