Department of Microbiology Faculty & Researcher Works

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Epistasis Analysis of Four Genes from Anabaena sp. Strain PCC 7120 Suggests a Connection between PatA and PatS in Heterocyst Pattern Formation
(American Society for Microbiology, 2005-12) Orozco, Christine C.; Risser, Douglas D.; Callahan, Sean M.
The hetR, patA, hetN, and patS genes are part of a regulatory network that regulates the differentiation and patterning of heterocysts in the filamentous cyanobacterium Anabaena sp. strain PCC 7120. In this report, the epistatic interactions of mutant alleles of these four genes have been used to refine our understanding of their relationships to one another. The hetR gene was necessary for differentiation in genetic backgrounds that normally give rise to excessive differentiation, supporting its role as the master regulator of differentiation and indicating that HetR directly regulates factors in addition to hetR and patS genes that regulate differentiation. A functional patS gene was necessary for the delayed multiple-contiguous-heterocyst phenotype observed in hetN mutants as well as for the relative lack of intercalary heterocysts in patA mutants. Epistasis results with mutant alleles of these three genes suggested that PatA attenuates the negative effects of both PatS and HetN on differentiation and promotes differentiation independent of its antagonistic effects on PatS and HetN activity. Cooverxpression of patS and hetR in a synthetic operon indicated that patS acts at a point downstream of hetR transcription in the regulatory network controlling differentiation. A model for the regulation of differentiation that is consistent with these and previous findings is presented.
Mutagenesis of hetR Reveals Amino Acids Necessary for HetR Function in the Heterocystous Cyanobacterium Anabaena sp. Strain PCC 7120
(American Society for Microbiology, 2007-01) Risser, Douglas D.; Callahan, Sean M.
HetR is the master regulator of heterocyst differentiation in the filamentous cyanobacterium Anabaena sp. strain PCC 7120. Genetic selection was used to identify 33 amino acid substitutions in HetR that reduced the proportion of cells undergoing heterocyst differentiation to less than 2%. Conservative substitutions in the wild-type HetR protein revealed three mutations that dramatically reduced the amount of heterocyst differentiation when the mutant allele was present in place of the wild-type allele on a replicating plasmid in a mutant lacking hetR on the chromosome. An H69Y substitution resulted in heterocyst formation among less than 0.1% of cells, and D17E and G36A substitutions resulted in a Het- phenotype, compared to heterocyst formation among approximately 25% of cells with the wild-type hetR under the same conditions. The D17E substitution prevented DNA binding activity exhibited by wild-type HetR in mobility shift assays, whereas G36A and H69Y substitutions had no affect on DNA binding. D17E, G36A, and H69Y substitutions also resulted in higher levels of the corresponding HetR protein than of the wild-type protein when each was expressed from an inducible promoter in a hetR deletion strain, suggesting an effect on HetR protein turnover. Surprisingly, C48A and S152A substitutions, which were previously reported to result in a Het- phenotype, were found to have no effect on heterocyst differentiation or patterning when the corresponding mutations were introduced into an otherwise wild-type genetic background in Anabaena sp. strain PCC 7120. The clustering of mutations that satisfied the positive selection near the amino terminus suggests an important role for this part of the protein in HetR function.
Analysis of LuxR Regulon Gene Expression during Quorum Sensing in Vibrio fischeri
(American Society for Microbiology, 2007-03) Qin, Nan; Callahan, Sean M.; Dunlap, Paul V.; Stevens, Ann M.
