Papers by Oddur Vilhelmsson
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Lichens are defined as the specific symbiotic structure comprising a fungus and a green alga and/... more Lichens are defined as the specific symbiotic structure comprising a fungus and a green alga and/or cyanobacterium. Up until recently, non-photobiont endothallic bacteria, while known to be present in large numbers, have generally been dismissed as functionally irrelevant cohabitants of the lichen thallus, or even environmental contaminants. Recent analyses of lichen meta-genomes and innovative co-culture experiments have uncovered a functionally complex community that appears to contribute to a healthy lichen thallus in several ways. Lichen-associated bacteriomes are typically dominated by several lineages of Proteobacteria, some of which may be specific for lichen species. Recent work has implicated members of these lineages in several important ecophysi-ological roles. These include nutrient scavenging, including mobilization of iron and phosphate, nitrogen fixation, cellulase, xylanase and amylase activities, and oxidation of recalcitrant compounds, e.g. aromatics and aliphatics. Production of volatile organic compounds, conferring antibacterial and antifungal activity, has also been demonstrated for several lichen-associated isolates. In the present paper we review the nature of non-phototrophic endolichenic bacteria associated with lichens, and give insight into the current state of knowledge on their importance the lichen symbiotic association.
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Journal of food protection, 2000
Staphylococcus aureus is the most osmotolerant foodborne pathogen, and outbreaks of staphylococca... more Staphylococcus aureus is the most osmotolerant foodborne pathogen, and outbreaks of staphylococcal food poisoning are often linked to foods of reduced water activity (a(w)) values. While it is generally known that the thermal tolerance of microorganisms increases as the a(w) of the heating menstruum is decreased, surprisingly little research has examined the influence of growth medium a(w) on microbial thermal tolerance. In the present study, we show that growth of S. aureus at an a(w) value of 0.94 leads to the development of dramatically enhanced thermal tolerance (i.e., less than 1 log reduction after heating for 20 min at 60 degrees C). We further show that the identity of the accumulated compatible solute within cells grown at low a(w) can also influence the overall level of thermal tolerance of S. aureus. Finally, we provide evidence that the synthesis of general stress and/or osmotic stress proteins is required for the development of enhanced thermal tolerance of S. aureus at...
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Simpson/Food Biochemistry and Food Processing, 2012
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Thesis (Ph.D.)--Pennsylvania State University, 2000. Microfilm (positive)
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Martin/The Ecological Genomics of Fungi, 2013
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Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics, 2003
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While generally described as a bipartite mutualistic association between fungi and algae or cyano... more While generally described as a bipartite mutualistic association between fungi and algae or cyanobacteria, lichens also host diverse and heretofore little explored communities of nonphototrophic endolichenic bacteria. The composition and possible roles of these bacterial communities in the lichen symbiotic association constitute an emerging field of research. Saxicolous (rock-dwelling) seashore lichens present an unusual environment, characterized by rapid fluctuations in temperature , salinity, exposure to solar radiation, etc. The present study focuses on the bacterial biota associated with 4 species of crustose, halophilic, saxicolous seashore lichens found in northern Iceland. A denaturing gradient gel electrophoresis based characterization of the composition of the lichen-associated microbiotas indicated that they are markedly lichen-species-specific and clearly distinguishable from the environmental microbiota represented by control sampling. A collection of bacterial strains was investigated and partially identified by 16S rDNA sequencing. The strains were found to belong to 7 classes: Alphaproteobacteria, Bacilli, Actinobacteria, Flavobacteria, Cytophagia, Sphingobacteria, and Gammaproteobacteria. Several isolates display only a modest level of similarity to their nearest relatives found in GenBank, suggesting that they comprise previously undescribed taxa. Selected strains were tested for inorganic phosphate solubilization and biodegradation of several biopolymers, such as barley-glucan, xylan, chitosan, and lignin. The results support a nutrient-scavenging role of the associate microbiota