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1.
Nat Commun ; 12(1): 3475, 2021 06 09.
Artigo em Inglês | MEDLINE | ID: mdl-34108457

RESUMO

How thylakoid membranes are generated to form a metabolically active membrane network and how thylakoid membranes orchestrate the insertion and localization of protein complexes for efficient electron flux remain elusive. Here, we develop a method to modulate thylakoid biogenesis in the rod-shaped cyanobacterium Synechococcus elongatus PCC 7942 by modulating light intensity during cell growth, and probe the spatial-temporal stepwise biogenesis process of thylakoid membranes in cells. Our results reveal that the plasma membrane and regularly arranged concentric thylakoid layers have no physical connections. The newly synthesized thylakoid membrane fragments emerge between the plasma membrane and pre-existing thylakoids. Photosystem I monomers appear in the thylakoid membranes earlier than other mature photosystem assemblies, followed by generation of Photosystem I trimers and Photosystem II complexes. Redistribution of photosynthetic complexes during thylakoid biogenesis ensures establishment of the spatial organization of the functional thylakoid network. This study provides insights into the dynamic biogenesis process and maturation of the functional photosynthetic machinery.


Assuntos
Membranas Intracelulares/metabolismo , Tilacoides/metabolismo , Proteínas de Bactérias/metabolismo , Membranas Intracelulares/ultraestrutura , Luz , Microscopia Eletrônica , Modelos Biológicos , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , Multimerização Proteica , Proteômica , Synechococcus/crescimento & desenvolvimento , Synechococcus/metabolismo , Synechococcus/ultraestrutura , Tilacoides/ultraestrutura
2.
Elife ; 102021 06 16.
Artigo em Inglês | MEDLINE | ID: mdl-34132636

RESUMO

The cyanobacterium Synechocystis secretes a specific sulphated polysaccharide to form floating cell aggregates.


Assuntos
Synechocystis , Transporte Biológico , Synechocystis/genética
3.
mSphere ; 6(1)2021 01 13.
Artigo em Inglês | MEDLINE | ID: mdl-33441411

RESUMO

In filamentous heterocyst-forming (N2-fixing) cyanobacteria, septal junctions join adjacent cells, mediating intercellular communication, and are thought to traverse the septal peptidoglycan through nanopores. Fluorescence recovery after photobleaching (FRAP) analysis with the fluorescent marker calcein showed that cultures of Anabaena sp. strain PCC 7120 grown in the presence of combined nitrogen contained a substantial fraction of noncommunicating cells (58% and 80% of the tested vegetative cells in nitrate- and ammonium-grown cultures, respectively), whereas cultures induced for nitrogen fixation contained far fewer noncommunicating cells (16%). A single filament could have communicating and noncommunicating cells. These observations indicate that all (or most of) the septal junctions in a cell can be coordinately regulated and are coherent with the need for intercellular communication, especially under diazotrophic conditions. Consistently, intercellular exchange was observed to increase in response to N deprivation and to decrease rapidly in response to the presence of ammonium in the medium or to nitrate assimilation. Proteins involved in the formation of septal junctions have been identified in Anabaena and include SepJ, FraC, and FraD. Here, we reevaluated rates of intercellular transfer of calcein and the number of nanopores in mutants lacking these proteins and found a strong positive correlation between the two parameters only in cultures induced for nitrogen fixation. Thus, whereas the presence of a substantial number of noncommunicating cells appears to impair the correlation, data obtained in diazotrophic cultures support the idea that the nanopores are the structures that hold the septal junctions.IMPORTANCE Multicellularity is found in bacteria as well as in eukaryotes, and the filamentous heterocyst-forming (N2-fixing) cyanobacteria represent a simple and ancient paradigm of multicellular organisms. Multicellularity generally involves cell-cell adhesion and communication. The cells in the cyanobacterial filaments are joined by proteinaceous septal junctions that mediate molecular diffusion. The septal junctions traverse the septal peptidoglycan, which bears holes termed nanopores. Our results show that the septal junctions can be coordinately regulated in a cell and emphasize the relationship between septal junctions and nanopores to build intercellular communication structures, which are essential for the multicellular behavior of heterocyst-forming cyanobacteria.


