Search Results (45)

Cyanobacteria negatively affect zooplankton through several mechanisms including mechanical interference, toxicity, and poor food quality due to a shortage of essential lipids. To understand the nature of each of these mechanisms, they should be examined independently. The goal of our study was to assess the influence of cyanobacteria food quality on the competitive outcomes between the small-bodied Daphnia longispina and the large-bodied Daphnia magna. We conducted life-table experiments to assess R* (population threshold food concentration), competition experiments to determine the outcome of competition, and computer simulation experiments at high levels of food supply, which are difficult to realize in laboratory conditions. We used two types of food: the high-quality green algae Chlamydomonas klinobasis (GREEN) and the cyanobacterium Synechococcus elongatus (CYANO), which contains low levels of essential lipids, but is non-toxic and unicellular. We found that the small-bodied D. longispina was a superior competitor in GREEN, while the large-bodied D. magna was more abundant in CYANO. We established that the species ratio in GREEN was dependent on competitive interaction, while abundances of daphnids in CYANO were controlled by poor food quality. Since cyanobacteria act as a powerful force for structuring cladoceran communities, the role of competition for food between these two Daphnia species greatly declined under their effects. Full article

Solar photovoltaic technology has consistently been regarded as a crucial direction for the development of clean energy systems in the future. Bio-photovoltaics (BPV), an emerging solar energy utilization technology, is mainly based on the photosynthesis process of photoautotrophic organisms to convert solar energy into electrical energy and output a photocurrent via extracellular electron transfer. As the fundamental unit of the bio-photovoltaic system, the stability of photosynthetic microorganisms under fluctuating and stressful light and heat conditions is likely to have a significant influence on the efficiency of bio-photovoltaic devices. However, this aspect has often been overlooked in previous bio-photovoltaics research. This study took an important cyanobacteria chassis strain, Synechococ elongatus PCC 7942, as the model organism and explored the impact of physiological robustness optimization on its performance as a bio-photovoltaic functional unit. In this work, two types of BPV systems, namely the suspension mode and the biofilm attachment mode, were assembled to evaluate the electricity-generating activity of Synechococcus cells. Overall, the latter demonstrated a remarkable photoelectric output performance. When its light and temperature tolerance was enhanced through FoF1-ATP synthase engineering, the optimized Synechococcus strain exhibited stronger photosynthetic physiology and photoelectric output activity. Under the condition of a light intensity of 2400 μmol photons/m²/s, the maximum photocurrent output of the Synechococcus-based BPV device was increased significantly by 41% over the system based on the wild-type control strain. The results of this study provided a new perspective for the future development and optimization of bio-photovoltaics. Full article

Cyanobacterial cytochrome c6 (Cyt c6) is crucial for electron transfer between the cytochrome b6f complex and photosystem I (PSI), playing a key role in photosynthesis and enhancing adaptation to extreme environments. This study investigates the high-resolution crystal structures of Cyt c6 from Synechococcus elongatus PCC 7942 and Synechocystis PCC 6803, focusing on its dimerization mechanisms and functional implications for photosynthesis. Cyt c6 was expressed in Escherichia coli using a dual-plasmid co-expression system and characterized in both oxidized and reduced states. X-ray crystallography revealed three distinct crystal forms, with asymmetric units containing 2, 4, or 12 molecules, all of which consist of repeating dimeric structures. Structural comparisons across species indicated that dimerization predominantly occurs through hydrophobic interactions within a conserved motif around the heme crevice, despite notable variations in dimer positioning. We propose that the dimerization of Cyt c6 enhances structural stability, optimizes electron transfer kinetics, and protects the protein from oxidative damage. Furthermore, we used AlphaFold3 to predict the structure of the PSI-Cyt c6 complex, revealing specific interactions that may facilitate efficient electron transfer. These findings provide new insights into the functional role of Cyt c6 dimerization and its contribution to improving cyanobacterial photosynthetic electron transport. Full article

Microalgae and cyanobacteria are photosynthetic microorganisms with significant biotechnological potential for the production of bioactive compounds, making them a promising resource for diverse industrial applications. This study presents the development and validation of a modular, droplet-based microfluidic photobioreactor (µPBR) designed for high-throughput screening and cultivation under controlled light conditions. The µPBR, based on polytetrafluoroethylene (PTFE) tubing and a 4-channel LED illumination system, enables precise modulation of light intensity, wavelength, and photoperiod, facilitating dose–response experiments. Synechococcus elongatus UTEX 2973 and Chlorella vulgaris were used to demonstrate the system’s capacity to support photosynthetic growth under various conditions. The results indicate that continuous illumination, particularly under blue and mixed blue-red light, promotes higher autofluorescence and chlorophyll a content in cyanobacteria Synechococcus elongatus UTEX2973, while Chlorella vulgaris achieved optimal growth under a 16:8 light-dark cycle with moderate light intensity. This µPBR offers not only a flexible, scalable platform for optimizing growth parameters but also allows for the investigation of highly resolved dose response screenings of environmental stressors such as salinity. The presented findings highlight its potential for advancing microalgal biotechnology research and applications. Full article

