Editorial

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3 pages, 189 KiB

Open AccessEditorial

Cellular and Molecular Strategies in Cyanobacterial Survival—“In Memory of Prof. Dr. Wolfgang Lockau”

by Khaled A. Selim and Iris Maldener

Life 2021, 11(2), 132; https://doi.org/10.3390/life11020132 - 09 Feb 2021

Cited by 2 | Viewed by 2255

Abstract

Aerobic life on Earth evolved about 3 [...] Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

Research

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16 pages, 2861 KiB

Open AccessArticle

Inactivation of Three RG(S/T)GR Pentapeptide-Containing Negative Regulators of HetR Results in Lethal Differentiation of Anabaena PCC 7120

by Ivan Khudyakov, Grigory Gladkov and Jeff Elhai

Life 2020, 10(12), 326; https://doi.org/10.3390/life10120326 - 04 Dec 2020

Cited by 7 | Viewed by 2680

Abstract

The filamentous cyanobacterium Anabaena sp. PCC 7120 produces, during the differentiation of heterocysts, a short peptide PatS and a protein HetN, both containing an RGSGR pentapeptide essential for activity. Both act on the master regulator HetR to guide heterocyst pattern formation by controlling [...] Read more.

The filamentous cyanobacterium Anabaena sp. PCC 7120 produces, during the differentiation of heterocysts, a short peptide PatS and a protein HetN, both containing an RGSGR pentapeptide essential for activity. Both act on the master regulator HetR to guide heterocyst pattern formation by controlling the binding of HetR to DNA and its turnover. A third small protein, PatX, with an RG(S/T)GR motif is present in all HetR-containing cyanobacteria. In a nitrogen-depleted medium, inactivation of patX does not produce a discernible change in phenotype, but its overexpression blocks heterocyst formation. Mutational analysis revealed that PatX is not required for normal intercellular signaling, but it nonetheless is required when PatS is absent to prevent rapid ectopic differentiation. Deprivation of all three negative regulators—PatS, PatX, and HetN—resulted in synchronous differentiation. However, in a nitrogen-containing medium, such deprivation leads to extensive fragmentation, cell lysis, and aberrant differentiation, while either PatX or PatS as the sole HetR regulator can establish and maintain a semiregular heterocyst pattern. These results suggest that tight control over HetR by PatS and PatX is needed to sustain vegetative growth and regulated development. The mutational analysis has been interpreted in light of the opposing roles of negative regulators of HetR and the positive regulator HetL. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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18 pages, 1178 KiB

Open AccessArticle

Rapid Transcriptional Reprogramming Triggered by Alteration of the Carbon/Nitrogen Balance Has an Impact on Energy Metabolism in Nostoc sp. PCC 7120

by Peter J. Gollan, Dorota Muth-Pawlak and Eva-Mari Aro

Life 2020, 10(11), 297; https://doi.org/10.3390/life10110297 - 20 Nov 2020

Cited by 5 | Viewed by 3025

Abstract

Nostoc (Anabaena) sp. PCC 7120 is a filamentous cyanobacterial species that fixes N₂ to nitrogenous compounds using specialised heterocyst cells. Changes in the intracellular ratio of carbon to nitrogen (C/N balance) is known to trigger major transcriptional reprogramming of the [...] Read more.

Nostoc (Anabaena) sp. PCC 7120 is a filamentous cyanobacterial species that fixes N₂ to nitrogenous compounds using specialised heterocyst cells. Changes in the intracellular ratio of carbon to nitrogen (C/N balance) is known to trigger major transcriptional reprogramming of the cell, including initiating the differentiation of vegetative cells to heterocysts. Substantial transcriptional analysis has been performed on Nostoc sp. PCC 7120 during N stepdown (low to high C/N), but not during C stepdown (high to low C/N). In the current study, we shifted the metabolic balance of Nostoc sp. PCC 7120 cultures grown at 3% CO₂ by introducing them to atmospheric conditions containing 0.04% CO₂ for 1 h, after which the changes in gene expression were measured using RNAseq transcriptomics. This analysis revealed strong upregulation of carbon uptake, while nitrogen uptake and metabolism and early stages of heterocyst development were downregulated in response to the shift to low CO₂. Furthermore, gene expression changes revealed a decrease in photosynthetic electron transport and increased photoprotection and reactive oxygen metabolism, as well a decrease in iron uptake and metabolism. Differential gene expression was largely attributed to change in the abundances of the metabolites 2-phosphoglycolate and 2-oxoglutarate, which signal a rapid shift from fluent photoassimilation to glycolytic metabolism of carbon after transition to low CO₂. This work shows that the C/N balance in Nostoc sp. PCC 7120 rapidly adjusts the metabolic strategy through transcriptional reprogramming, enabling survival in the fluctuating environment. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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22 pages, 1871 KiB

