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Articles 31 - 53 of 53
Full-Text Articles in Microbiology
Characterization Of Mazfsa, An Endoribonuclease From Staphylococcus Aureus, Zhibiao Fu, Niles P. Donegan, Guido Memmi, Ambrose L. Cheung
Characterization Of Mazfsa, An Endoribonuclease From Staphylococcus Aureus, Zhibiao Fu, Niles P. Donegan, Guido Memmi, Ambrose L. Cheung
Dartmouth Scholarship
The mazEF homologs of Staphylococcus aureus, designated mazEF(sa), have been shown to cotranscribe with the sigB operon under stress conditions. In this study, we showed that MazEF(Sa), as with their Escherichia coli counterparts, compose a toxin-antitoxin module wherein MazF(Sa) leads to rapid cell growth arrest and loss in viable CFU upon overexpression. MazF(Sa) is a novel sequence-specific endoribonuclease which cleaves mRNA to inhibit protein synthesis. Using ctpA mRNA as the model substrate both in vitro and in vivo, we demonstrated that MazF(Sa) cleaves single-strand RNA preferentially at the 5' side of the first U or 3' side of the second …
A Serratia Marcescens Oxyr Homolog Mediates Surface Attachment And Biofilm Formation, Robert M. Q. Shanks, Nicholas A. Stella, Eric J. Kalivoda, Megan R. Doe
A Serratia Marcescens Oxyr Homolog Mediates Surface Attachment And Biofilm Formation, Robert M. Q. Shanks, Nicholas A. Stella, Eric J. Kalivoda, Megan R. Doe
Dartmouth Scholarship
OxyR is a conserved bacterial transcription factor with a regulatory role in oxidative stress response. From a genetic screen for genes that modulate biofilm formation in the opportunistic pathogen Serratia marcescens, mutations in an oxyR homolog and predicted fimbria structural genes were identified. S. marcescens oxyR mutants were severely impaired in biofilm formation, in contrast to the hyperbiofilm phenotype exhibited by oxyR mutants of Escherichia coli and Burkholderia pseudomallei. Further analysis revealed that OxyR plays a role in the primary attachment of cells to a surface. Similar to what is observed in other bacterial species, S. marcescens OxyR …
Parasites Alter Community Structure, Chelsea L. Wood, James E. Byers, Kathryn L. Cottingham, Irit Altman
Parasites Alter Community Structure, Chelsea L. Wood, James E. Byers, Kathryn L. Cottingham, Irit Altman
Dartmouth Scholarship
Parasites often play an important role in modifying the physiology and behavior of their hosts and may, consequently, mediate the influence hosts have on other components of an ecological community. Along the northern Atlantic coast of North America, the dominant herbivorous snail Littorina littorea structures rocky intertidal communities through strong grazing pressure and is frequently parasitized by the digenean trematode Cryptocotyle lingua. We hypothesized that the effects of parasitism on host physiology would induce behavioral changes in L. littorea, which in turn would modulate L. littorea's influence on intertidal community composition. Specifically, we hypothesized that C. lingua …
Inverse Regulation Of Biofilm Formation And Swarming Motility By Pseudomonas Aeruginosa Pa14, Nicky C. Caiazza, Judith H. Merritt, Kimberly M. Brothers, George A. O'Toole
Inverse Regulation Of Biofilm Formation And Swarming Motility By Pseudomonas Aeruginosa Pa14, Nicky C. Caiazza, Judith H. Merritt, Kimberly M. Brothers, George A. O'Toole
Dartmouth Scholarship
We previously reported that SadB, a protein of unknown function, is required for an early step in biofilm formation by the opportunistic pathogen Pseudomonas aeruginosa. Here we report that a mutation in sadB also results in increased swarming compared to the wild-type strain. Our data are consistent with a model in which SadB inversely regulates biofilm formation and swarming motility via its ability both to modulate flagellar reversals in a viscosity-dependent fashion and to influence the production of the Pel exopolysaccharide. We also show that SadB is required to properly modulate flagellar reversal rates via chemotaxis cluster IV (CheIV cluster). …