Assuntos
Anabaena/citologia , Anabaena/metabolismo , Citoesqueleto/metabolismo , Fixação de Nitrogênio , Anabaena/genética , Proteínas de Bactérias/genética , Citoesqueleto/ultraestrutura , Fluoresceínas/metabolismo , Regulação Bacteriana da Expressão Gênica , Microscopia Eletrônica de Transmissão , Nanoporos
4.
Life (Basel) ; 10(11)2020 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-33114175

RESUMO

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.

5.
Nat Plants ; 6(9): 1179-1191, 2020 09.
Artigo em Inglês | MEDLINE | ID: mdl-32895528

RESUMO

The thylakoid membranes of cyanobacteria form a complex intracellular membrane system with a distinctive proteome. The sites of biogenesis of thylakoid proteins remain uncertain, as do the signals that direct thylakoid membrane-integral proteins to the thylakoids rather than to the plasma membrane. Here, we address these questions by using fluorescence in situ hybridization to probe the subcellular location of messenger RNA molecules encoding core subunits of the photosystems in two cyanobacterial species. These mRNAs cluster at thylakoid surfaces mainly adjacent to the central cytoplasm and the nucleoid, in contrast to mRNAs encoding proteins with other locations. Ribosome association influences the distribution of the photosynthetic mRNAs on the thylakoid surface, but thylakoid affinity is retained in the absence of ribosome association. However, thylakoid association is disrupted in a mutant lacking two mRNA-binding proteins, which probably play roles in targeting photosynthetic proteins to the thylakoid membrane.


Assuntos
Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Membrana Celular/metabolismo , Cianobactérias/genética , Cianobactérias/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Membrana Celular/genética , Hibridização in Situ Fluorescente , Transporte Proteico/genética , Tilacoides/genética , Tilacoides/metabolismo
6.
Annu Rev Microbiol ; 74: 633-654, 2020 09 08.
Artigo em Inglês | MEDLINE | ID: mdl-32689916

RESUMO

Photosynthetic membranes are typically densely packed with proteins, and this is crucial for their function in efficient trapping of light energy. Despite being crowded with protein, the membranes are fluid systems in which proteins and smaller molecules can diffuse. Fluidity is also crucial for photosynthetic function, as it is essential for biogenesis, electron transport, and protein redistribution for functional regulation. All photosynthetic membranes seem to maintain a delicate balance between crowding, order, and fluidity. How does this work in phototrophic bacteria? In this review, we focus on two types of intensively studied bacterial photosynthetic membranes: the chromatophore membranes of purple bacteria and the thylakoid membranes of cyanobacteria. Both systems are distinct from the plasma membrane, and both have a distinctive protein composition that reflects their specialized roles. Chromatophores are formed from plasma membrane invaginations, while thylakoid membranes appear to be an independent intracellular membrane system. We discuss the techniques that can be applied to study the organization and dynamics of these membrane systems, including electron microscopy techniques, atomic force microscopy, and many variants of fluorescence microscopy. We go on to discuss the insights that havebeen acquired from these techniques, and the role of membrane dynamics in the physiology of photosynthetic membranes. Membrane dynamics on multiple timescales are crucial for membrane function, from electron transport on timescales of microseconds to milliseconds to regulation and biogenesis on timescales of minutes to hours. We emphasize the open questions that remain in the field.


Assuntos
Cromatóforos Bacterianos/metabolismo , Cianobactérias/metabolismo , Fotossíntese/fisiologia , Tilacoides/metabolismo , Cianobactérias/química , Cianobactérias/genética , Transporte de Elétrons , Microscopia/classificação , Microscopia/métodos , Fotossíntese/genética , Tilacoides/química
7.
Nat Plants ; 6(7): 869-882, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-32665651