The regulation of the lux operon (luxICDABEG) of Vibrio fischeri has been intensively studied as a model for quorum sensing in proteobacteria. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis previously identified several non-Lux proteins in V. fischeri MJ-100 whose expression was dependent on LuxR and 3-oxo-hexanoyl L-homoserine lactone (3-oxo-C6-HSL). To determine if the LuxR-dependent regulation of the genes encoding these proteins was due to direct transcriptional control by LuxR and 3-oxo-C6-HSL or instead was due to indirect control via an unidentified regulatory element, promoters of interest were cloned into a lacZ reporter and tested for their LuxR and 3-oxo-C6-HSL dependence in recombinant Escherichia coli. The promoters for qsrP, acfA, and ribB were found to be directly activated via LuxR-3-oxo-C6-HSL. The sites of transcription initiation were established via primer extension analysis. Based on this information and the position of the lux box-binding site near position -40, all three promoters appear to have a class II-type promoter structure. In order to more fully characterize the LuxR regulon in V. fischeri MJ-100, real-time reverse transcription-PCR was used to study the temporal expression of qsrP, acfA, and ribB during the exponential and stationary phases of growth, and electrophoretic mobility shift assays were used to compare the binding affinities of LuxR to the promoters under investigation. Taken together, the results demonstrate that regulation of the production of QsrP, RibB, and AcfA is controlled directly by LuxR at the level of transcription, thereby establishing that there is a LuxR regulon in V. fischeri MJ-100 whose genes are coordinately expressed during mid-exponential growth.
HetF and PatA Control Levels of HetR in Anabaena sp. Strain PCC 7120
(American Society for Microbiology, 2008-10) Risser, Douglas D.; Callahan, Sean M.
Anabaena sp. strain PCC 7120 is a filamentous cyanobacterium that differentiates heterocysts in response to deprivation of combined nitrogen. A hetF deletion strain lacked heterocysts and had aberrant cell morphology. Site-directed mutagenesis of the predicted active-site histidine and cysteine residues of this putative caspasehemoglobinase fold protease abolished HetF function, supporting the hypothesis that HetF is a protease. Deletion of patA, which is necessary for the formation of most intercalary heterocysts, or hetF resulted in an increase in HetR protein, and extra copies of hetF on a plasmid functionally bypassed the deletion of patA. A hetR-gfp translational fusion expressed from an inducible promoter demonstrated that hetF-dependent downregulation of HetR levels occurs rapidly in vegetative cells, as well as developing heterocysts. “Mosaic” filaments in which only one cell of a filament had a copy of hetR or hetF indicated that hetF is required for differentiation only in cells that will become heterocysts. hetF was required for transcription from a hetRdependent transcription start point of the hetR promoter and induction of transcription from the patS promoter. The inverse correlation between the level of HetR protein and transcription from hetR-dependent promoters suggests that the transcriptional activity of HetR is regulated by HetF and PatA.
Genetic and cytological evidence that heterocyst patterning is regulated by inhibitor gradients that promote activator decay
(Proceedings of the National Academy of Sciences of the United States of America, 2009-11) Risser, Douglas D.; Callahan, Sean M.
The formation of a pattern of differentiated cells from a group of seemingly equivalent, undifferentiated cells is a central paradigm of developmental biology. Several species of filamentous cyanobacteria differentiate nitrogen-fixing heterocysts at regular intervals along unbranched filaments to form a periodic pattern of two distinct cell types. This patterning has been used to exemplify application of the activator-inhibitor model to periodic patterns in biology. The activator-inhibitor model proposes that activators and inhibitors of differentiation diffuse from source cells to form concentration gradients that in turn mediate patterning, but direct visualization of concentration gradients of activators and inhibitors has been difficult. Here we show that the periodic pattern of heterocysts produced by cyanobacteria relies on two inhibitors of heterocyst differentiation, PatS and HetN, in a manner consistent with the predictions of the activator-inhibitor model. Concentration gradients of the activator, HetR, were observed adjacent to heterocysts, the natural source of PatS and HetN, as well as adjacent to vegetative cells that were manipulated to overexpress a gene encoding either of the inhibitors. Gradients of HetR relied on posttranslational decay of HetR. Deletion of both patS and hetN genes prevented the formation of gradients of HetR, and a derivative of the inhibitors was shown to promote decay of HetR in a concentration-dependent manner. Our results provide strong support for application of the activator-inhibitor model to heterocyst patterning and, more generally, the formation of periodic patterns in biological systems.