Vulnerability Of Pathogenic Biofilms To Micavibrio Aeruginosavorus, Daniel Kadouri, Nel C. Venzon, George A. O'Toole
Vulnerability Of Pathogenic Biofilms To Micavibrio Aeruginosavorus, Daniel Kadouri, Nel C. Venzon, George A. O'Toole
Dartmouth Scholarship
The host specificity of the gram-negative exoparasitic predatory bacterium Micavibrio aeruginosavorus was examined. M. aeruginosavorus preyed on Pseudomonas aeruginosa, as previously reported, as well as Burkholderia cepacia, Klebsiella pneumoniae, and numerous clinical isolates of these species. In a static assay, a reduction in biofilm biomass was observed as early as 3 hours after exposure to M. aeruginosavorus, and an ∼100-fold reduction in biofilm cell viability was detected following a a 24-h exposure to the predator. We observed that an initial titer of Micavibrio as low as 10 PFU/well or a time of exposure to the predator as short as 30 …
Gammaherpesvirus Persistence Alters Key Cd8 T-Cell Memory Characteristics And Enhances Antiviral Protection, Joshua J. Obar, Shinichiro Fuse, Erica K. Leung, Sarah C. Bellfy, Edward J. Usherwood
Gammaherpesvirus Persistence Alters Key Cd8 T-Cell Memory Characteristics And Enhances Antiviral Protection, Joshua J. Obar, Shinichiro Fuse, Erica K. Leung, Sarah C. Bellfy, Edward J. Usherwood
Dartmouth Scholarship
In herpesvirus infections, the virus persists for life but is contained through T-cell-mediated immune surveillance. How this immune surveillance operates is poorly understood. Recent studies of other persistent infections have indicated that virus persistence is associated with functional deficits in the CD8(+) T-cell response. To test whether this is the case in a herpesvirus infection, we used a mutant murine gammaherpesvirus that is defective in its ability to persist in the host. By comparing the immune response to this virus with a revertant virus that can persist, we were able to dissect the changes in the antiviral CD8(+) T-cell response …
Saccharomyces Cerevisiae-Based Molecular Tool Kit For Manipulation Of Genes From Gram-Negative Bacteria, Robert M. Q. Shanks, Nicky C. Caiazza, Shannon M. Hinsa, Christine M. Toutain, George A. O'Toole
Saccharomyces Cerevisiae-Based Molecular Tool Kit For Manipulation Of Genes From Gram-Negative Bacteria, Robert M. Q. Shanks, Nicky C. Caiazza, Shannon M. Hinsa, Christine M. Toutain, George A. O'Toole
Dartmouth Scholarship
A tool kit of vectors was designed to manipulate and express genes from a wide range of gram-negative species by using in vivo recombination. Saccharomyces cerevisiae can use its native recombination proteins to combine several amplicons in a single transformation step with high efficiency. We show that this technology is particularly useful for vector design. Shuttle, suicide, and expression vectors useful in a diverse group of bacteria are described and utilized. This report describes the use of these vectors to mutate clpX and clpP of the opportunistic pathogen Pseudomonas aeruginosa and to explore their roles in biofilm formation and surface …
Talking To Themselves: Autoregulation And Quorum Sensing In Fungi, Deborah A. Hogan
Talking To Themselves: Autoregulation And Quorum Sensing In Fungi, Deborah A. Hogan
Dartmouth Scholarship
Extracellular autoinducing compounds in the supernatants of microbial cultures were first recognized for their roles in the induction of genetic competence in gram-positive bacteria and in the regulation of light production in marine vibrios. In 1994, this form of population-level regulation in microbes was dubbed “quorum sensing” since it enabled bacterial cells to chemically measure the density of the surrounding population. Subsequently, many examples of cell density-dependent regulation by extracellular factors have been found in diverse microorganisms. The widespread incidence of diverse quorum-sensing systems strongly suggests that regulation in accordance with cell density is important for the success of microbes …
