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Algae play critical roles in the carbon dioxide (CO 2 ) exchange between the water bodies and the atmosphere. However, the effects of prokaryotic and eukaryotic algae on carbon utilization, CO 2 flux, and the underlying mechanisms remain poorly understood. Therefore, this study investigated the differences in carbon preferences and CO 2 fluxes under different algal dominance days. Our research revealed that dissolved inorganic carbon (DIC) concentration fluctuations had a limited effect on the relative abundance of algae. However, shifts in dominant algal phyla induced changes in DIC, with Cyanobacteria preferring HCO 3 - and Chlorophyta preferring CO 2 sinks compared with that of Cyanobacteria. During the Cyanobacteria dominance days, the lower DIC concentration did not result in a reduction in CO 2 emissions. However, increases in the dissolved organic carbon concentration provided a favorable environment for Cyanobacteria, which promoted CO 2 emissions. However, increases in the dissolved organic carbon concentration provided a favorable environment for Cyanobacteria, which promoted CO 2 emissions. The CCM model indicated that the growth of Chlorophyta resulted in CO 2 leakage rates up to 0.97 times lower compared to Cyanobacteria, accelerating CO 2 leakage rates up to 0.97 times lower compared to Cyanobacteria, accelerating CO 2 sink was stronger on Chlorophyta dominance days than on Cyanobacteria dominance days. This study emphasized the influence of algal phyla on CO 2 sink was stronger on Chlorophyta dominance days than on Cyanobacteria dominance days. This study emphasized the influence of algal phyla on CO 2 fluxes, revealing the significant CO 2 sink associated with Chlorophyta. Further research should investigate how to manipulate environmental factors to favor Chlorophyta growth and effectively reduce CO 2 emissions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The PII superfamily consists of widespread signal transduction proteins found in all domains of life. In addition to canonical PII proteins involved in C/N sensing, structurally similar PII-like proteins evolved to fulfill diverse, yet poorly understood cellular functions. In cyanobacteria, the bicarbonate transporter SbtA is co-transcribed with the conserved PII-like protein, SbtB, to augment intracellular inorganic carbon levels for efficient CO 2 fixation. We identified SbtB as a sensor of various adenine nucleotides including the second messenger nucleotides cyclic AMP (cAMP) and c-di-AMP. Moreover, many SbtB proteins possess a C-terminal extension with a disulfide bridge of potential redox-regulatory function, which we call R-loop. Here, we reveal an unusual ATP/ADP apyrase (diphosphohydrolase) activity of SbtB that is controlled by the R-loop. We followed the sequence of hydrolysis reactions from ATP over ADP to AMP in crystallographic snapshots and unravel the structural mechanism by which changes of the R-loop redox state modulate apyrase activity. We further gathered evidence that this redox state is controlled by thioredoxin, suggesting that it is generally linked to cellular metabolism, which is supported by physiological alterations in site-specific mutants of the SbtB protein. Finally, we present a refined model of how SbtB regulates SbtA activity, in which both the apyrase activity and its redox regulation play a central role. This highlights SbtB as a central switch point in cyanobacterial cell physiology, integrating not only signals from the energy state (adenyl-nucleotide binding) and the carbon supply via cAMP binding but also from the day/night status reported by the C-terminal redox switch.

Photorespiration and oxygenic photosynthesis are intimately linked processes. It has been shown that under the present day atmospheric conditions cyanobacteria and all eukaryotic phototrophs need functional photorespiration to grow autotrophically. The question arises as to when this essential partnership evolved, i.e. can we assume a coevolution of both processes from the beginning or did photorespiration evolve later to compensate for the generation of 2-phosphoglycolate (2PG) due to Rubisco's oxygenase reaction? This question is mainly discussed here using phylogenetic analysis of proteins involved in the 2PG metabolism and the acquisition of different carbon concentrating mechanisms (CCMs). The phylogenies revealed that the enzymes involved in the photorespiration of vascular plants have diverse origins, with some proteins acquired from cyanobacteria as ancestors of the chloroplasts and others from heterotrophic bacteria as ancestors of mitochondria in the plant cell. Only phosphoglycolate phosphatase was found to originate from Archaea. Notably glaucophyte algae, the earliest branching lineage of Archaeplastida, contain more photorespiratory enzymes of cyanobacterial origin than other algal lineages or land plants indicating a larger initial contribution of cyanobacterial-derived proteins to eukaryotic photorespiration. The acquisition of CCMs is discussed as a proxy for assessing the timing of periods when photorespiratory activity may have been enhanced. The existence of CCMs also had marked influence on the structure and function of photorespiration. Here, we discuss evidence for an early and continuous coevolution of photorespiration, CCMs and photosynthesis starting from cyanobacteria via algae, to land plants., (© The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

