Claudia C Häse

Oregon State University, Corvallis, Oregon, United States

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Publications (45)165.49 Total impact

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    ABSTRACT: Vibrio tubiashii is reported to be a bacterial pathogen of larval Eastern oysters (Crassostrea virginica) and Pacific oysters (Crassostrea gigas) and has been associated with major hatchery crashes, causing shortages in seed oysters for commercial shellfish producers. Another bacterium, Vibrio coralliilyticus, a well-known coral pathogen, has recently been shown to elicit mortality in fish and shellfish. Several strains of V. coralliilyticus, such as ATCC 19105 and Pacific isolates RE22 and RE98, were misidentified as V. tubiashii until recently. We compared the mortalities caused by two V. tubiashii and four V. coralliilyticus strains in Eastern and Pacific oyster larvae. The 50% lethal dose (LD50) of V. coralliilyticus in Eastern oysters (defined here as the dose required to kill 50% of the population in 6 days) ranged from 1.1 × 104 to 3.0 × 104 CFU/ml seawater; strains RE98 and RE22 were the most virulent. This study shows that V. coralliilyticus causes mortality in Eastern oyster larvae. Results for Pacific oysters were similar, with LD50s between 1.2 × 104 and 4.0 × 104 CFU/ml. Vibrio tubiashii ATCC 19106 and ATCC 19109 were highly infectious toward Eastern oyster larvae but were essentially nonpathogenic toward healthy Pacific oyster larvae at dosages of ≥1.1 × 104 CFU/ml. These data, coupled with the fact that several isolates originally thought to be V. tubiashii are actually V. coralliilyticus, suggest that V. coralliilyticus has been a more significant pathogen for larval bivalve shellfish than V. tubiashii, particularly on the U.S. West Coast, contributing to substantial hatchery-associated morbidity and mortality in recent years.
    Applied and Environmental Microbiology 10/2014; 81(1). DOI:10.1128/AEM.02930-14 · 3.67 Impact Factor
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    ABSTRACT: The Na+ translocating NADH:quinone oxidoreductase (Na+-NQR) is a unique respiratory enzyme catalyzing the electron transfer from NADH to quinone coupled with the translocation of sodium ions across the membrane. Typically, Vibrio spp., including Vibrio cholerae, have this enzyme but lack the proton-pumping NADH:ubiquinone oxidoreductase (Complex I). Thus, Na+-NQR should significantly contribute to multiple aspects of V. cholerae physiology; however, no detailed characterization of this aspect has been reported so far. In this study, we broadly investigated the effects of loss of Na+-NQR on V. cholerae physiology by using Phenotype Microarray (Biolog), transcriptome and metabolomics analyses. We found that the V. cholerae ΔnqrA-F mutant showed multiple defects in metabolism detected by Phenotype Microarray. Transcriptome analysis revealed that the V. cholerae ΔnqrA-F mutant up-regulates 31 genes and down-regulates 55 genes in both early and mid-growth phases. The most up-regulated genes included the cadA and cadB genes, encoding a lysine decarboxylase and a lysine/cadaverine antiporter, respectively. Increased CadAB activity was further suggested by the metabolomics analysis. The down-regulated genes include sialic acid catabolism genes. Metabolomic analysis also suggested increased reductive pathway of TCA cycle and decreased purine metabolism in the V. cholerae ΔnqrA-F mutant. Lack of Na+-NQR did not affect any of the Na+ pumping-related phenotypes of V. cholerae suggesting that other secondary Na+ pump(s) can compensate for Na+ pumping activity of Na+-NQR. Overall, our study provides important insights into the contribution of Na+-NQR to V. cholerae physiology.
