Photosynthetic, respiratory and extracellular electron transport pathways in cyanobacteria

Lea‐Smith, David J.; Bombelli, Paolo; Vasudevan, Ravendran; Howe, Christopher J.

doi:10.1016/j.bbabio.2015.10.007

Cited by 213 publications

(167 citation statements)

References 80 publications

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“…Having reached a PSI array, reduced plastocyanin or cytochrome c 6 molecules will find many options for docking to an oxidized PSI within a confined area of a few hundred nm 2 , optimizing the supply of oxidized plastocyanin or cytochrome c 6 for turnover at cytb 6 f complexes. The product of PSI turnover is reduced ferredoxin, like plastocyanin a small, rapidly diffusible electron carrier; PSI arrays act as a central point of supply of reduced ferredoxin for cyclic electron transport, pigment biosynthesis, nitrate, nitrite, and sulfite metabolism, and CO 2 fixation (Lea-Smith et al, 2015).…”

Section: Discussionmentioning

confidence: 99%

“…PSI is the dominant photosystem in cyanobacteria and it carries out a pivotal role in cyanobacterial metabolism by supplying the electrons for diverse processes such as pigment biosynthesis; nitrate, nitrite, and sulfite metabolism; and CO 2 fixation (Lea-Smith et al, 2015). Despite the biological importance of PSI, the native organization of this complex in cyanobacterial thylakoid membranes is poorly understood; see Supplemental Figure 1 for a schematic diagram of photosynthetic electron flow in cyanobacterial membranes.…”

Section: Introductionmentioning

confidence: 99%

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Lateral Segregation of Photosystem I in Cyanobacterial Thylakoids

et al. 2017

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Photosystem I (PSI) is the dominant photosystem in cyanobacteria and it plays a pivotal role in cyanobacterial metabolism. Despite its biological importance, the native organization of PSI in cyanobacterial thylakoid membranes is poorly understood. Here, we use atomic force microscopy (AFM) to show that ordered, extensive macromolecular arrays of PSI complexes are present in thylakoids from Thermosynechococcus elongatus, Synechococcus sp PCC 7002, and Synechocystis sp PCC 6803. Hyperspectral confocal fluorescence microscopy and three-dimensional structured illumination microscopy of Synechocystis sp PCC 6803 cells visualize PSI domains within the context of the complete thylakoid system. Crystallographic and AFM data were used to build a structural model of a membrane landscape comprising 96 PSI trimers and 27,648 chlorophyll a molecules. Rather than facilitating intertrimer energy transfer, the close associations between PSI primarily maximize packing efficiency; short-range interactions with Complex I and cytochrome b 6 f are excluded from these regions of the membrane, so PSI turnover is sustained by long-distance diffusion of the electron donors at the membrane surface. Elsewhere, PSI-photosystem II contact zones provide sites for docking phycobilisomes and the formation of megacomplexes. PSI-enriched domains in cyanobacteria might foreshadow the partitioning of PSI into stromal lamellae in plants, similarly sustained by long-distance diffusion of electron carriers.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Lateral Segregation of Photosystem I in Cyanobacterial Thylakoids

et al. 2017

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“…An additional advantage is that unlike phospholipids or proteins, hydrocarbons do not contain either phosphorus or nitrogen, which are limited in many environments, notably in the open ocean where Synechococcus and Prochlorococcus species dominate (Flombaum et al, 2013). Moreover, the nonreactive properties of hydrocarbons make them resistant to oxidative damage (Valentine and Reddy, 2015), which is a major issue in cyanobacteria due to constant electron production from photosynthesis and respiration (Lea-Smith et al, 2016a). Hydrocarboninduced membrane curvature may therefore represent a unique, low-risk, and efficient system of inducing flexibility and reducing permeability in one of the most biologically important and ancient membrane systems on the planet.…”