RESUMO

Cyanobacterial thylakoid membranes represent the active sites for both photosynthetic and respiratory electron transport. We used high-resolution atomic force microscopy to visualize the native organization and interactions of photosynthetic complexes within the thylakoid membranes from the model cyanobacterium Synechococcus elongatus PCC 7942. The thylakoid membranes are heterogeneous and assemble photosynthetic complexes into functional domains to enhance their coordination and regulation. Under high light, the chlorophyll-binding proteins IsiA are strongly expressed and associate with Photosystem I (PSI), forming highly variable IsiA-PSI supercomplexes to increase the absorption cross-section of PSI. There are also tight interactions of PSI with Photosystem II (PSII), cytochrome b6f, ATP synthase and NAD(P)H dehydrogenase complexes. The organizational variability of these photosynthetic supercomplexes permits efficient linear and cyclic electron transport as well as bioenergetic regulation. Understanding the organizational landscape and environmental adaptation of cyanobacterial thylakoid membranes may help inform strategies for engineering efficient photosynthetic systems and photo-biofactories.


Assuntos
Fotossíntese , Adaptação Fisiológica , Clorofila/metabolismo , Transporte de Elétrons , Luz , Microscopia de Força Atômica , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Synechococcus/fisiologia , Synechococcus/ultraestrutura , Tilacoides/fisiologia , Tilacoides/ultraestrutura
8.
J Bacteriol ; 202(12)2020 05 27.
Artigo em Inglês | MEDLINE | ID: mdl-32253342

RESUMO

Multicellularity in Cyanobacteria played a key role in their habitat expansion, contributing to the Great Oxidation Event around 2.45 billion to 2.32 billion years ago. Evolutionary studies have indicated that some unicellular cyanobacteria emerged from multicellular ancestors, yet little is known about how the emergence of new unicellular morphotypes from multicellular ancestors occurred. Our results give new insights into the evolutionary reversion from which the Gloeocapsopsis lineage emerged. Flow cytometry and microscopy results revealed morphological plasticity involving the patterned formation of multicellular morphotypes sensitive to environmental stimuli. Genomic analyses unveiled the presence of multicellularity-associated genes in its genome. Calcein-fluorescence recovery after photobleaching (FRAP) experiments confirmed that Gloeocapsopsis sp. strain UTEX B3054 carries out cell-to-cell communication in multicellular morphotypes but at slower time scales than filamentous cyanobacteria. Although traditionally classified as unicellular, our results suggest that Gloeocapsopsis displays facultative multicellularity, a condition that may have conferred ecological advantages for thriving as an extremophile for more than 1.6 billion years.IMPORTANCE Cyanobacteria are among the few prokaryotes that evolved multicellularity. The early emergence of multicellularity in Cyanobacteria (2.5 billion years ago) entails that some unicellular cyanobacteria reverted from multicellular ancestors. We tested this evolutionary hypothesis by studying the unicellular strain Gloeocapsopsis sp. UTEX B3054 using flow cytometry, genomics, and cell-to-cell communication experiments. We demonstrate the existence of a well-defined patterned organization of cells in clusters during growth, which might change triggered by environmental stimuli. Moreover, we found genomic signatures of multicellularity in the Gloeocapsopsis genome, giving new insights into the evolutionary history of a cyanobacterial lineage that has thrived in extreme environments since the early Earth. The potential benefits in terms of resource acquisition and the ecological relevance of this transient behavior are discussed.


Assuntos
Evolução Biológica , Cianobactérias/genética , Extremófilos/genética , Cianobactérias/classificação , Cianobactérias/fisiologia , Ecossistema , Extremófilos/classificação , Extremófilos/fisiologia , Genoma Bacteriano , Genômica , Filogenia
9.
J Bacteriol ; 201(19)2019 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-31262837

