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Approximately one-third of global CO 2 assimilation is performed by the pyrenoid, a liquid-like organelle found in most algae and some plants. Specialized pyrenoid-traversing membranes are hypothesized to drive CO 2 assimilation in the pyrenoid by delivering concentrated CO 2 , but how these membranes are made to traverse the pyrenoid matrix remains unknown. Here we show that proteins SAGA1 and MITH1 cause membranes to traverse the pyrenoid matrix in the model alga Chlamydomonas reinhardtii. Mutants deficient in SAGA1 or MITH1 lack matrix-traversing membranes and exhibit growth defects under CO 2 -limiting conditions. Expression of SAGA1 and MITH1 together in a heterologous system, the model plant Arabidopsis thaliana, produces matrix-traversing membranes. Both proteins localize to matrix-traversing membranes. SAGA1 binds to the major matrix component, Rubisco, and is necessary to initiate matrix-traversing membranes. MITH1 binds to SAGA1 and is necessary for extension of membranes through the matrix. Our data suggest that SAGA1 and MITH1 cause membranes to traverse the matrix by creating an adhesive interaction between the membrane and matrix. Our study identifies and characterizes key factors in the biogenesis of pyrenoid matrix-traversing membranes, demonstrates the importance of these membranes to pyrenoid function and marks a key milestone toward pyrenoid engineering into crops for improving yields., Competing Interests: Competing interests Princeton University has submitted U.S. patent application 63/678,898 (2024) on aspects of the findings., (© 2024. The Author(s).)

CO 2 fixation is commonly limited by inefficiency of the CO 2 -fixing enzyme Rubisco. Eukaryotic algae concentrate and fix CO 2 in phase-separated condensates called pyrenoids, which complete up to one-third of global CO 2 fixation. Condensation of Rubisco in pyrenoids is dependent on interaction with disordered linker proteins that show little conservation between species. We developed a sequence-independent bioinformatic pipeline to identify linker proteins in green algae. We report the linker from Chlorella and demonstrate that it binds a conserved site on the Rubisco large subunit. We show that the Chlorella linker phase separates Chlamydomonas Rubisco and that despite their separation by ~800 million years of evolution, the Chlorella linker can support the formation of a functional pyrenoid in Chlamydomonas. This cross-species reactivity extends to plants, with the Chlorella linker able to drive condensation of some native plant Rubiscos in vitro and in planta. Our results represent an exciting frontier for pyrenoid engineering in plants, which is modelled to increase crop yields., (© 2024. The Author(s).)

