Enhancement of UV Light Sensitivity of a Vibrio parahaemolyticus O3:K6 Pandemic Strain Due to Natural Lysogenization by a Telomeric Phage

Abstract

The Vibrio parahaemolyticus O3:K6 pandemic clonal strain was first observed in southern Chile in 2004 and has since caused approximately 8,000 seafood-related diarrhea cases in this region. The massive proliferation of the original clonal population offers a unique opportunity to study the evolution of a bacterial pathogen in its natural environment by detection and characterization of emerging bacterial variants. Here, we describe a group of pandemic variants characterized by the presence of a 42-kb extrachromosomal DNA that can be recovered by alkaline extraction. Upon treatment with mitomycin C, these variants lyse with production of a myovirus containing DNA of equal size to the plasmid but which cannot be recovered by alkaline extraction. Plasmid and phage DNAs show similar restriction patterns corresponding to enzyme sites in a circular permutation. Sequenced regions showed 81 to 99% nucleotide similarity to bacteriophage VHML of Vibrio harveyi. Altogether these observations indicate that the 42-kb plasmid corresponds to a prophage, consisting of a linear DNA with terminal hairpins of a telomeric temperate phage with a linear genome. Bacteria containing the prophage were 7 to 15 times more sensitive to UV radiation, likely due to phage induction by UV irradiation as plasmid curing restored the original sensitivity. The enhanced UV sensitivity could have a significant role in reducing the survival and propagation capability of the V. parahaemolyticus pandemic strain in the ocean.

Identification of Outer Membrane Proteins Altered in Response to UVC-Radiation in Vibrio parahaemolyticus and Vibrio alginolyticus

“…This absorption creates damage in the DNA by altering the nucleotide base pairing, thereby creating new linkages between adjacent nucleotides on the same DNA strand [6]. Several investigators have determined the effects of UV radiation on the inhibition of growth [7] and damage of protein, RNA, and DNA for Vibrio [8,9]. All these effects have been related directly or indirectly to genomic damage arising out of primary photochemical changes in nucleic acids.…”

The Linear Plasmid Prophage Vp58.5 of Vibrio parahaemolyticus Is Closely Related to the Integrating Phage VHML and Constitutes a New Incompatibility Group of Telomere Phages

“…There are some reports on the presence of tel and repA in prophages (VP882, VHML, and Vp58.5) of marine Vibrio strains (28,41). V. parahaemolyticus phage VP882 is a close relative of the Halomonas phage ⌽HAP-1 (26).…”

“…However, it was surmised that VHML integrates into the Vibrio chromosome (28,29). Phage VP58.5 was isolated from a V. parahaemolyticus strain belonging to the serovar O3:K6 pandemic clonal complex (41). During the last several years, this clone has been associated with many seafood-borne diarrhea outbreaks in Southeast Asia and South America, particularly Chile (5,12,13,15).…”

“…Based on the previous determination of partial DNA sequences of phage VP58.5, approximately 100 oligonucleotide primers deduced from the annotated sequence of VHML were employed for genome sequencing (28,41). One hundred to two hundred nanograms of DNA from CsCl-purified phages was used as template.…”

“…E. coli and V. parahaemolyticus strains were cultivated in LuriaBertani (LB) broth (38) at 37°C under shaking conditions (200 to 225 rpm). For the cultivation of V. parahaemolyticus, LB broth was supplemented with sodium chloride to a final concentration of 3% (wt/vol) (41). Solid media contained 1.8% (wt/vol) agar.…”