Microbial community dynamics in polar hypersaline springs: viral ecology and sulfur cycling
Notice bibliographique
Résumé
Astrobiology spans a range of disciplines. Experimental work in this field is essential to constraining the likelihood of life's origin, evolution and detectability. The work described in this thesis focuses on the microbial ecology of an extreme environment. Microbes that inhabit such environments demonstrate deviations on biological processes such as might be found under conditions disparate from those thought of as hospitable for life. This work focuses on two polar hypersaline springs in the Canadian High Arctic, considered extreme by their low temperature, high salinity and low oxygen. Within those springs, this work focuses on two processes: 1) microbial mortality by viruses; and 2) sulfur isotope biosignatures of microbial metabolism. The abundance of viruses from Arctic hypersaline spring water and sediment environments was investigated and the first estimates of contact rates between viruses and bacteria in sediments were modeled. The oligotrophic nature of these springs maintains some of the lowest virus-bacteria ratios and contact rates observed in natural environments to date, indicating that viruses do not play a major lytic role in these springs. Comparison of these results to reports from marine sediments identifies a viral biogeographic divide in deep-sea sediments that separates shallower bacterial communities controlled by lytic viruses from deeper ones that are not. Complementary viral dynamics experiments were performed in sediments of the same springs. This work addresses 1) the trophic hypothesis of viral influence on microbial growth and 2) the relationship between oligotrophy and lysogenic replication. These sediments maintain extremely low rates of microbial growth and viral production and a substantial fraction of viruses are extremely resistant to decay. These viruses contribute to microbial mortality, but are not the primary cause of such. A substantial fraction of microbes in these sediments appear to be lysogens, harboring inducible provirus, yet temperate viruses do not seem to account for a large fraction of the in situ population of virions. These findings support the trophic hypothesis, but offer limited support for an increasing frequency of lysogens in oligotrophic environments. These findings extend the range of geochemical conditions under which viral dynamics have been explored and suggest that viruses are able to maintain a role in microbial mortality even in extremely low biomass environments, potentially by means of resisting decay. The preserved signals of biological isotopic fractionation of sulfur in one of the two springs was described, as were the accompanying sulfate reducing microorganisms that inhabit its sediments. This work addresses the influence that environmental chemistry and genomic diversity have on the fractionation of sulfur isotopes across a small spatial scale. These sediments show little variation in sulfur fractionation, despite differences in several of the characters known to contribute to the extent of fractionation by cultured sulfate reducing isolates. To address the discrepancy between measured and modeled cell-specific sulfate reduction rates (csSRR) and isotopic fractionation; environmental data from the spring was incorporated into a thermodynamic-based model. The model indicated a likely cause of deviation from predicted fractionation values was a greater than measured csSRR, suggesting heterogeneous activity among that group. Employing the same model to address the unexpected lack of correlation between dsrB alpha diversity metrics and isotope fractionation between stations, kinetic parameters associated with the apr gene in the sulfate reduction pathway were found to have greater influence on expressed fractionation factor than the dsr gene.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,001 |
| Études des sciences et des technologies | 0,001 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».