Improving photosynthesis, the fundamental process by which plants convert light energy into chemical energy, is a key area of research with great potential for enhancing sustainable agricultural productivity and addressing global food security challenges. This perspective delves into the latest advancements and approaches aimed at optimizing photosynthetic efficiency. Our discussion encompasses the entire process, beginning with light harvesting and its regulation and progressing through the bottleneck of electron transfer. We then delve into the carbon reactions of photosynthesis, focusing on strategies targeting the enzymes of the Calvin-Benson-Bassham (CBB) cycle. Additionally, we explore methods to increase carbon dioxide (CO2) concentration near the Rubisco, the enzyme responsible for the first step of CBB cycle, drawing inspiration from various photosynthetic organisms, and conclude this section by examining ways to enhance CO2 delivery into leaves. Moving beyond individual processes, we discuss two approaches to identifying key targets for photosynthesis improvement: systems modeling and the study of natural variation. Finally, we revisit some of the strategies mentioned above to provide a holistic view of the improvements, analyzing their impact on nitrogen use efficiency and on canopy photosynthesis., Competing Interests: Conflict of interest statement. K.N. is an inventor on a patent “Transgenic plants with increased photosynthesis efficiency and growth” US20230183731A1, and K.N. and D.P.-T. are inventors on a patent application “Methods of screening for plant gain of function mutations and compositions therefor” US20230323480A1. All other authors declare no competing interests., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Synechococcus sp. PCC 11901 (PCC 11901) is a fast-growing marine cyanobacterial strain that has a capacity for sustained biomass accumulation to very high cell densities, comparable to that achieved by commercially relevant heterotrophic organisms. However, genetic tools to engineer PCC 11901 for biotechnology applications are limited. Here we describe a suite of tools based on the CyanoGate MoClo system to unlock the engineering potential of PCC 11901. First, we characterized neutral sites suitable for stable genomic integration that do not affect growth even at high cell densities. Second, we tested a suite of constitutive promoters, terminators, and inducible promoters including a 2,4-diacetylphloroglucinol (DAPG)-inducible PhlF repressor system, which has not previously been demonstrated in cyanobacteria and showed tight regulation and a 228-fold dynamic range of induction. Lastly, we developed a DAPG-inducible dCas9-based CRISPR interference (CRISPRi) system and a modular method to generate markerless mutants using CRISPR-Cas12a. Based on our findings, PCC 11901 is highly responsive to CRISPRi-based repression and showed high efficiencies for single insertion (31% to 81%) and multiplex double insertion (25%) genome editing with Cas12a. We envision that these tools will lay the foundations for the adoption of PCC 11901 as a robust model strain for engineering biology and green biotechnology., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Approximately one-third of global CO 2 assimilation is performed by the pyrenoid 1 , a liquid-like organelle found in most algae and some plants 2 . Specialized membranes are hypothesized to drive CO 2 assimilation in the pyrenoid by delivering concentrated CO 2 3,4 , but their biogenesis and function have not been experimentally characterized. Here, we show that homologous proteins SAGA1 and MITH1 mediate the biogenesis of the pyrenoid membrane tubules in the model alga Chlamydomonas reinhardtii and are sufficient to reconstitute pyrenoid-traversing membranes in a heterologous system, the plant Arabidopsis thaliana . SAGA1 localizes to the regions where thylakoid membranes transition into tubules and is necessary to initiate tubule formation. MITH1 localizes to the tubules and is necessary for their extension through the pyrenoid. Tubule-deficient mutants exhibit growth defects under CO 2 -limiting conditions, providing evidence for the function of membrane tubules in CO 2 delivery to the pyrenoid. Furthermore, these mutants form multiple aberrant condensates of pyrenoid matrix, indicating that a normal tubule network promotes the coalescence of a single pyrenoid. The reconstitution of pyrenoid-traversing membranes in a plant represents a key milestone toward engineering a functional pyrenoid into crops for improving crop yields. More broadly, our study demonstrates the functional importance of pyrenoid membranes, identifies key biogenesis factors, and paves the way for the molecular characterization of pyrenoid membranes across the tree of life.

Cyanobacteria are a diverse and ecologically important group of photosynthetic prokaryotes that contribute significantly to the global carbon cycle through the capture of CO 2 as biomass. Cyanobacterial biotechnology could play a key role in a sustainable bioeconomy through negative emissions technologies (NETs), such as carbon sequestration or bioproduction. However, the primary issues of low productivities and high infrastructure costs currently limit the commercialisation of such applications. The isolation of several fast-growing strains and recent advancements in molecular biology tools now offer promising new avenues for improving yields, including metabolic engineering approaches guided by high-throughput screening and metabolic models. Furthermore, emerging research on engineering coculture communities could help to develop more robust culturing systems to support broader NET applications., Competing Interests: Declaration of Competing Interest Nothing declared., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The pyrenoid is a chloroplastic microcompartment in which most algae and some terrestrial plants condense the primary carboxylase, Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) as part of a CO 2 -concentrating mechanism that improves the efficiency of CO 2 capture. Engineering a pyrenoid-based CO 2 -concentrating mechanism (pCCM) into C3 crop plants is a promising strategy to enhance yield capacities and resilience to the changing climate. Many pyrenoids are characterized by a sheath of starch plates that is proposed to act as a barrier to limit CO 2 diffusion. Recently, we have reconstituted a phase-separated "proto-pyrenoid" Rubisco matrix in the model C3 plant Arabidopsis thaliana using proteins from the alga with the most well-studied pyrenoid, Chlamydomonas reinhardtii [N. Atkinson, Y. Mao, K. X. Chan, A. J. McCormick, Nat. Commun. 11 , 6303 (2020)]. Here, we describe the impact of introducing the Chlamydomonas proteins StArch Granules Abnormal 1 (SAGA1) and SAGA2, which are associated with the regulation of pyrenoid starch biogenesis and morphology. We show that SAGA1 localizes to the proto-pyrenoid in engineered Arabidopsis plants, which results in the formation of atypical spherical starch granules enclosed within the proto-pyrenoid condensate and adjacent plate-like granules that partially cover the condensate, but without modifying the total amount of chloroplastic starch accrued. Additional expression of SAGA2 further increases the proportion of starch synthesized as adjacent plate-like granules that fully encircle the proto-pyrenoid. Our findings pave the way to assembling a diffusion barrier as part of a functional pCCM in vascular plants, while also advancing our understanding of the roles of SAGA1 and SAGA2 in starch sheath formation and broadening the avenues for engineering starch morphology., Competing Interests: Competing interests statement:The authors declare no competing interest.

