191 research outputs found
Interaction of the Membrane-bound GlnK-AmtB Complex with the Master Regulator of Nitrogen Metabolism TnrA inBacillus subtilis
No full textP-II proteins are widespread and highly conserved signal transduction proteins occurring in bacteria, Archaea, and plants and play pivotal roles in controlling nitrogen assimilatory metabolism. This study reports on biochemical properties of the P-II-homologue GlnK (originally termed NrgB) in Bacillus subtilis (BsGlnK). Like other P-II proteins, the native BsGlnK protein has a trimeric structure and readily binds ATP in the absence of divalent cations, whereas 2-oxoglutarate is only weakly bound. In contrast to other P-II-like proteins, Mg2+ severely affects its ATP-binding properties. BsGlnK forms a tight complex with the membrane-bound ammonium transporter AmtB (NrgA), from which it can be relieved by millimolar concentrations of ATP. Immunoprecipitation and co-localization experiments identified a novel interaction between the BsGlnK-AmtB complex and the major transcription factor of nitrogen metabolism, TnrA. In vitro in the absence of ATP, TnrA is completely tethered to membrane (AmtB)-bound GlnK, whereas in extracts from BsGlnK- or AmtB-deficient cells, TnrA is entirely soluble. The presence of 4 mM ATP leads to concomitant solubilization of BsGlnK and TnrA. This ATP-dependent membrane re-localization of TnrA by BsGlnK/AmtB may present a novel mechanism to control the global nitrogen-responsive transcription regulator TnrA in B. subtilis under certain physiological conditions
Structural Analysis of the PP2C Phosphatase tPphA from Thermosynechococcus elongatus: A Flexible Flap Subdomain Controls Access to the Catalytic Site
No full textThe homologue of the phosphoprotein I'll phosphatase PphA from Thermosynechococcus elongatus, termed tPphA, was identified and its structure was resolved in two different space groups, C222(1) and P4(1)2(1)2, at a resolution of 1.28 and 3.05 angstrom, respectively. tPphA belongs to a large and widely distributed subfamily of Mg2+/Mn2+-dependent phosphatases of the PPM superfamily characterized by the lack of catalytic and regulatory domains. The core structure of tPphA shows a high degree of similarity to the two PPM structures identified so far. In contrast to human PP2C, but similar to Mycobacterium tuberculosis phosphatase PstP, the catalytic centre exhibits a third metal ion in addition to the dinuclear metal centre universally conserved in all PPM members. The fact that the third metal is only liganded by amino acids, which are universally conserved in all PPM members, implies that the third metal could be general for all members of this family. As a specific feature of tPphA, a flexible subdomain, previously recognized as a flap domain, could be revealed. Comparison of different structural isomers of tPphA as well as site-specific mutagenesis implied that the flap domain is involved in substrate binding and catalytic activity. The structural arrangement of the flap domain was accompanied by a large side-chain movement of an Arg residue (Arg169) at the basis of the flap. Mutation of this residue strongly impaired protein stability as well as catalytic activity, emphasizing the importance of this amino acid for the regional polysterism of the flap subdomain and confirming the assumption that flap domain flexibility is involved in catalysis. (C) 2007 Elsevier Ltd. All rights reserved
Clear differences in metabolic and morphological adaptations of akinetes of two Nostocales living in different habitats
No full textAkinetes are resting spore-like cells formed by some heterocyst-forming filamentous cyanobacteria for surviving long periods of unfavourable conditions. We studied the development of akinetes in two model strains of cyanobacterial cell differentiation, the planktonic freshwater Anabaena variabilis ATCC 29413 and the terrestrial or symbiotic Nostoc punctiforme ATCC 29133, in response to low light and phosphate starvation. The best trigger of akinete differentiation of Anabaena variabilis was low light; that of N. punctiforme was phosphate starvation. Light and electron microscopy revealed that akinetes of both species differed from vegetative cells by their larger size, different cell morphology and large number of intracellular