PHOSPHOLIPID FATTY ACIDS AS BIOMASS PROXIES AND THEIR USE IN CHARACTERIZING DEEP TERRESTRIAL SUBSURFACE MICROBIAL COMMUNITIES
Bibliographic record
Abstract
Understanding the distribution, abundances and metabolic activities of microbial life in the subsurface is fundamental to our understanding of the role microbes play in many areas of inquiry such as terrestrial biogeochemical cycling and the search for extraterrestrial life. The deep terrestrial subsurface is known to harbor microbial life at depths of up to several kilometers where, in some cases, organisms live independently from the photosphere and atmosphere. Ancient fracture fluids trapped within the crystalline basement of the Canadian Precambrian Shield have been shown to be preserved on geologic timescales (millions to billions of years). Significant challenges exist when probing the deep terrestrial subsurface including the low biomass abundance, heterogeneous distribution of biomass, and the potential for matrix effects during sampling and analysis. This Master’s thesis project has two main parts. The first study utilizes phospholipid fatty acid (PLFA) analysis to determine the extent of mineral matrices on the effectiveness of PLFA extraction and analysis from deep terrestrial subsurface samples. This was done by creating a bacterial dilution series of known concentration to inoculate one of two mineral matrices, granite or bentonite. This study revealed the presence of significant influence of mineral matrices on PLFA extraction and demonstrated the unreliability of PLFA-based biomass conversion factors with respect to complex microbial communities. The second study in this thesis combine PLFA analysis with stable carbon isotope analysis to characterize microbial communities associated with fracture fluids with mean residence times of ~1.4 Ga from boreholes located ~2.4km below the surface in Kidd Creek Mine, in Timmins, Ontario. Characterizing communities in subsurface systems has large implications for the search for life on other planets and moons, acting as an analogue environment. Large volumes of water from two boreholes, 12261 and 12299, were passively filtered for 6-12 months to collect microbial biomass. Borehole adjacent biofilms were also collected along with mine service water, which served as a control. All samples had significant biomass associated with them but were distinct in PLFA fingerprint and δ13C – PLFA signatures indicating the presence of three distinct microbial communities living in association with the fracture fluids and gases. These results have implications for the potential existence of ancient deep subsurface communities that have survived geologic time in isolation, in particular with relation to the subsurface of Mars, as well as give us insight into life on the early Earth.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".