In recent years, a plethora of new synthetic biology tools for use in cyanobacteria have been published; however, their reported characterizations often cannot be reproduced, greatly limiting the comparability of results and hindering their applicability. In this interlaboratory study, the reproducibility of a standard microbiological experiment for the cyanobacterial model organism Synechocystis sp. PCC 6803 was assessed. Participants from eight different laboratories quantified the fluorescence intensity of mVENUS as a proxy for the transcription activity of the three promoters P J 23100 , P rhaBAD , and P petE over time. In addition, growth rates were measured to compare growth conditions between laboratories. By establishing strict and standardized laboratory protocols, reflecting frequently reported methods, we aimed to identify issues with state-of-the-art procedures and assess their effect on reproducibility. Significant differences in spectrophotometer measurements across laboratories from identical samples were found, suggesting that commonly used reporting practices of optical density values need to be supplemented by cell count or biomass measurements. Further, despite standardized light intensity in the incubators, significantly different growth rates between incubators used in this study were observed, highlighting the need for additional reporting requirements of growth conditions for phototrophic organisms beyond the light intensity and CO 2 supply. Despite the use of a regulatory system orthogonal to Synechocystis sp. PCC 6803, P rhaBAD , and a high level of protocol standardization, ∼32% variation in promoter activity under induced conditions was found across laboratories, suggesting that the reproducibility of other data in the field of cyanobacteria might be affected similarly.

Rubisco catalyses the first rate-limiting step in CO2 fixation and is responsible for the vast majority of organic carbon present in the biosphere. The function and regulation of Rubisco remain an important research topic and a longstanding engineering target to enhance the efficiency of photosynthesis for agriculture and green biotechnology. The most abundant form of Rubisco (Form I) consists of eight large and eight small subunits, and is found in all plants, algae, cyanobacteria, and most phototrophic and chemolithoautotrophic proteobacteria. Although the active sites of Rubisco are located on the large subunits, expression of the small subunit regulates the size of the Rubisco pool in plants and can influence the overall catalytic efficiency of the Rubisco complex. The small subunit is now receiving increasing attention as a potential engineering target to improve the performance of Rubisco. Here we review our current understanding of the role of the small subunit and our growing capacity to explore its potential to modulate Rubisco catalysis using engineering biology approaches., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Many photosynthetic species have evolved CO2-concentrating mechanisms (CCMs) to improve the efficiency of CO2 assimilation by Rubisco and reduce the negative impacts of photorespiration. However, the majority of plants (i.e. C3 plants) lack an active CCM. Thus, engineering a functional heterologous CCM into important C3 crops, such as rice (Oryza sativa) and wheat (Triticum aestivum), has become a key strategic ambition to enhance yield potential. Here, we review recent advances in our understanding of the pyrenoid-based CCM in the model green alga Chlamydomonas reinhardtii and engineering progress in C3 plants. We also discuss recent modeling work that has provided insights into the potential advantages of Rubisco condensation within the pyrenoid and the energetic costs of the Chlamydomonas CCM, which, together, will help to better guide future engineering approaches. Key findings include the potential benefits of Rubisco condensation for carboxylation efficiency and the need for a diffusional barrier around the pyrenoid matrix. We discuss a minimal set of components for the CCM to function and that active bicarbonate import into the chloroplast stroma may not be necessary for a functional pyrenoid-based CCM in planta. Thus, the roadmap for building a pyrenoid-based CCM into plant chloroplasts to enhance the efficiency of photosynthesis now appears clearer with new challenges and opportunities., (© The Author(s) 2022. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Synechococcus sp. PCC 11901 reportedly demonstrates the highest, most sustained growth of any known cyanobacterium under optimized conditions. Due to its recent discovery, our knowledge of its biology, including the factors underlying sustained, fast growth, is limited. Furthermore, tools specific for genetic manipulation of PCC 11901 are not established. Here, we demonstrate that PCC 11901 shows faster growth than other model cyanobacteria, including the fast-growing species Synechococcus elongatus UTEX 2973, under optimal growth conditions for UTEX 2973. Comparative genomics between PCC 11901 and Synechocystis sp. PCC 6803 reveal conservation of most metabolic pathways but PCC 11901 has a simplified electron transport chain and reduced light harvesting complex. This may underlie its superior light use, reduced photoinhibition, and higher photosynthetic and respiratory rates. To aid biotechnology applications, we developed a vitamin B 12 auxotrophic mutant but were unable to generate unmarked knockouts using two negative selectable markers, suggesting that recombinase- or CRISPR-based approaches may be required for repeated genetic manipulation. Overall, this study establishes PCC 11901 as one of the most promising species currently available for cyanobacterial biotechnology and provides a useful set of bioinformatics tools and strains for advancing this field, in addition to insights into the factors underlying its fast growth phenotype.

