Special Issue "The Emerging Role of Cyanobacteria in Green Biotechnology"

A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Microbial Biotechnology".

Deadline for manuscript submissions: closed (31 August 2019).

Special Issue Editors

Prof. Dr. Saul Purton
E-Mail Website
Guest Editor
Institute of Structural and Molecular Biology, Darwin Building, University College London, Gower Street, London WC1E 6BT, UK
Interests: algal biotechnology; synthetic biology; chloroplast genetic engineering; oral vaccines and anti-microbials; photosynthesis
Special Issues, Collections and Topics in MDPI journals
Dr. Alistair McCormick
E-Mail Website
Guest Editor
SynthSys & Institute of Molecular Plant Sciences, School of Biological Sciences, University of Edinburgh, King's Buildings, Edinburgh EH9 3BF, UK
Interests: cyanobacteria; photosynthesis; synthetic biology
Special Issues, Collections and Topics in MDPI journals
Dr. David Lea-Smith
E-Mail Website
Guest Editor
School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
Interests: cyanobacteria; photosynthesis; light harvesting; synthetic biology; hydrocarbon cycling
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Over the past few years, significant progress has been made in our fundamental understanding of metabolic regulation in cyanobacteria and the rich metabolic diversity of this ancient photosynthetic phylum. Furthermore, many novel synthetic biology-based approaches and whole genome modelling systems have been developed, while new model species are also emerging. National investments in automated, high-throughput services offer new opportunities to implement microbial-based experiments at much larger scales. This confluence of new knowledge, tools, and resources is likely to drive forward the identification and engineering of faster-growing, more robust, and higher-yielding cyanobacterial cell factories, which will help to expand the commercial use of cyanobacteria in the green industrial biotechnology sector in the coming decade. This Special Issue invites original research papers and reviews that cover all aspects of cyanobacterial research; from fundamental studies of metabolism and regulation, strain characterization, genetic enhancement, to cultivation technologies and downstream processing.

Prof. Dr. Saul Purton
Dr. Alistair McCormick
Dr. David Lea-Smith
Guest Editors

Manuscript Submission Information

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Published Papers (6 papers)