Temporal and Spatial Regulation of the Four Transcription Start Sites of hetR from Anabaena sp. Strain PCC 7120
(American Society for Microbiology, 2009-12) Rajagopalan, Ramya; Callahan, Sean M.
The filamentous cyanobacterium Anabaena sp. strain PCC 7120 forms nitrogen-fixing heterocysts in a periodic pattern in response to combined-nitrogen limitation in the environment. The master regulator of heterocyst differentiation, HetR, is necessary for both pattern formation and commitment of approximately every 10th cell of a filament to differentiation into a heterocyst. In this study, the individual contributions of four transcriptional start points (tsps) in regulation of transcription of hetR were assessed, and the effects of the regulatory genes patS, hetN, and patA on transcription from the tsps were determined. The tsp located at nucleotide -271 relative to the translational start site (-271 tsp) was the most tightly regulated tsp, and fluorescence from a -271 tsp-green fluorescent protein (GFP) reporter fusion was observed initially in groups of two cells and later in single cells arranged in a spatial pattern that mimicked the pattern of heterocysts that emerged. Conversely, the fluorescence from the -184 and -728/-696 tsp-GFP reporter fusions was uniform throughout filaments. Transcription from the -271 tsp was severely downregulated in a strain in which the patA gene, which encodes a positive regulator of differentiation, was deleted, and it was not detectable in strains overexpressing the genes encoding the negative regulators of differentiation, patS and hetN. In strains lacking the -271 tsp of hetR, pattern formation, the timing of commitment to differentiation, and the number of cells that differentiated into heterocysts were affected. Taken together, these results demonstrate the role of regulation of the -271 tsp of hetR in the genetic network that governs heterocyst pattern formation and differentiation.
Maintenance of heterocyst patterning in a filamentous cyanobacterium
(Taylor & Francis Group, 2010-04) Zhu, Mei; Callahan, Sean M.; Allen, John S.
In the absence of sufficient combined nitrogen, some filamentous cyanobacteria differentiate nitrogenfixing heterocysts at approximately every 10th cell position. As cells between heterocysts grow and divide, this initial pattern is maintained by the differentiation of a single cell approximately midway between existing heterocysts. This paper introduces a mathematical model for the maintenance of the periodic pattern of heterocysts differentiated by Anabaena sp. strain PCC 7120 based on the current experimental knowledge of the system. The model equations describe a non-diffusing activator (HetR) and two inhibitors (PatS and HetN) that undergo diffusion in a growing one-dimensional domain. The inhibitors in this model have distinct diffusion rates and temporal expression patterns. These unique aspects of the model reflect recent experimental findings regarding the molecular interactions that regulate patterning in Anabaena. Output from the model is in good agreement with both the temporal and spatial characteristics of the pattern maintenance process observed experimentally.
Transcriptional Regulation of the Heterocyst Patterning Gene patA from Anabaena sp. Strain PCC 7120
(American Society for Microbiology, 2010-07) Young-Robbins, Shirley S.; Risser, Douglas D.; Moran, Jennifer R.; Haselkorn, Robert; Callahan, Sean M.
The filamentous cyanobacterium Anabaena sp. strain PCC 7120 forms a periodic pattern of nitrogen-fixing heterocysts when grown in the absence of combined nitrogen. PatA is necessary for proper patterning of heterocysts along filaments. In this study, apparent transcriptional start points (tsps) were identified at nucleotides -305, -614, and -645 relative to the translational start site (-305, -614, and -645 tsps). Transcriptional reporter fusions were used to show that transcription from the -305 tsp was induced in all cells of filaments in response to nitrogen deprivation, required hetR for induction, and increased in a patA mutant. Transcription from -614/-645 tsp reporter fusions was spatially regulated and occurred primarily in cells that would become heterocysts. Complementation of a patA mutant strain by alleles encoding substitutions in, or deletion of, the putative phosphoacceptor C-terminal domain indicates that the PATAN domain can function independently of the C-terminal domain of PatA. Localization of a ring of PatA-GFP at sites of cell division, as well as the formation of enlarged cells with altered cell morphology when patA was overexpressed, suggests that PatA may participate in cell division.