granules. Anabaena variabilis akinetes had a multilayer envelope; those of N. punctiforme had a simpler envelope. During akinete development of Anabaena variabilis, the amount of the storage compounds cyanophycin and glycogen increased transiently, whereas in N. punctiforme, cyanophycin and lipid droplets increased transiently. Photosynthesis and respiration decreased during akinete differentiation in both species, and remained at a low level in mature akinetes. The clear differences in the metabolic and morphological adaptations of akinetes of the two species could be related to their different lifestyles. The results pave the way for genetic and functional studies of akinete differentiation in these species.Fil: Perez, Rebeca. University of Tübingen; AlemaniaFil: Forchhammer, Karl. University of Tübingen; AlemaniaFil: Salerno, Graciela Lidia. Fundación para Investigaciones Biológicas Aplicadas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología; ArgentinaFil: Maldener, Iris. University of Tübingen; Alemani
Interactions between the PII protein and its receptors revealed by NanoBiT technology
No full textThe PII proteins are notable members of a vast and ancient protein family involved in signal transduction. These
molecules are found in all living organisms and are primarily recognized for their ability to sense metabolites such
as ATP, ADP, and 2-oxoglutarate (2-OG). When the effector molecules are non-covalently bound by PII, they
cause several structural changes in PII proteins, particularly in their flexible T-loops, which serve as dynamic
modules for protein-protein interactions. The interpretation of metabolic data sent by PII is dependent on the
binding state of metabolites and the resulting conformation of PII receptors. To thoroughly investigate the complex
interactions between PII and target proteins, analytical methods that maintain the natural cellular milieu are
needed.
In light of the limitations inherent in alternative methodologies such as immobilization on sensor surfaces in
Surface-Plasmon-Resonance (SPR) and Biolayer Interferometry (BLI), as well as the reliance on sizable
fluorescence proteins in Förster Resonance Energy Transfer (FRET), our research endeavors focused on the
development of an innovative NanoBiT sensor. The focus of this sensor is on the interaction of the PII protein
derived from Synechocystis sp. PCC6803 with the PII-interacting protein X (PipX), N-acetyl-L glutamate kinase
(NAGK) and the PII-interacting regulator of arginine synthesis (PirA). Using the NanoBiT technology, we have
attained an advanced comprehension, enabling the calculation of KD values for the PII-NAGK and PII-PipX
complexes, which have not been previously reported. The test also demonstrated an increased level of sensitivity,
allowing for the detection of low-affinity interactions, such as the one seen between the PII-S49E variant and
NAGK. The study also highlights astounding proof indicating that the development of the PII-NAGK complex is
impacted by the presence of ADP, which reduces the complex affinity. Additional analysis by the NanoBiT
method and enzymatic assays provided further evidence that the PII-NAGK complex exhibits specific feed forward activation in response to increasing concentrations of NAG. These two sensors were also applied to
investigate the real time metabolic fluctuations in response to nitrogen upshift or nitrogen depletion treatments.
Furthermore, our exploration extended to a small protein encoded by the ssr0692 gene in Synechocystis sp. PCC
6803. The protein regulates the flux into the ornithine-ammonia cycle (OAC), a pivotal mechanism for the
accumulation and redistribution of nitrogen in cyanobacteria. The regulation described in this context arises from
the connection between the PII protein and the OAC cycle. PII traditionally regulates the key enzyme NAGK,
which catalyzes arginine production. The Ssr0692 protein competes with NAGK for PII binding, resulting in the
inhibition of NAGK activation and a consequent reduction in arginine synthesis. In light of its function, we have
identified it as the PII Interacting Regulator of Arginine Synthesis (PirA). The interaction between PirA and PII
depends on the presence of ADP and is hindered by mutations in PII that affect the structure of the T-loop.
