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181 results on '"Yeager, Chris M."'

2. Drought conditioning of rhizosphere microbiome influences maize water use traits

Author

Carter, Kelsey R., Nachtsheim, Abigael C., Dickman, L. Turin, Moore, Eric R., Negi, Sangeeta, Heneghan, John P., Sabella, Anthony J., Steadman, Christina R., Albright, Michaeline B. N., Anderson-Cook, Christine M., Comas, Louise H., Harris, Rose J., Heikoop, Jeffrey M., Lubbers, Nicholas, Marina, Oana C., Musa, Dea, Newman, Brent D., Perkins, George B., Twary, Scott, Yeager, Chris M., and Sevanto, Sanna

Published
2023
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3. An ecophysiological explanation for manganese enrichment in rock varnish

Author

Lingappa, Usha F, Yeager, Chris M, Sharma, Ajay, Lanza, Nina L, Morales, Demosthenes P, Xie, Gary, Atencio, Ashley D, Chadwick, Grayson L, Monteverde, Danielle R, Magyar, John S, Webb, Samuel M, Valentine, Joan Selverstone, Hoffman, Brian M, and Fischer, Woodward W

Subjects
Biotechnology, Antioxidants, Cyanobacteria, Ecological and Environmental Phenomena, Geologic Sediments, Manganese, Microbiota, Oxidation-Reduction, Sunlight, Water, desert varnish, manganese, oxidative stress, rock varnish
Abstract

Desert varnish is a dark rock coating that forms in arid environments worldwide. It is highly and selectively enriched in manganese, the mechanism for which has been a long-standing geological mystery. We collected varnish samples from diverse sites across the western United States, examined them in petrographic thin section using microscale chemical imaging techniques, and investigated the associated microbial communities using 16S amplicon and shotgun metagenomic DNA sequencing. Our analyses described a material governed by sunlight, water, and manganese redox cycling that hosts an unusually aerobic microbial ecosystem characterized by a remarkable abundance of photosynthetic Cyanobacteria in the genus Chroococcidiopsis as the major autotrophic constituent. We then showed that diverse Cyanobacteria, including the relevant Chroococcidiopsis taxon, accumulate extraordinary amounts of intracellular manganese-over two orders of magnitude higher manganese content than other cells. The speciation of this manganese determined by advanced paramagnetic resonance techniques suggested that the Cyanobacteria use it as a catalytic antioxidant-a valuable adaptation for coping with the substantial oxidative stress present in this environment. Taken together, these results indicated that the manganese enrichment in varnish is related to its specific uptake and use by likely founding members of varnish microbial communities.

Published
2021

21. Diazotrophic community structure and function in two successional stages of biological soil crusts from the Colorado plateau and Chihuahuan desert

Author

Yeager, Chris M.; Kuske, Cheryl R., Kornosky, Jennifer L., Housman, David C., Grote, Edmund E., and Belnap, Jayne

Subjects
Colorado Plateau -- Research, Chihuahuan Desert -- Research, Chihuahuan Desert -- Environmental policy, Nitrogen-fixing microorganisms -- Research, Nitrogen-fixing microorganisms -- Causes of, Biological sciences
Abstract

A study was conducted to characterize the community structure and activity of N2 fixing microorganisms in soil crusts from Chihuahua desert as well as from the Colorado plateau. It was found that functionally biological soil crusts play important roles in soil stability, water retention and flow.

Published
2004

24. Requirement of DNA repair mechanisms for survival of Burkholderia cepacia G4 upon degradation of trichloroethylene

Author

Yeager, Chris M., Bottomly, Peter J., and Arp, Daniel J.

Subjects
Biodegradation -- Research, Trichloroethylene -- Research, DNA repair -- Research, Biological sciences
Abstract

Burkholderia cepacia G4 can degrade trichloroethylene (TCE) as long as its DNA repair mechanism is intact. This bacterium is more resistant to the toxic effects of TCE than other bacteria and for this reason is considered a potential agent for TCE biodegradation.

Published
2001

25. Two distinct monooxygenases for alkane oxidation in Nocardioides sp. strain CF8

Author

Hamamura, Natsuko, Yeager, Chris M., and Arp, Daniel J.