Phycocyanin (PC) is a soluble blue pigment-protein primarily harvested from the cyanobacterium Arthrospira platensis. PC is in high demand from several industries, but its narrow stability range limits potential applications. Here, a pilot scale (120 L total) batch production, extraction and purification process for thermostable PC (Te-PC) from a Synechocystis sp. PCC 6803 'Olive' strain expressing the PC operon cpcBACD from Thermosynechococcus elongatus BP-1 on a self-replicating vector is presented. Batch cultivation without antibiotics had no impact on growth or Te-PC production and optimisation of growth conditions resulted in Te-PC contents of 75.3 ± 1.7 mg g DW -1 . Wet biomass was harvested following chitosan-based flocculation with a 97 ± 2% efficiency, and Te-PC was extracted by high pressure homogenisation. Subsequent purification by heat-treatment and two-step ammonium sulfate precipitation removed chlorophyll and allophycocyanin contamination, resulting in Te-PC purities of 2.9 ± 0.7 and a mean Te-PC recovery of 84 ± 12%., (Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Phycocyanin (PC) is a soluble phycobiliprotein found within the light-harvesting phycobilisome complex of cyanobacteria and red algae, and is considered a high-value product due to its brilliant blue colour and fluorescent properties. However, commercially available PC has a relatively low temperature stability. Thermophilic species produce more thermostable variants of PC, but are challenging and energetically expensive to cultivate. Here, we show that the PC operon from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 ( cpcBACD ) is functional in the mesophile Synechocystis sp. PCC 6803. Expression of cpcBACD in an 'Olive' mutant strain of Synechocystis lacking endogenous PC resulted in high yields of thermostable PC (112 ± 1 mg g -1 DW) comparable to that of endogenous PC in wild-type cells. Heterologous PC also improved the growth of the Olive mutant, which was further supported by evidence of a functional interaction with the endogenous allophycocyanin core of the phycobilisome complex. The thermostability properties of the heterologous PC were comparable to those of PC from T. elongatus , and could be purified from the Olive mutant using a low-cost heat treatment method. Finally, we developed a scalable model to calculate the energetic benefits of producing PC from T. elongatus in Synechocystis cultures. Our model showed that the higher yields and lower cultivation temperatures of Synechocystis resulted in a 3.5-fold increase in energy efficiency compared to T. elongatus , indicating that producing thermostable PC in non-native hosts is a cost-effective strategy for scaling to commercial production., Competing Interests: There are no competing interests to declare., (© 2021 The Authors.)

Three-dimensional printing applications in separation science are currently limited by the lack of materials compatible with chromatographic operations and three-dimensional printing technologies. In this work, we propose a new material for Digital Light Processing printing to fabricate functional ion exchange monoliths in a single step. Through copolymerization of the bifunctional monomer [2-(acryloyloxy)ethyl] trimethylammonium chloride, monolithic structures with quaternary amine ligands were fabricated. The novel formulation was optimized in terms of protein binding and recovery, microporous structure, and its swelling susceptibility by increasing its cross-link density and employing cyclohexanol and dodecanol as pore forming agents. In static conditions, the material demonstrated a maximum binding capacity of 104.2 ± 10.6 mg/mL for bovine serum albumin, in line with commercially available materials. Its anion exchange behavior was validated by separating bovine serum albumin and myoglobin on a monolithic bed with Schoen gyroid morphology. The same column geometry was tested for the purification of C-phycocyanin from clarified as well as cell-laden Arthrospira platensis feedstocks. This represents the first demonstration of one-step printed stationary phases to capture proteins directly from solid-laden feedstocks. We believe that the material presented here represents a significant improvement towards implementation of three-dimensional printed chromatography media in the field of separation science., (© 2020 The Authors. Journal of Separation Science published by Wiley-VCH GmbH.)