Therefore, we propose that PirA serves as a crucial mediator, directing flux into nitrogen storage compounds by
considering both the availability of nitrogen and the energy level of the cell
Analyse der Funktion des Sll0783 Proteins in der PHB Bildung von Synechocystis PCC 6803: die entscheidene Rolle von NADPH im Stickstoffmangel
No full textNitrogen frequently is a limiting nutrient in natural habitats. Therefore, cyanobacteria as well as other autotrophic organisms have developed multiple strategies to adapt to nitrogen deficiency. Transcriptomic analyses of the strain Synechocystis PCC 6803 under nitrogen-deficient conditions revealed a highly induced gene (sll0783 ), which is annotated as conserved protein with unknown function. This gene is part of a cluster with seven genes and in the upstream region lies a predicted NtcA-binding site. Homologues of this cluster occur in some unicellular, non-diazotrophic cyanobacteria, in several alpha-, beta- and gamma-proteobacteria as well as in some gram-positives. The common link between the heterotrophic bacteria seems to be the ability of nitrogen fixation and production of polyhydroxybutyrate (PHB), whereas among the cyanobacteria only Synechocystis PCC 6803 can accumulate PHB.
In this work, a knockout mutant of this gene in Synechocystis PCC 6803 was
characterised. This mutant was unable to accumulate PHB, a carbon and energy storage compound. The levels of precursor metabolites such as glycogen and acetyl-CoA were not reduced. The impairment in PHB accumulation correlated with a loss of PHB synthase activity during prolonged nitrogen starvation.
We could show that the PHB synthase activity appeared to be a target
of activity regulation, which was influenced by the NADPH/NADP+ ratio. The
loss of PHB synthase activity in the Sll0783 mutant was caused by decreased
NADPH/NADP+ ratio, which plays a crucial role in PHB synthesis.Stickstoff ist häufig ein limitierender Nährstoff in natürlichen Lebensräumen. Aus diesem Grund haben Cyanobakterien und andere autotrophe Organismen verschiedene Strategien entwickelt, um sich an diese Mangelbedingung anzupassen. Transkriptomanalysen des Cyanobakteriums Synechocystis PCC 6803 zeigten, dass das Gen sll0783 unter Stickstoffmangelbedingungen besonders stark induziert wird. sll0783 codiert für ein konserviertes Protein mit unbekannter Funktion und ist Teil eines Clusters mit sieben Genen. Im Promotorbereich befindet sich ein NtcA-Bindemotiv. Homologe dieses Clusters sind in einigen einzelligen, nicht-diazotrophen Cyanobakterien, in mehreren alpha-, beta- und gamma-Proteobakterien, sowie in einigen grampositiven Bakterien nachgewiesen worden. Das gemeinsame Bindeglied zwischen den heterotrophen Bakterien ist die Fähigkeit Stickstoff zu fixieren und Polyhydroxybutyrat (PHB), ein Kohlenstoff- und Energiespeicher, einzulagern. Unter den Cyanobakterien ist nur Synechocystis PCC 6803 in der Lage PHB zu bilden.
In dieser Arbeit wurde eine Knockout-Mutante des Gens sll0783 in Synechocystis PCC 6803 charakterisiert. Diese Mutante konnte nach Stickstoffentzug kein PHB mehr bilden. Während die Glykogen- und Acetyl-CoA-Konzentrationen in der Mutante nicht verringert waren, korrelierte die verminderte PHB-Bildung mit dem Verlust der PHB-Synthase-Aktivität. Es konnte gezeigt werden, dass die PHB-Synthase einer Aktivitätsregulierung unterliegt, welche durch das NADPH/NADP+-Verhältnis beeinflusst wird. Der Verlust der PHB-Synthase-Aktivität in der Sll0783-Mutante wurde durch ein reduziertes NADPH/NADP+-Verhältnis verursacht. Dies spielt eine Entscheidende Rolle in der PHB-Synthese
Unraveling the Function of Sll0944 in the Regulation of Carbon and Nitrogen Metabolism in Synechocystis sp. PCC6803
No full textCyanobakterien sind als die Pioniere der oxygenen Photosynthese anerkannt und haben vor zwei Milliarden Jahren maßgeblich zur Umgestaltung der Erdat-mosphäre beigetragen. Im Laufe ihrer Evolution haben sie eine Vielzahl von Anpassungsmechanismen entwickelt, um sich an ständig wechselnde Umwelt-bedingungen zu gewöhnen. Ein zentraler Bestandteil dieser Anpassungen ist das regulatorische Netzwerk des Stickstoff-Regulations-Proteins PII. In dem nicht-diazotrophen Cyanobakterium Synechocystis sp. PCC 6803 steuert PII eine Vielzahl von Stoffwechselprozessen, die für die Aufrechterhaltung der Kohlenstoff- und Stickstoff-Homöostase essentiell sind. Die Regulation erfolgt über die Bindung von ATP, ADP und 2-Oxoglutarat, die je nach Energie- und Nährstoffverfügbarkeit als Signalmoleküle dienen. Unter Bedingungen eines ausgeglichenen Energiehaushalts und ausreichender Nährstoffversorgung ge-währleistet PII eine effiziente Bereitstellung von Aminosäurevorläufern und re-guliert die Fettsäuresynthese. Zudem hemmt es die Aktivierung des globalen Stickstoff-Transkriptionsregulators NtcA durch Bindung an das PII-interagierende Protein X.
