Plants, algae, and cyanobacteria fix carbon dioxide to organic carbon with the Calvin–Benson (CB) cycle. Phosphoribulokinase (PRK) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) are essential ...CB-cycle enzymes that control substrate availability for the carboxylation enzyme Rubisco. PRK consumes ATP to produce the Rubisco substrate ribulose bisphosphate (RuBP). GAPDH catalyzes the reduction step of the CB cycle with NADPH to produce the sugar glyceraldehyde 3-phosphate (GAP), which is used for regeneration of RuBP and is the main exit point of the cycle. GAPDH and PRK are coregulated by the redox state of a conditionally disordered protein CP12, which forms a ternary complex with both enzymes. However, the structural basis of CB-cycle regulation by CP12 is unknown. Here, we show how CP12 modulates the activity of both GAPDH and PRK. Using thermophilic cyanobacterial homologs, we solve crystal structures of GAPDH with different cofactors and CP12 bound, and the ternary GAPDH-CP12-PRK complex by electron cryo-microscopy, we reveal that formation of the N-terminal disulfide preorders CP12 prior to binding the PRK active site, which is resolved in complex with CP12. We find that CP12 binding to GAPDH influences substrate accessibility of all GAPDH active sites in the binary and ternary inhibited complexes. Our structural and biochemical data explain how CP12 integrates responses from both redox state and nicotinamide dinucleotide availability to regulate carbon fixation.
► First report on hongdechloris, a Chl f-containing filamentous cyanobacterium. ► The fluorescence emission peak of 748nm was identified as due to Chl f. ► Chl f is a red-light induced chlorophyll.
A ...Chl f-containing filamentous cyanobacterium was purified from stromatolites and named as Halomicronema hongdechloris gen., sp. nov. after its phylogenetic classification and the morphological characteristics. Hongdechloris contains four main carotenoids and two chlorophylls, a and f. The ratio of Chl f to Chl a is reversibly changed from 1:8 under red light to an undetectable level of Chl f under white-light culture conditions. Phycobiliproteins were induced under white light growth conditions. A fluorescence emission peak of 748nm was identified as due to Chl f. The results suggest that Chl f is a red-light inducible chlorophyll.
The origin of oxygenic photosynthesis in Cyanobacteria led to the rise of oxygen on Earth ~2.3 billion years ago, profoundly altering the course of evolution by facilitating the development of ...aerobic respiration and complex multicellular life. Here we report the genomes of 41 uncultured organisms related to the photosynthetic Cyanobacteria (class Oxyphotobacteria), including members of the class Melainabacteria and a new class of Cyanobacteria (class Sericytochromatia) that is basal to the Melainabacteria and Oxyphotobacteria. All members of the Melainabacteria and Sericytochromatia lack photosynthetic machinery, indicating that phototrophy was not an ancestral feature of the Cyanobacteria and that Oxyphotobacteria acquired the genes for photosynthesis relatively late in cyanobacterial evolution. We show that all three classes independently acquired aerobic respiratory complexes, supporting the hypothesis that aerobic respiration evolved after oxygenic photosynthesis.
Photosynthesis evolved in eukaryotes by the endosymbiosis of a cyanobacterium, the future plastid, within a heterotrophic host. This primary endosymbiosis occurred in the ancestor of Archaeplastida, ...a eukaryotic supergroup that includes glaucophytes, red algae, green algae, and land plants 1–4. However, although the endosymbiotic origin of plastids from a single cyanobacterial ancestor is firmly established, the nature of that ancestor remains controversial: plastids have been proposed to derive from either early- or late-branching cyanobacterial lineages 5–11. To solve this issue, we carried out phylogenomic and supernetwork analyses of the most comprehensive dataset analyzed so far including plastid-encoded proteins and nucleus-encoded proteins of plastid origin resulting from endosymbiotic gene transfer (EGT) of primary photosynthetic eukaryotes, as well as wide-ranging genome data from cyanobacteria, including novel lineages. Our analyses strongly support that plastids evolved from deep-branching cyanobacteria and that the present-day closest cultured relative of primary plastids is Gloeomargarita lithophora. This species belongs to a recently discovered cyanobacterial lineage widespread in freshwater microbialites and microbial mats 12, 13. The ecological distribution of this lineage sheds new light on the environmental conditions where the emergence of photosynthetic eukaryotes occurred, most likely in a terrestrial-freshwater setting. The fact that glaucophytes, the first archaeplastid lineage to diverge, are exclusively found in freshwater ecosystems reinforces this hypothesis. Therefore, not only did plastids emerge early within cyanobacteria, but the first photosynthetic eukaryotes most likely evolved in terrestrial-freshwater settings, not in oceans as commonly thought.
•Plastids branch early in the cyanobacterial tree•Gloeomargarita-like cyanobacteria are the closest modern relatives of plastids•The first eukaryotic algae most likely evolved in freshwater environments
Ponce-Toledo et al. report extensive phylogenomic analyses supporting the idea that plastids derive from early-branching cyanobacteria related to the extant lineage including the cultured species Gloeomargarita lithophora. Based on their ecological distribution, primary photosynthetic eukaryotes probably originated in freshwater or terrestrial environments.