Structure of transcription factor HetR required for heterocyst differentiation in cyanobacteria
(Proceedings of the National Academy of Sciences of the United States of America, 2011-04) Kim, Youngchang; Joachimiak, Grazyna; Ye, Zi; Binkowski, T. Andrew; Zhang, Rongguang; Gornicki, Piotr; Callahan, Sean M.; Hess, Wolfgang R.; Haselkorn, Robert; Joachimiak, Andrzej
HetR is an essential regulator of heterocyst development in cyanobacteria. HetR binds to a DNA palindrome upstream of the hetP gene. We report the crystal structure of HetR from Fischerella at 3.0 Å. The protein is a dimer comprised of a central DNA-binding unit containing the N-terminal regions of the two subunits organized with two helix-turn-helix motifs; two globular flaps extending in opposite directions; and a hood over the central core formed from the C-terminal subdomains. The flaps and hood have no structural precedent in the protein database, therefore representing new folds. The structural assignments are supported by sitedirected mutagenesis and DNA-binding studies. We suggest that HetR serves as a scaffold for assembly of transcription components critical for heterocyst development.
Recruitment in the sea: bacterial genes required for inducing larval settlement in a polychaete worm
(Nature, 2012-01) Huang, Ying; Callahan, Sean M.; Hadfield, Michael G.
Metamorphically competent larvae of the marine tubeworm Hydroides elegans can be induced to metamorphose by biofilms of the bacterium Pseudoalteromonas luteoviolacea strain HI1. Mutational analysis was used to identify four genes that are necessary for metamorphic induction and encode functions that may be related to cell adhesion and bacterial secretion systems. No major differences in biofilm characteristics, such as biofilm cell density, thickness, biomass and EPS biomass, were seen between biofilms composed of P. luteoviolacea (HI1) and mutants lacking one of the four genes. The analysis indicates that factors other than those relating to physical characteristics of biofilms are critical to the inductive capacity of P. luteoviolacea (HI1), and that essential inductive molecular components are missing in the non-inductive deletion-mutant strains.
Vibrio owensii Induces the Tissue Loss Disease Montipora White Syndrome in the Hawaiian Reef Coral Montipora capitata
(PLOS, 2012-10) Ushijima, Blake; Smith, Ashley; Aeby, Greta S.; Callahan, Sean M.
Incidences of coral disease in the Indo-Pacific are increasing at an alarming rate. In particular, Montipora white syndrome, a tissue-loss disease found on corals throughout the Hawaiian archipelago, has the potential to degrade Hawaii’s reefs. To identify the etiologic agent of Montipora white syndrome, bacteria were isolated from a diseased fragment of Montipora capitata and used in a screen for virulent strains. A single isolate, designated strain OCN002, recreated disease signs in 53% of coral fragments in laboratory infection trials when added to a final concentration of 107 cells/ml of seawater. In addition to displaying similar signs of disease, diseased coral fragments from the field and those from infection trials both had a dramatic increase in the abundance of associated culturable bacteria, with those of the genus Vibiro well represented. Bacteria isolated from diseased fragments used in infection trails were shown to be descendants of the original OCN002 inocula based on both the presence of a plasmid introduced to genetically tag the strain and the sequence of a region of the OCN002 genome. In contrast, OCN002 was not re-isolated from fragments that were exposed to the strain but did not develop tissue loss. Sequencing of the rrsH gene, metabolic characterization, as well as multilocus sequence analysis indicated that OCN002 is a strain of the recently described species Vibrio owensii. This investigation of Montipora white syndrome recognizes V. owensii OCN002 as the first bacterial coral pathogen identified from Hawaii’s reefs and expands the range of bacteria known to cause disease in corals.