    PLoS ONE 05/2014; 9(5):e97083. DOI:10.1371/journal.pone.0097083 · 3.23 Impact Factor
  • Alisha M Aagesen · Claudia C Häse ·
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    ABSTRACT: During the warmer summer months, oysters are conditioned to spawn, resulting in massive physiological efforts for gamete production. Moreover, the higher temperatures during the summer typically result in increased bacteria populations in oysters. We hypothesized that these animals are under multiple stresses that lead to possible immune system impairments during the summer months that can possibly lead to death. Here we show that in the summer and the fall animals exposed to a short heat stress respond similarly, resulting in a general trend of more bacteria being found in heat shocked animals than their non-heat shocked counterparts. We also show that naturally occurring bacterial populations are effected by a heat shock. In addition, oysters artificially contaminated with Vibrio parahaemolyticus were also affected by a heat shock. Heat shocked animals contained higher concentrations of V. parahaemolyticus in their tissues and hemolymph than control animals and this was consistent for animals examined during summer and fall. Finally, oyster hemocyte interactions with V. parahaemolyticus differed based on the time of the year. Overall, these findings demonstrate that seasonal changes and/or a short heat shock is sufficient to impact bacterial retention, particularly V. parahaemolyticus, in oysters and this line of research might lead to important considerations for animal harvesting procedures.
    Food Microbiology 04/2014; 38:93-103. DOI:10.1016/ · 3.33 Impact Factor
  • Frances M Biel · Fred A Allen · Claudia C Häse ·
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    ABSTRACT: Vibrio tubiashii has been linked to disease outbreaks in molluscan species, including oysters, geoducks, and clams, and shellfish hatcheries in the Pacific Northwest have been plagued by intermittent vibriosis outbreaks since 2006. Like V. tubiashii, Vibrio coralliilyticus has recently been described as an oyster pathogen in addition to its role in coral disease. Here, we describe an autolysis phenotype in V. tubiashii and its close relative V. coralliilyticus and characterize the effects of environmental conditions on this phenotype. We also explored whether the survivors of autolysis were resistant to the phenotype and if material from the autolysed culture would either regrow or have a population of viable cells. Ultimately, this work contributes to the larger understanding of bacterial population dynamics as it relates to aquaculture pathogens.
    Canadian Journal of Microbiology 02/2014; 60(2):57-63. DOI:10.1139/cjm-2013-0654 · 1.22 Impact Factor
  • Yusuke Minato · Sara R Fassio · Rylan L Reddekopp · Claudia C Häse ·
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    ABSTRACT: Two virulence factors produced by Vibrio cholerae, cholera toxin (CT) and toxin-corregulated pilus (TCP), are indispensable for cholera infection. ToxT is the central regulatory protein involved in activation of CT and TCP expression. We previously reported that lack of a respiration-linked sodium-translocating NADH-ubiquinone oxidoreductase (Na(+)-NQR) significantly increases toxT transcription. In this study, we further characterized this link and found that Na(+)-NQR affects toxT expression only at the early-log growth phase, whereas lack of Na(+)-NQR decreases CT production after the mid-log growth phase. Such decreased CT production was independent of toxT and ctxB transcription. Supplementing a respiratory substrate, L-lactate, into the growth media restored CT production in the nqrA-F mutant, suggesting that decreased CT production in the Na(+)-NQR mutant is dependent on electron transport chain (ETC) activity. This notion was supported by the observations that two chemical inhibitors, a Na(+)-NQR specific inhibitor 2-n-Heptyl-4-hydroxyquinoline N-oxide (HQNO) and a succinate dehydrogenase (SDH) inhibitor, thenoyltrifluoroacetone (TTFA), strongly inhibited CT production in both classical and El Tor biotype strains of V. cholerae. Accordingly, we propose the main respiratory enzyme of V. cholerae, as a potential drug target to treat cholera because human mitochondria do not contain Na(+)-NQR orthologs.
    Microbial Pathogenesis 12/2013; 66. DOI:10.1016/j.micpath.2013.12.002 · 1.79 Impact Factor
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    ABSTRACT: Na+/H+ antiporters are ubiquitous membrane proteins that play a central role in the ion homeostasis of cells. In this study, we examined the possible role of Na+/H+ antiport in Yersinia pestis virulence and found that Y. pestis strains lacking the major Na+/H+ antiporters, NhaA and NhaB, are completely attenuated in an in vivo model of plague. The Y. pestis derivative strain lacking the nhaA and nhaB genes showed markedly decreased survival in blood and blood serum ex vivo. Complementation of either nhaA or nhaB in trans restored the survival of the Y. pestis nhaA nhaB double deletion mutant in blood. The nhaA nhaB double deletion mutant also showed inhibited growth in an artificial serum medium, Opti-MEM, and a rich LB-based medium with Na+ levels and pH values similar to those for blood. Taken together, these data strongly suggest that intact Na+/H+ antiport is indispensable for the survival of Y. pestis in the bloodstreams of infected animals and thus might be regarded as a promising noncanonical drug target for infections caused by Y. pestis and possibly for those caused by other blood-borne bacterial pathogens.