We investigated the catalytic activity and inhibition of the β-class carbonic anhydrase (CA, EC 4.2.1.1) CahB1, from the relict cyanobacterium Coleofasciculus chthonoplastes (previously denominated Microcoleus chthonoplastes). The enzyme showed good activity as a catalyst for the CO2 hydration, with a kcat of 2.4 × 10(5)s(-1) and a kcat/Km of 6.3 × 10(7)M(-1)s(-1). A range of inorganic anions and small molecules were investigated as inhibitors of CahB1. Perchlorate and tetrafluoroborate did not inhibit the enzyme (KIs >200 mM) whereas selenate and selenocyanide were ineffective inhibitors too, with KIs of 29.9-48.61 mM. The halides, pseudohalides, carbonate, bicarbonate, trithiocarbonate and a range of heavy metal ions-containing anions were submillimolar-millimolar inhibitors (KIs in the range of 0.15-0.90 mM). The best CahB1 inhibitors were N,N-diethyldithiocarbamate, sulfamate, sulfamide, phenylboronic acid and phenylarsonic acid, with KIs in the range of 8-75 μM, whereas acetazolamide inhibited the enzyme with a KI of 76 nM. This is the first kinetic and inhibition study of a cyanobacterial CA. As these enzymes are widespread in many cyanobacteria, being crucial for the carbon concentrating mechanism which assures substrate to RubisCO for the CO2 fixation by these organisms, a detailed kinetic/inhibition study may be essential for a better understanding of this superfamily of metalloenzymes and for potential biotechnological applications in biomimetic CO2 capture processes., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Aquatic photosynthetic microorganisms, cyanobacteria and microalgae, account for almost half of the world's photosynthesis. They absorb carbon di oxide (CO2) as the major substrate to support photosynthesis, the beginning of energy flow into living organisms and one of the primary processes comprising the global carbon cycle. Among all photosynthetic mechanisms, inorganic carbon transport into ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is one of the major limiting steps in photosynthetic carbon fixation which involves active transport of HCO3−, CO2and/or H+, or an energized biochemical mechanism. In fact, a unique system “carbon concentrating mechanism (CCM)” manages the inorganic carbon assimilation, accumulation of CO2around RuBisCO, and utilization in algal cells. However, the information on mechanism of CO2uptake and fixation inside the algal cells is limited. In order to make strategies for enhancement of CO2fixation, understanding of CCM is crucial. Thus, this review provides an overview of advances in CCM research, the comparative state of the art and reports on the CO2uptake model in cyanobacteria and microalgae. The review also discusses the challenges and future perspectives associated with algal CCM research. [ABSTRACT FROM AUTHOR]

Transgenic potato ( Solanum tuberosum L. cv. Desiree) plants expressing components of a novel cyanobacterial photorespiratory glycolate catabolism pathway were developed. Transgenic plant expressing glcD1 (glycolate dehydrogenase I) gene was referred to as synGDH and transgenic plants expressing gcl (glyoxylate carboligase) and tsr (tartronic semialdehyde reductase) genes simultaneously were designated as synGT. Both synGDH and synGT plants showed stable gene transformation, integration and expression. Enhanced glyoxylate contents in synGDH plants were detected as compared to synGT and non-transgenic (NT) plants. Phenotypic evaluation revealed that synGDH plants accumulated 11 % higher dry weight, while, tuber weight was 38 and 16 % higher than NT and synGT, respectively. Upon challenging the plants in high temperature and high light conditions synGDH plants maintained higher Fv/ Fm and showed less bleaching of chlorophyll as compared to synGT and NT plants. These results indicate that genetic transformation of complete pathway in one plant holds promising outcomes in terms of biomass accumulation to meet future needs for food and energy. [ABSTRACT FROM AUTHOR]