Open AccessArticle

Heterocyst Development and Diazotrophic Growth of Anabaena variabilis under Different Nitrogen Availability

by Nur Syahidah Zulkefli and Soon-Jin Hwang

Life 2020, 10(11), 279; https://doi.org/10.3390/life10110279 - 13 Nov 2020

Cited by 15 | Viewed by 3103

Abstract

Nitrogen is globally limiting primary production in the ocean, but some species of cyanobacteria can carry out nitrogen (N) fixation using specialized cells known as heterocysts. However, the effect of N sources and their availability on heterocyst development is not yet fully understood. [...] Read more.

Nitrogen is globally limiting primary production in the ocean, but some species of cyanobacteria can carry out nitrogen (N) fixation using specialized cells known as heterocysts. However, the effect of N sources and their availability on heterocyst development is not yet fully understood. This study aimed to evaluate the effect of various inorganic N sources on the heterocyst development and cellular growth in an N-fixing cyanobacterium, Anabaena variabilis. Growth rate, heterocyst development, and cellular N content of the cyanobacteria were examined under varying nitrate and ammonium concentrations. A. variabilis exhibited high growth rate both in the presence and absence of N sources regardless of their concentration. Ammonium was the primary source of N in A. variabilis. Even the highest concentrations of both nitrate (1.5 g L⁻¹ as NaNO₃) and ammonium (0.006 g L⁻¹ as Fe-NH₄-citrate) did not exhibit an inhibitory effect on heterocyst development. Heterocyst production positively correlated with the cell N quota and negatively correlated with vegetative cell growth, indicating that both of the processes were interdependent. Taken together, N deprivation triggers heterocyst production for N fixation. This study outlines the difference in heterocyst development and growth in A. variabilis under different N sources. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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8 pages, 1177 KiB

Open AccessCommunication

Heavy Metal Stress Alters the Response of the Unicellular Cyanobacterium Synechococcus elongatus PCC 7942 to Nitrogen Starvation

by Khaled A. Selim and Michael Haffner

Life 2020, 10(11), 275; https://doi.org/10.3390/life10110275 - 07 Nov 2020

Cited by 9 | Viewed by 2609

Abstract

Non-diazotrophic cyanobacteria are unable to fix atmospheric nitrogen and rely on combined nitrogen for growth and development. In the absence of combined nitrogen sources, most non-diazotrophic cyanobacteria, e.g., Synechocystis sp. PCC 6803 or Synechococcus elongatus PCC 7942, enter a dormant stage called chlorosis. [...] Read more.

Non-diazotrophic cyanobacteria are unable to fix atmospheric nitrogen and rely on combined nitrogen for growth and development. In the absence of combined nitrogen sources, most non-diazotrophic cyanobacteria, e.g., Synechocystis sp. PCC 6803 or Synechococcus elongatus PCC 7942, enter a dormant stage called chlorosis. The chlorosis process involves switching off photosynthetic activities and downregulating protein biosynthesis. Addition of a combined nitrogen source induces the regeneration of chlorotic cells in a process called resuscitation. As heavy metals are ubiquitous in the cyanobacterial biosphere, their influence on the vegetative growth of cyanobacterial cells has been extensively studied. However, the effect of heavy metal stress on chlorotic cyanobacterial cells remains elusive. To simulate the natural conditions, we investigated the effects of long-term exposure of S. elongatus PCC 7942 cells to both heavy metal stress and nitrogen starvation. We were able to show that elevated heavy metal concentrations, especially for Ni²⁺, Cd²⁺, Cu²⁺ and Zn²⁺, are highly toxic to nitrogen starved cells. In particular, cells exposed to elevated concentrations of Cd²⁺ or Ni²⁺ were not able to properly enter chlorosis as they failed to degrade phycobiliproteins and chlorophyll a and remained greenish. In resuscitation assays, these cells were unable to recover from the simultaneous nitrogen starvation and Cd²⁺ or Ni²⁺ stress. The elevated toxicity of Cd²⁺ or Ni²⁺ presumably occurs due to their interference with the onset of chlorosis in nitrogen-starved cells, eventually leading to cell death. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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14 pages, 3077 KiB