RESUMO

Motile strains of the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 readily aggregate into flocs, or floating multicellular assemblages, when grown in liquid culture. As described here, we used confocal imaging to probe the structure of these flocs, and we developed a quantitative assay for floc formation based on fluorescence imaging of 6-well plates. The flocs are formed from strands of linked cells, sometimes packed into dense clusters but also containing voids with very few cells. Cells within the dense clusters show signs of nutrient stress, as judged by the subcellular distribution of green fluorescent protein (GFP)-tagged Vipp1 protein. We analyzed the effects on flocculation of a series of mutations that alter piliation and motility, including Δhfq, ΔpilB1, ΔpilT1, and ΔushA mutations and deletion mutations affecting major and minor pilins. The extent of flocculation is increased in the hyperpiliated ΔpilT1 mutant, but active cycles of pilus extension and retraction are not required for flocculation. Deletion of PilA1, the major subunit of type IV pili, has no effect on flocculation; however, flocculation is lost in mutants lacking an operon coding for the minor pilins PilA9 to -11. Therefore, minor pilins appear crucial for flocculation. We show that flocculation is a tightly regulated process that is promoted by blue light perception by the cyanobacteriochrome Cph2. Floc formation also seems to be a highly cooperative process. A proportion of nonflocculating Δhfq cells can be incorporated into wild-type flocs, but the presence of a high proportion of Δhfq cells disrupts the large-scale architecture of the floc.IMPORTANCE Some bacteria form flocs, which are multicellular floating assemblages of many thousands of cells. Flocs have been relatively little studied compared to surface-adherent biofilms, but flocculation could play many physiological roles, be a crucial factor in marine carbon burial, and enable more efficient biotechnological cell harvesting. We studied floc formation and architecture in the model cyanobacterium Synechocystis sp. strain PCC 6803, using mutants to identify specific cell surface structures required for floc formation. We show that floc formation is regulated by blue and green light perceived by the photoreceptor Cph2. The flocs have a characteristic structure based on strands of linked cells aggregating into dense clusters. Cells within the dense clusters show signs of nutrient stress, pointing to a disadvantage of floc formation.


Assuntos
Proteínas de Bactérias/genética , Proteínas de Membrana/metabolismo , Mutação , Synechocystis/crescimento & desenvolvimento , Aderência Bacteriana , Proteínas de Bactérias/metabolismo , Técnicas Bacteriológicas , Fímbrias Bacterianas/genética , Floculação , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Fator Proteico 1 do Hospedeiro/genética , Proteínas de Membrana/genética , Diester Fosfórico Hidrolases/genética , Proteínas Recombinantes/metabolismo , Synechocystis/genética , Synechocystis/metabolismo
10.
Org Biomol Chem ; 17(15): 3752-3759, 2019 04 10.
Artigo em Inglês | MEDLINE | ID: mdl-30840015

RESUMO

Two truncated analogues of the polyenyl photoprotective xanthomonadin pigments have been synthesised utilising an iterative Heck-Mizoroki (HM)/iododeboronation cross coupling approach and investigated as models of the natural product photoprotective agents in bacteria. Despite the instability of these types of compounds, both analogues proved to be sufficiently stable to allow isolation, spectroscopic analysis and biological studies of their photoprotective behaviour which showed that despite their shorter polyene chain length, they retained the ability to protect bacteria from photochemical damage; i.e. incorporation of one compound into E. coli provided photoprotective activity against singlet oxygen analogous to the natural photoprotective mechanisms employed by Xanthomonas bacteria, answering key questions about what minimal functionality is required to impart photoprotection, potentially leading to new classes of photoprotective and antioxidants compounds.


Assuntos
Antibacterianos/farmacologia , Antioxidantes/farmacologia , Escherichia coli/efeitos dos fármacos , Polienos/química , Protetores Solares/farmacologia , Antibacterianos/síntese química , Antibacterianos/química , Antioxidantes/síntese química , Antioxidantes/química , Testes de Sensibilidade Microbiana , Estrutura Molecular , Protetores Solares/síntese química , Protetores Solares/química
11.
Life (Basel) ; 9(1)2018 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-30577420

RESUMO

Heterocyst-forming cyanobacteria are multicellular organisms that grow as chains of cells (filaments or trichomes) in which the cells exchange regulators and nutrients. In this article, we review the morphological, physiological and genetic data that have led to our current understanding of intercellular communication in these organisms. Intercellular molecular exchange appears to take place by simple diffusion through proteinaceous structures, known as septal junctions, which connect the adjacent cells in the filament and traverse the septal peptidoglycan through perforations known as nanopores. Proteins that are necessary to produce, and that may be components of, the septal junctions-SepJ, FraC and FraD-have been identified in the heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120 model. Additionally, several proteins that are necessary to produce a normal number of nanopores and functional septal junctions have been identified, including AmiC-type amidases, peptidoglycan-binding proteins and some membrane transporters. Available reports and reevaluation of intercellular molecular transfer data for some mutants of Anabaena suggest that the septal junctions can be regulated, likely by a mechanism of gating.

