A survey for phosphoglucose isomerase with lysyl aminopeptidase activity in Vibrionaceae and non-Vibrio pathogens

Purification and Host Specificity of Predatory Halobacteriovorax Isolates from Seawater

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-μm 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.

Fluorogenic Membrane Overlays to Enumerate Total and Fecal Escherichia coli and Total Vibrionaceae in Shellfish and Seawater

Three assays were developed to enumerate total and fecal Escherichia coli and total Vibrionaceae in shellfish, seawater, and other foods and environmental samples. Assays involve membrane overlays of overnight colonies on nonselective agar plates to detect beta-glucuronidase and lysyl aminopeptidase activities for E. coli and Vibrionaceae, respectively. Cellulose membranes containing the substrates 4-methylumbeferyl-beta-D-glucuronide (MUG) produced a bright blue fluorescence when overlaid onto E. coli, while L-lysyl-7-amino-4-trifluoromethylcoumarin produced green fluorescent foci when overlaid onto Vibrionaceae family members. A multiplex assay was also developed for simultaneously enumerating total E. coli and total Vibrionaceae in oysters and seawater. Overall, 65% of overlaid E. coli (non-O157:H7) were MUG-positive, compared with 62% as determined by the most-probable-number-MUG assay. The overlays are rapid, simple, and cost effective for quantification purposes. This research provides practical alternatives for monitoring bacterial indicators and potential pathogens in complex samples, including molluscan shellfish.

Glucose-6-phosphate isomerase is an endogenous inhibitor to myofibril-bound serine proteinase of crucian carp (Carassius auratus)

Glucose-6-phosphate isomerase (GPI) was purified to homogeneity from the skeletal muscle of crucian carp ( Carassius auratus ) by ammonium sulfate fractionation, column chromatographies of Q-Sepharose, SP-Sepharose, and Superdex 200 with a yield of 8.0%, and purification folds of 468. The molecular mass of GPI was 120 kDa as estimated by gel filtration, while on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two subunits (55 and 65 kDa) were identified, suggesting that it is a heterodimer. Interestingly, GPI revealed specific inhibitory activity toward a myofibril-bound serine proteinase (MBSP) from crucian carp, while no inhibitory activity was identified toward other serine proteinases, such as white croaker MBSP and crucian carp trypsin. Kinetic analysis showed that GPI is a competitive inhibitor toward MBSP, and the K(i) was 0.32 microM. Our present results indicated that the multifunctional protein GPI is an endogenous inhibitor to MBSP and may play a significant role in the regulation of muscular protein metabolism in vivo.

Specificity of a Vibrio vulnificus aminopeptidase toward kinins and other peptidyl substrates

Recently, phosphoglucose isomerase with a lysyl aminopeptidase (PGI-LysAP) activity was identified in Vibrio vulnificus. In this paper, we demonstrate the proteolytic cleavage of human-derived peptides by PGI-LysAP of V. vulnificus using three approaches: (i) a quantitative fluorescent ninhydrin assay for free lysine, (ii) matrix-assisted laser desorption ionization-two-stage time of flight mass spectrometry (MALDI-TOF-TOF), and (iii) Tricine gel electrophoresis. PGI-LysAP hydrolyzed bradykinin, Lys-bradykinin, Lys-(des-Arg9)-bradykinin, neurokinin A, Met-Lys-bradykinin, histatin 8, and a myosin light chain fragment. We detected the proteolytic release of free L-lysine from peptide digests using a rapid, simple, sensitive, and quantitative fluorescent ninhydrin assay, and results were confirmed by MALDI-TOF-TOF. The use of the fluorescent ninhydrin assay to quantitatively detect free lysine hydrolyzed from peptides is the first application of its kind and serves as a paradigm for future studies. The visualization of peptide hydrolysis was accomplished by Tricine gel electrophoresis. Proteolytic processing of kinins alters their affinities toward specific cellular receptors and initiates signal transduction mechanisms responsible for inflammation, vasodilation, and enhanced vascular permeability. By applying novel approaches to determine the proteolytic potential of bacterial enzymes, we demonstrate that PGI-LysAP has broad exopeptidase activity which may enhance V. vulnificus invasiveness by altering peptides involved in signal transduction pathways.

Development of a simple and rapid fluorogenic procedure for identification of vibrionaceae family members

We describe a simple colony overlay procedure for peptidases (COPP) for the rapid fluorogenic detection and quantification of Vibrionaceae from seawater, shellfish, sewage, and clinical samples. The assay detects phosphoglucose isomerase with a lysyl aminopeptidase activity that is produced by Vibrionaceae family members. Overnight cultures are overlaid for 10 min with membranes containing a synthetic substrate, and the membranes are examined for fluorescent foci under UV illumination. Fluorescent foci were produced by all the Vibrionaceae tested, including Vibrio spp., Aeromonas spp., and Plesiomonas spp. Fluorescence was not produced by non-Vibrionaceae pathogens. Vibrio cholerae strains O1, O139, O22, and O155 were strongly positive. Seawater and oysters were assayed, and 87 of 93 (93.5%) of the positive isolates were identified biochemically as Vibrionaceae, principally Vibrio vulnificus, Vibrio parahaemolyticus, Aeromonas hydrophila, Photobacterium damselae, and Shewanella putrefaciens. None of 50 nonfluorescent isolates were Vibrionaceae. No Vibrionaceae were detected in soil, and only A. hydrophila was detected in sewage. The COPP technique may be particularly valuable in environmental and food-testing laboratories and for monitoring water quality in the aquaculture industry.