Under standard laboratory conditions, Synechococcus elongatus PCC 7942 lacks EcaA^Syn, a periplasmic carbonic anhydrase (CA). In this study, a S. elongatus transformant was created that expressed the homologous EcaA^Cya from Cyanothece sp. ATCC 51142. This additional external CA had no discernible effect on the adaptive responses and physiology of cells exposed to changes similar to those found in S. elongatus natural habitats, such as fluctuating CO₂ and HCO₃⁻ concentrations and ratios, oxidative or light stress, and high CO₂. The transformant had a disadvantage over wild-type cells under certain conditions (Na⁺ depletion, a reduction in CO₂). S. elongatus cells lacked their own EcaA^Syn in all experimental conditions. The results suggest the presence in S. elongatus of mechanisms that limit the appearance of EcaA^Syn in the periplasm. For the first time, we offer data on the expression pattern of CCM-associated genes during S. elongatus adaptation to CO₂ replacement with HCO₃⁻, as well as cell transfer to high CO₂ levels (up to 100%). An increase in CO₂ concentration coincides with the suppression of the NDH-1₄ system, which was previously thought to function constitutively. Full article

Yeast two-hybrid approaches, which are based on fusion proteins that must co-localise to the nucleus to reconstitute the transcriptional activity of GAL4, have greatly contributed to our understanding of the nitrogen interaction network of cyanobacteria, the main hubs of which are the trimeric PII and the monomeric PipX regulators. The bacterial two-hybrid system, based on the reconstitution in the E. coli cytoplasm of the adenylate cyclase of Bordetella pertussis, should provide a relatively faster and presumably more physiological assay for cyanobacterial proteins than the yeast system. Here, we used the bacterial two-hybrid system to gain additional insights into the cyanobacterial PipX interaction network while simultaneously assessing the advantages and limitations of the two most popular two-hybrid systems. A comprehensive mutational analysis of PipX and bacterial two-hybrid assays were performed to compare the outcomes between yeast and bacterial systems. We detected interactions that were previously recorded in the yeast two-hybrid system as negative, as well as a “false positive”, the self-interaction of PipX, which is rather an indirect interaction that is dependent on PII homologues from the E. coli host, a result confirmed by Western blot analysis with relevant PipX variants. This is, to our knowledge, the first report of the molecular basis of a false positive in the bacterial two-hybrid system. Full article

The conserved cyanobacterial protein PipX is part of a complex interaction network with regulators involved in essential processes that include metabolic homeostasis and ribosome assembly. Because PipX interactions depend on the relative levels of their different partners and of the effector molecules binding to them, in vivo studies are required to understand the physiological significance and contribution of environmental factors to the regulation of PipX complexes. Here, we have used the NanoBiT complementation system to analyse the regulation of complex formation in Synechococcus elongatus PCC 7942 between PipX and each of its two best-characterized partners, PII and NtcA. Our results confirm previous in vitro analyses on the regulation of PipX-PII and PipX-NtcA complexes by 2-oxoglutarate and on the regulation of PipX-PII by the ATP/ADP ratio, showing the disruption of PipX-NtcA complexes due to increased levels of ADP-bound PII in Synechococcus elongatus. The demonstration of a positive role of PII on PipX-NtcA complexes during their initial response to nitrogen starvation or the impact of a PipX point mutation on the activity of PipX-PII and PipX-NtcA reporters are further indications of the sensitivity of the system. This study reveals additional regulatory complexities in the PipX interaction network, opening a path for future research on cyanobacteria. Full article

The sesquiterpene β-caryophyllene (BCP) is a major component of various plant essential oils, to which it confers a unique spicy aroma. It is mainly used as a fragrance additive in the food, cosmetic and perfume industries, with an annual consumption ranging between 100 and 1000 metric tons worldwide. Recently, BCP has attracted attention as a promising precursor for the production of high-density fuels and for its various biological activities and pharmacological effects. These include antioxidant, anti-inflammatory, anticancer, immune–modulatory, and many other activities. Due to its underlying mechanisms, β-caryophyllene interacts with various human receptors, including CB2 of the endocannabinoid system, which defines it as a phytocannabinoid with therapeutic potential for certain serious conditions. Due to β-caryophyllene’s high utility, various green and sustainable strategies for its production in microorganisms have been developed. This article provides an update on the state-of-the-art in this field to identify directions for further development to extend the compound’s potential. Full article