13.
Elife ; 62017 12 12.
Artigo em Inglês | MEDLINE | ID: mdl-29231807

RESUMO

Bacteria contain large numbers of negatively-charged proteins to avoid the electrostatic interactions with ribosomes that would dramatically reduce protein diffusion.


Assuntos
Proteínas de Escherichia coli/química , Proteínas de Escherichia coli/metabolismo , Escherichia coli/metabolismo , Ribossomos/metabolismo , Eletricidade Estática , Difusão , Escherichia coli/citologia , Concentração Osmolar
14.
Mol Plant ; 10(11): 1434-1448, 2017 11 06.
Artigo em Inglês | MEDLINE | ID: mdl-29017828

RESUMO

The structural dynamics and flexibility of cell membranes play fundamental roles in the functions of the cells, i.e., signaling, energy transduction, and physiological adaptation. The cyanobacterial thylakoid membrane represents a model membrane that can conduct both oxygenic photosynthesis and respiration simultaneously. In this study, we conducted direct visualization of the global organization and mobility of photosynthetic complexes in thylakoid membranes from a model cyanobacterium, Synechococcus elongatus PCC 7942, using high-resolution atomic force, confocal, and total internal reflection fluorescence microscopy. We visualized the native arrangement and dense packing of photosystem I (PSI), photosystem II (PSII), and cytochrome (Cyt) b6f within thylakoid membranes at the molecular level. Furthermore, we functionally tagged PSI, PSII, Cyt b6f, and ATP synthase individually with fluorescent proteins, and revealed the heterogeneous distribution of these four photosynthetic complexes and determined their dynamic features within the crowding membrane environment using live-cell fluorescence imaging. We characterized red light-induced clustering localization and adjustable diffusion of photosynthetic complexes in thylakoid membranes, representative of the reorganization of photosynthetic apparatus in response to environmental changes. Understanding the organization and dynamics of photosynthetic membranes is essential for rational design and construction of artificial photosynthetic systems to underpin bioenergy development. Knowledge of cyanobacterial thylakoid membranes could also be extended to other cell membranes, such as chloroplast and mitochondrial membranes.


Assuntos
Cianobactérias/metabolismo , Fotossíntese/fisiologia , Cianobactérias/genética , Microscopia de Força Atômica , Fotossíntese/genética , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Tilacoides/metabolismo
15.
FEMS Microbiol Rev ; 41(6): 900-922, 2017 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-29077840

RESUMO

The natural light environment is important to many prokaryotes. Most obviously, phototrophic prokaryotes need to acclimate their photosynthetic apparatus to the prevailing light conditions, and such acclimation is frequently complemented by motility to enable cells to relocate in search of more favorable illumination conditions. Non-phototrophic prokaryotes may also seek to avoid light at damaging intensities and wavelengths, and many prokaryotes with diverse lifestyles could potentially exploit light signals as a rich source of information about their surroundings and a cue for acclimation and behavior. Here we discuss our current understanding of the ways in which bacteria can perceive the intensity, wavelength and direction of illumination, and the signal transduction networks that link light perception to the control of motile behavior. We discuss the problems of light perception at the prokaryotic scale, and the challenge of directional light perception in small bacterial cells. We explain the peculiarities and the common features of light-controlled motility systems in prokaryotes as diverse as cyanobacteria, purple photosynthetic bacteria, chemoheterotrophic bacteria and haloarchaea.


