A broad-host-range lytic phage vB_VhaS-R18L as a candidate against vibriosis

Abstract

Vibriosis is one of the most common bacterial diseases that cause high rates of mortality and considerable economic losses in aquaculture. Phage therapy has been considered as a promising alternative method to antibiotics in the biocontrol of infectious diseases. Genome sequencing and characterization of the phage candidates are prerequisites before field applications to ensure environmental safety. In this study, a lytic phage, named vB_VhaS-R18L (R18L), was isolated from the coastal seawater of Dongshan Island, China. The phage was characterized in terms of morphology, genetic content, infection kinetics, lytic profile, and virion stability. Transmission electronic microscopy indicated that R18L is siphovirus-like, comprising an icosahedral head (diameter 88.6 ± 2.2 nm) and a long noncontractile tail (225 × 11 nm). Genome analysis indicated R18L to be a double-stranded DNA virus with a genome size of 80,965 bp and a G + C content of 44.96%. No genes that encode known toxins or genes implicated in lysogeny control were found in R18L. A one-step growth experiment showed that R18L had a latent period of approximately 40 min and a burst size of 54 phage particles per infected cell. R18L showed lytic activity against a wide range of at least five Vibrio species (V. alginolyticus, V. cholerae, V. harveyi, V. parahemolyticus, and V. proteolyticus). R18L was relatively stable at pH 6–11 and at temperatures ranging from 4°C to 50°C. The broad lytic activity across Vibrio species and the stability in the environment make R18L a potential candidate for phage therapy in controlling vibriosis in aquaculture systems.

Biologic and genomic characterization of a novel virulent Aeromonas hydrophila phage phiA051, with high homology to prophages

“…Phage phiA051 could only lyse A. hydrophila A009, A013, A019 and A051 out of 68 tested Aeromonas strains (including 24 strains of A. hydrophila ), implying that it has a narrow host range compare with some of phages that have been reported ( 38 , 51–59 ).…”

Characterization of a Vibriophage Infecting Pathogenic Vibrio harveyi

“…Additionally, R21Y maintained high lytic activity over varying environmental conditions (4-55 • C and pH 4-10). R21Y showed better thermal tolerance than vB_VhaM_pir03 (45 • C) [21], VPMCC5 (45 • C) [50], vB_VhaS_MAG7 (45 • C) [54], V-YDF132 (50 • C) [49], and vB_VhaS-R18L (50 • C) [53] and greater acid tolerance than V-YDF132 (pH 5-11) and vB_VhaS-R18L (pH 6-11). Thus, R21Y can remain stable and exert bactericidal activity in practical applications, suggesting that it is a promising candidate for biological control of V. harveyi disease.…”

“…The plaque diameter and burst size of R21Y were 0.69 ± 0.15 mm and 35 plaque-forming units (PFU) per cell, respectively. From a comparative analysis of phage R21Y with vibriophages VB_VhaS-R18L (2.0 mm, 54 PFU/cell) [53] and vB_VpS_PG28 (1.5-2.0 mm, 103 PFU/cell) [55], it is intuitively apparent that a larger burst size would result in a larger plaque size. i.e., the plaque size of Vibrio phages is positively correlated with burst size, which concurs with the classical model [56].…”

“…This pathway is the primary pathway for glucose degradation and energy production. PPDK exists in bacteria, protists, and plants but has been found in only a few Vibrio siphoviruses [35,48,53,57]. When R21Y infects host cells, expression of the PPDK gene may aid the host's carbohydrate metabolism, resulting in more energy for the phage progeny.…”