    Infection and immunity 06/2013; 81(9). DOI:10.1128/IAI.00071-13 · 3.73 Impact Factor
  • Dima N Gharaibeh · Frances M Biel · Claudia C Häse ·
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    ABSTRACT: Vibrio tubiashii has been linked to disease outbreaks in molluscan species, including oysters, geoducks, and clams. In particular, oyster hatcheries in the Pacific Northwest have been plagued by intermittent vibriosis since 2006. Accurate detection of vibrios, including V. tubiashii, is critical to the hatcheries in order to allow for rapid remediation efforts. The current methods for detection of Vibrio spp. are not ideal for use at the hatchery. Plating samples requires time and is not sensitive to extracelluar pathogenic products, such as the secreted zinc-metalloprotease, VtpA. Other sensitive methods to detect bacteria, such as qPCR, require a high level of laboratory skills and expensive supplies that are prohibitive for use at hatchery sites. Thus, hatcheries would benefit from a sensitive, simple method to detect V. tubiashii and its secreted toxin. Here, we describe the development of two inexpensive and highly specific tests for the shellfish-toxic zinc-metalloprotease secreted by V. tubiashii: enzyme-linked immunoassays (ELISA) and a lateral flow immunoassay (dipstick assay). Both technologies rely on a set of monoclonal antibodies used in a sandwich format, with the capture antibody recognizing a different epitope than the detection antibody on the mature VtpA protein. Both assays are quantitative and give colorimetric readouts. The sandwich ELISA was sensitive when VtpA was diluted into PBS, but was markedly less sensitive in conditions that correlate with the environment of hatchery-derived samples, such as in the presence of seawater, algae, or oyster larvae. In contrast, the dipstick assay remained very sensitive in the presence of these contaminants, is less work-intensive, and much more rapid, making this format the preferred assay method for detecting VtpA on site in a hatchery or environmental setting.
    Journal of microbiological methods 05/2013; 94(2). DOI:10.1016/j.mimet.2013.05.009 · 2.03 Impact Factor
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    Yusuke Minato · Sara R Fassio · Claudia C Häse ·
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    ABSTRACT: We previously found that inhibition of the TCA cycle, either through mutations or chemical inhibition, increased toxT transcription in Vibrio cholerae. In this study, we found that the addition of malonate, an inhibitor of succinate dehydrogenase (SDH), decreased toxT transcription in V. cholerae, an observation inconsistent with the previous pattern observed. Unlike another SDH inhibitor, 2-thenoyltrifluoroacetone (TTFA), which increased toxT transcription and slightly inhibited V. cholerae growth, malonate inhibited toxT transcription in both the wild-type strain and TCA cycle mutants, suggesting malonate-mediated inhibition of virulence gene expression is independent to TCA cycle activity. Addition of malonate also inhibited ctxB and tcpA expressions but did not affect aphA, aphB, tcpP and toxR expressions. Malonate inhibited cholera toxin (CT) production in both V. cholerae classical biotype strains O395N1 and CA401, and El Tor biotype strain, N16961. Consistent with previous reports, we confirmed that these strains of V. cholerae did not utilize malonate as a primary carbon source. However, we found that the addition of malonate to the growth medium stimulated V. cholerae growth. All together, these results suggest that metabolizing malonate as a nutrient source negatively affects virulence gene expression in V. cholerae.
    PLoS ONE 05/2013; 8(5):e63336. DOI:10.1371/journal.pone.0063336 · 3.23 Impact Factor
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    Alisha M Aagesen · Sureerat Phuvasate · Yi-Cheng Su · Claudia C Häse ·
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    ABSTRACT: Vibrio parahaemolyticus can resist oyster depuration, suggesting that it possesses specific factors for persistence. We show that type I pili, type IV pili, and both flagellar systems contribute to V. parahaemolyticus persistence in Pacific oysters whereas type III secretion systems and phase variation do not.