Subjects
Microbial enzymes -- Research, Nocardia asteroides -- Research, Oxidases -- Research, Biological sciences
Abstract

Researchers present evidence that Nocardioides sp. strain CF8 has two different alkane monooxygenases. One is expressed in cells grown on alkanes above C(sub 6).

Published
2001

26. Cytotoxicity associated with trichloroethylene oxidation in Burkholderia cepacia G4

Author

Yeager, Chris M., Bottomley, Peter J., and Arp, Daniel J.

Subjects
Biodegradation -- Research, Trichloroethylene -- Health aspects, Biological sciences
Abstract

Trichloroethylene (TCE) oxidation by Burkholderia cepacia G4 is toxic to the bacterium. This occurs because reactive intermediates generated during TCE oxidation can inactivate not only the oxygenase, but also other cellular constituents as well.

Published
2001

27. Inactivation of toluene 2-monooxygenase in Burkholderia cepacia G4 by alkynes

Author

Yeager, Chris M., Bottomley, Peter J., Arp, Daniel J., and Hyman, Michael R.

Subjects
Toluene -- Research, Acetylene -- Research, Oxidases -- Research, Bacterial growth -- Research, Biological sciences
Abstract

Research was conducted to examine the inactivation of toluene 2-monooxygenase in Burkholderia cepacia G4 by alkynes. Results demonstrate that different alkynes serve as potent inhibitors of the toluene-dependent growth of B. cepacia. Findings also reveal that toluene 2-monooxygenase activity is specifically inactivated by the compounds. Therefore, alkynes represent a general class of mechanism-based inactivators for toluene 2-monooxygenase activity in B. cepacia G4.

Published
1999

29. Nagasaki sediments reveal that long-term fate of plutonium is controlled by select organic matter moieties

Author

Lin, Peng, primary, Xu, Chen, additional, Kaplan, Daniel I., additional, Chen, Hongmei, additional, Yeager, Chris M., additional, Xing, Wei, additional, Sun, Luni, additional, Schwehr, Kathleen A., additional, Yamazaki, Hideo, additional, Saito-Kokubu, Yoko, additional, Hatcher, Patrick G., additional, and Santschi, Peter H., additional

Published
2019
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32. Microbial Transformation of Iodine: From Radioisotopes to Iodine Deficiency

Author

Yeager, Chris M., Amachi, Seigo, Grandbois, Russell, Kaplan, Daniel I., Xu, Chen, Schwehr, Kathy A., Santschi, Peter H., Yeager, Chris M., Amachi, Seigo, Grandbois, Russell, Kaplan, Daniel I., Xu, Chen, Schwehr, Kathy A., and Santschi, Peter H.

Abstract

Iodine is a biophilic element that is important for human health, both as an essential component of several thyroid hormones and, on the other hand, as a potential carcinogen in the form of radioiodine generated by anthropogenic nuclear activity. Iodine exists in multiple oxidation states (−1, 0, +1, +3, +5, and +7), primarily as molecular iodine (I2), iodide (I−), iodate , or organic iodine (org-I). The mobility of iodine in the environment is dependent on its speciation and a series of redox, complexation, sorption, precipitation, and microbial reactions. Over the last 15 years, there have been significant advances in iodine biogeochemistry, largely spurred by renewed interest in the fate of radioiodine in the environment. We review the biogeochemistry of iodine, with particular emphasis on the microbial processes responsible for volatilization, accumulation, oxidation, and reduction of iodine, as well as the exciting technological potential of these fascinating microorganisms and enzymes.

Published
2017

33. Changes in nitrogen-fixing and ammonia-oxidizing bacterial communities in soil of a mixed conifer forest after wildfire

Author

Yeager, Chris M., Northup, Diana E., Grow, Christy C., Barns, Susan M., and Kuske, Cheryl R.

Subjects
Coniferous forests -- Environmental aspects, Wildfires -- Environmental aspects, Nitrogen-fixing microorganisms -- Distribution, Nitrogen-fixing microorganisms -- Environmental aspects, Company distribution practices, Biological sciences
Abstract

The effects of forest fire on two important groups of N-cycling bacteria in soil, the nitrogen-fixing and ammonia-oxidizing bacteria are examined. PCR results indicated that the soil biomass and proportion of nitrogen-fixing and ammonia-oxidizing species was less in soil from the fire-impacted sites than from the unburned sites.