Assuntos
Fenômenos Fisiológicos Bacterianos/efeitos da radiação , Luz , Fotossíntese
16.
Artigo em Inglês | MEDLINE | ID: mdl-28929086

RESUMO

Filamentous cyanobacteria have developed a strategy to perform incompatible processes in one filament by differentiating specialized cell types, N2-fixing heterocysts and CO2-fixing, photosynthetic, vegetative cells. These bacteria can be considered true multicellular organisms with cells exchanging metabolites and signaling molecules via septal junctions, involving the SepJ and FraCD proteins. Previously, it was shown that the cell wall lytic N-acetylmuramyl-L-alanine amidase, AmiC2, is essential for cell-cell communication in Nostoc punctiforme. This enzyme perforates the septal peptidoglycan creating an array of nanopores, which may be the framework for septal junction complexes. In Anabaena sp. PCC 7120, two homologs of AmiC2, encoded by amiC1 and amiC2, were identified and investigated in two different studies. Here, we compare the function of both AmiC proteins by characterizing different Anabaena amiC mutants, which was not possible in N. punctiforme, because there the amiC1 gene could not be inactivated. This study shows the different impact of each protein on nanopore array formation, the process of cell-cell communication, septal protein localization, and heterocyst differentiation. Inactivation of either amidase resulted in significant reduction in nanopore count and in the rate of fluorescent tracer exchange between neighboring cells measured by FRAP analysis. In an amiC1 amiC2 double mutant, filament morphology was affected and heterocyst differentiation was abolished. Furthermore, the inactivation of amiC1 influenced SepJ localization and prevented the filament-fragmentation phenotype that is characteristic of sepJ or fraC fraD mutants. Our findings suggest that both amidases are to some extent redundant in their function, and describe a functional relationship of AmiC1 and septal proteins SepJ and FraCD.


Assuntos
Anabaena/enzimologia , Proteínas de Bactérias/metabolismo , Parede Celular/enzimologia , Junções Intercelulares/metabolismo , Nanoporos/ultraestrutura , Amidoidrolases/genética , Amidoidrolases/metabolismo , Anabaena/genética , Proteínas de Bactérias/genética , Comunicação Celular , Citoesqueleto/metabolismo , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Microscopia Eletrônica de Transmissão , Microscopia de Fluorescência , Mutação , Peptidoglicano/genética , Peptidoglicano/metabolismo
18.
Curr Opin Plant Biol ; 37: 109-115, 2017 06.
Artigo em Inglês | MEDLINE | ID: mdl-28472718

RESUMO

Cyanobacteria are able to move directly towards or away from a light source, a process called phototaxis. Recent studies have revealed that the spherical unicellular cyanobacterium Synechocystis sp. PCC 6803 exhibits a cell polarity in response to unidirectional illumination and that micro-optic properties of cyanobacterial cells are the basis of their directional light sensing. Further functional and physiological studies highlight a very complex control of cyanobacterial phototaxis by sensory proteins, histidine kinases and response regulators. Notably, PATAN domain response regulators appear to participate in directional control of phototaxis in the cyanobacterium Synechocystis sp. PCC 6803. In this review we explain the problem of directional light sensing at the small scale of bacteria and discuss our current understanding of signal transduction in cyanobacterial phototaxis.


Assuntos
Cianobactérias/fisiologia , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Cianobactérias/genética , Cianobactérias/metabolismo , Luz , Fototaxia/efeitos da radiação , Transdução de Sinais/efeitos da radiação , Synechocystis/genética , Synechocystis/metabolismo , Synechocystis/fisiologia
19.
mBio ; 8(1)2017 01 03.
Artigo em Inglês | MEDLINE | ID: mdl-28049144