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Research

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Article
A Storable Mediatorless Electrochemical Biosensor for Herbicide Detection
Microorganisms 2019, 7(12), 630; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms7120630 - 29 Nov 2019
Cited by 8 | Viewed by 1342
Abstract
A novel mediatorless photo-bioelectrochemical sensor operated with a biofilm of the cyanobacterium Synechocystis PCC6803 wt. for herbicide detection with long term stability (>20 days) was successfully developed and tested. Photoanodic current generation was obtained in the absence of artificial mediators. The inhibitory [...] Read more.
A novel mediatorless photo-bioelectrochemical sensor operated with a biofilm of the cyanobacterium Synechocystis PCC6803 wt. for herbicide detection with long term stability (>20 days) was successfully developed and tested. Photoanodic current generation was obtained in the absence of artificial mediators. The inhibitory effect on photocurrent of three commonly used herbicides (i.e., atrazine, diuron, and paraquat) was used as a means of measuring their concentrations in aqueous solution. The injection of atrazine and diuron into the algal medium caused an immediate photocurrent drop due to the inhibition of photosynthetic electron transport. The detected concentrations were suitable for environmental analysis, as revealed by a comparison with the freshwater quality benchmarks set by the Environmental Protection Agency of the United States (US EPA). In contrast, paraquat caused an initial increase (~2 h) of the photocurrent effect of about 200%, as this compound can act as a redox mediator between the cells and the anode. A relatively long-term stability of the biosensor was demonstrated, by keeping anodes colonized with cyanobacterial biofilm in the dark at 4 °C. After 22 days of storage, the performance in terms of the photocurrent was comparable with the freshly prepared biosensor. This result was confirmed by the measurement of chlorophyll content, which demonstrated preservation of the cyanobacterial biofilm. The capacity of this biosensor to recover after a cold season or other prolonged environmental stresses could be a key advantage in field applications, such as in water bodies and agriculture. This study is a step forward in the biotechnological development and implementation of storable mediatorless electrochemical biosensors for herbicide detection. Full article
(This article belongs to the Special Issue The Emerging Role of Cyanobacteria in Green Biotechnology)
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Article
A Comparison of Constitutive and Inducible Non-Endogenous Keto-Carotenoids Biosynthesis in Synechocystis sp. PCC 6803
Microorganisms 2019, 7(11), 501; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms7110501 - 28 Oct 2019
Cited by 1 | Viewed by 1301
Abstract
The model cyanobacterium Synechocystis sp. PCC 6803 has gained significant attention as an alternative and sustainable source for biomass, biofuels and added-value compounds. The latter category includes keto-carotenoids, which are molecules largely employed in a wide spectrum of industrial applications in the food, [...] Read more.
The model cyanobacterium Synechocystis sp. PCC 6803 has gained significant attention as an alternative and sustainable source for biomass, biofuels and added-value compounds. The latter category includes keto-carotenoids, which are molecules largely employed in a wide spectrum of industrial applications in the food, feed, nutraceutical, cosmetic and pharmaceutical sectors. Keto-carotenoids are not naturally synthesized by Synechocystis, at least in any significant amounts, but their accumulation can be induced by metabolic engineering of the endogenous carotenoid biosynthetic pathway. In this study, the accumulation of the keto-carotenoids astaxanthin and canthaxanthin, resulting from the constitutive or temperature-inducible expression of the CrtW and CrtZ genes from Brevundimonas, is compared. The benefits and drawbacks of the two engineering approaches are discussed. Full article
(This article belongs to the Special Issue The Emerging Role of Cyanobacteria in Green Biotechnology)
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Article
Cyanobacterial Growth in Minimally Amended Anaerobic Digestion Effluent and Flue-Gas
Microorganisms 2019, 7(10), 428; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms7100428 - 09 Oct 2019
Cited by 3 | Viewed by 881
Abstract
Anaerobic digestion (AD) is an important industrial process, particularly in a biorefinery approach. The liquid effluent and carbon dioxide in the off-gas, can be used to produce high-value products through the cultivation of cyanobacteria. Growth on AD effluent is often limited due to [...] Read more.
Anaerobic digestion (AD) is an important industrial process, particularly in a biorefinery approach. The liquid effluent and carbon dioxide in the off-gas, can be used to produce high-value products through the cultivation of cyanobacteria. Growth on AD effluent is often limited due to substrate limitation or inhibitory compounds. This study demonstrates the successful cultivation of Synechococcus on minimally amended AD effluent, supplemented with MgSO4 and diluted with seawater. An 8 L airlift reactor illustrated growth in a pilot scale setup. Higher biomass yields were observed for cyanobacteria grown in diluted AD effluent compared to minimal medium, with 60% total nitrogen removal in the effluent. It was demonstrated that controlling the pH, increasing dissolved salt concentrations and adding MgSO4 to the effluent allowed for the successful cultivation of the cyanobacterium, circumventing the addition of clean water for effluent dilution. This could ultimately increase the feasibility of anaerobic digestion-microalgae integrated biorefineries. Full article
(This article belongs to the Special Issue The Emerging Role of Cyanobacteria in Green Biotechnology)
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Article
Transcriptional Terminators Allow Leak-Free Chromosomal Integration of Genetic Constructs in Cyanobacteria
Microorganisms 2019, 7(8), 263; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms7080263 - 16 Aug 2019
Cited by 2 | Viewed by 1528
Abstract
Cyanobacteria are promising candidates for sustainable bioproduction of chemicals from sunlight and carbon dioxide. However, the genetics and metabolism of cyanobacteria are less well understood than those of model heterotrophic organisms, and the suite of well-characterised cyanobacterial genetic tools and parts is less [...] Read more.
Cyanobacteria are promising candidates for sustainable bioproduction of chemicals from sunlight and carbon dioxide. However, the genetics and metabolism of cyanobacteria are less well understood than those of model heterotrophic organisms, and the suite of well-characterised cyanobacterial genetic tools and parts is less mature and complete. Transcriptional terminators use specific RNA structures to halt transcription and are routinely used in both natural and recombinant contexts to achieve independent control of gene expression and to ‘insulate’ genes and operons from one another. Insulating gene expression can be particularly important when heterologous or synthetic genetic constructs are inserted at genomic locations where transcriptional read-through from chromosomal promoters occurs, resulting in poor control of expression of the introduced genes. To date, few terminators have been described and characterised in cyanobacteria. In this work, nineteen heterologous, synthetic or putative native Rho-independent (intrinsic) terminators were tested in the model freshwater cyanobacterium, Synechocystis sp. PCC 6803, from which eleven strong terminators were identified. A subset of these strong terminators was then used to successfully insulate a chromosomally–integrated, rhamnose-inducible rhaBAD expression system from hypothesised ‘read-through’ from a neighbouring chromosomal promoter, resulting in greatly improved inducible control. The addition of validated strong terminators to the cyanobacterial toolkit will allow improved independent control of introduced genes. Full article
(This article belongs to the Special Issue The Emerging Role of Cyanobacteria in Green Biotechnology)
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Review