    Applied and Environmental Microbiology 03/2013; 79(10). DOI:10.1128/AEM.00314-13 · 3.67 Impact Factor
  • Yusuke Minato · Sara R Fassio · Alan J Wolfe · Claudia C Häse ·
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    ABSTRACT: ToxT is the central regulatory protein involved in activation of the main virulence genes in Vibrio cholerae. We have identified transposon insertions in central metabolism genes, whose disruption increases toxT transcription. These disrupted genes encode the primary respiration-linked sodium pump (NADH-ubiquinone oxidoreductase or NQR) and certain tricarboxylic acid (TCA) cycle enzymes. Observations made following stimulation of respiration in the nqr mutant or chemical inhibition of NQR activity in the TCA cycle mutants led to the hypothesis that NQR affects toxT transcription via the TCA cycle. That toxT transcription increased when the growth medium was supplemented with citrate, but decreased with oxaloacetate, focused our attention on the TCA cycle substrate acetyl-coenzyme A (acetyl-CoA) and its non-TCA cycle metabolism. Indeed, both the nqr and TCA cycle mutants increased acetate excretion. A similar correlation between acetate excretion and toxT transcription was observed in the tolC mutant and upon amino acid (NRES) supplementation. Since acetate and its tendency to decrease pH exerted no strong effect on toxT transcription, and since disruption of the major acetate excretion pathway increased toxT transcription, we propose that toxT transcription is regulated by either acetyl-CoA or some close derivative.
    Microbiology 02/2013; 159(Pt_4). DOI:10.1099/mic.0.064865-0 · 2.56 Impact Factor
  • Alisha M Aagesen · Claudia C Häse ·
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    ABSTRACT: Bacterial surface structures called pili have been studied extensively for their role as possible colonization factors. Most sequenced Vibrio genomes predict a variety of pili genes in these organisms, including several types of type IV pili. In particular, the mannose-sensitive hemagglutinin (MSHA) and the PilA pili, also known as the chitin-regulated pilus (ChiRP), are type IVa pili commonly found in Vibrio genomes and have been shown to play a role in the colonization of Vibrio species in the environment and/or host tissue. Here, we report sequence comparisons of two type IVa pilin subunit genes, mshA and pilA, and their corresponding amino acid sequences, for several strains from the three main human pathogenic Vibrio species, V. cholerae, V. parahaemolyticus, and V. vulnificus. We identified specific groupings of these two genes in V. cholerae, whereas V. parahaemolyticus and V. vulnificus strains had no apparent allelic clusters, and these genes were strikingly divergent. These results were compared with other genes from the MSHA and PilA operons as well as another Vibrio pili from the type IVb group, the toxin co-regulated pilus (TCP) from V. cholerae. Our data suggest that a selective pressure exists to cause these strains to vary their MSHA and PilA pilin subunits. Interestingly, V. cholerae strains possessing TCP have the same allele for both mshA and pilA. In contrast, V. cholerae isolates without TCP have polymorphisms in their mshA and pilA sequences similar to what was observed for both V. parahaemolyticus and V. vulnificus. This data suggests a possible linkage between host interactions and maintaining a highly conserved type IV pili sequence in V. cholerae. Although the mechanism underlying this intriguing diversity has yet to be elucidated, our analyses are an important first step towards gaining insights into the various aspects of Vibrio ecology.
    Microbial Ecology 03/2012; 64(2):509-24. DOI:10.1007/s00248-012-0021-2 · 3.12 Impact Factor
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    ABSTRACT: Vibrio cholerae has adapted to a wide range of salinity, pH and osmotic conditions, enabling it to survive passage through the host and persist in the environment. Among the many proteins responsible for bacterial survival under these diverse conditions, we have identified Vc-NhaP1 as a K(+)(Na(+))/H(+) antiporter essential for V. cholerae growth at low environmental pH. Deletion of the V. cholerae nhaP1 gene caused growth inhibition when external potassium was either limited (100 mM and below) or in excess (400 mM and above). This growth defect was most apparent at mid-exponential phase, after 4-6 h of culture. Using a pH-sensitive GFP, cytosolic pH was shown to be dependent on K(+) in acidic external conditions in a Vc-NhaP1-dependent manner. When functionally expressed in an antiporterless Escherichia coli strain and assayed in everted membrane vesicles, Vc-NhaP1 operated as an electroneutral alkali cation/proton antiporter, exchanging K(+) or Na(+) ions for H(+) within a broad pH range (7.25-9.0). These data establish the putative V. cholerae NhaP1 protein as a functional K(+)(Na(+))/H(+) antiporter of the CPA1 family that is required for bacterial pH homeostasis and growth in an acidic environment.