Sara Positively Controls Bap-Dependent Biofilm Formation In Staphylococcus Aureus, María P. Trotonda, Adhar C. Manna, Ambrose L. Cheung, Iñigo Lasa, José R. Penadés
Sara Positively Controls Bap-Dependent Biofilm Formation In Staphylococcus Aureus, María P. Trotonda, Adhar C. Manna, Ambrose L. Cheung, Iñigo Lasa, José R. Penadés
Dartmouth Scholarship
The biofilm-associated protein Bap is a staphylococcal surface protein involved in biofilm formation. We investigated the influence of the global regulatory locus sarA on bap expression and Bap-dependent biofilm formation in three unrelated Staphylococcus aureus strains. The results showed that Bap-dependent biofilm formation was diminished in the sarA mutants by an agr-independent mechanism. Complementation studies using a sarA clone confirmed that the defect in biofilm formation was due to the sarA mutation. As expected, the diminished capacity to form biofilms in the sarA mutants correlated with the decreased presence of Bap in the bacterial surface. Using transcriptional fusion and …
Susceptibility Of Biofilms To Bdellovibrio Bacteriovorus Attack, Daniel Kadouri, George A. O'Toole
Susceptibility Of Biofilms To Bdellovibrio Bacteriovorus Attack, Daniel Kadouri, George A. O'Toole
Dartmouth Scholarship
Biofilms are communities of microorganisms attached to a surface, and the growth of these surface attached communities is thought to provide microorganisms with protection against a range of biotic and abiotic agents. The capability of the gram-negative predatory bacterium Bdellovibrio bacteriovorus to control and reduce an existing Escherichia coli biofilm was evaluated in a static assay. A reduction in biofilm biomass was observed as early as 3 h after exposure to the predator, and an 87% reduction in crystal violet staining corresponding to a 4-log reduction in biofilm cell viability was seen after a 24-h exposure period. We observed that …
Cellulose Utilization By Clostridium Thermocellum: Bioenergetics And Hydrolysis Product Assimilation, Yi-Heng P. Zhang, Lee R. Lynd
Cellulose Utilization By Clostridium Thermocellum: Bioenergetics And Hydrolysis Product Assimilation, Yi-Heng P. Zhang, Lee R. Lynd
Dartmouth Scholarship
The bioenergetics of cellulose utilization by Clostridium thermocellum was investigated. Cell yield and maintenance parameters, Y(X/ATP)True = 16.44 g cell/mol ATP and m = 3.27 mmol ATP/g cell per hour, were obtained from cellobiose-grown chemostats, and it was shown that one ATP is required per glucan transported. Experimentally determined values for G(ATP)P-T (ATP from phosphorolytic beta-glucan cleavage minus ATP for substrate transport, mol ATP/mol hexose) from chemostats fed beta-glucans with degree of polymerization (DP) 2-6 agreed well with the predicted value of (n-2)/n [corrected] (n = mean cellodextrin DP assimilated). A mean G(ATP)(P-T) value of 0.52 +/- 0.06 was calculated …
Sara Is An Essential Positive Regulator Of Staphylococcus Epidermidis Biofilm Development, Maria A. Tormo, Miguel Marti, Jaione Valle, Adhar C. Manna
Sara Is An Essential Positive Regulator Of Staphylococcus Epidermidis Biofilm Development, Maria A. Tormo, Miguel Marti, Jaione Valle, Adhar C. Manna
Dartmouth Scholarship