The cyanobacterial strain Cyanobacterium sp. IPPAS B-1200 isolated from Lake Balkhash is characterized by high relative amounts of myristic (30%) and myristoleic (10%) acids. The remaining fatty acids (FAs) are represented mainly by palmitic (20%) and palmitoleic (40%) acids. We expressed the genes for lysophosphatidic acid acyltransferase (LPAAT; EC 2.3.1.51) and Δ9 fatty acid desaturase (FAD; EC 1.14.19.1) from Cyanobacterium sp. IPPAS B-1200 in Synechococcus elongatus PCC 7942, which synthesizes myristic and myristoleic acids at the level of 0.5–1% and produces mainly palmitic (~60%) and palmitoleic (35%) acids. S. elongatus cells that expressed foreign LPAAT synthesized myristic acid at 26%, but did not produce myristoleic acid, suggesting that Δ9-FAD of S. elongatus cannot desaturate FAs with chain lengths less than C16. Synechococcus cells that co-expressed LPAAT and Δ9-FAD of Cyanobacterium synthesized up to 45% palmitoleic and 9% myristoleic acid, suggesting that Δ9-FAD of Cyanobacterium is capable of desaturating saturated acyl chains of any length. Full article

Phycosphere niches host rich microbial consortia that harbor dynamic algae–bacteria interactions with fundamental significance in varied natural ecosystems. Hence, culturing the uncultured microbial majority of the phycosphere microbiota is vital for deep understanding of the intricate mechanisms governing the dynamic interactions, and also to provide novel and rich microbial resources, and to discover new natural bioactive metabolites. Synechococcus elongatus PCC 7942 is a robust model cyanobacterium widely used in environment, synthesis biology, and biotechnology research. To expand the number of novel phycosphere species that were brought into culture and to discover the natural bioactivities, we presented a new yellow-pigmented bacterium named ABI-127-1, which was recovered from the phycosphere of PCC 7942, using an optimized bacterial isolation procedure. Combined polyphasic taxonomic and phylogenomic characterization was performed to confidently identify the new isolate as a potential novel species belonging to the genus Qipengyuania. The observed bioactivity of strain ABI-127-1 with promoting potential towards the growth and CO₂ fixation efficiency of the host microalgae was measured. Additionally, the bacterial production of active bioflocculant exopolysaccharides was evaluated after culture optimization. Thus, these findings revealed the potential environmental and biotechnological implications of this new microalgae growth-promoting bacterium isolated from the phycosphere microenvironment. Full article

Cyanobacteria were among the oldest organisms to undertake oxygenic photosynthesis and have an essential impact on the atmosphere and carbon/nitrogen cycles on the planet. The thylakoid membrane of cyanobacteria represents an intricate compartment that houses a variety of multi-component (pigment–)protein complexes, assembly factors, and regulators, as well as transporters involved in photosynthetic light reactions, and respiratory electron transport. How these protein components are incorporated into membranes during thylakoid formation and how individual complexes are regulated to construct the functional machinery remains elusive. Here, we carried out an in-depth statistical analysis of the thylakoid proteome data obtained during light-induced thylakoid membrane biogenesis in the model cyanobacterium Synechococcus elongatus PCC 7942. A total of 1581 proteins were experimentally quantified, among which 457 proteins demonstrated statistically significant variations in abundance at distinct thylakoid biogenesis stages. Gene Ontology and KEGG enrichment analysis revealed that predominantly photosystems, light-harvesting antennae, ABC transporters, and pathway enzymes involved in oxidative stress responses and protein folding exhibited notable alternations in abundance between high light and growth light. Moreover, through cluster analysis the 1581 proteins were categorized into six distinct clusters that have significantly different trajectories of the change in their abundance during thylakoid development. Our study provides insights into the physiological regulation for the membrane integration of protein components and functionally linked complexes during the cyanobacterial TM biogenesis process. The findings and analytical methodologies developed in this study may be valuable for studying the global responses of TM biogenesis and photosynthetic acclimation in plants and algae. Full article