    Microbiology 01/2012; 158(Pt 4):1094-105. DOI:10.1099/mic.0.056119-0 · 2.56 Impact Factor
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    Yusuke Minato · Robert L Siefken · Claudia C Häse ·
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    ABSTRACT: A Vibrio cholerae tolC mutant showed increased toxT expression in M9 medium, but not in the presence of four amino acids that induce cholera toxin production, and in LB with high osmolarity but not high pH or temperature. TolC did not affect expression of other regulatory genes in the ToxR regulon.
    Journal of bacteriology 08/2011; 193(20):5850-2. DOI:10.1128/JB.05222-11 · 2.81 Impact Factor
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    Craig T Resch · Judith L Winogrodzki · Claudia C Häse · Pavel Dibrov ·
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    ABSTRACT: Na+/H+ antiporters are integral membrane proteins that exchange Na+ for H+ across the cytoplasmic or organellar membranes of virtually all living cells. They are essential for control of cellular pH, volume homeostasis, and regulation of Na+ levels. Na+/H+ antiporters have become increasingly characterized and are now becoming important drug targets. The recently identified NhaP family of Na+/H+ antiporters, from the CPA1 superfamily, contains proteins with a surprisingly broad collective range of transported cations, exchanging protons for alkali cations such as Na+, Li+, K+, or Rb+ as well as for Ca2+ and, possibly, NH4+. Questions about ion selectivity and the physiological impact of each particular NhaP antiporter are far from trivial. For example, Vc-NhaP2 from Vibrio cholerae has recently been shown to function in vivo as a specific K+/H+ antiporter while retaining the ability to exchange H+ for Na+ and bind (but not exchange with H+) Li+ in a competitive manner. These and other findings reviewed in this communication make antiporters of the NhaP type attractive systems to study intimate molecular mechanisms of cation exchange. In an evolutionary perspective, the NhaP family seems to be a phylogenetic entity undergoing active divergent evolution. In this minireview, to rationalize peculiarities of the cation specificity in the NhaP family, the "size-exclusion principle" and the idea of "ligand shading" are discussed.
    Biochemistry and Cell Biology 04/2011; 89(2):130-7. DOI:10.1139/o10-149 · 2.15 Impact Factor
  • Yi-Cheng Su · Qianru Yang · Claudia Häse ·
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    ABSTRACT: The efficacy of refrigerated-seawater depuration for reducing Vibrio parahaemolyticus levels in Pacific oyster (Crassostrea gigas) was investigated. Raw Pacific oysters were inoculated with a mixed culture of five clinical strains of V. parahaemolyticus (10(5) to 10(6) most probable number [MPN] per g) and depurated with refrigerated seawater (5 degrees C) in a laboratory-scale recirculation system equipped with a 15-W gamma UV sterilizer. Depuration with refrigerated seawater for 96 h reduced V. parahaemolyticus populations by >3.0 log MPN/g in oysters harvested in the winter. However, 144 h of depuration at 5 degrees C was required to achieve a 3-log reduction in oysters harvested in the summer. Depuration with refrigerated seawater at 5 degrees C for up to 144 h caused no significant fatality in the Pacific oyster and could be applied as a postharvest treatment to reduce V. parahaemolyticus contamination in Pacific oysters. Further studies are needed to validate the efficacy of the depuration process for reducing naturally accumulated V. parahaemolyticus in oysters.