Inorganic carbon (C i ) is the major sink for photosynthetic reductant in organisms capable of oxygenic photosynthesis. In the absence of abundant C i , the cyanobacterium Synechocystis sp. strain PCC6803 expresses a high affinity C i acquisition system, the CO 2 -concentrating mechanisms (CCM), controlled by the transcriptional regulator CcmR and the metabolites NADP + and α-ketoglutarate, which act as co-repressors of CcmR by modulating its DNA binding. The CCM thus responds to internal cellular redox changes during the transition from C i -replete to C i -limited conditions. However, the actual changes in the metabolic state of the NADPH/NADP + system that occur during the transition to C i -limited conditions remain ill-defined. Analysis of changes in the redox state of cells experiencing C i limitation reveals systematic changes associated with physiological adjustments and a trend towards the quinone and NADP pools becoming highly reduced. A rapid and persistent increase in F 0 was observed in cells reaching the C i -limited state, as was the induction of photoprotective fluorescence quenching. Systematic changes in the fluorescence induction transients were also observed. As with Chl fluorescence, a transient reduction of the NADPH pool (‘M’ peak), is assigned to State 2→ State 1 transition associated with increased electron flow to NADP + . This was followed by a characteristic decline, which was abolished by C i limitation or inhibition of the Calvin –Benson–Bassham (CBB) cycle and is thus assigned to the activation of the CBB cycle. The results are consistent with the proposed regulation of the CCM and provide new information on the nature of the Chl and NADPH fluorescence induction curves. [ABSTRACT FROM AUTHOR]

The articles in this special issue of Photosynthesis Research arose from the presentations given at the Eighth International Symposium on Inorganic Carbon Uptake by Aquatic Photosynthetic Organisms held from May 27 to June 1, 2013 in New Orleans, Louisiana USA. The meeting covered all the aspects of CO concentrating mechanisms (CCMs) present in photosynthetic bacteria, microalgae and macrophytes, and spanned disciplines from the molecular biology of CCMs to the importance of CCMs in aquatic ecosystems. The publications in this special issue represent our current understanding of CCMs and highlight recent advances in the field. The influences of CCMs on algal biofuel production as well as recent efforts to use the CCM to improve crop plants are also explored. [ABSTRACT FROM AUTHOR]

This review presents an overview of the two ways that cyanobacteria, algae, and plants have adapted to high O and low CO concentrations in the environment. First, the process of photorespiration enables photosynthetic organisms to recycle phosphoglycolate formed by the oxygenase reaction catalyzed by ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Second, there are a number of carbon concentrating mechanisms that increase the CO concentration around Rubisco which increases the carboxylase reaction enhancing CO fixation. This review also presents possibilities for the beneficial modification of these processes with the goal of improving future crop yields. [ABSTRACT FROM AUTHOR]

Oxygenic photosynthesis would not be possible without photorespiration in the present day O2-rich atmosphere. It is now generally accepted that cyanobacteria-like prokaryotes first evolved oxygenic photosynthesis, which was later conveyed via endosymbiosis into a eukaryotic host, which then gave rise to the different groups of algae and streptophytes. For photosynthetic CO2 fixation, all these organisms use Rubis CO, which catalyses both the carboxylation and the oxygenation of ribulose 1,5-bisphosphate. One of the reaction products of the oxygenase reaction, 2-phosphoglycolate (2 PG), represents the starting point of the photorespiratory C2 cycle, which is considered largely responsible for recapturing organic carbon via conversion to the Calvin-Benson cycle ( CBC) intermediate 3-phosphoglycerate, thereby detoxifying critical intermediates. Here we discuss possible scenarios for the evolution of this process toward the well-defined 2 PG metabolism in extant plants. While the origin of the C2 cycle core enzymes can be clearly dated back towards the different endosymbiotic events, the evolutionary scenario that allowed the compartmentalised high flux photorespiratory cycle is uncertain, but probably occurred early during the algal radiation. The change in atmospheric CO2/ O2 ratios promoting the acquisition of different modes for inorganic carbon concentration mechanisms, as well as the evolutionary specialisation of peroxisomes, clearly had a dramatic impact on further aspects of land plant photorespiration. [ABSTRACT FROM AUTHOR]

Cyanobacteria (as well as many chemoautotrophs) actively pump inorganic carbon (in the form of HCO) into the cytosol in order to enhance the overall efficiency of carbon fixation. The success of this approach is dependent upon the presence of carboxysomes-large, polyhedral, cytosolic bodies which sequester ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) and carbonic anhydrase. Carboxysomes seem to function by allowing ready passage of HCO into the body, but hindering the escape of evolved CO, promoting the accumulation of CO in the vicinity of RubisCO and, consequently, efficient carbon fixation. This selectivity is mediated by a thin shell of protein, which envelops the carboxysome's enzymatic core and uses narrow pores to control the passage of small molecules. In this review, we summarize recent advances in understanding the organization and functioning of these intriguing, and ecologically very important molecular machines. [ABSTRACT FROM AUTHOR]