Open AccessArticle

Over Expression of the Cyanobacterial Pgr5-Homologue Leads to Pseudoreversion in a Gene Coding for a Putative Esterase in Synechocystis 6803

by Ketty Margulis, Hagit Zer, Hagar Lis, Hanan Schoffman, Omer Murik, Ginga Shimakawa, Anja Krieger-Liszkay and Nir Keren

Life 2020, 10(9), 174; https://doi.org/10.3390/life10090174 - 03 Sep 2020

Cited by 7 | Viewed by 2961

Abstract

Pgr5 proteins play a major direct role in cyclic electron flow paths in plants and eukaryotic phytoplankton. The genomes of many cyanobacterial species code for Pgr5-like proteins but their function is still uncertain. Here, we present evidence that supports a link between the [...] Read more.

Pgr5 proteins play a major direct role in cyclic electron flow paths in plants and eukaryotic phytoplankton. The genomes of many cyanobacterial species code for Pgr5-like proteins but their function is still uncertain. Here, we present evidence that supports a link between the Synechocystis sp. PCC6803 Pgr5-like protein and the regulation of intracellular redox balance. The knockout strain, pgr5KO, did not display substantial phenotypic response under our experimental conditions, confirming results obtained in earlier studies. However, the overexpression strain, pgr5OE, accumulated 2.5-fold more chlorophyll than the wild type and displayed increased content of photosystems matching the chlorophyll increase. As a result, electron transfer rates through the photosynthetic apparatus of pgr5OE increased, as did the amount of energy stored as glycogen. While, under photoautotrophic conditions, this metabolic difference had only minor effects, under mixotrophic conditions, pgr5OE cultures collapsed. Interestingly, this specific phenotype of pgr5OE mutants displayed a tendency for reverting, and cultures which previously collapsed in the presence of glucose were now able to survive. DNA sequencing of a pgr5OE strain revealed a second site suppression mutation in slr1916, a putative esterase associated with redox regulation. The phenotype of the slr1916 knockout is very similar to that of the strain reported here and to that of the pmgA regulator knockout. These data demonstrate that, in Synechocystis 6803, there is strong selection against overexpression of the Pgr5-like protein. The pseudoreversion event in a gene involved in redox regulation suggests a connection of the Pgr5-like protein to this network. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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14 pages, 2312 KiB

Open AccessArticle

Diurnal Regulation of In Vivo Localization and CO₂-Fixing Activity of Carboxysomes in Synechococcus elongatus PCC 7942

by Yaqi Sun, Fang Huang, Gregory F. Dykes and Lu-Ning Liu

Life 2020, 10(9), 169; https://doi.org/10.3390/life10090169 - 29 Aug 2020

Cited by 8 | Viewed by 3092

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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16 pages, 3046 KiB

Open AccessArticle

DnaK3 Is Involved in Biogenesis and/or Maintenance of Thylakoid Membrane Protein Complexes in the Cyanobacterium Synechocystis sp. PCC 6803

by Adrien Thurotte, Tobias Seidel, Ruven Jilly, Uwe Kahmann and Dirk Schneider

Life 2020, 10(5), 55; https://doi.org/10.3390/life10050055 - 30 Apr 2020

Cited by 4 | Viewed by 2866

Abstract

DnaK3, a highly conserved cyanobacterial chaperone of the Hsp70 family, binds to cyanobacterial thylakoid membranes, and an involvement of DnaK3 in the biogenesis of thylakoid membranes has been suggested. As shown here, light triggers synthesis of DnaK3 in the cyanobacterium Synechocystis sp. PCC [...] Read more.