    Journal of food protection 06/2010; 73(6):1111-5. · 1.85 Impact Factor
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    ABSTRACT: The existence of bacterial K(+)/H(+) antiporters that prevent the overaccumulation of potassium in the cytoplasm was predicted by Peter Mitchell almost 50 years ago. The importance of K(+)/H(+) antiport for bacterial physiology is widely recognized, but its molecular mechanisms remain underinvestigated. Here, we demonstrate that a putative Na(+)/H(+) antiporter, Vc-NhaP2, protects cells of Vibrio cholerae growing at pH 6.0 from high concentrations of external K(+). Resistance of V. cholerae to Na(+) was found to be independent of Vc-NhaP2. When assayed in inside-out membrane vesicles derived from antiporter-deficient Escherichia coli, Vc-NhaP2 catalyzed the electroneutral K(+)(Rb(+))/H(+) exchange with a pH optimum of approximately 7.75 with an apparent K(m) for K(+) of 1.62 mM. In the absence of K(+), it exhibited Na(+)/H(+) antiport, albeit rather weakly. Interestingly, while Vc-NhaP2 cannot exchange Li(+) for protons, elimination of functional Vc-NhaP2 resulted in a significantly higher Li(+) resistance of V. cholerae cells growing at pH 6.0, suggesting the possibility of Vc-NhaP2-mediated Li(+)/K(+) antiport. The peculiar cation specificity of Vc-NhaP2 and the presence of its two additional paralogues in the same genome make this transporter an attractive model for detailed analysis of the structural determinants of the substrate specificity in alkali cation exchangers.
    Biochemistry 02/2010; 49(11):2520-8. DOI:10.1021/bi902173y · 3.02 Impact Factor
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    Hiroaki Hasegawa · Claudia C Häse ·
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    ABSTRACT: Vibrio tubiashii, a causative agent of severe shellfish larval disease, produces multiple extracellular proteins, including a metalloprotease (VtpA), as potential virulence factors. We previously reported that VtpA is toxic for Pacific oyster (Crassostrea gigas) larvae. In this study, we show that extracellular protease production by V. tubiashii was much reduced by elevated salt concentrations, as well as by elevated temperatures. In addition, V. tubiashii produced dramatically less protease in minimal salts medium supplemented with glucose or sucrose as the sole carbon source than with succinate. We identified a protein that belongs to the TetR family of transcriptional regulators, VtpR, which showed high homology with V. cholerae HapR. We conclude that VtpR activates VtpA production based on the following: (i) a VtpR-deficient V. tubiashii mutant did not produce extracellular proteases, (ii) the mutant showed reduced expression of a vtpA-lacZ fusion, and (iii) VtpR activated vtpA-lacZ in a V. cholerae heterologous background. Moreover, we show that VtpR activated the expression of an additional metalloprotease gene (vtpB). The deduced VtpB sequence showed high homology with a metalloprotease, VhpA, from V. harveyi. Furthermore, the vtpR mutant strain produced reduced levels of extracellular hemolysin, which is attributed to the lower expression of the V. tubiashii hemolysin genes (vthAB). The VtpR-deficient mutant also had negative effects on bacterial motility and did not demonstrate toxicity to oyster larvae. Together, these findings establish that the V. tubiashii VtpR protein functions as a global regulator controlling an array of potential virulence factors.
    Applied and Environmental Microbiology 10/2009; 75(24):7602-9. DOI:10.1128/AEM.01016-09 · 3.67 Impact Factor
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    Hiroaki Hasegawa · Dima N Gharaibeh · Erin J Lind · Claudia C Häse ·
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    ABSTRACT: Vibrio tubiashii, a pathogen of shellfish larvae and juveniles, produces several extracellular products. Here, we document that culture supernatants of several marine Vibrio species showed toxicity to oyster larvae. Treatment of these supernatants with EDTA not only severely diminished proteolytic activities, but also dramatically reduced toxicity to the larvae. Culture supernatants of metalloprotease-deficient mutants of V. tubiashii, V. cholerae, and V. splendidus were impaired in their ability to cause larval death compared to the wild type strains. Culture supernatants of Pseudomonas aeruginosa, known to contain several secreted proteases, showed virtually no toxicity to oyster larvae. Purified V. tubiashii protease A (VtpA), but not the prototype metalloprotease, thermolysin from Bacillus thermoproteolyticus, was highly toxic to the larvae. In addition, toxicity of purified VtpA was much greater for 6-d-old oyster larvae than for 16-d-old larvae. Together, these results indicated that culture supernatants of a variety of Vibrio species are highly toxic to oyster larvae and that the production of a metalloprotease is required for this effect. We propose that there are, as yet uncharacterized, specific substrates contained in larval tissue that are degraded by VtpA as well as certain homologous metalloproteases produced by other marine Vibrio species which, in turn, may contribute to vibriosis.