Structures of complexes comprised of Fischerella transcription factor HetR with Anabaena DNA targets
(Proceedings of the National Academy of Sciences of the United States of America, 2013-04) Kim, Youngchang; Ye, Zi; Joachimiak, Grazyna; Videau, Patrick; Young, Jasmine; Hurd, Kathryn; Callahan, Sean M.; Gornicki, Piotr; Zhao, Jindong; Haselkorn, Robert; Joachimiak, Andrzej
HetR is an essential regulator of heterocyst development in cyanobacteria. Many mutations in HetR render Anabaena incapable of nitrogen fixation. The protein binds to a DNA palindrome upstream of hetP and other genes. We have determined the crystal structures of HetR complexed with palindromic DNA targets, 21, 23, and 29 bp at 2.50-, 3.00-, and 3.25-Å resolution, respectively. The highest-resolution structure shows fine details of specific protein–DNA interactions. The lower-resolution structures with longer DNA duplexes have similar interaction patterns and show how the flap domains interact with DNA in a sequence nonspecific fashion. Fifteen of 15 protein–DNA contacts predicted on the basis of the structure were confirmed by single amino acid mutations that abolished binding in vitro and complementation in vivo. A striking feature of the structure is the association of glutamate 71 from each subunit of the HetR dimer with three successive cytosines in each arm of the palindromic target, a feature that is conserved among all known heterocyst-forming cyanobacteria sequenced to date.
Draft Genome Sequence of Vibrio coralliilyticus strain OCN008 Isolated from Kāneʻohe Bay, Hawaiʻi.
(American Society for Microbiology, 2013-10) Ushijima, Blake; Videau, Patrick; Aeby, Greta S.; Callahan, Sean M.
Vibrio coralliilyticus is a Gram-negative bacterium found in seawater and is associated with diseased marine organisms. Strains of V. coralliilyticus have been shown to infect coral from multiple genera. We report the draft genome sequence of V. coralliilyticus strain OCN008, the third V. coralliilyticus genome to be sequenced.
Expanding the Direct HetR Regulon in Anabaena sp. Strain PCC 7120
(American Society for Microbiology, 2013-12) Videau, Patrick; Ni, Shuisong; Rivers, Orion S.; Ushijima, Blake; Feldmann, Erik A.; Cozy, Loralyn M.; Kennedy, Michael A.; Callahan, Sean M.
In response to a lack of environmental combined nitrogen, the filamentous cyanobacterium Anabaena sp. strain PCC 7120 differentiates nitrogen-fixing heterocyst cells in a periodic pattern. HetR is a transcription factor that coordinates the regulation of this developmental program. An inverted repeat-containing sequence in the hepA promoter required for proheterocyst-specific transcription was identified based on sequence similarity to a previously characterized binding site for HetR in the promoter of hetP. The binding affinity of HetR for the hepA site is roughly an order of magnitude lower than that for the hetP binding site. A BLAST search of the Anabaena genome identified 166 hepA-like sites that occur as single or tandem sites (two binding sites separated by 13 bp). The vast majority of these sites are present in predicted intergenic regions. HetR bound five representative single binding sites in vitro, and binding was abrogated by transversions in the binding sites that conserved the inverted repeat nature of the sites. Binding to four representative tandem sites was not observed. Transcriptional fusions of the green fluorescent protein gene gfp with putative promoter regions associated with the representative binding sites indicated that HetR could function as either an activator or repressor and that activation was cell-type specific. Taken together, we have expanded the direct HetR regulon and propose a model in which three categories of HetR binding sites, based on binding affinity and nucleotide sequence, contribute to three of the four phases of differentiation.