DnaK3, a highly conserved cyanobacterial chaperone of the Hsp70 family, binds to cyanobacterial thylakoid membranes, and an involvement of DnaK3 in the biogenesis of thylakoid membranes has been suggested. As shown here, light triggers synthesis of DnaK3 in the cyanobacterium Synechocystis sp. PCC 6803, which links DnaK3 to the biogenesis of thylakoid membranes and to photosynthetic processes. In a DnaK3 depleted strain, the photosystem content is reduced and the photosystem II activity is impaired, whereas photosystem I is regular active. An impact of DnaK3 on the activity of other thylakoid membrane complexes involved in electron transfer is indicated. In conclusion, DnaK3 is a versatile chaperone required for biogenesis and/or maintenance of thylakoid membrane-localized protein complexes involved in electron transfer reactions. As mentioned above, Hsp70 proteins are involved in photoprotection and repair of PS II in chloroplasts. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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16 pages, 2958 KiB

Open AccessArticle

The Nitrogen Stress-Repressed sRNA NsrR1 Regulates Expression of all1871, a Gene Required for Diazotrophic Growth in Nostoc sp. PCC 7120

by Isidro Álvarez-Escribano, Manuel Brenes-Álvarez, Elvira Olmedo-Verd, Agustín Vioque and Alicia M. Muro-Pastor

Life 2020, 10(5), 54; https://doi.org/10.3390/life10050054 - 29 Apr 2020

Cited by 2 | Viewed by 2900

Abstract

Small regulatory RNAs (sRNAs) are post-transcriptional regulators of bacterial gene expression. In cyanobacteria, the responses to nitrogen availability, that are mostly controlled at the transcriptional level by NtcA, involve also at least two small RNAs, namely NsiR4 (nitrogen stress-induced RNA 4) and NsrR1 [...] Read more.

Small regulatory RNAs (sRNAs) are post-transcriptional regulators of bacterial gene expression. In cyanobacteria, the responses to nitrogen availability, that are mostly controlled at the transcriptional level by NtcA, involve also at least two small RNAs, namely NsiR4 (nitrogen stress-induced RNA 4) and NsrR1 (nitrogen stress-repressed RNA 1). Prediction of possible mRNA targets regulated by NsrR1 in Nostoc sp. PCC 7120 allowed, in addition to previously described nblA, the identification of all1871, a nitrogen-regulated gene encoding a protein of unknown function that we describe here as required for growth at the expense of atmospheric nitrogen (N₂). We show that transcription of all1871 is induced upon nitrogen step-down independently of NtcA. All1871 accumulation is repressed by NsrR1 and its expression is stronger in heterocysts, specialized cells devoted to N₂ fixation. We demonstrate specific interaction between NsrR1 and the 5′ untranslated region (UTR) of the all1871 mRNA, that leads to decreased expression of all1871. Because transcription of NsrR1 is partially repressed by NtcA, post-transcriptional regulation by NsrR1 would constitute an indirect way of NtcA-mediated regulation of all1871. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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15 pages, 4206 KiB

Open AccessArticle

On the Role and Production of Polyhydroxybutyrate (PHB) in the Cyanobacterium Synechocystis sp. PCC 6803

by Moritz Koch, Kenneth W. Berendzen and Karl Forchhammer

Life 2020, 10(4), 47; https://doi.org/10.3390/life10040047 - 22 Apr 2020

Cited by 37 | Viewed by 5453

Abstract

The cyanobacterium Synechocystis sp. PCC 6803 is known for producing polyhydroxybutyrate (PHB) under unbalanced nutrient conditions. Although many cyanobacteria produce PHB, its physiological relevance remains unknown, since previous studies concluded that PHB is redundant. In this work, we try to better understand the [...] Read more.