in the seashore lichen symbiotic association. Résumé : Bien que les lichens soient généralement décrits comme une association mutualiste bipartite entre un champignon et une algue ou une cyanobactérie, ils abritent également une flore diversifiée de bactéries endolichéniques non phototrophes aux attributs encore mal connus. La composition de ces communautés bactériennes et leurs rôles possibles au sein de l'association symbiotique du lichen sont au centre d'un domaine de recherche en émergence. Les lichens saxicoles (poussant sur les rochers) des littoraux présentent un environnement peu commun caractérisé par des fluctuations rapides de température, de salinité, d'exposition aux rayons solaires, etc. La présente étude s'intéresse a ` la flore bactérienne associée a ` quatre espèces de lichens crustacés, halophiles, saxicoles des littoraux du nord de l'Islande. La composition des microflores associées aux lichens, analysée par DGGE, s'est révélée hautement spécifique au lichen et facilement distinguable de la microflore environnementale de l'échantillon témoin. Un ensemble de souches bactériennes a été examiné et identifié partiellement par séquençage de l'ADNr 16S. On a constaté que les souches appartenaient a ` 7 classes : Alphaproteobacteria, Bacilli, Actinobacteria, Flavobacteria, Cytophagia, Sphingobacteria et Gammaproteobacteria. Sept isolats n'affichaient qu'une similitude modérée avec leur plus proche parent retrouvé dans GenBank, ce qui laisse croire qu'ils représenteraient un taxon nouvellement défini. Chez des souches choisies, on a analysé la capacité de solubilisation du phosphate et de biodégradation de plusieurs biopolymères, notamment le-glucane d'orge, le xylane, le chitosane et la lignine. Les résultats viennent étayer le rôle de collecte de nutriments que l'on attribue a ` la microflore liée a ` l'association symbiotique du lichen littoral. [Traduit par la Rédaction]
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Although lichens are generally described as mutualistic symbioses of fungi and photosynthetic par... more Although lichens are generally described as mutualistic symbioses of fungi and photosynthetic partners, they also harbour a diverse non-phototrophic microbiota, which is now regarded as a significant part of the symbiosis. However, the role of the non-phototrophic microbiota within the lichen is still poorly known, although possible functions have been suggested, including phosphate solubilization and various lytic activities. In the present study we focus on the bacterial biota associated with the foliose lichen Peltigera membranacea. To address our hypotheses on possible roles of the non-phototrophic microbiota, we used a metagenomic approach. A DNA library of bacterial sequence contigs was constructed from the lichen thallus material and the bacterial microbiota DNA sequence was analysed in terms of phylogenetic diversity and functional gene composition. Analysis of about 30 000 such bacterial contigs from the P. membranacea metagenome revealed significant representation of several genes involved in phosphate solubilization and biopolymer degradation.
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While generally described as a bipartite mutualistic association between fungi and algae or cyano... more While generally described as a bipartite mutualistic association between fungi and algae or cyanobacteria, lichens also host diverse and heretofore little explored communities of nonphototrophic endolichenic bacteria. The composition and possible roles of these bacterial communities in the lichen symbiotic association constitute an emerging field of research. Saxicolous (rock-dwelling) seashore lichens present an unusual environment, characterized by rapid fluctuations in temperature, salinity, exposure to solar radiation, etc. The present study focuses on the bacterial biota associated with 4 species of crustose, halophilic, saxicolous seashore lichens found in northern Iceland. A denaturing gradient gel electrophoresis based characterization of the composition of the lichen-associated microbiotas indicated that they are markedly lichen-species-specific and clearly distinguishable from the environmental microbiota represented by control sampling. A collection of bacterial strains was investigated and partially identified by 16S rDNA sequencing. The strains were found to belong to 7 classes: Alphaproteobacteria, Bacilli, Actinobacteria, Flavobacteria, Cytophagia, Sphingobacteria, and Gammaproteobacteria. Several isolates display only a modest level of similarity to their nearest relatives found in GenBank, suggesting that they comprise previously undescribed taxa. Selected strains were tested for inorganic phosphate solubilization and biodegradation of several biopolymers, such as barley β-glucan, xylan, chitosan, and lignin. The results support a nutrient-scavenging role of the associate microbiota in the seashore lichen symbiotic association.