Microcystinase (MlrA) was first described in 1996. Since then MlrA peptidase activity has proven to be both the most efficient enzymatic process and the most specific catalyst of all known microcystins detoxification pathways. Furthermore, MlrA and the MlrABC degradation pathway are presently the only enzymatic processes with clear genetic and biochemical descriptions available for microcystins degradation, greatly facilitating modern applied genetics for any relevant technological development. Recently, there has been increasing interest in the potential of sustainable, biologically inspired alternatives to current industrial practice, with note that biological microcystins degradation is the primary detoxification process found in nature. While previous reviews have broadly discussed microbial biodegradation processes, here we present a review focused specifically on MlrA. Following a general overview, we briefly highlight the initial discovery and present understanding of the MlrABC degradation pathway, before discussing the genetic and biochemical aspects of MlrA. We then review the potential biotechnology applications of MlrA in the context of available literature with emphasis on the optimization of MlrA for in situ applications including (i) direct modulation of Mlr activity within naturally existing populations, (ii) bioaugmentation of systems with introduced biodegradative capacity via whole cell biocatalysts, and (iii) bioremediation via direct MlrA application., Competing Interests: Declaration of Competing Interest J. Dexter has a patent pending (WO2018017828A1), with US10787489B2 granted. All other authors declare no conflict of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Cyanobacteria utilize sunlight to convert carbon dioxide into a wide variety of secondary metabolites and show great potential for green biotechnology applications. Although cyanobacterial synthetic biology is less mature than for other heterotrophic model organisms, there are now a range of molecular tools available to modulate and control gene expression. One area of gene regulation that still lags behind other model organisms is the modulation of gene transcription, particularly transcription termination. A vast number of intrinsic transcription terminators are now available in heterotrophs, but only a small number have been investigated in cyanobacteria. As artificial gene expression systems become larger and more complex, with short stretches of DNA harboring strong promoters and multiple gene expression cassettes, the need to stop transcription efficiently and insulate downstream regions from unwanted interference is becoming more important. In this study, we adapted a dual reporter tool for use with the CyanoGate MoClo Assembly system that can quantify and compare the efficiency of terminator sequences within and between different species. We characterized 34 intrinsic terminators in Escherichia coli , Synechocystis sp. PCC 6803, and Synechococcus elongatus UTEX 2973 and observed significant differences in termination efficiencies. However, we also identified five terminators with termination efficiencies of >96% in all three species, indicating that some terminators can behave consistently in both heterotrophic species and cyanobacteria., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Gale, Wang and McCormick.)

Engineering the small subunit of the key CO 2 -fixing enzyme Rubisco (SSU, encoded by rbcS ) in plants currently poses a significant challenge, as many plants have polyploid genomes and SSUs are encoded by large multigene families. Here, we used CRISPR-Cas9-mediated genome editing approach to simultaneously knock-out multiple rbcS homologs in the model tetraploid crop tobacco ( Nicotiana tabacum cv . Petit Havana). The three rbcS homologs rbcS_S1a, rbcS_S1b and rbcS_T1 account for at least 80% of total rbcS expression in tobacco. In this study, two multiplexing guide RNAs (gRNAs) were designed to target homologous regions in these three genes. We generated tobacco mutant lines with indel mutations in all three genes, including one line with a 670 bp deletion in rbcS-T1 . The Rubisco content of three selected mutant lines in the T 1 generation was reduced by ca . 93% and mutant plants accumulated only 10% of the total biomass of wild-type plants. As a second goal, we developed a proof-of-principle approach to simultaneously introduce a non-native rbcS gene while generating the triple SSU knockout by co-transformation into a wild-type tobacco background. Our results show that CRISPR-Cas9 is a viable tool for the targeted mutagenesis of rbcS families in polyploid species and will contribute to efforts aimed at improving photosynthetic efficiency through expression of superior non-native Rubisco enzymes in plants., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2020 Donovan, Mao, Orr, Carmo-Silva and McCormick.)

