Photosynthesis and Respiration in Cyanobacteria

Wim FJ Vermaas, Arizona State University, Tempe, Arizona, USA

Published online: April 2001

DOI: 10.1038/npg.els.0001670

Cyanobacteria are among the very few groups that can perform oxygenic photosynthesis and respiration simultaneously in the same compartment, and some cyanobacterial species are able to fix nitrogen. This combination of metabolic pathways is unusual and this metabolic flexibility may be responsible for the evolutionary hardiness of the cyanobacteria and their ability to thrive under a wide range of conditions.

Keywords: cytochrome b6f complex; soluble electron carriers; oxidases; electron transfer; succinate dehydrogenase

Figure 1. Outline of membranes and compartments in a cyanobacterial cell. The cytoplasmic membrane separates the cytoplasm from the periplasm; this membrane system is involved in respiration but not in photosynthesis, and is yellow due to the presence of carotenoids. Thylakoid membranes catalyse both photosynthetic and respiratory electron transport; they contain chlorophyll and therefore are green. Thylakoids are vase-shaped, and occur in pairs (the view represented here corresponds to a cross-sectional cut through the vase). One pair of membranes envelops the next pair, much like a set of Russian dolls. The space between a pair of thylakoid membranes is the thylakoid lumen, into which protons are deposited upon photosynthetic and respiratory electron transport in thylakoids. The resulting proton gradient across the thylakoids is used for ATP synthesis. The space between two pairs of thylakoids is contiguous with the cytoplasm of the cell.
Figure 2. Schematic representation of the intersecting photosynthetic and respiratory electron transport pathways in thylakoid membranes of the cyanobacterium Synechocystis sp. PCC 6803. Arrows indicate electron transfer reactions, and thunderbolts designate light that sets into motion the redox reactions in the two photosystems. The thickness of each arrow is an approximate indication of the rate of the corresponding reaction. Electron transfer complexes that are specifically involved in photosynthetic electron transfer are PS II and PS I, whereas those specific for respiratory electron flow include NDH-1, SDH, and the terminal oxidase. PQ, cyt b6f and PC are shared by both pathways. The electron transfer arrows involving SDH are drawn in both directions, as the difference in midpoint redox potentials between the PQ/PQH2 and fumarate/succinate redox couples is small and therefore electron flow can occur in both directions depending on the relative concentrations of PQ, PQH2, succinate and fumarate. Abbreviations: cyt b6f, the cytochrome b6f complex; Fdox and Fdred, ferredoxin in oxidized and reduced forms, respectively; NADP(H), nicotinamide – adenine dinucleotide phosphate (reduced form); NDH-1, type 1 NADPH dehydrogenase; Ox, terminal oxidase; PC, plastocyanin; PQ, plastoquinone; PS I, photosystem I; PS II, photosystem II; SDH, succinate dehydrogenase.
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Microbial Photosynthesis | Microbial Respiration and Fermentation
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Article Title: Photosynthesis and Respiration in Cyanobacteria
 
How to Cite close
Vermaas, Wim FJ(Apr 2001) Photosynthesis and Respiration in Cyanobacteria. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001670]