The cyanobacterium Synechocystis sp. PCC 6803 is known for producing polyhydroxybutyrate (PHB) under unbalanced nutrient conditions. Although many cyanobacteria produce PHB, its physiological relevance remains unknown, since previous studies concluded that PHB is redundant. In this work, we try to better understand the physiological conditions that are important for PHB synthesis. The accumulation of intracellular PHB was higher when the cyanobacterial cells were grown under an alternating day–night rhythm as compared to continuous light. In contrast to previous reports, a reduction of PHB was observed when the cells were grown under conditions of limited gas exchange. Since previous data showed that PHB is not required for the resuscitation from nitrogen starvation, a series of different abiotic stresses were applied to test if PHB is beneficial for its fitness. However, under none of the tested conditions did cells containing PHB show a fitness advantage compared to a PHB-free-mutant (ΔphaEC). Additionally, the distribution of PHB in single cells of a population Synechocystis cells was analyzed via fluorescence-activated cell sorting (FACS). The results showed a considerable degree of phenotypic heterogeneity at the single cell level concerning the content of PHB, which was consistent over several generations. These results improve our understanding about how and why Synechocystis synthesizes PHB and gives suggestions how to further increase its production for a biotechnological process. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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Review

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33 pages, 4853 KiB

Open AccessReview

Structural Determinants and Their Role in Cyanobacterial Morphogenesis

by Benjamin L. Springstein, Dennis J. Nürnberg, Gregor L. Weiss, Martin Pilhofer and Karina Stucken

Life 2020, 10(12), 355; https://doi.org/10.3390/life10120355 - 17 Dec 2020

Cited by 13 | Viewed by 8622

Abstract

Cells have to erect and sustain an organized and dynamically adaptable structure for an efficient mode of operation that allows drastic morphological changes during cell growth and cell division. These manifold tasks are complied by the so-called cytoskeleton and its associated proteins. In [...] Read more.

Cells have to erect and sustain an organized and dynamically adaptable structure for an efficient mode of operation that allows drastic morphological changes during cell growth and cell division. These manifold tasks are complied by the so-called cytoskeleton and its associated proteins. In bacteria, FtsZ and MreB, the bacterial homologs to tubulin and actin, respectively, as well as coiled-coil-rich proteins of intermediate filament (IF)-like function to fulfil these tasks. Despite generally being characterized as Gram-negative, cyanobacteria have a remarkably thick peptidoglycan layer and possess Gram-positive-specific cell division proteins such as SepF and DivIVA-like proteins, besides Gram-negative and cyanobacterial-specific cell division proteins like MinE, SepI, ZipN (Ftn2) and ZipS (Ftn6). The diversity of cellular morphologies and cell growth strategies in cyanobacteria could therefore be the result of additional unidentified structural determinants such as cytoskeletal proteins. In this article, we review the current advances in the understanding of the cyanobacterial cell shape, cell division and cell growth. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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15 pages, 1793 KiB

Open AccessReview

Small but Smart: On the Diverse Role of Small Proteins in the Regulation of Cyanobacterial Metabolism

by Fabian Brandenburg and Stephan Klähn

Life 2020, 10(12), 322; https://doi.org/10.3390/life10120322 - 01 Dec 2020

Cited by 18 | Viewed by 4542

Abstract

Over the past few decades, bioengineered cyanobacteria have become a major focus of research for the production of energy carriers and high value chemical compounds. Besides improvements in cultivation routines and reactor technology, the integral understanding of the regulation of metabolic fluxes is [...] Read more.

Over the past few decades, bioengineered cyanobacteria have become a major focus of research for the production of energy carriers and high value chemical compounds. Besides improvements in cultivation routines and reactor technology, the integral understanding of the regulation of metabolic fluxes is the key to designing production strains that are able to compete with established industrial processes. In cyanobacteria, many enzymes and metabolic pathways are regulated differently compared to other bacteria. For instance, while glutamine synthetase in proteobacteria is mainly regulated by covalent enzyme modifications, the same enzyme in cyanobacteria is controlled by the interaction with unique small proteins. Other prominent examples, such as the small protein CP12 which controls the Calvin–Benson cycle, indicate that the regulation of enzymes and/or pathways via the attachment of small proteins might be a widespread mechanism in cyanobacteria. Accordingly, this review highlights the diverse role of small proteins in the control of cyanobacterial metabolism, focusing on well-studied examples as well as those most recently described. Moreover, it will discuss their potential to implement metabolic engineering strategies in order to make cyanobacteria more definable for biotechnological applications. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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24 pages, 2338 KiB

Open AccessReview

Stress Signaling in Cyanobacteria: A Mechanistic Overview

by Raphaël Rachedi, Maryline Foglino and Amel Latifi

Life 2020, 10(12), 312; https://doi.org/10.3390/life10120312 - 26 Nov 2020

Cited by 24 | Viewed by 4623

Abstract

Cyanobacteria are highly diverse, widely distributed photosynthetic bacteria inhabiting various environments ranging from deserts to the cryosphere. Throughout this range of niches, they have to cope with various stresses and kinds of deprivation which threaten their growth and viability. In order to adapt [...] Read more.

