A cyanobacterial sigma factor F controls biofilm-promoting genes through intra- and intercellular pathways.

Cyanobacteria frequently constitute integral components of microbial communities known as phototrophic biofilms, which are widespread in various environments. Moreover, assemblages of these organisms, which serve as an expression platform, simplify harvesting the biomass, thereby holding significant industrial relevance. Previous studies of the model cyanobacterium PCC 7942 revealed that its planktonic growth habit results from a biofilm-suppression mechanism that depends on an extracellular inhibitor, an observation that opens the door to investigating cyanobacterial intercellular communication.

Cell specialization in cyanobacterial biofilm development revealed by expression of a cell-surface and extracellular matrix protein.

Cyanobacterial biofilms are ubiquitous and play important roles in diverse environments, yet, understanding of the processes underlying the development of these aggregates is just emerging. Here we report cell specialization in formation of Synechococcus elongatus PCC 7942 biofilms-a hitherto unknown characteristic of cyanobacterial social behavior. We show that only a quarter of the cell population expresses at high levels the four-gene ebfG-operon that is required for biofilm formation.

Transcriptomic and Phenomic Investigations Reveal Elements in Biofilm Repression and Formation in the Cyanobacterium PCC 7942.

Biofilm formation by photosynthetic organisms is a complex behavior that serves multiple functions in the environment. Biofilm formation in the unicellular cyanobacterium PCC 7942 is regulated in part by a set of small secreted proteins that promotes biofilm formation and a self-suppression mechanism that prevents their expression. Little is known about the regulatory and structural components of the biofilms in PCC 7942, or response to the suppressor signal(s).

Impairment of a cyanobacterial glycosyltransferase that modifies a pilin results in biofilm development.

A biofilm inhibiting mechanism operates in the cyanobacterium Synechococcus elongatus. Here, we demonstrate that the glycosyltransferase homologue, Ogt, participates in the inhibitory process - inactivation of ogt results in robust biofilm formation. Furthermore, a mutational approach shows requirement of the glycosyltransferase activity for biofilm inhibition.

A Cyanobacterial Component Required for Pilus Biogenesis Affects the Exoproteome.

Protein secretion as well as the assembly of bacterial motility appendages are central processes that substantially contribute to fitness and survival. This study highlights distinctive features of the mechanism that serves these functions in cyanobacteria, which are globally prevalent photosynthetic prokaryotes that significantly contribute to primary production. Our studies of biofilm development in the cyanobacterium uncovered a novel component required for the biofilm self-suppression mechanism that operates in this organism.

Solution NMR structure of Se0862, a highly conserved cyanobacterial protein involved in biofilm formation.

Biofilms are accumulations of microorganisms embedded in extracellular matrices that protect against external factors and stressful environments. Cyanobacterial biofilms are ubiquitous and have potential for treatment of wastewater and sustainable production of biofuels. But the underlying mechanisms regulating cyanobacterial biofilm formation are unclear.

An uncultured marine cyanophage encodes an active phycobilisome proteolysis adaptor protein NblA.

Phycobilisomes (PBS) are large water-soluble membrane-associated complexes in cyanobacteria and some chloroplasts that serve as light-harvesting antennae for the photosynthetic apparatus. When deplete of nitrogen or sulphur, cyanobacteria readily degrade their phycobilisomes allowing the cell to replenish these vanishing nutrients. The key regulator in the degradation process is NblA, a small protein (∼6 kDa), which recruits proteases to the PBS.

A microcin processing peptidase-like protein of the cyanobacterium Synechococcus elongatus is essential for secretion of biofilm-promoting proteins.

Small secreted compounds, e.g. microcins, are characterized by a double-glycine (GG) secretion motif that is cleaved off upon maturation.

Nitrogen chlorosis in unicellular cyanobacteria - a developmental program for surviving nitrogen deprivation.

Cyanobacteria evolved sophisticated mechanisms allowing them to cope with environmental depletion of combined nitrogen. Here, we describe progress in understanding the processes involved in acclimation of nondiazotrophic cyanobacteria to nitrogen shortage, known as nitrogen chlorosis. The process includes immediate metabolic changes and degradation of light harvesting complexes as well as long-term acclimation responses.

Decomposition of cyanobacterial light harvesting complexes: NblA-dependent role of the bilin lyase homolog NblB.

Phycobilisomes, the macromolecular light harvesting complexes of cyanobacteria are degraded under nutrient-limiting conditions. This crucial response is required to adjust light excitation to the metabolic status and avoid damage by excess excitation. Phycobilisomes are comprised of phycobiliproteins, apo-proteins that covalently bind bilin chromophores.

Type 4 pili are dispensable for biofilm development in the cyanobacterium Synechococcus elongatus.

The hair-like cell appendages denoted as type IV pili are crucial for biofilm formation in diverse eubacteria. The protein complex responsible for type IV pilus assembly is homologous with the type II protein secretion complex. In the cyanobacterium Synechococcus elongatus PCC 7942, the gene Synpcc7942_2071 encodes an ATPase homologue of type II/type IV systems.

Expanding the Genetic Code of a Photoautotrophic Organism.

The photoautotrophic freshwater cyanobacterium Synechococcus elongatus is widely used as a chassis for biotechnological applications as well as a photosynthetic bacterial model. In this study, a method for expanding the genetic code of this cyanobacterium has been established, thereby allowing the incorporation of unnatural amino acids into proteins. This was achieved through UAG stop codon suppression, using an archaeal pyrrolysyl orthogonal translation system.

Small secreted proteins enable biofilm development in the cyanobacterium Synechococcus elongatus.