    Diseases of Aquatic Organisms 07/2009; 85(2):123-31. DOI:10.3354/dao02070 · 1.75 Impact Factor
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    Hiroaki Hasegawa · Claudia C Häse ·
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    ABSTRACT: Vibrio tubiashii is a re-emerging pathogen of molluscs that secretes a variety of extracellular products (ECPs), including a metalloprotease and a cytolysin/haemolysin. Previously, we reported that the V. tubiashii haemolysin locus consists of two ORFs (vthB and vthA), similar to that of the homologous haemolysin genes (vvhB and vvhA) found in Vibrio vulnificus. Here, we demonstrate that the concomitant expression of both V. tubiashii genes resulted in significantly higher haemolytic activity than the vthA gene alone. In addition, we created a VthAB- mutant strain of V. tubiashii that was virtually devoid of haemolytic activity in liquid media. Interestingly, significant production of an additional haemolysin(s) was observed on blood plates. Moreover, we have previously reported that in V. tubiashii, proteolytic and haemolytic activities are inversely produced during bacterial growth. Here, we study this correlation in more detail and present evidence that the VtpA metalloprotease inhibits haemolytic activity in culture supernatants, based on the following evidence: (i) loss of metalloprotease activity by either mutation or EDTA inhibition resulted in increased haemolytic activity; (ii) overexpression of the vtpA gene resulted in decreased haemolytic activity; (iii) purified VtpA metalloprotease directly diminished haemolytic activity by purified VthA haemolysin. Importantly, we found not only that vthAB gene expression remained high throughout growth but also that there were no dramatic differences in vthAB gene expression between the parent and VtpA- mutant strains. Thus, our results strongly suggest that the V. tubiashii metalloprotease directly targets its haemolysin.
    Microbiology 05/2009; 155(Pt 7):2296-305. DOI:10.1099/mic.0.028605-0 · 2.56 Impact Factor
  • Dima N Gharaibeh · Hiroaki Hasegawa · Claudia C Häse ·
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    ABSTRACT: Vibrio tubiashii has recently re-emerged as a pathogen of bivalve larvae, causing a marked increase in the mortality of these species within shellfish rearing facilities. This has resulted in substantial losses of seed production and thus created the need for specific as well as sensitive detection methods for this pathogen. In this project, quantitative PCR (qPCR) primers were developed and optimized based upon analysis of the V. tubiashii vtpA gene sequence, encoding a metalloprotease known to cause larval mortality. Standard curves were developed utilizing dilutions of known quantities of V. tubiashii cells that were compared to colony forming unit (CFU) plate counts. The assay was optimized for detection of vtpA with both lab-grown V. tubiashii samples and filter-captured environmental seawater samples seeded with V. tubiashii. In addition, the primers were confirmed to specifically detect only V. tubiashii when tested against a variety of non-target Vibrio species. Validation of the assay was completed by analyzing samples obtained from a shellfish hatchery. The development of this rapid and sensitive assay for quantitative detection of V. tubiashii will accurately determine levels of this bacterium in a variety of seawater samples, providing a useful tool for oyster hatcheries and a method to assess the presence of this bacterium in the current turbulent ocean environment.
    Journal of Microbiological Methods 03/2009; 76(3):262-8. DOI:10.1016/j.mimet.2008.12.001 · 2.03 Impact Factor

Publication Stats

2k Citations
165.49 Total Impact Points


  • 2003-2014
    • Oregon State University
      • • Department of Biomedical Sciences
      • • Department of Microbiology
      Corvallis, Oregon, United States
  • 2001-2003
    • University of Manitoba
      • Department of Microbiology
      Winnipeg, Manitoba, Canada
  • 2002
    • Nagoya University
      • Graduate School of Science
      Nagoya, Aichi, Japan
  • 2000-2002
    • St. Jude Children's Research Hospital
      • Department of Infectious Diseases
      Memphis, Tennessee, United States
  • 1999
    • Harvard Medical School
      • Department of Microbiology and Immunobiology
      Boston, Massachusetts, United States
  • 1995-1997
    • University of Western Australia
      Perth City, Western Australia, Australia