Unsere Ergebnisse belegen eine entscheidende Rolle von PII bei der Regulation der Kohlenstoffspeicherung unter Stickstoffmangelbedingungen. Wir konnten zeigen, dass der PII-interagierende Regulator des Kohlenstoffstoffwechsels (PirC) die Umwandlung fixierten Kohlenstoffs von der Glykolyse zur Glykogen-synthese durch Hemmung der 2,3-Bisphosphoglycerat-unabhängigen Phos-phoglycerat-Mutase beeinflusst. Diese Hemmung wird durch PII reguliert, wobei die Bindung von PirC an PII von den intrazellulären Konzentrationen von ATP, ADP und 2-Oxoglutarat abhängt. Strukturanalysen deuten darauf hin, dass PirC spezifisch mit cyanobakterien-spezifischen Elementen der Phosphoglyce-rat-Mutase interagiert und somit deren Aktivität beeinflusst. Unsere Studie legt den Grundstein für die Entwicklung von Synechocystis sp. PCC 6803 als Chas-sisorganismus für die nachhaltige Produktion von Polyhydroxybutyrat (PHB) und anderen wertvollen Verbindungen. Durch gezielte genetische Modifikatio-nen konnten wir Stämme generieren, die bis zu 80% ihres Trockengewichts in Form von PHB speichern.Cyanobacteria are considered to be the inventors of oxygenic photosynthesis. Two billion years ago, they shaped the atmosphere by releasing oxygen. Through this time, they evolved various species with plenty of mechanisms to adapt to the constantly changing environment. Among all those mechanisms, some structures became established and further functions evolved around this basis. One of the most prominent examples of this is the regulatory network of the nitrogen-regulatory protein PII. In the non-diazotroph cyanobacterium Syn-echocystis sp. PCC 6803, PII regulates a plethora of reactions that maintain the Carbon/Nitrogen homeostasis. The regulations depend on the binding of either ATP or ADP during high energy and nitrogen availability and 2-oxoglutarate (2-OG) during low nitrogen availability. In a balanced proportion of energy and nutrition, PII ensures sufficient amounts of amino acid precursors by activating the phosphoenol pyruvate carboxylase and mitigating the fatty acid synthesis. It also binds the PII interacting protein X to prevent the activation of the global nitrogen transcriptional regulator NtcA. With the increase of 2-oxoglutarate, PII releases its binding partners, which cancels its regulations. It was suggested that PII also regulate carbon storage during low nitrogen availability.