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Review
Emerging Species and Genome Editing Tools: Future Prospects in Cyanobacterial Synthetic Biology
Microorganisms 2019, 7(10), 409; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms7100409 - 29 Sep 2019
Cited by 21 | Viewed by 3874
Abstract
Recent advances in synthetic biology and an emerging algal biotechnology market have spurred a prolific increase in the availability of molecular tools for cyanobacterial research. Nevertheless, work to date has focused primarily on only a small subset of model species, which arguably limits [...] Read more.
Recent advances in synthetic biology and an emerging algal biotechnology market have spurred a prolific increase in the availability of molecular tools for cyanobacterial research. Nevertheless, work to date has focused primarily on only a small subset of model species, which arguably limits fundamental discovery and applied research towards wider commercialisation. Here, we review the requirements for uptake of new strains, including several recently characterised fast-growing species and promising non-model species. Furthermore, we discuss the potential applications of new techniques available for transformation, genetic engineering and regulation, including an up-to-date appraisal of current Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR associated protein (CRISPR/Cas) and CRISPR interference (CRISPRi) research in cyanobacteria. We also provide an overview of several exciting molecular tools that could be ported to cyanobacteria for more advanced metabolic engineering approaches (e.g., genetic circuit design). Lastly, we introduce a forthcoming mutant library for the model species Synechocystis sp. PCC 6803 that promises to provide a further powerful resource for the cyanobacterial research community. Full article
(This article belongs to the Special Issue The Emerging Role of Cyanobacteria in Green Biotechnology)
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Other

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Brief Report
Zymobacter palmae Pyruvate Decarboxylase is Less Effective Than That of Zymomonas mobilis for Ethanol Production in Metabolically Engineered Synechocystis sp. PCC6803
Microorganisms 2019, 7(11), 494; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms7110494 - 27 Oct 2019
Cited by 1 | Viewed by 1435
Abstract
To produce bioethanol from model cyanobacteria such as Synechocystis, a two gene cassette consisting of genes encoding pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) are required to transform pyruvate first to acetaldehyde and then to ethanol. However the partition of pyruvate to [...] Read more.
To produce bioethanol from model cyanobacteria such as Synechocystis, a two gene cassette consisting of genes encoding pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) are required to transform pyruvate first to acetaldehyde and then to ethanol. However the partition of pyruvate to ethanol comes at a cost, a reduction in biomass and pyruvate availability for other metabolic processes. Hence strategies to divert flux to ethanol as a biofuel in Synechocystis are of interest. PDC from Zymobacter palmae (ZpPDC) has been reported to have a lower Km then the Zymomonas mobilis PDC (ZmPDC), which has traditionally been used in metabolic engineering constructs. The Zppdc gene was combined with the native slr1192 alcohol dehydrogenase gene (adhA) in an attempt to increase ethanol production in the photoautotrophic cyanobacterium Synechocystis sp. PCC 6803 over constructs created with the traditional Zmpdc. Native (Zppdc) and codon optimized (ZpOpdc) versions of the ZpPDC were cloned into a construct where pdc expression was controlled via the psbA2 light inducible promoter from Synechocystis sp. PCC 6803. These constructs were transformed into wildtype Synechocystis sp. PCC 6803 for expression and ethanol production. Ethanol levels were then compared with identical constructs containing the Zmpdc. While strains with the Zppdc (UL071) and ZpOpdc (UL072) constructs did produce ethanol, levels were lower compared to a control strain (UL070) expressing the pdc from Zymomonas mobilis. All constructs demonstrated lower biomass productivity illustrating that the flux from pyruvate to ethanol has a major effect on biomass and ultimately overall biofuel productivity. Thus the utilization of a PDC with a lower Km from Zymobacter palmae unusually did not result in enhanced ethanol production in Synechocystis sp. PCC 6803. Full article
(This article belongs to the Special Issue The Emerging Role of Cyanobacteria in Green Biotechnology)
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