Search

Anthropogenic emissions of carbon dioxide (CO2) contribute to global warming. Limiting temperature rise requires negative emission techniques to retract the emitted CO2 from the atmosphere. Through photosynthesis, ecosystems naturally sequester and store carbon. Enhancing these processes forms the basis of biological sequestration strategies. Ecosystems are a sink of atmospheric CO2 and significantly impact the global carbon cycle. The fixed carbon is converted into biomass, a portion of which enters the soil carbon pool and can be sequestered for millennia. The formation of stable soil organic carbon (SOC) depends on land use, management practices, and the use of amendments. Employing best management practices and carbon boosting approaches such as conservation agriculture, agroforestry, biochar, afforestation, and restoration of wetlands can improve SOC stocks and create a positive soil carbon budget, especially in degraded ecosystems. . Carbon fixation by plants and microbes is fundamental to biological sequestration. Regulating the properties and expression of the enzymes involved and introducing novel pathways for carbon capture can enhance carbon fixation efficiency and positively affect yield. This review discusses biological carbon sequestration strategies highlighting the recent findings in the effects and potential of soil carbon boosting approaches in carbon mitigation and the prospects of genetic engineering in enhancing carbon fixation.

Increasing carbon dioxide (CO 2 ) emission has already become a dire threat to the human race and Earth's ecology. Microalgae are recommended to be engineered as CO 2 fixers in biorefinery, which play crucial roles in responding climate change and accelerating the transition to a sustainable future. This review sorted through each segment of microalgal biorefinery to explore the potential for its practical implementation and commercialization, offering valuable insights into research trends and identifies challenges that needed to be addressed in the development process. Firstly, the known mechanisms of microalgal photosynthetic CO 2 fixation and the approaches for strain improvement were summarized. The significance of process regulation for strengthening fixation efficiency and augmenting competitiveness was emphasized, with a specific focus on CO 2 and light optimization strategies. Thereafter, the massive potential of microalgal refineries for various bioresource production was discussed in detail, and the integration with contaminant reclamation was mentioned for economic and ecological benefits. Subsequently, economic and environmental impacts of microalgal biorefinery were evaluated via life cycle assessment (LCA) and techno-economic analysis (TEA) to lit up commercial feasibility. Finally, the current obstacles and future perspectives were discussed objectively to offer an impartial reference for future researchers and investors., 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 © 2023. Published by Elsevier B.V.)

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 ccmK3. 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., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Raphidiopsis raciborskii is a widely distributed, potentially toxic cyanobacterium described as a tropical-subtropical species. However, its occurrence in temperate regions has been expanding. Understanding the environmental factors underlying the expansion and colonization success of Raphidiopsis has been the object of numerous studies. However, less is known regarding its responses to pH and inorganic carbon in water. Thus, the aim of the present study was to investigate the effects of changes in pH and dissolved inorganic carbon on growth and saxitoxins production in the strain R. raciborskii ITEP-A1. We incubated batch cultures with different unbuffered and buffered pH (neutral-acid and alkaline) and inorganic carbon availability (CO 2 -rich air bubbling and the addition of NaHCO 3 ) to assess the effect of these factors on the growth, toxin production as well as saxitoxins composition of the cyanobacterium. The carbon concentrating mechanism (CCM) system of ITEP-A1 was also characterized by an in silico analysis of its previously sequenced genome. The growth and saxitoxins production of R. raciborskii were affected. The addition of sodium bicarbonate and air bubbling enhanced the growth of the cyanobacterium in alkaline pH. In contrast, saxitoxins production and relative toxicity were decreased. Moreover, significant changes in the cellular composition of saxitoxins were strongly related to pH changes. ITEP-A1 potentially expresses the low-flux bicarbonate transporter BicA, an efficient CCM which uptakes most of its carbon from HCO 3 - . Hence, increasing the diffusion of CO 2 in alkaline eutrophic lakes is likely to increase R. raciborskii dominance, but produce less toxic blooms., 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 © 2020 Elsevier B.V. All rights reserved.)

Autotrophic bacteria rely on various mechanisms to increase intracellular concentrations of inorganic forms of carbon (i.e., bicarbonate and CO 2 ) in order to improve the efficiency with which they can be converted to organic forms. Transmembrane bicarbonate transporters and carboxysomes play key roles in accumulating bicarbonate and CO 2 , but other regulatory elements of carbon concentration mechanisms in bacteria are less understood. In this study, after analyzing the genomic regions around α-type carboxysome operons, we characterize a protein that is conserved across these operons but has not been previously studied. On the basis of a series of apo- and ligand-bound crystal structures and supporting biochemical data, we show that this protein, which we refer to as the carboxysome-associated PII protein (CPII), represents a new and distinct subfamily within the broad superfamily of previously studied PII regulatory proteins, which are generally involved in regulating nitrogen metabolism in bacteria. CPII undergoes dramatic conformational changes in response to ADP binding, and the affinity for nucleotide binding is strongly enhanced by the presence of bicarbonate. CPII therefore appears to be a unique type of PII protein that senses bicarbonate availability, consistent with its apparent genomic association with the carboxysome and its constituents., (Copyright © 2016 Elsevier Ltd. All rights reserved.)