This work clarified PII's involvement in carbon storage regulation during chloro-sis. The novel discovered that the PII interacting regulator of carbon metabo-lism (PirC) changes the direction of fixed CO2 from lower glycolysis to glycogen synthesis by inhibiting the 2,3-bisphosphoglycerate-independent phospho-glycerate mutase. PII regulates this inhibition by binding the PirC during high ADP and ATP and releasing it during high 2-OG levels. PirC mediates the inhi-bition by interacting with two cyanobacteria-exclusive structural elements with-in their phosphoglycerate mutase. Furthermore, the elements also have a strong influence on the activity of the enzyme. This work also created the basis on which Synechocystis sp. PCC 6803 can be edited to create a chassis for the sustainable production of polyhydroxybutyrate (PHB) or other metabo-lism-derived valuable compounds. A strain derived from this work produced 80 % PHB of their cell dry mass
Novel structures of PII signal transduction proteins from oxygenic phototropic organisms
No full textPII proteins constitute one of the most widely distributed families of signal transduction proteins, whose representatives are present in archaea, bacteria and plants. They play a pivotal role to control the nitrogen, carbon and energy status of the cell in response to the central metabolites ATP, ADP and 2-oxoglutarate (2-OG). These signals from central metabolites are integrated by PII proteins and transmitted to the regulatory targets (protein modifying enzymes, metabolic enzymes, transporters and transcription factors). In oxygenic phototrophic organisms, from cyanobacteria to higher plants, the controlling enzyme of arginine synthesis, N-acetyl-L-glutamate kinase (NAGK) is a major PII target, whose activity responds to the cellular metabolites via PII signalling. In this work, novel crystal structures of PII signal transduction proteins from oxygenic phototrophs (Synechococcus elongatus and Chlamydomonas reinhardtii) in the presence of signalling metabolites and in complex with NAGK are reported. These structures give deeper insights into PII-mediated mechanism and regulation which are in accordance with the obtained biochemical data. The novel role of glutamine as a signalling molecule in C. reinhardtii is elucidated for the first time, which highlights the nitrogen regulation at a different level. Further, the interpretation of these structures together with the comparison of aminoacid sequences sheds light on the evolutionary adaptation of PII signal transduction from cyanobacteria to plastids
Von der Metabolitenwahrnehmung zur Proteinregulation durch Synechococcus elongatus PCC 7942 PII Protein
No full textPII signal transduction proteins have key functions in coordination of central metabolism by integrating signals from carbon, nitrogen and energy status of the cell. They bind the metabolites ATP, ADP and 2-oxoglutarate (2-OG) and control enzymes, transporters and transcription factors involved in nitrogen metabolism. Depending on its effector molecule binding status, PII from Synechococcus elongatus binds a small protein termed PipX, which is a co-activator of the transcription factor NtcA, and regulates the key enzyme of the cyclic ornithine pathway, N-acetyl-L-glutamate kinase (NAGK). This study shows that PII and NAGK from bacteria (S. elongatus) and plants (Arabidopsis thaliana) can functionally complement each other in vitro, demonstrating a strong conservation of this regulatory mechanism through 1.2 billion years of separate evolution. There are two contact interfaces in the PII-NAGK complex from S. elongatus. One of them includes a salt bridge of PII E85 residue with R233 of NAGK. Consequently, E85-PII mutants loose the ability to interact with NAGK. We found PII variants (I86N and I86T) that were able to bind to a NAGK variant (R233A), which was previously shown to be unable to bind wild type PII protein. Based on the crystal structure and biochemical analysis of the I86N PII variant we propose a two-step model for the mechanism of PII-NAGK complex formation. In an initiating step, a contact between R233 of NAGK and E85 of PII initiates the bending of the extended T-loop of PII, followed by a second step, where a bended T-loop deeply inserts into the NAGK clefts to form the tight complex. The 2-OG is a key molecule in PII-mediated signal transduction. Crystal structures of S. elongatus wild type PII identified the site of 2-OG binding located in the vicinity of the ATP-binding site between the subunit clefts. The site is formed by the ATP-ligated Mg2+ ion and PII residues of the T-loop itself, which adopts a unique bend conformation. The structures of PII trimers with one or two bound 2-OG