Staphylococcus epidermidis biofilm formation is associated with the production of the polysaccharide intercellular adhesin (PIA)--poly-N-acetylglucosamine polysaccharide (PNAG) by the products of the icaADBC operon. Recent evidence indicates that SarA, a central regulatory element that controls the production of Staphylococcus aureus virulence factors, is essential for the synthesis of PIA/PNAG and the ensuing biofilm development in this species. Based on the presence of a sarA homolog, we hypothesized that SarA could also be involved in the regulation of the biofilm formation process in S. epidermidis. To investigate this, we constructed nonpolar sarA deletions in two genetically unrelated S. epidermidis clinical strains, …
A Three-Component Regulatory System Regulates Biofilm Maturation And Type Iii Secretion In Pseudomonas Aeruginosa, Sherry L. Kuchma, John P. Connolly, George A. O'Toole
A Three-Component Regulatory System Regulates Biofilm Maturation And Type Iii Secretion In Pseudomonas Aeruginosa, Sherry L. Kuchma, John P. Connolly, George A. O'Toole
Dartmouth Scholarship
Biofilms are structured communities found associated with a wide range of surfaces. Here we report the identification of a three-component regulatory system required for biofilm maturation by Pseudomonas aeruginosa strain PA14. A transposon mutation that altered biofilm formation in a 96-well dish assay originally defined this locus, which is comprised of genes for a putative sensor histidine kinase and two response regulators and has been designated sadARS. Nonpolar mutations in any of the sadARS genes result in biofilms with an altered mature structure but do not confer defects in growth or early biofilm formation, swimming, or twitching motility. After …
Identification Of Sarv (Sa2062), A New Transcriptional Regulator, Is Repressed By Sara And Mgra (Sa0641) And Involved In The Regulation Of Autolysis In Staphylococcus Aureus, Adhar C. Manna, Susham S. Ingavale, Marybeth Maloney, Willem Van Wamel, Ambrose L. Cheung
Identification Of Sarv (Sa2062), A New Transcriptional Regulator, Is Repressed By Sara And Mgra (Sa0641) And Involved In The Regulation Of Autolysis In Staphylococcus Aureus, Adhar C. Manna, Susham S. Ingavale, Marybeth Maloney, Willem Van Wamel, Ambrose L. Cheung
Dartmouth Scholarship
The expression of genes involved in the pathogenesis of Staphylococcus aureus is known to be controlled by global regulatory loci, including agr, sarA, sae, arlRS, lytSR, and sarA-like genes. Here we described a novel transcriptional regulator called sarV of the SarA protein family. The transcription of sarV is low or undetectable under in vitro conditions but is significantly augmented in sarA and mgrA (norR or rat) (SA0641) mutants. The sarA and mgrA genes act as repressors of sarV expression, as confirmed by transcriptional fusion and Northern analysis data. Purified SarA and MgrA proteins bound specifically to separate regions of the …
Sadb Is Required For The Transition From Reversible To Irreversible Attachment During Biofilm Formation By Pseudomonas Aeruginosa Pa14, Nicky C. Caiazza, George A. O'Toole
Sadb Is Required For The Transition From Reversible To Irreversible Attachment During Biofilm Formation By Pseudomonas Aeruginosa Pa14, Nicky C. Caiazza, George A. O'Toole
Dartmouth Scholarship
Current models of biofilm formation by Pseudomonas aeruginosa propose that (i) planktonic cells become surface associated in a monolayer, (ii) surface-associated cells form microcolonies by clonal growth and/or aggregation, (iii) microcolonies transition to a mature biofilm comprised of exopolysaccharide-encased macrocolonies, and (iv) cells exit the mature biofilm and reenter the planktonic state. Here we report a new class of P. aeruginosa biofilm mutant that defines the transition from reversible to irreversible attachment and is thus required for monolayer formation. The transposon insertion carried by the sadB199 mutant was mapped to open reading frame PA5346 of P. aeruginosa PA14 and encodes …