Cyanobacteria are highly diverse, widely distributed photosynthetic bacteria inhabiting various environments ranging from deserts to the cryosphere. Throughout this range of niches, they have to cope with various stresses and kinds of deprivation which threaten their growth and viability. In order to adapt to these stresses and survive, they have developed several global adaptive responses which modulate the patterns of gene expression and the cellular functions at work. Sigma factors, two-component systems, transcriptional regulators and small regulatory RNAs acting either separately or collectively, for example, induce appropriate cyanobacterial stress responses. The aim of this review is to summarize our current knowledge about the diversity of the sensors and regulators involved in the perception and transduction of light, oxidative and thermal stresses, and nutrient starvation responses. The studies discussed here point to the fact that various stresses affecting the photosynthetic capacity are transduced by common mechanisms. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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19 pages, 1783 KiB

Open AccessReview

The Role of the Cyanobacterial Type IV Pilus Machinery in Finding and Maintaining a Favourable Environment

by Fabian D. Conradi, Conrad W. Mullineaux and Annegret Wilde

Life 2020, 10(11), 252; https://doi.org/10.3390/life10110252 - 23 Oct 2020

Cited by 14 | Viewed by 4530

Abstract

Type IV pili (T4P) are proteinaceous filaments found on the cell surface of many prokaryotic organisms and convey twitching motility through their extension/retraction cycles, moving cells across surfaces. In cyanobacteria, twitching motility is the sole mode of motility properly characterised to date and [...] Read more.

Type IV pili (T4P) are proteinaceous filaments found on the cell surface of many prokaryotic organisms and convey twitching motility through their extension/retraction cycles, moving cells across surfaces. In cyanobacteria, twitching motility is the sole mode of motility properly characterised to date and is the means by which cells perform phototaxis, the movement towards and away from directional light sources. The wavelength and intensity of the light source determine the direction of movement and, sometimes in concert with nutrient conditions, act as signals for some cyanobacteria to form mucoid multicellular assemblages. Formation of such aggregates or flocs represents an acclimation strategy to unfavourable environmental conditions and stresses, such as harmful light conditions or predation. T4P are also involved in natural transformation by exogenous DNA, secretion processes, and in cellular adaptation and survival strategies, further cementing the role of cell surface appendages. In this way, cyanobacteria are finely tuned by external stimuli to either escape unfavourable environmental conditions via phototaxis, exchange genetic material, and to modify their surroundings to fit their needs by forming multicellular assemblies. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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15 pages, 1437 KiB

Open AccessReview

Function and Benefits of Natural Competence in Cyanobacteria: From Ecology to Targeted Manipulation

by Alexandra M. Schirmacher, Sayali S. Hanamghar and Julie A. Z. Zedler

Life 2020, 10(11), 249; https://doi.org/10.3390/life10110249 - 22 Oct 2020

Cited by 13 | Viewed by 6546

Abstract

Natural competence is the ability of a cell to actively take up and incorporate foreign DNA in its own genome. This trait is widespread and ecologically significant within the prokaryotic kingdom. Here we look at natural competence in cyanobacteria, a group of globally [...] Read more.

