Purification and host specificity of predatory halobacteriovorax isolated from seawater

Authors: Richards, Gary; FAY, JOHNNA - University Of Delaware; Uknalis, Joseph; Olanya, Modesto; Watson, Michael

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2015
Publication Date: 2/15/2016
Citation: Richards, G.P., Fay, J.P., Uknalis, J., Olanya, O.M., Watson, M.A. 2016. Purification and host specificity of predatory halobacteriovorax isolated from seawater. Applied and Environmental Microbiology. 82(3):922-927.

Interpretive Summary: Seawater contains many bacteria which can contaminate shellfish making the shellfish unsafe to eat. Among these bacteria are members of the genus Vibrio and Salmonella, as well as various strains of E. coli. A bacterial predator known as Halobacteriovorax (formerly called Bacteriovorax) is commonly found in seawater and can readily kill dangerous vibrios and other organisms, potentially making the shellfish safer to eat. This study characterized four Halobacteriovorax that can kill an important shellfish-associated pathogen known as Vibrio parahaemolyticus and showed that these bacteria preferentially infect and kill V. parahaemolyticus over other species of vibrios or non-vibrios. New Halobacteriovorax against E. coli and Salmonella were also isolated from seawater and partially characterized as a prerequisite to developing processing interventions to remove these pathogens from oysters. These newly isolated Halobacteriovorax had the ability to infect and kill both E. coli and Salmonella, but not V. parahaemolyticus. Overall, Bacteriovorax in general were rather host specific, infecting a relatively narrow range of bacteria. A simple but novel method to purify Halobacteriovorax was developed in order to make this study possible.

Technical Abstract: Halobacteriovorax (formerly Bacteriovorax) are small predatory bacteria found in the marine environment and may serve as biocontrol agents against pathogens in fish and shellfish. Four strains of Halobacteriovorax originally isolated in Vibrio parahaemolyticus O3:K6 host cells were separated from their host by an enrichment-filtration-dilution technique for specificity testing in other bacteria. This technique was necessitated by the fact that 0.45-um filtration alone was unable to remove infectious Vibrio minicells, as determined by scanning electron microscopy and cultural methods. Purified Halobacteriovorax strains were screened for infectivity toward other strains of V. parahaemolyticus as well as V. vulnificus, V. alginolyticus, Escherichia coli O157:H7 and Salmonella enteritidis serovar Typhimurium DT104, all potential threats to seafood safety. They showed high host specificity, infecting only strains of V. parahaemolyticus. Halobacteriovorax against E. coli and S. Typhimurium were isolated from a tidal river at 5 ppt salinity and their host specificities were determined. Halobacteriovorax against E. coli was able to infect E. coli at 5 and 30 ppt salinity, as well as S. Typhimurium at 5 ppt salinity indicating a broad salinity range and dual host specificity for this isolate. It did not infect any of the Vibrio species. Halobacteriovorax against S. Typhimurium also infected E. coli, but did not infect vibrios. In this study, Halobacteriovorax were shown to be a diverse group of bacteria which individually appear to have narrow host specificity, but collectively are likely to serve as predators against a broad spectrum of bacteria found in the marine environment.