The trpE Gene Negatively Regulates Differentiation of Heterocysts at the Level of Induction in Anabaena sp. Strain PCC 7120
(American Society for Microbiology, 2014-11) Videau, Patrick; Cozy, Loralyn M.; Young, Jasmine E.; Ushijima, Blake; Oshiro, Reid T.; Rivers, Orion S.; Burger, Andrew H.; Callahan, Sean M.
Levels of 2-oxoglutarate (2-OG) reflect nitrogen status in many bacteria. In heterocystous cyanobacteria, a spike in the 2-OG level occurs shortly after the removal of combined nitrogen from cultures and is an integral part of the induction of heterocyst differentiation. In this work, deletion of one of the two annotated trpE genes in Anabaena sp. strain PCC 7120 resulted in a spike in the 2-OG level and subsequent differentiation of a wild-type pattern of heterocysts when filaments of the mutant were transferred from growth on ammonia to growth on nitrate. In contrast, 2-OG levels were unaffected in the wild type, which did not differentiate under the same conditions. An inverted-repeat sequence located upstream of trpE bound a central regulator of differentiation, HetR, in vitro and was necessary for HetR-dependent transcription of a reporter fusion and complementation of the mutant phenotype in vivo. Functional complementation of the mutant phenotype with the addition of tryptophan suggested that levels of tryptophan, rather than the demonstrated anthranilate synthase activity of TrpE, mediated the developmental response of the wild type to nitrate. A model is presented for the observed increase in 2-OG in the trpE mutant.
Complete Genome Sequence of Vibrio coralliilyticus Strain OCN014, Isolated from a Diseased Coral at Palmyra Atoll
(American Society for Microbiology, 2014-12) Ushijima, Blake; Videau, Patrick; Poscablo, Donna; Vine, Veronica; Salcedo, May; Aeby, Greta; Callahan, Sean M.
Vibrio coralliilyticus is a marine gammaproteobacterium that has been implicated as an etiological agent of disease for multiple coral genera on reefs worldwide. We report the complete genome of V. coralliilyticus strain OCN014, isolated from a diseased Acropora cytherea colony off the western reef terrace of Palmyra Atoll.
Complete Genome Sequence of Pseudoalteromonas sp. Strain OCN003, Isolated from Kāneʻohe Bay, Oʻahu, Hawaii
(American Society for Microbiology, 2015-01) Beurmann, Silvia; Videau, Patrick; Ushijima, Blake; Smith, Ashley M.; Aeby, Greta S.; Callahan, Sean M.; Belcaid, Mahdi
Pseudoalteromonas sp. strain OCN003 is a marine gammaproteobacterium that was isolated from a diseased colony of the common Hawaiian reef coral, Montipora capitata, found on a reef surrounding Moku o Loʻe in Kāneʻohe Bay, Hawaii. Here, we report the complete genome of Pseudoalteromonas sp. strain OCN003.
First Record of Black Band Disease in the Hawaiian Archipelago: Response, Outbreak Status, Virulence, and a Method of Treatment
(PLOS, 2015-03) Aeby, Greta S.; Work, Thierry M.; Runyon, Christina M.; Shore-Maggio, Amanda; Ushijima, Blake; Videau, Patrick; Beurmann, Silvia; Callahan, Sean M.
A high number of coral colonies, Montipora spp., with progressive tissue loss were reported from the north shore of Kaua‘i by a member of the Eyes of the Reef volunteer reporting network. The disease has a distinct lesion (semi-circular pattern of tissue loss with an adjacent dark band) that was first observed in Hanalei Bay, Kaua‘i in 2004. The disease, initially termed Montipora banded tissue loss, appeared grossly similar to black band disease (BBD), which affects corals worldwide. Following the initial report, a rapid response was initiated as outlined in Hawai‘i’s rapid response contingency plan to determine outbreak status and investigate the disease. Our study identified the three dominant bacterial constituents indicative of BBD (filamentous cyanobacteria, sulfate-reducing bacteria, sulfide-oxidizing bacteria) in coral disease lesions from Kaua‘i, which provided the first evidence of BBD in the Hawaiian archipelago. A rapid survey at the alleged outbreak site found disease to affect 6-7% of the montiporids, which is higher than a prior prevalence of less than 1% measured on Kaua‘i in 2004, indicative of an epizootic. Tagged colonies with BBD had an average rate of tissue loss of 5.7 cm2/day over a two-month period. Treatment of diseased colonies with a double band of marine epoxy, mixed with chlorine powder, effectively reduced colony mortality. Within two months, treated colonies lost an average of 30% less tissue compared to untreated controls.
