Abstract
Carboxysomes are the specific CO2-fixing microcompartments in all cyanobacteria. Although it is known that the organization and subcellular localization of carboxysomes are dependent on external light conditions and are highly relevant to their functions, how carboxysome organization and function are actively orchestrated in natural diurnal cycles has remained elusive. Here, we explore the dynamic regulation of carboxysome positioning and carbon fixation in the model cyanobacterium Synechococcus elongatus PCC 7942 in response to diurnal light-dark cycles, using live-cell confocal imaging and Rubisco assays. We found that carboxysomes are prone to locate close to the central line along the short axis of the cell and exhibit a greater preference of polar distribution in the dark phase, coupled with a reduction in carbon fixation. Moreover, we show that deleting the gene encoding the circadian clock protein KaiA could lead to an increase in carboxysome numbers per cell and reduced portions of pole-located carboxysomes. Our study provides insight into the diurnal regulation of carbon fixation in cyanobacteria and the general cellular strategies of cyanobacteria living in natural habitat for environmental acclimation.
Highlights
The extraordinary ability of cyanobacteria to survive in diverse ecosystems and adapt to extremes of environmental stress is ascribed to their metabolic robustness and tunability [1]
To determine whether carboxysome abundance and subcellular organization are regulated during diurnal cycles, we first made a Syn7942 mutant by transforming a luciferase reporter plasmid pAM2195 [47] into wild-type (WT) Syn7942 cells
We characterized the effects of diurnal light-dark cycles on carboxysome biosynthesis, In this work, we characterized the effects of diurnal light-dark cycles on carboxysome subcellular localization and function in Syn7942
Summary
The extraordinary ability of cyanobacteria to survive in diverse ecosystems and adapt to extremes of environmental stress is ascribed to their metabolic robustness and tunability [1]. As cyanobacterial cells rely directly on light for photosynthesis, their abilities to respond to changes in the environmental light conditions are indispensable [2,3,4,5,6,7,8,9,10]. It has been shown that the expression of many genes and metabolic activities in cyanobacteria are subject to the circadian rhythm that are regulated by an intrinsic circadian clock [11,12]. This regulation is of physiological importance to improve fitness and facilitate adaptation to diurnal light-dark cycles [13,14,15,16,17]. Most of laboratory studies on cyanobacterial physiology are still performed under constant light, given the limitations of practical operations and considerations [18]
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