molecules explain the anticooperativity of the effector binding sites and demonstrate the inter-subunit communication inside the trimer. PII binds ATP and 2-OG in a synergistic manner, with the ATP-binding sites also accepting ADP. Different ADP/ATP ratios strongly affected the properties of PII signalling including 2-OG binding and interactions with its target proteins. ADP modulates PII signalling to the receptor NAGK primarily at low 2-OG levels and antagonises the inhibitory effect of 2-OG for PII-PipX interaction. Apparently PII has a fine-tuned mechanism of sensing both changing energy charge and carbon/nitrogen balance at the same time.PII Signalproteine spielen eine Schlüsselrole in der Regulation des zellulären Zentralmetabolismus in Bezug auf den Kohlenstoff-, Stickstoff- und Energiestatus der Zelle. Sie binden die Metabolite ATP, ADP und 2-OG (2-Oxoglutarat) und kontrollieren Enzyme, Transporter und Transkriptionsfaktoren, die an Stickstoffmetabolismus beteiligt sind. Abhängig von dem gebundenen Effektormolekül, interagiert PII aus Synechococcus elongatus mit PipX, einen co-Aktivator des Transkriptionsfaktors NtcA, und reguliert das Schlüsselenzym des zyklischen Ornitinwegs, N-Acetyl-L-Glutamatkinase (NAGK). Im Komplex interagieren PII und NAGK unter anderen über eine Salzbrücke zwischen E85 von PII und R233 von NAGK. PII Varianten, die eine Mutation an der Aminosäure 85 haben, verlieren die Fähigkeit mit NAGK zu interagieren. Wir haben zwei PII-Varianten entdeckt, die die NAGK-Variante R233A binden können, obwohl dieses Enzym mit Wildtyp PII nicht interagiert. Aufgrund der Kristallstruktur und biochemischen Analysen von I86N PII, haben wir einen zweistufigen Mechanismus der PII-NAGK-Komplexbildung vorgeschlagen. Außerdem haben wir gezeigt, dass PII und NAGK aus Bakterien (S. elongatus) und Pflanzen (Arabidopsis thaliana) sich gegenseitig in vitro funktionell ersetzen können, was die starke Konservierung von PII-Signaltransduktion demonstriert.
2-Oxoglutarat ist ein zentrales Molekül in der PII-vermittelten Signaltransduktion. Kristallstrukturen von S. elongatus Wildtyp PII haben die 2-OG-Bindungsstelle in der Nähe von der Nukleotidbindungsstelle identifiziert. Die 2-OG-Bindungsstelle wird vom ATP-gebundenen Mg2+-Ion und vom PII-T-loop gebildet. Dabei nimmt dieser Loop eine vorher nicht bekannte Konformation ein. PII-Strukturen mit einem, zwei und drei gebundenen 2-OG Molekülen klären den Mechanismus der antikooperativen Ligandenbindung an PII auf. ATP-Bindungstellen am PII-Protein können auch von ADP besetzt werden. Verschiedene ATP/ADP-Verhältnisse beeinflussen die Signaltransduktioneigenschaften des PII-Proteins. ADP verhindert 2-OG-Bindung an PII und behebt den negativen Effekt von 2-OG auf die PII-PipX-Interaktion. Die PII-Regulation der NAG-Kinase wird durch ADP vor allen bei niedrigen 2-OG-Konzentrationen moduliert. Offensichtlich, spricht PII auf feinste Änderungen bezüglich des Energie- und Kohlenstoff/Stickstoff-Status der Zelle an und verändert entsprechend seine Eigenschaften als Signaltransduktionprotein
The Cellular Roles of the PII-like Protein SbtB and its Effector Molecule 3′,5′-c-di-Adenosine-5′-Monophosphate (c-di-AMP)
No full textThe signaling transduction proteins of the PII superfamily, such as the PII-like protein SbtB,
represent an ancient and exceptionally well-preserved protein family ubiquitously across all
domains of life. Within cyanobacteria, SbtB serves as the main regulator of the carbon
concentrating mechanism (CCM) and inorganic carbon (Ci) acclimation and is co-expressed
from a bicistronic operon with the sodium-dependent bicarbonate transporter (SbtA). SbtB
regulates bicarbonate uptake by direct interaction with all three cyanobacterial bicarbonate
transporters: SbtA, BicA, and BCT1, in response to fluctuations in Ci levels and the adenylate
energy charge (AEC). This study proposes a novel model for SbtB-mediated regulation of SbtA,
emphasizing the significance of the flexible SbtB T-loop structure for this interaction, akin to
the canonical PII T-loop in target protein interactions. In the AMP-bound state, corresponding
to low Ci (LC) supply, SbtB inserts its T-loop into the inter-domain cleft of SbtA, inducing an
inward-open conformation that facilitates substrate secretion into the cytoplasm while
inhibiting backward bicarbonate transport. However, the cellular function of SbtB extends
beyond bicarbonate uptake, significantly impacting central carbon metabolism and Ci
acclimation. In the absence of SbtB in the slr1513 knockout mutant (ΔsbtB), CCM-associated
gene expression, including the master Ci acclimation regulator NdhR, is broadly affected,
resulting in a constitutively LC pre-acclimated state.
