dThis study shows that naturally occurring Vibrio predatory bacteria (VPB) exert a major role in controlling pathogenic vibrios in seawater and shellfish. The growth and persistence of Vibrio parahaemolyticus and Vibrio vulnificus were assessed in natural seawater and in the Eastern oyster, Crassostrea virginica. The pathogens examined were V. vulnificus strain VV1003, V. parahaemolyticus O1:KUT (KUT stands for K untypeable), and V. parahaemolyticus O3:K6 and corresponding O3:K6 mutants deficient in the toxRS virulence regulatory gene or the rpoS alternative stress response sigma factor gene. Vibrios were selected for streptomycin resistance, which facilitated their enumeration. In natural seawater, oysters bioconcentrated each Vibrio strain for 24 h at 22°C; however, counts rapidly declined to near negligible levels by 72 h. In natural seawater with or without oysters, vibrios decreased more than 3 log units to near negligible levels within 72 h. Neither toxRS nor rpoS had a significant effect on Vibrio levels. In autoclaved seawater, V. parahaemolyticus O3:K6 counts increased 1,000-fold over 72 h. Failure of the vibrios to persist in natural seawater and oysters led to screening of the water samples for VPB on lawns of V. parahaemolyticus O3:K6 host cells. Many VPB, including Bdellovibrio and like organisms (BALOs; Bdellovibrio bacteriovorus and Bacteriovorax stolpii) and Micavibrio aeruginosavorus-like predators, were detected by plaque assay and electron microscopic analysis of plaque-purified isolates from Atlantic, Gulf Coast, and Hawaiian seawater. When V. parahaemolyticus O3:K6 was added to natural seawater containing trace amounts of VPB, Vibrio counts diminished 3 log units to nondetectable levels, while VPB increased 3 log units within 48 h. We propose a new paradigm that VPB are important modulators of pathogenic vibrios in seawater and oysters.

is a Gram-negative gammaproteobacterium found in the marine environment. Three strains of pigmented were isolated from seawater and partially characterized by inhibition studies, electron microscopy, and analysis for proteolytic enzymes. Growth inhibition and death occurred around colonies of on lawns of the naturally occurring marine pathogens ,, ,, and Inhibition also occurred on lawns of but not on O157:H7 or serovar Typhimurium. Inhibition was not pH associated, but it may have been related to the secretion of a cysteine protease with strong activity, as detected with a synthetic fluorogenic substrate. This diffusible enzyme was secreted from all three strains. Direct overlay of the colonies with synthetic fluorogenic substrates demonstrated the activity of two aminopeptidase Bs, a trypsin-like serine protease, and enzymes reactive against substrates for cathepsin G-like and caspase 1-like proteases. In seawater cultures, scanning electron microscopy revealed numerous vesicles tethered to the outer surface of and a novel mechanism of direct transfer of these vesicles to Vesicles digested holes in cells, while the congregated around the vibrios in a predatory fashion. This transfer of vesicles and vesicle-associated digestion of holes were not observed in other bacteria, suggesting that vesicle binding may be mediated by host-specific receptors. In conclusion, we show two mechanisms by which inhibits and/or kills competing bacteria, involving the secretion of antimicrobial substances and the direct transfer of digestive vesicles to competing bacteria. species are widespread in nature and reduce competing microflora by the production of antimicrobial compounds. We isolated three strains of and characterized secreted and cell-associated proteolytic enzymes, which may have antimicrobial properties. We identified a second method by which kills It involves the direct transfer of apparently lytic vesicles from the surface of the strains to the surface of cells, with subsequent digestion of holes in the cell walls. Enzymes associated with these vesicles are likely responsible for the digestion of holes in the cell walls. has potential applications in aquaculture and food safety, in control of the formation of biofilms in the environment, and in food processing. These findings may facilitate the probiotic use of to inactivate pathogens and may lead to the isolation of enzymes and other antimicrobial compounds of pharmacological value.

