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Abstract To understand the effects of secondary minerals on changes in the mechanical properties of upper mantle rocks due to phase mixing, we conducted high‐strain torsion experiments on aggregates of iron‐rich olivine + orthopyroxene (opx) with opx volume fractions offopx = 0.15, 0.26, and 0.35. For samples with larger amounts of opx,fopx = 0.26 and 0.35, the value of the stress exponent decreases with increasing strain fromn ≈ 3 for γ ≲ 5 ton ≈ 2 for 5 ≲ γ ≲ 25, indicating that the deformation mechanism changes as strain increases. In contrast, for samples withfopx = 0.15, the stress exponent is constant atn ≈ 3.3 for 1 ≲ γ ≲ 25, suggesting that no change in deformation mechanism occurs with increasing strain for samples with smaller amounts of opx. The microstructures of samples with larger amounts of opx provide insight into the change in deformation mechanism derived from the mechanical data. Elongated grains align subparallel to the shear direction for samples of all three compositions deformed to lower strains. However, strain weakening with grain size reduction and the formation of a thoroughly mixed, fine‐grained texture only develops in samples withfopx = 0.26 and 0.35 deformed to higher strains of γ ≳ 16. These mechanical and associated microstructural properties imply that rheological weakening due to phase mixing only occurs in the samples with largerfopx, which is an important constraint for understanding strain localization in the upper mantle of Earth.
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This content will become publicly available on December 1, 2025
Phenotypic Plasticity During Organofluorine Degradation Revealed by Adaptive Evolution
ABSTRACT A major factor limiting the biodegradation of organofluorine compounds has been highlighted as fluoride anion toxicity produced by defluorinating enzymes. Here, two highly active defluorinases with different activities were constitutively expressed inPseudomonas putidaATCC 12633 to examine adaption to fluoride stress. Each strain was grown on α‐fluorophenylacetic acid as the sole carbon source via defluorination to mandelic acid, and each showed immediate fluoride release and delayed growth. Adaptive evolution was performed for each recombinant strain by serial transfer. Both strains adapted to show a much shorter lag and a higher growth yield. The observed adaptation occurred rapidly and reproducibly, within 50 generations each time. After adaption, growth with 50–70 mM α‐fluorophenylacetic acid was significantly faster with more fluoride release than a preadapted culture due to larger cell populations. Genomic sequencing of both pre‐ and postadapted strain pairs revealed decreases in the defluorinase gene content. With both defluorinases, adaption produced a 56%–57% decrease in the plasmid copy number. Additionally, during adaption of the strain expressing the faster defluorinase, two plasmids were present: the original and a derivative in which the defluorinase gene was deleted. An examination of the enzyme rates in the pathway suggested that the defluorinase rate was concurrently optimised for pathway flux and minimising fluoride toxicity. The rapid alteration of plasmid copy number and mutation was consistent with other studies on microbial responses to stresses such as antibiotics. The data presented here support the idea that fluoride stress is significant during the biodegradation of organofluorine compounds and suggest engineered strains will be under strong selective pressure to decrease fluoride stress.
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- Award ID(s):
- 2343831
- PAR ID:
- 10590219
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Microbial Biotechnology
- Volume:
- 17
- Issue:
- 12
- ISSN:
- 1751-7915
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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