Natural competence is the ability of a cell to actively take up and incorporate foreign DNA in its own genome. This trait is widespread and ecologically significant within the prokaryotic kingdom. Here we look at natural competence in cyanobacteria, a group of globally distributed oxygenic photosynthetic bacteria. Many cyanobacterial species appear to have the genetic potential to be naturally competent, however, this ability has only been demonstrated in a few species. Reasons for this might be due to a high variety of largely uncharacterised competence inducers and a lack of understanding the ecological context of natural competence in cyanobacteria. To shed light on these questions, we describe what is known about the molecular mechanisms of natural competence in cyanobacteria and analyse how widespread this trait might be based on available genomic datasets. Potential regulators of natural competence and what benefits or drawbacks may derive from taking up foreign DNA are discussed. Overall, many unknowns about natural competence in cyanobacteria remain to be unravelled. A better understanding of underlying mechanisms and how to manipulate these, can aid the implementation of cyanobacteria as sustainable production chassis. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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20 pages, 2997 KiB

Open AccessReview

Extracellular Vesicles: An Overlooked Secretion System in Cyanobacteria

by Steeve Lima, Jorge Matinha-Cardoso, Paula Tamagnini and Paulo Oliveira

Life 2020, 10(8), 129; https://doi.org/10.3390/life10080129 - 31 Jul 2020

Cited by 16 | Viewed by 8124

Abstract

In bacteria, the active transport of material from the interior to the exterior of the cell, or secretion, represents a very important mechanism of adaptation to the surrounding environment. The secretion of various types of biomolecules is mediated by a series of multiprotein [...] Read more.

In bacteria, the active transport of material from the interior to the exterior of the cell, or secretion, represents a very important mechanism of adaptation to the surrounding environment. The secretion of various types of biomolecules is mediated by a series of multiprotein complexes that cross the bacterial membrane(s), each complex dedicated to the secretion of specific substrates. In addition, biological material may also be released from the bacterial cell in the form of vesicles. Extracellular vesicles (EVs) are bilayered, nanoscale structures, derived from the bacterial cell envelope, which contain membrane components as well as soluble products. In cyanobacteria, the knowledge regarding EVs is lagging far behind compared to what is known about, for example, other Gram-negative bacteria. Here, we present a summary of the most important findings regarding EVs in Gram-negative bacteria, discussing aspects of their composition, formation processes and biological roles, and highlighting a number of technological applications tested. This lays the groundwork to raise awareness that the release of EVs by cyanobacteria likely represents an important, and yet highly disregarded, survival strategy. Furthermore, we hope to motivate future studies that can further elucidate the role of EVs in cyanobacterial cell biology and physiology. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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16 pages, 2777 KiB

Open AccessReview

Distinctive Features of PipX, a Unique Signaling Protein of Cyanobacteria

by Jose I. Labella, Raquel Cantos, Paloma Salinas, Javier Espinosa and Asunción Contreras

Life 2020, 10(6), 79; https://doi.org/10.3390/life10060079 - 28 May 2020

Cited by 11 | Viewed by 3693

Abstract

PipX is a unique cyanobacterial protein identified by its ability to bind to PII and NtcA, two key regulators involved in the integration of signals of the nitrogen/carbon and energy status, with a tremendous impact on nitrogen assimilation and gene expression in cyanobacteria. [...] Read more.

PipX is a unique cyanobacterial protein identified by its ability to bind to PII and NtcA, two key regulators involved in the integration of signals of the nitrogen/carbon and energy status, with a tremendous impact on nitrogen assimilation and gene expression in cyanobacteria. PipX provides a mechanistic link between PII, the most widely distributed signaling protein, and NtcA, a global transcriptional regulator of cyanobacteria. PII, required for cell survival unless PipX is inactivated or down-regulated, functions by protein–protein interactions with transcriptional regulators, transporters, and enzymes. In addition, PipX appears to be involved in a wider signaling network, supported by the following observations: (i) PII–PipX complexes interact with PlmA, an as yet poorly characterized transcriptional regulator also restricted to cyanobacteria; (ii) the pipX gene is functionally connected with pipY, a gene encoding a universally conserved pyridoxal phosphate binding protein (PLPBP) involved in vitamin B6 and amino acid homeostasis, whose loss-of-function mutations cause B6-dependent epilepsy in humans, and (iii) pipX is part of a relatively robust, six-node synteny network that includes pipY and four additional genes that might also be functionally connected with pipX. In this overview, we propose that the study of the protein–protein interaction and synteny networks involving PipX would contribute to understanding the peculiarities and idiosyncrasy of signaling pathways that are conserved in cyanobacteria. Full article

(This article belongs to the Special Issue Cellular and Molecular Strategies in Cyanobacterial Survival)

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