Published
2005

36. Plutonium Partitioning Behavior to Humic Acids from Widely Varying Soils Is Related to Carboxyl-Containing Organic Compounds

Author

Lin, Peng, Xu, Chen, Zhang, Saijin, Fujitake, Nobuhide, Kaplan, Daniel I., Yeager, Chris M., Sugiyama, Yuko, Schwehr, Kathleen A., and Santschi, Peter H.

Abstract

In order to examine the influence of the HA molecular composition on the partitioning of Pu, ten different kinds of humic acids (HAs) of contrasting chemical composition, collected and extracted from different soil types around the world were equilibrated with groundwater at low Pu concentrations (10–14M). Under mildly acidic conditions (pH ∼ 5.5), 29 ± 24% of the HAs were released as colloidal organic matter (>3 kDa to <0.45 μm), yet this HA fraction accounted for a vast majority of the bound Pu, 76 ± 13% on average. In comparison, the particulate HA fraction bound only 8 ± 4% on average of the added Pu. The truly dissolved Pu fraction was typically <1%. Pu binding was strongly and positively correlated with the concentrations of organic nitrogen in both particulate (>0.45 μm) and colloidal phases in terms of activity percentage and partitioning coefficient values (logKd). Based on molecular characterization of the HAs by solid state 13C nuclear magnetic resonance (NMR) and elemental analysis, Pu binding was correlated to the concentration of carboxylate functionalities and nitrogen groups in the particulate and colloidal phases. The much greater tendency of Pu to bind to colloidal HAs than to particulate HA has implications on whether NOM acts as a Pu source or sink during natural or man-induced episodic flooding.

Published
2024
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42. Response to Comment on “Iodine-129 and Iodine-127 Speciation in Groundwater at Hanford Site, U.S.: Iodate Incorporation into Calcite”

Author

Zhang, Saijin, primary, Xu, Chen, additional, Creeley, Danielle, additional, Ho, Yi-Fang, additional, Li, Hsiu-Ping, additional, Grandbois, Russell, additional, Schwehr, Kathleen A., additional, Kaplan, Daniel I., additional, Yeager, Chris M., additional, Wellman, Dawn, additional, and Santschi, Peter H., additional

Published
2013
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44. Molecular environment of stable iodine and radioiodine (129I) in natural organic matter: Evidence inferred from NMR and binding experiments at environmentally relevant concentrations

Author

Xu, Chen, primary, Zhong, Junyan, additional, Hatcher, Patrick G., additional, Zhang, Saijin, additional, Li, Hsiu-Ping, additional, Ho, Yi-Fang, additional, Schwehr, Kathleen A., additional, Kaplan, Daniel I., additional, Roberts, Kimberly A., additional, Brinkmeyer, Robin, additional, Yeager, Chris M., additional, and Santschi, Peter H., additional

Published
2012
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45. Bacterial Production of Organic Acids Enhances H2O2-Dependent Iodide Oxidation

Author

Li, Hsiu-Ping, primary, Yeager, Chris M., additional, Brinkmeyer, Robin, additional, Zhang, Saijin, additional, Ho, Yi-Fang, additional, Xu, Chen, additional, Jones, Whitney L., additional, Schwehr, Kathleen A., additional, Otosaka, Shigeyoshi, additional, Roberts, Kimberly A., additional, Kaplan, Daniel I., additional, and Santschi, Peter H., additional

Published
2012
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48. Sequestration and Remobilization of Radioiodine (129I) by Soil Organic Matter and Possible Consequences of the Remedial Action at Savannah River Site

Author

Xu, Chen, primary, Miller, Eric J, additional, Zhang, Saijin, additional, Li, Hsiu-Ping, additional, Ho, Yi-Fang, additional, Schwehr, Kathleen A, additional, Kaplan, Daniel I., additional, Otosaka, Shigeyoshi, additional, Roberts, Kimberly A, additional, Brinkmeyer, Robin, additional, Yeager, Chris M., additional, and Santschi, Peter H., additional

Published
2011
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