RESUMO

Heterocyst-forming cyanobacteria grow as filaments in which intercellular molecular exchange takes place. During the differentiation of N2-fixing heterocysts, regulators are transferred between cells. In the diazotrophic filament, vegetative cells that fix CO2 through oxygenic photosynthesis provide the heterocysts with reduced carbon and heterocysts provide the vegetative cells with fixed nitrogen. Intercellular molecular transfer has been traced with fluorescent markers, including calcein, 5-carboxyfluorescein, and the sucrose analogue esculin, which are observed to move down their concentration gradient. In this work, we used fluorescence recovery after photobleaching (FRAP) assays in the model heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120 to measure the temperature dependence of intercellular transfer of fluorescent markers. We find that the transfer rate constants are directly proportional to the absolute temperature. This indicates that the "septal junctions" (formerly known as "microplasmodesmata") linking the cells in the filament allow molecular exchange by simple diffusion, without any activated intermediate state. This constitutes a novel mechanism for molecular transfer across the bacterial cytoplasmic membrane, in addition to previously characterized mechanisms for active transport and facilitated diffusion. Cyanobacterial septal junctions are functionally analogous to the gap junctions of metazoans. IMPORTANCE: Although bacteria are frequently considered just as unicellular organisms, there are bacteria that behave as true multicellular organisms. The heterocyst-forming cyanobacteria grow as filaments in which cells communicate. Intercellular molecular exchange is thought to be mediated by septal junctions. Here, we show that intercellular transfer of fluorescent markers in the cyanobacterial filament has the physical properties of simple diffusion. Thus, cyanobacterial septal junctions are functionally analogous to metazoan gap junctions, although their molecular components appear unrelated. Like metazoan gap junctions, the septal junctions of cyanobacteria allow the rapid intercellular exchange of small molecules, without stringent selectivity. Our finding expands the repertoire of mechanisms for molecular transfer across the plasma membrane in prokaryotes.


Assuntos
Anabaena/química , Anabaena/metabolismo , Difusão , Corantes Fluorescentes/análise , Transporte Biológico , Temperatura
20.
J Bacteriol ; 199(7)2017 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-28096449

RESUMO

When deprived of combined nitrogen, some filamentous cyanobacteria contain two cell types: vegetative cells that fix CO2 through oxygenic photosynthesis and heterocysts that are specialized in N2 fixation. In the diazotrophic filament, the vegetative cells provide the heterocysts with reduced carbon (mainly in the form of sucrose) and heterocysts provide the vegetative cells with combined nitrogen. Septal junctions traverse peptidoglycan through structures known as nanopores and appear to mediate intercellular molecular transfer that can be traced with fluorescent markers, including the sucrose analog esculin (a coumarin glucoside) that is incorporated into the cells. Uptake of esculin by the model heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120 was inhibited by the α-glucosides sucrose and maltose. Analysis of Anabaena mutants identified components of three glucoside transporters that move esculin into the cells: GlsC (Alr4781) and GlsP (All0261) are an ATP-binding subunit and a permease subunit of two different ABC transporters, respectively, and HepP (All1711) is a major facilitator superfamily (MFS) protein that was shown previously to be involved in formation of the heterocyst envelope. Transfer of fluorescent markers (especially calcein) between vegetative cells of Anabaena was impaired by mutation of glucoside transporter genes. GlsP and HepP interact in bacterial two-hybrid assays with the septal junction-related protein SepJ, and GlsC was found to be necessary for the formation of a normal number of septal peptidoglycan nanopores and for normal subcellular localization of SepJ. Therefore, beyond their possible role in nutrient uptake in Anabaena, glucoside transporters influence the structure and function of septal junctions.IMPORTANCE Heterocyst-forming cyanobacteria have the ability to perform oxygenic photosynthesis and to assimilate atmospheric CO2 and N2 These organisms grow as filaments that fix these gases specifically in vegetative cells and heterocysts, respectively. For the filaments to grow, these types of cells exchange nutrients, including sucrose, which serves as a source of reducing power and of carbon skeletons for the heterocysts. Movement of sucrose between cells in the filament takes place through septal junctions and has been traced with a fluorescent sucrose analog, esculin, that can be taken up by the cells. Here, we identified α-glucoside transporters of Anabaena that mediate uptake of esculin and, notably, influence septal structure and the function of septal junctions.


Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Anabaena/metabolismo , Regulação Bacteriana da Expressão Gênica/fisiologia , Glucosídeos/metabolismo , Transportadores de Cassetes de Ligação de ATP/genética , Anabaena/genética , Proteínas de Bactérias/metabolismo , Transporte Biológico , Esculina/metabolismo , Mutação , Ligação Proteica
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