Investigation of diversity of unusual pigments and novel photosynthetic apparatus in aerobic anoxygenic phototrophic bacteria
Bibliographic record
Abstract
Photosynthetic complexes produced by aerobic anoxygenic phototrophs (AAP) Roseicyclus mahoneyensis, strain ML6, Chromocurvus halotolerans, EG19 and Charonomicrobium ambiphototrophicum, EG17 were studied to examine unusual pigments, proteins and photosynthetic function. We found ML6 spontaneously mutates to lose its light harvesting (LH) complex 2, or reaction centre (RC) and LH1, resulting in mutants ML6(BN9O), ML6(B) and ML6(DB). EG19 and EG17 contain a red-shifted LH1 complex, and EG17 is the first AAP known to photosynthesize both aerobically and anaerobically. From all organisms, membranes and complexes were purified. Flash induced difference spectra revealed ML6, ML6(BN9O), EG19 and EG17 were photosynthetically active aerobically, though only EG17 was capable of rapid electron transport without oxygen. ML6(B) and ML6(DB) were not capable of photosynthesis. Action spectra universally showed that bacteriochlorophyll and bacteriopheophytin were the primary LH pigments and carotenoids were not involved in photosynthesis. Redox midpoint potentials of the QA, P+ and RC-bound cytochrome were typical of AAP, except for the QA of EG17 (+5mV, between what is expected for AAP and anaerobic purple non-sulfur bacteria). RC, LH1 and LH2 subunits were of typical sizes. The exception was the LH1 of EG19 and EG17, which was slightly larger than previously published. Strain EG19 excretes an orange-brown compound into the growth medium, previously hypothesized to be a siderophore. We identified it as a catechol siderophore, measuring approximately 800Da. It is hydrophilic and may contain the amino acids valine, proline, aspartate, 2-aminobutenoic acid, and N-acetyl-L-glutamate. Lastly, a sampling trip to Central Gold Mine, Nopiming Provincial Park, Canada was undertaken to study the presence of AAP in this extreme environment. Abundant AAP were found and five were chosen for study: strains NM4.16, NM4.18, C4, C9, and C11. All are mesophiles, grow on complex media, and tolerate a wide range of pH, temperature and salinity. Isolates were highly resistant to the toxic metalloid oxides tellurite, tellurate, selenite, selenate, metavanadate and orthometavanadate and reduced tellurite to tellurium. All are α-Proteobacteria, with C4 and NM4.16 closely related to Porphyrobacter colymbi (99.4% and 99.7% sequence similarity, respectively), C9 to Brevundimonas variabilis (99.1%), C11 to Brevundimonas bacteroides (98.6%), and NM4.18 to Erythromonas ursincola (98.5%).
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".