Morphological and isotopic changes of heterocystous cyanobacteria in response to N₂ partial pressure

Abstract

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 (N2) are more elusive. In this study, we examine two potential biological indicators of atmospheric N2: 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 N2 partial pressure (pN2) conditions. Here, we examine the effect of variable pN2 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 (εfix = −2.71 ± 0.09‰) and show that, with decreasing pN2, 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 pN2, ultimately contributing to a better understanding of Earth's atmospheric evolution.

Mission to Planet Earth: The First Two Billion Years

“…Oxidative weathering would have introduced a new source of N into the atmosphere, and subducted oxidized sediments may have changed the redox state of the mantle wedge and further enabled N 2 outgassing (Mikhail and Sverjensky 2014). Advances in N-cycle modeling (Johnson and Goldblatt 2018) coupled with the development of additional geological markers of air density (Goosmann et al 2018;Silverman et al 2018) will test this model.…”

Flutuação temporal de cianotoxinas (Microcistina) no rio Tapajós (Santarém, Amazônia-Brasil)

“…Algumas espécies de cianobactérias são capazes de fixar nitrogênio atmosférico (diazotróficas), sendo favorecidas durante a limitação de nitrogênio no ambiente aquático em detrimento de outros grupos fitoplanctônicos [64,65]. O gênero Dolichospermum, encontrado em 75% dos meses amostrados, é reconhecido como produtor de heterocistos, estruturas celulares capazes de fixar nitrogênio atmosférico [66,67,68].…”

Isoreader: An R package to read stable isotope data files for reproducible research

“…The isoreader package enables efficient and reproducible reading and processing of stable isotope data directly from the data files no matter which operating system (Windows, Mac, Linux). It is already being used for stable isotope data processing in several laboratories and recent publications including Silverman et al (2019), Cheng et al (2019), Ingalls et al (2020), andSuarez et al (2020). The isoreader package was designed to be easily extendable with readers for new file formats, and provides data export functionality to Python using the shared R/Python feather file format.…”