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Bacterial life in the Netherworld – the culturable microbiota of Vatnshellir cave, 2013
Bacterial life in the Netherworld – the culturable microbiota of Vatnshellir cave
Lava tubes con... more Bacterial life in the Netherworld – the culturable microbiota of Vatnshellir cave
Lava tubes contain unique and little explored microbial habitats. Vatnshellir in the Purkhólahraun lava field presents several examples of the type of macroscopic microbial mats commonly termed ‘cave slime’. We sampled cave slime and other microbial habitats in Vatnshellir and cultured and isolated bacteria on several media, including oligotrophic ones. Forty-nine isolates have been identified by means of partial 16S rRNA gene sequencing. They were found to belong to nineteen genera in six classes. Most of the Vatnshellir bacteria are primarily heterotrophic, although nearly half of the strains tested were able to scavenge inorganic phosphate from a culture medium and the several tested strains could fix atmospheric nitrogen, indicating that the Vatnshellir microbiota is partly able to scavenge inorganic nutrients and may therefore possibly contribute to cave weathering. However, only could be shown to be iron-oxidizing under the conditions used. Several identified strains are closely related to bacteria associated with glaciers and cryoconite, underscoring the psychrotrophic and oligotrophic nature of the Vatnshellir environment. We conclude that Vatnshellir is host to a unique microbiota with clear conservation potential.
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Cold Regions Science and Technology
"The glacial river Jökulsá á Fjöllum,which originates in the Vatnajökull ice cap and flows throug... more "The glacial river Jökulsá á Fjöllum,which originates in the Vatnajökull ice cap and flows through a large basaltic tephra
desert on its way to discharge into the Arctic Ocean, presents a number of unique microbial habitats heretofore unexplored. We sampled river water, sediment and selected other biotopes at 12 sampling points along the river from source to mouth and generated a collection of 382 purified and confirmed reculturable psychrotrophic bacterial strains. Partial 16S rDNA sequencing yielded 19 genera and 4 non-genus specific assignments in 4 bacterial phyla, with pseudomonads and flavobacteria being particularly well represented. A large portion of the isolates produced extracellular enzymes at 15 °C, including amylase, betaglucanase, cellulase, protease and laccase."
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The river Glerá in Northern-Iceland presents a convenient model for the evaluation of anthropogen... more The river Glerá in Northern-Iceland presents a convenient model for the evaluation of anthropogenic effects on sub-Arctic river microbiota. The river originates in a pristine valley, flows past a landfill site where leachate merges into the river, and subsequently through a small urban area. Our aim was to
characterize the river microbiota in both its pristine and anthropogenically impacted state, particularly focusing on prospective surfactant degraders whose activity in the river water might contribute to the river’s self-purification capacity. We sampled river water and riverbed sediment at 10 sampling sites that spanned the river from its pristine source to the estuary for culturable bacteria and extractable DNA. A few other biotopes in the catchment area were also sampled. A confirmed pure and viable culture collection of 170 isolates was generated and partially analyzed for identification by 16S rRNA gene sequencing, and for biodegradation of selected surfactants as well as glycans, protein and triglyceride. Protein-degrading pseudomonads are strongly represented in the culture collection, many of whom can
also degrade selected surfactants. The collection also contains other members of the Gammaproteobacteria as well as the Alphaproteobacteria, Betaproteobacteria, Bacilli, Actinobacteria, Flavobacteria, and Sphingobacteria. Several isolates of all classes, except the Betaproteobacteria, displayed biodegradative
activity.
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Comparative Biochemistry and Physiology D-genomics & Proteomics, 2008
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British Journal of Nutrition, 2004
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Applied and Environmental Microbiology, 2002
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Papers by Oddur Vilhelmsson
Lava tubes contain unique and little explored microbial habitats. Vatnshellir in the Purkhólahraun lava field presents several examples of the type of macroscopic microbial mats commonly termed ‘cave slime’. We sampled cave slime and other microbial habitats in Vatnshellir and cultured and isolated bacteria on several media, including oligotrophic ones. Forty-nine isolates have been identified by means of partial 16S rRNA gene sequencing. They were found to belong to nineteen genera in six classes. Most of the Vatnshellir bacteria are primarily heterotrophic, although nearly half of the strains tested were able to scavenge inorganic phosphate from a culture medium and the several tested strains could fix atmospheric nitrogen, indicating that the Vatnshellir microbiota is partly able to scavenge inorganic nutrients and may therefore possibly contribute to cave weathering. However, only could be shown to be iron-oxidizing under the conditions used. Several identified strains are closely related to bacteria associated with glaciers and cryoconite, underscoring the psychrotrophic and oligotrophic nature of the Vatnshellir environment. We conclude that Vatnshellir is host to a unique microbiota with clear conservation potential.