Summary
Human activities are causing a global proliferation of cyanobacterial harmful algal blooms (CHABs), yet we have limited understanding of how these events affect freshwater bacterial ...communities. Using weekly data from western Lake Erie in 2014, we investigated how the cyanobacterial community varied over space and time, and whether the bloom affected non‐cyanobacterial (nc‐bacterial) diversity and composition. Cyanobacterial community composition fluctuated dynamically during the bloom, but was dominated by Microcystis and Synechococcus OTUs. The bloom's progression revealed potential impacts to nc‐bacterial diversity. Nc‐bacterial evenness displayed linear, unimodal, or no response to algal pigment levels, depending on the taxonomic group. In addition, the bloom coincided with a large shift in nc‐bacterial community composition. These shifts could be partitioned into components predicted by pH, chlorophyll a, temperature, and water mass movements. Actinobacteria OTUs showed particularly strong correlations to bloom dynamics. AcI‐C OTUs became more abundant, while acI‐A and acI‐B OTUs declined during the bloom, providing evidence of niche partitioning at the sub‐clade level. Thus, our observations in western Lake Erie support a link between CHABs and disturbances to bacterial community diversity and composition. Additionally, the short recovery of many taxa after the bloom indicates that bacterial communities may exhibit resilience to CHABs.
Photosystems I and II convert solar energy into the chemical energy that powers life. Chlorophyll a photochemistry, using red light (680 to 700 nm), is near universal and is considered to define the ...energy "red limit" of oxygenic photosynthesis. We present biophysical studies on the photosystems from a cyanobacterium grown in far-red light (750 nm). The few long-wavelength chlorophylls present are well resolved from each other and from the majority pigment, chlorophyll a. Charge separation in photosystem I and II uses chlorophyll f at 745 nm and chlorophyll f (or d) at 727 nm, respectively. Each photosystem has a few even longer-wavelength chlorophylls f that collect light and pass excitation energy uphill to the photochemically active pigments. These photosystems function beyond the red limit using far-red pigments in only a few key positions.
Molecular surveys of aphotic habitats have indicated the presence of major uncultured lineages phylogenetically classified as members of the Cyanobacteria. One of these lineages has recently been ...proposed as a nonphotosynthetic sister phylum to the Cyanobacteria, the Melainabacteria, based on recovery of population genomes from human gut and groundwater samples. Here, we expand the phylogenomic representation of the Melainabacteria through sequencing of six diverse population genomes from gut and bioreactor samples supporting the inference that this lineage is nonphotosynthetic, but not the assertion that they are strictly fermentative. We propose that the Melainabacteria is a class within the phylogenetically defined Cyanobacteria based on robust monophyly and shared ancestral traits with photosynthetic representatives. Our findings are consistent with theories that photosynthesis occurred late in the Cyanobacteria and involved extensive lateral gene transfer and extends the recognized functionality of members of this phylum.
Cyanobacteria are a group of oxygenic phototrophs that have existed for at least 3.5 Ga. Photosynthetic CO sub(2) assimilation by cyanobacteria occurs via the Calvin cycle, with RuBisCO, its key ...enzyme, having very low affinity to CO sub(2). This is due to the fact that atmospheric CO sub(2) concentration in Archaean, when the photosynthetic apparatus evolved, was several orders higher than now. Later, in the epoch of Precambrian microbial communities, CO sub(2) content in the atmosphere decreased drastically. Thus, present-day phototrophs, including cyanobacteria, require adaptive mechanisms for efficient photosynthesis. In cyanobacterial cells, this function is performed by the CO sub(2)-concentrating mechanism (CCM), which creates elevated CO sub(2) concentrations in the vicinity of RuBisCO active centers, thus significantly increasing the rate of CO sub(2) fixation in the Calvin cycle. CCM has been previously studied only for freshwater and marine cyanobacteria. We were the first to investigate CCM in haloalkaliphilic cyanobacteria from soda lakes. Extremophilic haloalkaliphilic cyanobacteria were shown to possess a well-developed CCM with the structure and functional principles similar to those of freshwater and marine strains. Analysis of available data suggests that regulation of the amount of inorganic carbon transported into the cell is probably the general CCM function under these conditions.
Climate change scenarios predict that rivers, lakes, and reservoirs will experience increased temperatures, more intense and longer periods of thermal stratification, modified hydrology, and altered ...nutrient loading. These environmental drivers will have substantial effects on freshwater phytoplankton species composition and biomass, potentially favouring cyanobacteria over other phytoplankton. In this Review, we examine how several cyanobacterial eco-physiological traits, specifically, the ability to grow in warmer temperatures; buoyancy; high affinity for, and ability to store, phosphorus; nitrogen-fixation; akinete production; and efficient light harvesting, vary amongst cyanobacteria genera and may enable them to dominate in future climate scenarios. We predict that spatial variation in climate change will interact with physiological variation in cyanobacteria to create differences in the dominant cyanobacterial taxa among regions. Finally, we suggest that physiological traits specific to different cyanobacterial taxa may favour certain taxa over others in different regions, but overall, cyanobacteria as a group are likely to increase in most regions in the future.
► Climate change is predicted to favour cyanobacteria over other phytoplankton in freshwater ecosystems. ► We examined how cyanobacterial physiology may provide a competitive advantage. ► Different taxa, because of their traits, will respond to different aspects of changed climate. ► Cyanobacteria will most likely increase, but with noted taxa and geographical differences.
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