ABC Transporter Required for Intercellular Transfer of Developmental Signals in a Heterocystous Cyanobacterium
(American Society for Microbiology, 2015-06) Videau, Patrick; Rivers, Orion S.; Higa, Kelly C.; Callahan, Sean M.
In the filamentous cyanobacterium Anabaena, patS and hetN encode peptide-derived signals with many of the properties of morphogens. These signals regulate the formation of a periodic pattern of heterocysts by lateral inhibition of differentiation. Here we show that intercellular transfer of the patS- and hetN-dependent developmental signals from heterocysts to vegetative cells requires HetC, a predicted ATP-binding cassette transporter (ABC transporter). Relative to the wild type, in a hetC mutant differentiation resulted in a reduced number of heterocysts that were incapable of nitrogen fixation, but deletion of patS or hetN restored heterocyst number and function in a hetC background. These epistasis results suggest that HetC is necessary for conferring self-immunity to the inhibitors on differentiating cells. Nine hours after induction of differentiation, HetC was required for neither induction of transcription of patS nor intercellular transfer of the patS-encoded signal to neighboring cells. Conversely, in strains lacking HetC, the patS- and hetN-encoded signals were not transferred from heterocyst cells to adjacent vegetative cells. The results support a model in which the patS-dependent signal is initially transferred between vegetative cells in a HetC-independent fashion, but some time before morphological differentiation of heterocysts is complete, transfer of both signals transitions to a HetC-dependent process.
Vibrio coralliilyticus Strain OCN008 Is an Etiological Agent of Acute Montipora White Syndrome
(American Society for Microbiology, 2014-01) Ushijima, Blake; Videau, Patrick; Burger, Andrew H.; Shore-Maggio, Amanda; Runyon, Christina M.; Sudek, Mareike; Aeby, Greta S.; Callahan, Sean M.
Identification of a pathogen is a critical first step in the epidemiology and subsequent management of a disease. A limited number of pathogens have been identified for diseases contributing to the global decline of coral populations. Here we describe Vibrio coralliilyticus strain OCN008, which induces acute Montipora white syndrome (aMWS), a tissue loss disease responsible for substantial mortality of the coral Montipora capitata in Ka ne‘ohe Bay, Hawai‘i. OCN008 was grown in pure culture, recreated signs of disease in experimentally infected corals, and could be recovered after infection. In addition, strains similar to OCN008 were isolated from diseased coral from the field but not from healthy M. capitata. OCN008 repeatedly induced the loss of healthy M. capitata tissue from fragments under laboratory conditions with a minimum infectious dose of between 107 and 108 CFU/ml of water. In contrast, Porites compressa was not infected by OCN008, indicating the host specificity of the pathogen. A decrease in water temperature from 27 to 23°C affected the time to disease onset, but the risk of infection was not significantly reduced. Temperature-dependent bleaching, which has been observed with the V. coralliilyticus type strain BAA-450, was not observed during infection with OCN008. A comparison of the OCN008 genome to the genomes of pathogenic V. coralliilyticus strains BAA-450 and P1 revealed similar virulence-associated genes and quorum-sensing systems. Despite this genetic similarity, infections of M. capitata by OCN008 do not follow the paradigm for V. coralliilyticus infections established by the type strain.

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