desert on its way to discharge into the Arctic Ocean, presents a number of unique microbial habitats heretofore unexplored. We sampled river water, sediment and selected other biotopes at 12 sampling points along the river from source to mouth and generated a collection of 382 purified and confirmed reculturable psychrotrophic bacterial strains. Partial 16S rDNA sequencing yielded 19 genera and 4 non-genus specific assignments in 4 bacterial phyla, with pseudomonads and flavobacteria being particularly well represented. A large portion of the isolates produced extracellular enzymes at 15 °C, including amylase, betaglucanase, cellulase, protease and laccase."
characterize the river microbiota in both its pristine and anthropogenically impacted state, particularly focusing on prospective surfactant degraders whose activity in the river water might contribute to the river’s self-purification capacity. We sampled river water and riverbed sediment at 10 sampling sites that spanned the river from its pristine source to the estuary for culturable bacteria and extractable DNA. A few other biotopes in the catchment area were also sampled. A confirmed pure and viable culture collection of 170 isolates was generated and partially analyzed for identification by 16S rRNA gene sequencing, and for biodegradation of selected surfactants as well as glycans, protein and triglyceride. Protein-degrading pseudomonads are strongly represented in the culture collection, many of whom can
also degrade selected surfactants. The collection also contains other members of the Gammaproteobacteria as well as the Alphaproteobacteria, Betaproteobacteria, Bacilli, Actinobacteria, Flavobacteria, and Sphingobacteria. Several isolates of all classes, except the Betaproteobacteria, displayed biodegradative
activity.
Lava tubes contain unique and little explored microbial habitats. Vatnshellir in the Purkhólahraun lava field presents several examples of the type of macroscopic microbial mats commonly termed ‘cave slime’. We sampled cave slime and other microbial habitats in Vatnshellir and cultured and isolated bacteria on several media, including oligotrophic ones. Forty-nine isolates have been identified by means of partial 16S rRNA gene sequencing. They were found to belong to nineteen genera in six classes. Most of the Vatnshellir bacteria are primarily heterotrophic, although nearly half of the strains tested were able to scavenge inorganic phosphate from a culture medium and the several tested strains could fix atmospheric nitrogen, indicating that the Vatnshellir microbiota is partly able to scavenge inorganic nutrients and may therefore possibly contribute to cave weathering. However, only could be shown to be iron-oxidizing under the conditions used. Several identified strains are closely related to bacteria associated with glaciers and cryoconite, underscoring the psychrotrophic and oligotrophic nature of the Vatnshellir environment. We conclude that Vatnshellir is host to a unique microbiota with clear conservation potential.
desert on its way to discharge into the Arctic Ocean, presents a number of unique microbial habitats heretofore unexplored. We sampled river water, sediment and selected other biotopes at 12 sampling points along the river from source to mouth and generated a collection of 382 purified and confirmed reculturable psychrotrophic bacterial strains. Partial 16S rDNA sequencing yielded 19 genera and 4 non-genus specific assignments in 4 bacterial phyla, with pseudomonads and flavobacteria being particularly well represented. A large portion of the isolates produced extracellular enzymes at 15 °C, including amylase, betaglucanase, cellulase, protease and laccase."
characterize the river microbiota in both its pristine and anthropogenically impacted state, particularly focusing on prospective surfactant degraders whose activity in the river water might contribute to the river’s self-purification capacity. We sampled river water and riverbed sediment at 10 sampling sites that spanned the river from its pristine source to the estuary for culturable bacteria and extractable DNA. A few other biotopes in the catchment area were also sampled. A confirmed pure and viable culture collection of 170 isolates was generated and partially analyzed for identification by 16S rRNA gene sequencing, and for biodegradation of selected surfactants as well as glycans, protein and triglyceride. Protein-degrading pseudomonads are strongly represented in the culture collection, many of whom can
also degrade selected surfactants. The collection also contains other members of the Gammaproteobacteria as well as the Alphaproteobacteria, Betaproteobacteria, Bacilli, Actinobacteria, Flavobacteria, and Sphingobacteria. Several isolates of all classes, except the Betaproteobacteria, displayed biodegradative
activity.