A Dominant-Negative Fur Mutation In Bradyrhizobium Japonicum, Heather P. Benson, Kristin Levier, Mary Lou Guerinot
A Dominant-Negative Fur Mutation In Bradyrhizobium Japonicum, Heather P. Benson, Kristin Levier, Mary Lou Guerinot
Dartmouth Scholarship
In many bacteria, the ferric uptake regulator (Fur) protein plays a central role in the regulation of iron uptake genes. Because iron figures prominently in the agriculturally important symbiosis between soybean and its nitrogen-fixing endosymbiont Bradyrhizobium japonicum, we wanted to assess the role of Fur in the interaction. We identified a fur mutant by selecting for manganese resistance. Manganese interacts with the Fur protein and represses iron uptake genes. In the presence of high levels of manganese, bacteria with a wild-type copy of the furgene repress iron uptake systems and starve for iron, whereas fur mutants fail to …
Alpha-Toxin Is Required For Biofilm Formation By Staphylococcus Aureus, Nicky C. Caiazza, George A. O'Toole
Alpha-Toxin Is Required For Biofilm Formation By Staphylococcus Aureus, Nicky C. Caiazza, George A. O'Toole
Dartmouth Scholarship
Staphylococcus aureus is a common pathogen associated with nosocomial infections. It can persist in clinical settings and gain increased resistance to antimicrobial agents through biofilm formation. We have found that alpha-toxin, a secreted, multimeric, hemolytic toxin encoded by the hla gene, plays an integral role in biofilm formation. The hla mutant was unable to fully colonize plastic surfaces under both static and flow conditions. Based on microscopy studies, we propose that alpha-hemolysin is required for cell-to-cell interactions during biofilm formation.
Rhamnolipid Surfactant Production Affects Biofilm Architecture In Pseudomonas Aeruginosa Pao1, Mary E. Davey, Nicky C. Caiazza, George A. O'Toole
Rhamnolipid Surfactant Production Affects Biofilm Architecture In Pseudomonas Aeruginosa Pao1, Mary E. Davey, Nicky C. Caiazza, George A. O'Toole
Dartmouth Scholarship
In response to certain environmental signals, bacteria will differentiate from an independent free-living mode of growth and take up an interdependent surface-attached existence. These surface-attached microbial communities are known as biofilms. In flowing systems where nutrients are available, biofilms can develop into elaborate three-dimensional structures. The development of biofilm architecture, particularly the spatial arrangement of colonies within the matrix and the open areas surrounding the colonies, is thought to be fundamental to the function of these complex communities. Here we report a new role for rhamnolipid surfactants produced by the opportunistic pathogen Pseudomonas aeruginosa in the maintenance of biofilm architecture. …
The Cd154/Cd40 Interaction Required For Retrovirus-Induced Murine Immunodeficiency Syndrome Is Not Mediated By Upregulation Of The Cd80/Cd86 Costimulatory Molecules, Kathy A. Green, W. James Cook, Arlene H. Sharpe, William R. Green
The Cd154/Cd40 Interaction Required For Retrovirus-Induced Murine Immunodeficiency Syndrome Is Not Mediated By Upregulation Of The Cd80/Cd86 Costimulatory Molecules, Kathy A. Green, W. James Cook, Arlene H. Sharpe, William R. Green
Dartmouth Scholarship
C57BL/6 (B6) mice infected with LP-BM5 retroviruses develop disease, including an immunodeficiency similar to AIDS. This disease, murine AIDS (MAIDS), is inhibited by in vivo anti-CD154 monoclonal antibody treatment. The similar levels of insusceptibility of CD40−/− and CD154−/− B6 mice indicate that CD154/CD40 molecular interactions are required for MAIDS. CD4+ T and B cells, respectively, provide the CD154 and CD40 expression needed for MAIDS induction. Here, the required CD154/CD40 interaction is shown to be independent of CD80 and CD86 expression: CD80/CD86−/− B6 mice develop MAIDS after LP-BM5 infection.