Cyanobacteria, microorganisms performing oxygenic photosynthesis, must adapt their metabolic processes to environmental challenges such as day and night changes. PipX, a unique regulatory protein from cyanobacteria, provides a mechanistic link between the signalling protein PII, a widely conserved (in bacteria and plants) transducer of carbon/nitrogen/energy richness, and the transcriptional regulator NtcA, which controls a large regulon involved in nitrogen assimilation. PipX is also involved in translational regulation through interaction with the ribosome-assembly GTPase EngA. However, increases in the PipX/PII ratio are toxic, presumably due to the abnormally increased binding of PipX to other partner(s). Here, we present mutational and structural analyses of reported PipX-PII and PipX-NtcA complexes, leading to the identification of single amino acid changes that decrease or abolish PipX toxicity. Notably, 4 out of 11 mutations decreasing toxicity did not decrease PipX levels, suggesting that the targeted residues (F12, D23, L36, and R54) provide toxicity determinants. In addition, one of those four mutations (D23A) argued against the over-activation of NtcA as the cause of PipX toxicity. Most mutations at residues contacting PII decreased PipX levels, indicating that PipX stability would depend on its ability to bind to PII, a conclusion supported by the light-induced decrease of PipX levels in Synechococcus elongatus PCC7942 (hereafter S. elongatus). Full article

Due to their unique biochemical and spectroscopic properties, both heme and phycocyanobilin are widely applied in the medical and food industries. Synechocystis sp. PCC 6803 contains both heme and phycocyanin, and is capable of synthesizing phycocyanin using heme as a precursor. The aim of this study was to uncover viable metabolic targets in the porphyrin pathway from Synechocystis sp. PCC 6803 to promote the accumulation of heme and phycocyanin in the recombinant strains of microalgae. A total of 10 genes related to heme synthesis pathway derived from Synechococcus elongatus PCC 7942 and 12 genes related to endogenous heme synthesis were individually overexpressed in strain PCC 6803. The growth rate and pigment content (heme, phycocyanin, chlorophyll a and carotenoids) of 22 recombinant algal strains were characterized. Quantitative real-time PCR technology was used to investigate the molecular mechanisms underlying the changes in physiological indicators in the recombinant algal strains. Among the 22 mutant strains, the mutant overexpressing the haemoglobin gene (glbN) of strain PCC 6803 had the highest heme content, which was 2.5 times higher than the wild type; the mutant overexpressing the gene of strain PCC 7942 (hemF) had the highest phycocyanin content, which was 4.57 times higher than the wild type. Overall, the results suggest that genes in the porphyrin pathway could significantly affect the heme and phycocyanin content in strain PCC 6803. Our study provides novel crucial targets for promoting the accumulation of heme and phycocyanin in cyanobacteria. Full article

Genome streamlining, as a natural process in the evolution of microbes, has become a common approach for generating ideal chassis cells for synthetic biology studies and industrial applications. However, systematic genome reduction remains a bottleneck in the generation of such chassis cells with cyanobacteria, due to very time-consuming genetic manipulations. Synechococcus elongatus PCC 7942, a unicellular cyanobacterium, is a candidate for systematic genome reduction, as its essential and nonessential genes have been experimentally identified. Here, we report that at least 20 of the 23 over 10 kb nonessential gene regions could be deleted and that stepwise deletions of these regions could be achieved. A septuple-deletion mutant (genome reduced by 3.8%) was generated, and the effects of genome reduction on the growth and genome-wide transcription were investigated. In the ancestral triple to sextuple mutants (b, c, d, e1), an increasingly large number of genes (up to 998) were upregulated relative to the wild type, while slightly fewer genes (831) were upregulated in the septuple mutant (f). In a different sextuple mutant (e2) derived from the quintuple mutant d, much fewer genes (232) were upregulated. Under the standard conditions in this study, the mutant e2 showed a higher growth rate than the wild type, e1 and f. Our results indicate that it is feasible to extensively reduce the genomes of cyanobacteria for generation of chassis cells and for experimental evolutionary studies. Full article

Form I rubiscos evolved in Cyanobacteria ≥ 2.5 billion years ago and are enzymatically unique due to the presence of small subunits (RbcS) capping both ends of an octameric large subunit (RbcL) rubisco assembly to form a hexadecameric (L₈S₈) holoenzyme. Although RbcS was previously thought to be integral to Form I rubisco stability, the recent discovery of a closely related sister clade of octameric rubiscos (Form I’; L₈) demonstrates that the L₈ complex can assemble without small subunits (Banda et al. 2020). Rubisco also displays a kinetic isotope effect (KIE) where the 3PG product is depleted in ¹³C relative to ¹²C. In Cyanobacteria, only two Form I KIE measurements exist, making interpretation of bacterial carbon isotope data difficult. To aid comparison, we measured in vitro the KIEs of Form I’ (Candidatus Promineofilum breve) and Form I (Synechococcus elongatus PCC 6301) rubiscos and found the KIE to be smaller in the L₈ rubisco (16.25 ± 1.36‰ vs. 22.42 ± 2.37‰, respectively). Therefore, while small subunits may not be necessary for protein stability, they may affect the KIE. Our findings may provide insight into the function of RbcS and allow more refined interpretation of environmental carbon isotope data. Full article