Small proteins characterized by a double-glycine (GG) secretion motif, typical of secreted bacterial antibiotics, are encoded by the genomes of diverse cyanobacteria, but their functions have not been investigated to date. Using a biofilm-forming mutant of Synechococcus elongatus PCC 7942 and a mutational approach, we demonstrate the involvement of four small secreted proteins and their GG-secretion motifs in biofilm development. These proteins are denoted EbfG1-4 (enable biofilm formation with a GG-motif).

The proteolysis adaptor, NblA, is essential for degradation of the core pigment of the cyanobacterial light-harvesting complex.

The cyanobacterial light-harvesting complex, the phycobilisome, is degraded under nutrient limitation, allowing the cell to adjust light absorbance to its metabolic capacity. This large light-harvesting antenna comprises a core complex of the pigment allophycocyanin, and rod-shaped pigment assemblies emanating from the core. NblA, a low-molecular-weight protein, is essential for degradation of the phycobilisome.

To be or not to be planktonic? Self-inhibition of biofilm development.

The transition between planktonic growth and biofilm formation represents a tightly regulated developmental shift that has substantial impact on cell fate. Here, we highlight different mechanisms through which bacteria limit their own biofilm development. The mechanisms involved in these self-inhibition processes include: (i) regulation by secreted small molecules, which govern intricate signalling cascades that eventually decrease biofilm development, (ii) extracellular polysaccharides capable of modifying the physicochemical properties of the substratum and (iii) extracellular DNA that masks an adhesive structure.

Collapsing aged culture of the cyanobacterium Synechococcus elongatus produces compound(s) toxic to photosynthetic organisms.

Phytoplankton mortality allows effective nutrient cycling, and thus plays a pivotal role in driving biogeochemical cycles. A growing body of literature demonstrates the involvement of regulated death programs in the abrupt collapse of phytoplankton populations, and particularly implicates processes that exhibit characteristics of metazoan programmed cell death. Here, we report that the cell-free, extracellular fluid (conditioned medium) of a collapsing aged culture of the cyanobacterium Synechococcus elongatus is toxic to exponentially growing cells of this cyanobacterium, as well as to a large variety of photosynthetic organisms, but not to eubacteria.

The proteolysis adaptor, NblA, initiates protein pigment degradation by interacting with the cyanobacterial light-harvesting complexes.

Degradation of the cyanobacterial protein pigment complexes, the phycobilisomes, is a central acclimation response that controls light energy capture. The small protein, NblA, is essential for proteolysis of these large complexes, which may reach a molecular mass of up to 4 MDa. Interactions of NblA in vitro supported the suggestion that NblA is a proteolysis adaptor that labels the pigment proteins for degradation.

Self-suppression of biofilm formation in the cyanobacterium Synechococcus elongatus.

Biofilms are consortia of bacteria that are held together by an extracellular matrix. Cyanobacterial biofilms, which are highly ubiquitous and inhabit diverse niches, are often associated with biological fouling and cause severe economic loss. Information on the molecular mechanisms underlying biofilm formation in cyanobacteria is scarce.

Nutrient-associated elongation and asymmetric division of the cyanobacterium Synechococcus PCC 7942.

While tightly regulated, bacterial cell morphology may change substantially in response to environmental cues. Here we describe such changes in the cyanobacterium Synechococcus sp. strain PCC7942.

The role of the PsbU subunit in the light sensitivity of PSII in the cyanobacterium Synechococcus 7942.

In the present study we investigated the role of the PsbU subunit in the electron transport characteristics and light sensitivity of the Photosystem II complex. The experiments were performed by using an earlier characterized PsbU-less mutant of the cyanobacterium Synechococcus PCC 7942, which has enhanced antioxidant capacity (Balint et al. FEBS Lett.

Structural, functional, and mutational analysis of the NblA protein provides insight into possible modes of interaction with the phycobilisome.

The enormous macromolecular phycobilisome antenna complex (>4 MDa) in cyanobacteria and red algae undergoes controlled degradation during certain forms of nutrient starvation. The NblA protein (approximately 6 kDa) has been identified as an essential component in this process. We have used structural, biochemical, and genetic methods to obtain molecular details on the mode of action of the NblA protein.

Thylakoid membrane perforations and connectivity enable intracellular traffic in cyanobacteria.

Cyanobacteria, the progenitors of plant and algal chloroplasts, enabled aerobic life on earth by introducing oxygenic photosynthesis. In most cyanobacteria, the photosynthetic membranes are arranged in multiple, seemingly disconnected, concentric shells. In such an arrangement, it is unclear how intracellular trafficking proceeds and how different layers of the photosynthetic membranes communicate with each other to maintain photosynthetic homeostasis.

Crystallization of sparingly soluble stress-related proteins from cyanobacteria by controlled urea solublization.

The phycobilisome photosynthetic antenna complex, found in cyanobacteria and red-algae, interacts with proteins expressed specifically to deal with different forms of physiological stress. Under conditions of nutrient starvation, the NblA protein is required for the process that leads to phycobilisome degradation and bleaching of the cells. HspA, a 16.

Alanine dehydrogenase activity is required for adequate progression of phycobilisome degradation during nitrogen starvation in Synechococcus elongatus PCC 7942.

Degradation of the cyanobacterial light-harvesting antenna, the phycobilisome, is a general acclimation response that is observed under various stress conditions. In this study we identified a novel mutant of Synechococcus elongatus PCC 7942 that exhibits impaired phycobilisome degradation specifically during nitrogen starvation, unlike previously described mutants, which exhibit aberrant degradation under nitrogen, sulfur, and phosphorus starvation conditions. The phenotype of the new mutant, AldOmega, results from inactivation of ald (encoding alanine dehydrogenase).