Section: Resultsmentioning

confidence: 99%

Hydrocarbons Are Essential for Optimal Cell Size, Division, and Growth of Cyanobacteria

et al. 2016

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Cyanobacteria are intricately organized, incorporating an array of internal thylakoid membranes, the site of photosynthesis, into cells no larger than other bacteria. They also synthesize C15-C19 alkanes and alkenes, which results in substantial production of hydrocarbons in the environment. All sequenced cyanobacteria encode hydrocarbon biosynthesis pathways, suggesting an important, undefined physiological role for these compounds. Here, we demonstrate that hydrocarbon-deficient mutants of Synechococcus sp. PCC 7002 and Synechocystis sp. PCC 6803 exhibit significant phenotypic differences from wild type, including enlarged cell size, reduced growth, and increased division defects. Photosynthetic rates were similar between strains, although a minor reduction in energy transfer between the soluble light harvesting phycobilisome complex and membrane-bound photosystems was observed. Hydrocarbons were shown to accumulate in thylakoid and cytoplasmic membranes. Modeling of membranes suggests these compounds aggregate in the center of the lipid bilayer, potentially promoting membrane flexibility and facilitating curvature. In vivo measurements confirmed that Synechococcus sp. PCC 7002 mutants lacking hydrocarbons exhibit reduced thylakoid membrane curvature compared to wild type. We propose that hydrocarbons may have a role in inducing the flexibility in membranes required for optimal cell division, size, and growth, and efficient association of soluble and membrane bound proteins. The recent identification of C15-C17 alkanes and alkenes in microalgal species suggests hydrocarbons may serve a similar function in a broad range of photosynthetic organisms.

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“…12 The mechanisms and metabolic pathways involved in the redirection of electrons to the extracellular membrane are a matter of study and yet to be fully understood. 13,14 Good exoelectrogenic bacteria are those coupling respiration to an extracellular nal electron acceptor, and examples of exoelectrogens such as Shewanella oneidensis and Geobacter sulfurreducens have been reported extensively in the literature. In both cases, outer membrane c-cytochromes associated to extracellular respiratory pathways are responsible of direct electron transfer.…”

Section: -9mentioning

confidence: 99%

Tapping into cyanobacteria electron transfer for higher exoelectrogenic activity by imposing iron limited growth

et al. 2018

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The exoelectrogenic capacity of the cyanobacterium Synechococcus elongatus PCC7942 was studied in iron limited growth in order to establish conditions favouring extracellular electron transfer in cyanobacteria for photo-bioelectricity generation. Investigation into extracellular reduction of ferricyanide by Synechococcus elongatus PCC7942 demonstrated enhanced capability for the iron limited conditions in comparison to the iron sufficient conditions. Furtheremore, the significance of pH showed that higher rates of ferricyanide reduction occurred at pH 7, with a 2.7-fold increase with respect to pH 9.5 for iron sufficient cultures and 24-fold increase for iron limited cultures. The strategy presented induced exoelectrogenesis driven mainly by photosynthesis and an estimated redirection of the 28% of electrons from photosynthetic activity was achieved by the iron limited conditions. In addition, ferricyanide reduction in the dark by iron limited cultures also presented a significant improvement, with a 6-fold increase in comparison to iron sufficient cultures. Synechococcus elongatus PCC7942 ferricyanide reduction rates are unprecedented for cyanobacteria and they are comparable to those of microalgae. The redox activity of biofilms directly on ITO-coated glass, in the absence of any artificial mediator, was also enhanced under the iron limited conditions, implying that iron limitation increased exoelectrogenesis at the outer membrane level. Cyclic voltammetry of Synechococcus elongatus PCC7942 biofilms on ITO-coated glass showed a midpoint potential around 0.22 V vs. Ag/ AgCl and iron limited biofilms had the capability to sustain currents in a saturated-like fashion. The present work proposes an iron related exoelectrogenic capacity of Synechococcus elongatus PCC7942 and sets a starting point for the study of this strain in order to improve photo-bioelectricity and darkbioelectricity generation by cyanobacteria, including more sustainable mediatorless systems.

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Photosynthetic, respiratory and extracellular electron transport pathways in cyanobacteria

Cited by 213 publications

References 80 publications

Lateral Segregation of Photosystem I in Cyanobacterial Thylakoids

Lateral Segregation of Photosystem I in Cyanobacterial Thylakoids

Hydrocarbons Are Essential for Optimal Cell Size, Division, and Growth of Cyanobacteria

Tapping into cyanobacteria electron transfer for higher exoelectrogenic activity by imposing iron limited growth

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