The availability of inorganic carbon (C i) as the source for photosynthesis is fluctuating in aquatic environments. Despite the involvement of transcriptional regulators CmpR and NdhR in regulating genes encoding C i transporters at limiting CO 2 , the C i -sensing mechanism is largely unknown among cyanobacteria. Here we report that a cAMP-dependent transcription factor SyCRP1 mediates C i response in Synechocystis. The mutant ∆ sycrp1 exhibited a slow-growth phenotype and reduced maximum rate of bicarbonate-dependent photosynthetic electron transport (V max) compared to wild-type at the scarcity of CO 2. The number of carboxysomes was decreased significantly in the ∆ sycrp1 at low CO 2 consistent with its reduced V max. The DNA microarray analysis revealed the upregulation of genes encoding C i transporters in ∆sycrp1. The membrane-localized SyCRP1 was released into the cytosol in wild-type cells shifted from low to high CO 2 or upon cAMP treatment. Soluble His-tagged SyCRP1 was shown to target DNA-binding sites upstream of the C i -regulated genes sbtA and ccmK 3. In addition, cAMP enhanced the binding of SyCRP1 to its target sites. Our data collectively suggest that the C i is sensed through the second messenger cAMP releasing membrane-bound SyCRP1 into cytoplasm under sufficient CO 2 conditions. Hence, SyCRP1 is a possible regulator of carbon concentrating mechanism, and such a regulation might be mediated via sensing C i levels through cAMP in Synechocystis. • It has been known that cAMP receptor proteins (CRP) play a crucial role in regulation of gene expression in bacteria. • Transcription regulators of CCM genes were decribed previously, however C i -sensing mechanism in cyanobacteria is unclear. • A membrane associated Synechocystis CRP (SyCRP1), releases to cytosol when bound to CAMP to regulate CCM. • Thus, SyCRP1 mediates C i response through the signalling molecule cAMP in Synechocytis. [ABSTRACT FROM AUTHOR]

Cyanobacteria show high metabolic plasticity by re-allocating macromolecular resources in response to variations in both environmental inorganic carbon (Ci) and light. We grew cultures of the picoplanktonic cyanobacterium Synechococcus elongatus Nägeli across a 50-fold range of growth irradiance at either a dissolved [Ci] <0.1 mM, sufficient to induce strongly the carbon-concentrating mechanism (CCM) or a dissolved [Ci] of ∼4 mM, sufficient to strongly induce the CCM to basal constitutive activity. There was no detectable growth cost of acclimation to low Ci across the entire range of irradiance and growth was nearly light saturated at 50 l mol photons·m−2·s−1. Cells acclimated to low Ci significantly re-allocated macromolecular resources to support their CCM, while maintaining near homeostatis of metabolic flux per unit photosynthetic complex. Changing growth irradiance also drove re-organization of the photosynthetic machinery to balance excitation flux and metabolic demands, but flux per complex varied widely across the range of tolerable growth irradiances. Across the range of growth irradiance, low Ci cells had significantly less phycocyanin than high Ci cells, which corresponded to a lower PSII absorbance capacity. Furthermore, low Ci cells maintained more PSI per cell−1 than high Ci cells under high growth irradiance. Low Ci cells could therefore maintain more of their PSII reaction centers open at high growth irradiance than could high Ci cells, which experienced a significant PSII closure. Thus, acclimation to growth under high available Ci actually constrained acclimation to high light by restricting electron transport downstream from PSII in S. elongatus. [ABSTRACT FROM AUTHOR]

The interactive effects of inorganic carbon status, temperature and light on chlorosis induced by nitrogen deficiency, and the roles of Clp proteases in this process were investigated. In wild-type cultures grown in high or ambient CO2, following transfer to media lacking combined nitrogen, phycocyanin per cell dropped primarily through dilution of the pigment through cell division, and also suffered variable degrees of net degradation. When grown at high CO2 (5%), chlorophyll (Chl) suffered net degradation to a greater extent than phycocyanin. In marked contrast, growth at ambient CO2 resulted in Chl per cell dropping through dilution. Conditions that drove net Chl degradation in the wild-type resulted in little or no net Chl degradation in aclpPIinactivation mutant, with Chl content dropping largely through growth dilution in the mutant. The chlorotic response of aclpPIIinactivation strain was nearly the same as that of wild-type, although phycocyanin degradation may have been slightly accelerated in the former. [ABSTRACT FROM AUTHOR]