In Synechocystis sp. PCC 6803, SbtB has been identified as the primary receptor of the
second messenger, c-di-AMP. The SbtB:c-di-AMP complex regulates glycogen synthesis
through its interaction with the glycogen branching enzyme (GlgB), which is essential for
nighttime cyanobacterial survival.
While SbtB primarily influences cellular functions related to the central carbon metabolism,
c-di-AMP plays a multifaceted role in governing various cellular processes. These encompass
the maintenance of ion homeostasis, notably K+
, Na+
, and Mg2+, thus regulating
osmoprotection. C-di-AMP also exerts control over the central nitrogen metabolism, either
directly or indirectly, by modulating the expression of NtcA, which in turn impacts on the
process of chlorosis. Additionally, c-di-AMP plays a pivotal role in regulating the uptake of
glutamine by regulating the activity of the basic amino acid and glutamine transporter complex
BgtAB. Moreover, it is indispensable for facilitating chromatic acclimation by influencing the
expression of CpcL through Rbp2.Die Dissertation ist gesperrt bis zum 24. Juli 202
Interactions of Cyanobacteria with Predators
No full textAs photosynthetic organisms, Cyanobacteria play a crucial role in ecosystems. They are highly
adaptable and can be found in various habitats. During summer, cyanobacterial blooms, often with
toxin-producing species, pose a threat to humans and animals.
As primary producers, cyanobacteria are attractive prey for predators. Research on predatory
bacteria has gained increasing importance in recent years. However, only a few predatory bacteria
that prey on cyanobacteria are known, and their properties are poorly characterized. The defense
mechanisms of cyanobacteria against predatory bacteria are also unknown.
This work describes the interaction of the filamentous cyanobacterium Anabaena variabilis with
predatory bacteria. Initially, freshwater isolates were screened for predatory bacteria. Six isolates
were selected and examined in more detail using metagenome analysis and microscopy. Lysobacter
brunescens and Candidatus Venantispira tubingensis, a newly discovered bacterium, have been
identified as predatory bacteria of A. variabilis.
Candidatus Venantispira tubingensis belongs to the phylum Bacteroidota and is a representative of
a new genus in the family Saprospiraceae. It forms spiral, multicellular filaments up to 50 µm long
and it and close relatives have been found in Germany, Italy, New Mexico, and Costa Rica.
Venantispira preys on filamentous and unicellular cyanobacteria.
The cell surface of Venantispira carries outer membrane vesicle chains and smaller, possibly
adhesive filaments, which could play a role in the lysis mechanism. Venantispira moves along the
prey filament by alternating forward and backward movements until the prey cells finally lyse. This
mechanism has not yet been described for predatory bacteria.
Venantispira only lyses vegetative cells, while akinetes are not lysed. Therefore, akinetes play a role
in the defense A. variabilis against bacterial predators.
Further research is needed to fully understand the potential of the newly discovered bacterium
Candidatus Venantispira tubingensis. It has a broad prey spectrum and could thus provide a natural
way to control cyanobacterial blooms in freshwater. This could help reduce ecological damage
caused by toxin-producing blooms and protect drinking water reservoirs.Die Dissertation ist gesperrt bis zum 09. September 2026
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