c Halobacteriovorax (formerly Bacteriovorax) is a small predatory bacterium found in the marine environment and modulates bacterial pathogens in shellfish. Four strains of Halobacteriovorax originally isolated in Vibrio parahaemolyticus O3:K6 host cells were separated from their prey by an enrichment-filtration-dilution technique for specificity testing in other bacteria. This technique was essential, since 0.45-m filtration alone was unable to remove infectious Vibrio minicells, as determined by scanning electron microscopy and cultural methods. Purified Halobacteriovorax strains were screened for predation against other V. parahaemolyticus strains and against Vibrio vulnificus, Vibrio alginolyticus, Escherichia coli O157:H7, and Salmonella enterica serovar Typhimurium DT104, all potential threats to seafood safety. They showed high host specificity and were predatory only against strains of V. parahaemolyticus. In addition, strains of Halobacteriovorax that were predatory for E. coli O157:H7 and S. Typhimurium DT104 were isolated from a tidal river at 5 ppt salinity. In a modified plaque assay agar, they killed their respective prey over a broad range of salinities (5 to 30 ppt). Plaques became smaller as the salinity levels rose, suggesting that the lower salinities were optimal for the predators' replication. These species also showed broader host specificity, infectious against each other's original hosts as well as against V. parahaemolyticus strains. In summary, this study characterized strains of Halobacteriovorax which may be considered for use in the development of broad-based biocontrol technologies to enhance the safety of commercially marketed shellfish and other foods. Bdellovibrio and like organisms (BALO) are Gram-negative, aerobic bacteria which are predatory toward other Gram-negative bacteria and consist of freshwater/terrestrial and marine forms. Bdellovibrio and like organisms are divided into four genera, Bdellovibrio, Bacteriolyticum, Peredibacter, and Bacteriovorax, which was recently renamed Halobacteriovorax (1). These organisms enter into a susceptible host bacterium and reside within the periplasmic space where they utilize the cytoplasmic nutrients of the host to support growth and replication. The replicative form, known as a bdelloplast, elongates within the host and septates into progeny cells as the host is lysed, releasing cells capable of attacking more prey. Halobacteriovorax organisms are the marine forms, which are small, polar flagellated, highly motile, intracellular predators in the class Deltaproteobacteria family Halobacteriovoraceae (1).Bdellovibrio and like organisms, particularly the nonhalophilic Bdellovibrio bacteriovorus, have been proposed for use in reducing the levels of phytopathogens associated with bacterial blights in soybeans and rice (2, 3) and reducing the levels of Salmonella enterica serovar Typhimurium on freshwater fish fillets (4). Other uses involve the treatment of various infections in animals, including bovine keratoconjunctivitis caused by Mora...

Bacteriovorax were quantified in US Atlantic, Gulf, and Pacific seawater to determine baseline levels of these predatory bacteria and possible seasonal fluctuations in levels. Surface seawater was analyzed monthly for 1 year from Kailua-Kona, Hawaii; the Gulf Coast of Alabama; and four sites along the Delaware Bay. Screening for Bacteriovorax was performed on lawns of V. parahaemolyticus host cells. Direct testing of 7.5 mL portions of seawater from the Atlantic, Pacific, and Gulf coasts gave mean annual counts ≤12.2 PFU. Spikes in counts were observed at 3 out of 4 sites along the Delaware Bay 1 week after Hurricane Sandy. A comparison of summer versus winter counts showed significantly more Bacteriovorax (P ≤ 0.0001) in the Delaware Bay during the summer and significantly more (P ≤ 0.0001) in the Gulf during the winter, but no significant seasonal differences (P > 0.05) for Hawaiian seawater. Bacteriovorax counts only correlated with seawater salinity and temperature at one Delaware site (r = 0.79 and r = 0.65, resp.). There was a relatively strong negative correlation between temperature and Bacteriovorax levels (r = −0.585) for Gulf seawater. Selected isolates were sequenced and identified by phylogenetic analysis as Bacteriovorax clusters IX, X, XI, and XII.

Oyster gardening is a practice designed to restore habitat for marine life and to improve water quality. This study determined physical and chemical water-quality parameters at two oyster gardening sites in the Delaware Inland Bays and compared them with total aerobic bacteria and Vibrionaceae concentrations in Eastern oysters (Crassostrea virginica). One site was located at the end of a man-made canal, whereas the other was located in an open bay. Measured water parameters included temperature, dissolved oxygen (DO), salinity, pH, total nitrogen, nitrate, nitrite, total phosphorus, and total suspended solids. The highest Vibrionaceae levels, as determined by the colony overlay procedure for peptidases, were at the canal site in September (3.5 × 10(5) g(-1)) and at the bay site in August (1.9 × 10(5) g(-1)). Vibrionaceae levels were significantly greater during the duration of the study at the canal site (P = 0.01). This study provides the first baseline levels for total Vibrionaceae in the Delaware Inland Bays. Minimum DO readings at the bay and canal sites were 3.0 and 2.3 mg l(-1), respectively, far less than the state-targeted minimum threshold of 5.0 mg l(-1). Total phosphorus levels exceeded recommendations of ≤0.1 mg l(-1) at the bay and canal sites for all monthly samplings, with mean monthly highs at both sites ≥0.68 mg l(-1) in August. Nitrogen occasionally exceeded the recommended level of 1.0 mg l(-1) at both sites. Overall, waters were highly degraded from high phosphates, nitrogen, and total suspended solids as well as low DO.