Morphological and isotopic changes of heterocystous cyanobacteria in response to N 2 partial pressure.

Autor: Silverman SN; Department of Geological Sciences, University of Colorado Boulder, Boulder, Colorado.; Blue Marble Space Institute of Science, Seattle, Washington., Kopf SH; Department of Geological Sciences, University of Colorado Boulder, Boulder, Colorado., Bebout BM; Exobiology Branch, NASA Ames Research Center, Moffett Field, California., Gordon R; Gulf Specimen Marine Laboratory & Aquarium, Panacea, Florida.; Department of Obstetrics and Gynecology, C. S. Mott Center for Human Growth and Development, Wayne State University, Detroit, Michigan., Som SM; Blue Marble Space Institute of Science, Seattle, Washington.; Exobiology Branch, NASA Ames Research Center, Moffett Field, California.
Jazyk: angličtina
Zdroj: Geobiology [Geobiology] 2019 Jan; Vol. 17 (1), pp. 60-75. Date of Electronic Publication: 2018 Oct 05.
DOI: 10.1111/gbi.12312
Abstrakt: Earth's atmospheric composition has changed significantly over geologic time. Many redox active atmospheric constituents have left evidence of their presence, while inert constituents such as dinitrogen gas (N 2 ) are more elusive. In this study, we examine two potential biological indicators of atmospheric N 2 : the morphological and isotopic signatures of heterocystous cyanobacteria. Biological nitrogen fixation constitutes the primary source of fixed nitrogen to the global biosphere and is catalyzed by the oxygen-sensitive enzyme nitrogenase. To protect this enzyme, some filamentous cyanobacteria restrict nitrogen fixation to microoxic cells (heterocysts) while carrying out oxygenic photosynthesis in vegetative cells. Heterocysts terminally differentiate in a pattern that is maintained as the filaments grow, and nitrogen fixation imparts a measurable isotope effect, creating two biosignatures that have previously been interrogated under modern N 2 partial pressure (pN 2 ) conditions. Here, we examine the effect of variable pN 2 on these biosignatures for two species of the filamentous cyanobacterium Anabaena. We provide the first in vivo estimate of the intrinsic isotope fractionation factor of Mo-nitrogenase (ε fix  = -2.71 ± 0.09‰) and show that, with decreasing pN 2 , the net nitrogen isotope fractionation decreases for both species, while the heterocyst spacing decreases for Anabaena cylindrica and remains unchanged for Anabaena variabilis. These results are consistent with the nitrogen fixation mechanisms available in the two species. Application of these quantifiable effects to the geologic record may lead to new paleobarometric measurements for pN 2 , ultimately contributing to a better understanding of Earth's atmospheric evolution.
(© 2018 John Wiley & Sons Ltd.)
Databáze: MEDLINE
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