A Persistent, Productive, and Seasonally Dynamic Vibriophage Population within Pacific Oysters ( Crassostrea gigas )

Abstract

In an effort to understand the relationship between Vibrio and vibriophage populations, abundances of Vibrio spp. and viruses infecting Vibrio parahaemolyticus (VpVs) were monitored for a year in Pacific oysters and water collected from Ladysmith Harbor, British Columbia, Canada. Bacterial abundances were highly seasonal, whereas high titers of VpVs (0.5 ؋ 10 4 to 11 ؋ 10 4 viruses cm ؊3 ) occurred year round in oysters, even when V. parahaemolyticus was undetectable (<3 cells cm ؊3 ). Viruses were not detected (<10 ml ؊1 ) in the water column. Host-range studies demonstrated that 13 VpV strains could infect 62% of the V. parahaemolyticus strains from oysters (91 pairings) and 74% of the strains from sediments (65 pairings) but only 30% of the water-column strains (91 pairings). Ten viruses also infected more than one species among V. alginolyticus, V. natriegens, and V. vulnificus. As winter approached and potential hosts disappeared, the proportion of host strains that the viruses could infect decreased by ϳ50% and, in the middle of winter, only 14% of the VpV community could be plated on summer host strains. Estimates of virus-induced mortality on V. parahaemolyticus indicated that other host species were required to sustain viral production during winter when the putative host species was undetectable. The present study shows that oysters are likely one of the major sources of viruses infecting V. parahaemolyticus in oysters and in the water column. Furthermore, seasonal shifts in patterns of host range provide strong evidence that the composition of the virus community changes during winter.Viral infection of marine microbial communities (reviewed in references 17, 49, 63, and 64) has been associated with reduced primary production (23, 47, 50) and increased bacterial mortality through either lytic (21,39,42,46,62) or temperate (27,28,39,59,60) phage. Frequently, Vibrio spp. and vibriophage, which are common in seawater (4, 53) and easily culturable (16), have served as model systems in studies of host-virus interactions in the water column (see, for example, references 22, 33, 37, 43, 52, 54, and 61). Vibrio spp. are typically much more abundant in sediments (10 4 g Ϫ1 ) (41), plankton (10 9 g Ϫ1 ) (31), and shellfish (10 5 g Ϫ1 ) (1) than in the water column (ϳ10 ml Ϫ1 ) (5). In contrast, even though virus particles are extremely abundant in sediments (10 8 to 10 9 ml Ϫ1 ) (10, 15) and in the water column (ca. 10 7 to 10 8 ml Ϫ1 ) (64), vibriophage are most abundant in mollusks (10 5 to 10 8 g Ϫ1 ) (3, 14), relatively rare in the water column (ϳ2 ml Ϫ1 ) (34), and frequently undetectable in sediments.The marine bacterium Vibrio parahaemolyticus is a gastrointestinal pathogen that is abundant (10 4 g Ϫ1 ) (12) in oysters. It can cause disease in humans that consume raw shellfish, and in 1997 it was responsible for a major outbreak of disease in British Columbia (6). High abundances of viruses that infect V. parahaemolyticus (VpVs; 10 6 g Ϫ1 ) (3) also occur in oysters.However, with the exception of a study...

Isolation and Characterization of Bacteriophages Infecting the Fish Pathogen Flavobacterium psychrophilum

“…Eighteen of the 22 isolated phages showed unique host ranges of infectivity against 24 strains of F. psychrophilum, which all had unique phage susceptibility patterns. This high phage and host diversity within the Flavobacterium psychrophilum group supports recent studies of Cellulophaga baltica (13), Vibrio parahaemolyticus (6,7), and E. coli (e.g., references 10 and 24) and indicates that interactions between F. psychrophilum and their phages are characterized by a high degree of complexity at the strain level. The facts that phages were found in more than 50% of the analyzed samples and that 18 of 22 F. psychrophilum phage isolates were unique with respect to host range suggested that the obtained phage isolates most likely represent only a small fraction of the actual F. psychrophilum phage diversity in aquaculture.…”

Bacteriophage predation regulates microbial abundance and diversity in a full-scale bioreactor treating industrial wastewater

“…Although these methods work well for comparing total bacteria and total phage numbers in a given environment, they provide no data regarding specific phage-host interactions. For that purpose, one must isolate and study specific phagehost systems, as was done in this study and in a small number of other studies covering shorter time periods (Hantula et al, 1991;Comeau et al, 2005;Clokie et al, 2006). As phage abundance depends on the concentration of its specific host, it is preferable to isolate strains that are sufficiently dominant in the studied environment.…”

Virus-mediated transfer of nitrogen from heterotrophic bacteria to phytoplankton

“…Vibrio phages are typically speciesspecific, and often strain-specific (Comeau et al, 2005), and experiments have shown undetectable binding of PWH3a-P1 to natural populations of bacteria, even in the environment from which it was isolated (Hennes et al, 1995). Finally, even if PWH3a-P1 were able to bind to Vibrio spp., the estimated abundance of Vibrio spp.…”