Type 4 Pilus Biogenesis And Type Ii-Mediated Protein Secretion By Vibrio Cholerae Occur Independently Of The Tonb-Facilitated Proton Motive Force, Niranjan Bose, Shelley M. Payne, Ronald K. Taylor
Type 4 Pilus Biogenesis And Type Ii-Mediated Protein Secretion By Vibrio Cholerae Occur Independently Of The Tonb-Facilitated Proton Motive Force, Niranjan Bose, Shelley M. Payne, Ronald K. Taylor
Dartmouth Scholarship
In Vibrio cholerae, elaboration of toxin-coregulated pilus and protein secretion by the extracellular protein secretion apparatus occurred in the absence of both TonB systems. In contrast, the cognate putative ATPases were required for each process and could not substitute for each other.
The Mannose-Sensitive Hemagglutinin Of Vibrio Cholerae Promotes Adherence To Zooplankton, Deborah A. Chiavelli, Jane W. Marsh, Ronald K. Taylor
The Mannose-Sensitive Hemagglutinin Of Vibrio Cholerae Promotes Adherence To Zooplankton, Deborah A. Chiavelli, Jane W. Marsh, Ronald K. Taylor
Dartmouth Scholarship
The bacterium Vibrio cholerae, the etiological agent of cholera, is often found attached to plankton, a property that is thought to contribute to its environmental persistence in aquatic habitats. The V. cholerae O1 El Tor biotype and V. cholerae O139 strains produce a surface pilus termed the mannose-sensitive hemagglutinin (MSHA), whereas V. cholerae O1 classical biotype strains do not. Although V. cholerae O1 classical does not elaborate MSHA, the gene is present and expressed at a level comparable to that of the other strains. Since V. cholerae O1 El Tor and V. cholerae O139 have displaced V. cholerae O1 classical …
The Growth Of Simian Virus 40 (Sv40) Host Range/Adenovirus Helper Function Mutants In An African Green Monkey Cell Line That Constitutively Expresses The Sv40 Agnoprotein., Terryl P. Stacy, Michele Chamberlain, Susan Carswell, Charles N. Cole
The Growth Of Simian Virus 40 (Sv40) Host Range/Adenovirus Helper Function Mutants In An African Green Monkey Cell Line That Constitutively Expresses The Sv40 Agnoprotein., Terryl P. Stacy, Michele Chamberlain, Susan Carswell, Charles N. Cole
Dartmouth Scholarship
The simian virus 40 T-antigen carboxy-terminal mutants, dlA2459 and dlA2475, are cell line and temperature dependent for growth and plaque formation in monkey kidney cells. Although these mutants did form plaques on BSC-1 cells at 37 degrees C, they were about fivefold less efficient for plaque formation than wild-type simian virus 40. These mutants did not grow in CV-1 cells and did not synthesize agnoprotein in those cells. CV-1 cells which constitutively express the agnoprotein were permissive for mutant plaque formation. However, late mRNAs, virion proteins, and progeny virion yields did not accumulate to wild-type levels during mutant infection of …
A Study Of The Effects Of Different Substrates On Growth And Reproduction In Certain Coprophilic Agaricaceae, Raymond C. Brown
A Study Of The Effects Of Different Substrates On Growth And Reproduction In Certain Coprophilic Agaricaceae, Raymond C. Brown
Theses and Dissertations
Psilocybe mutans sp. nov. had ceased fruiting consistently in artificial culture several years prior to the initiation of this study. In the couse of this study fruiting bodies were produced on a number of different substrates. All cultures were inoculated by mycelial transfer or by spraying with a suspension of pre-germinated spores. All cultrues were incubated for one to two weeks in a constant-temperature room at 70°F. on a shelf fourteen inches below a fluorescent lighting fixture. Lighting was continuous with an intensity at shelf level of approximately 3,000 foot-candles. Fruiting on any particular substrate was improved if the substrate …