Photosynthetic CO 2 fixation in plants is limited by the inefficiency of the CO 2 -assimilating enzyme Rubisco. In most eukaryotic algae, Rubisco aggregates within a microcompartment known as the pyrenoid, in association with a CO 2 -concentrating mechanism that improves photosynthetic operating efficiency under conditions of low inorganic carbon. Recent work has shown that the pyrenoid matrix is a phase-separated, liquid-like condensate. In the alga Chlamydomonas reinhardtii, condensation is mediated by two components: Rubisco and the linker protein EPYC1 (Essential Pyrenoid Component 1). Here, we show that expression of mature EPYC1 and a plant-algal hybrid Rubisco leads to spontaneous condensation of Rubisco into a single phase-separated compartment in Arabidopsis chloroplasts, with liquid-like properties similar to a pyrenoid matrix. This work represents a significant initial step towards enhancing photosynthesis in higher plants by introducing an algal CO 2 -concentrating mechanism, which is predicted to significantly increase the efficiency of photosynthetic CO 2 uptake.

Human life intimately depends on plants for food, biomaterials, health, energy, and a sustainable environment. Various plants have been genetically improved mostly through breeding, along with limited modification via genetic engineering, yet they are still not able to meet the ever-increasing needs, in terms of both quantity and quality, resulting from the rapid increase in world population and expected standards of living. A step change that may address these challenges would be to expand the potential of plants using biosystems design approaches. This represents a shift in plant science research from relatively simple trial-and-error approaches to innovative strategies based on predictive models of biological systems. Plant biosystems design seeks to accelerate plant genetic improvement using genome editing and genetic circuit engineering or create novel plant systems through de novo synthesis of plant genomes. From this perspective, we present a comprehensive roadmap of plant biosystems design covering theories, principles, and technical methods, along with potential applications in basic and applied plant biology research. We highlight current challenges, future opportunities, and research priorities, along with a framework for international collaboration, towards rapid advancement of this emerging interdisciplinary area of research. Finally, we discuss the importance of social responsibility in utilizing plant biosystems design and suggest strategies for improving public perception, trust, and acceptance., Competing Interests: The authors declare that they have no conflicts of interest regarding the publication of this article., (Copyright © 2020 Xiaohan Yang et al.)

Approximately one-third of global CO 2 fixation occurs in a phase-separated algal organelle called the pyrenoid. The existing data suggest that the pyrenoid forms by the phase separation of the CO 2 -fixing enzyme Rubisco with a linker protein; however, the molecular interactions underlying this phase separation remain unknown. Here we present the structural basis of the interactions between Rubisco and its intrinsically disordered linker protein Essential Pyrenoid Component 1 (EPYC1) in the model alga Chlamydomonas reinhardtii. We find that EPYC1 consists of five evenly spaced Rubisco-binding regions that share sequence similarity. Single-particle cryo-electron microscopy of these regions in complex with Rubisco indicates that each Rubisco holoenzyme has eight binding sites for EPYC1, one on each Rubisco small subunit. Interface mutations disrupt binding, phase separation and pyrenoid formation. Cryo-electron tomography supports a model in which EPYC1 and Rubisco form a codependent multivalent network of specific low-affinity bonds, giving the matrix liquid-like properties. Our results advance the structural and functional understanding of the phase separation underlying the pyrenoid, an organelle that plays a fundamental role in the global carbon cycle.

