Title: Linking the Dynamic Response of the Carbon Dioxide-Concentrating Mechanism to Carbon Assimilation Behavior in Fremyella diplosiphon

Abstract

ABSTRACT Cyanobacteria use a carbon dioxide (CO ₂ )-concentrating mechanism (CCM) that enhances their carbon fixation efficiency and is regulated by many environmental factors that impact photosynthesis, including carbon availability, light levels, and nutrient access. Efforts to connect the regulation of the CCM by these factors to functional effects on carbon assimilation rates have been complicated by the aqueous nature of cyanobacteria. Here, we describe the use of cyanobacteria in a semiwet state on glass fiber filtration discs—cyanobacterial discs—to establish dynamic carbon assimilation behavior using gas exchange analysis. In combination with quantitative PCR (qPCR) and transmission electron microscopy (TEM) analyses, we linked the regulation of CCM components to corresponding carbon assimilation behavior in the freshwater, filamentous cyanobacterium Fremyella diplosiphon . Inorganic carbon (C _i ) levels, light quantity, and light quality have all been shown to influence carbon assimilation behavior in F. diplosiphon . Our results suggest a biphasic model of cyanobacterial carbon fixation. While behavior at low levels of CO ₂ is driven mainly by the C _i uptake ability of the cyanobacterium, at higher CO ₂ levels, carbon assimilation behavior is multifaceted and depends on C _i availability, carboxysome morphology, linear electron flow, and cell shape. Carbon responsemore » curves (CRCs) generated via gas exchange analysis enable rapid examination of CO ₂ assimilation behavior in cyanobacteria and can be used for cells grown under distinct conditions to provide insight into how CO ₂ assimilation correlates with the regulation of critical cellular functions, such as the environmental control of the CCM and downstream photosynthetic capacity. IMPORTANCE Environmental regulation of photosynthesis in cyanobacteria enhances organismal fitness, light capture, and associated carbon fixation under dynamic conditions. Concentration of carbon dioxide (CO ₂ ) near the carbon-fixing enzyme RubisCO occurs via the CO ₂ -concentrating mechanism (CCM). The CCM is also tuned in response to carbon availability, light quality or levels, or nutrient access—cues that also impact photosynthesis. We adapted dynamic gas exchange methods generally used with plants to investigate environmental regulation of the CCM and carbon fixation capacity using glass fiber-filtered cells of the cyanobacterium Fremyella diplosiphon . We describe a breakthrough in measuring real-time carbon uptake and associated assimilation capacity for cells grown in distinct conditions (i.e., light quality, light quantity, or carbon status). These measurements demonstrate that the CCM modulates carbon uptake and assimilation under low-C _i conditions and that light-dependent regulation of pigmentation, cell shape, and downstream stages of carbon fixation are critical for tuning carbon uptake and assimilation.« less

Authors:

Rohnke, Brandon A. ;

• Search DOE PAGES for author "Rohnke, Brandon A."
• Search DOE PAGES for ORCID "0000-0002-0872-8931"
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Rodríguez Pérez, Kiara J.; Montgomery, Beronda L. ;

• Search DOE PAGES for author "Montgomery, Beronda L."
• Search DOE PAGES for ORCID "0000-0003-2953-0956"
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Harwood, ed., Caroline S.

Publication Date:

2020-05-26

Research Org.:

Michigan State Univ., East Lansing, MI (United States). MSU-DOE Plant Research Laboratory

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1630757

Alternate Identifier(s):

OSTI ID: 1735826

Grant/Contract Number:  

FG02-91ER20021

Resource Type:

Published Article

Journal Name:

mBio (Online)

Additional Journal Information:

Journal Name: mBio (Online) Journal Volume: 11 Journal Issue: 3; Journal ID: ISSN 2150-7511

Publisher:

American Society for Microbiology

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES; Carbon dioxide assimilation; carbon dioxide concentration mechanism; carbon dioxide fixation; carboxysome; cyanobacteria; gas exchange