The primary CO2-fixing enzyme Rubisco limits the productivity of plants. The small subunit of Rubisco (SSU) can influence overall Rubisco levels and catalytic efficiency, and is now receiving increasing attention as a potential engineering target to improve the performance of Rubisco. However, SSUs are encoded by a family of nuclear rbcS genes in plants, which makes them challenging to engineer and study. Here we have used CRISPR/Cas9 [clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein 9] and T-DNA insertion lines to generate a suite of single and multiple gene knockout mutants for the four members of the rbcS family in Arabidopsis, including two novel mutants 2b3b and 1a2b3b. 1a2b3b contained very low levels of Rubisco (~3% relative to the wild-type) and is the first example of a mutant with a homogenous Rubisco pool consisting of a single SSU isoform (1B). Growth under near-outdoor levels of light demonstrated Rubisco-limited growth phenotypes for several SSU mutants and the importance of the 1A and 3B isoforms. We also identified 1a1b as a likely lethal mutation, suggesting a key contributory role for the least expressed 1B isoform during early development. The successful use of CRISPR/Cas here suggests that this is a viable approach for exploring the functional roles of SSU isoforms in plants., (© Crown copyright. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

The light-harvesting phycobilisome complex is an important component of photosynthesis in cyanobacteria and red algae. Phycobilisomes are composed of phycobiliproteins, including the blue phycobiliprotein phycocyanin, that are considered high-value products with applications in several industries. Remarkably, several cyanobacteria and red algal species retain the capacity to harvest light and photosynthesise under highly selective environments such as hot springs, and flourish in extremes of pH and elevated temperatures. These thermophilic organisms produce thermostable phycobiliproteins, which have superior qualities much needed for wider adoption of these natural pigment-proteins in the food, textile, and other industries. Here we review the available literature on the thermostability of phycobilisome components from thermophilic species and discuss how a better appreciation of phycobiliproteins from extreme environments will benefit our fundamental understanding of photosynthetic adaptation and could provide a sustainable resource for several industrial processes., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Cyanobacteria are key organisms in the global ecosystem, useful models for studying metabolic and physiological processes conserved in photosynthetic organisms, and potential renewable platforms for production of chemicals. Characterizing cyanobacterial metabolism and physiology is key to understanding their role in the environment and unlocking their potential for biotechnology applications. Many aspects of cyanobacterial biology differ from heterotrophic bacteria. For example, most cyanobacteria incorporate a series of internal thylakoid membranes where both oxygenic photosynthesis and respiration occur, while CO2 fixation takes place in specialized compartments termed carboxysomes. In this review, we provide a comprehensive summary of our knowledge on cyanobacterial physiology and the pathways in Synechocystis sp. PCC 6803 (Synechocystis) involved in biosynthesis of sugar-based metabolites, amino acids, nucleotides, lipids, cofactors, vitamins, isoprenoids, pigments and cell wall components, in addition to the proteins involved in metabolite transport. While some pathways are conserved between model cyanobacteria, such as Synechocystis, and model heterotrophic bacteria like Escherichia coli, many enzymes and/or pathways involved in the biosynthesis of key metabolites in cyanobacteria have not been completely characterized. These include pathways required for biosynthesis of chorismate and membrane lipids, nucleotides, several amino acids, vitamins and cofactors, and isoprenoids such as plastoquinone, carotenoids, and tocopherols. Moreover, our understanding of photorespiration, lipopolysaccharide assembly and transport, and degradation of lipids, sucrose, most vitamins and amino acids, and haem, is incomplete. We discuss tools that may aid our understanding of cyanobacterial metabolism, notably CyanoSource, a barcoded library of targeted Synechocystis mutants, which will significantly accelerate characterization of individual proteins., (© 2020 The Author(s).)

Cyanobacteria are a diverse group of prokaryotic photosynthetic organisms that can be genetically modified for the renewable production of useful industrial commodities. Recent advances in synthetic biology have led to development of several cloning toolkits such as CyanoGate, a standardized modular cloning system for building plasmid vectors for subsequent transformation or conjugal transfer into cyanobacteria. Here we outline a detailed method for assembling a self-replicating vector (e.g., carrying a fluorescent marker expression cassette) and conjugal transfer of the vector into the cyanobacterial strains Synechocystis sp. PCC 6803 or Synechococcus elongatus UTEX 2973. In addition, we outline how to characterize the performance of a genetic part (e.g., a promoter) using a plate reader or flow cytometry.

Photosynthetic efficiencies in plants are restricted by the CO2-fixing enzyme Rubisco but could be enhanced by introducing a CO2-concentrating mechanism (CCM) from green algae, such as Chlamydomonas reinhardtii (hereafter Chlamydomonas). A key feature of the algal CCM is aggregation of Rubisco in the pyrenoid, a liquid-like organelle in the chloroplast. Here we have used a yeast two-hybrid system and higher plants to investigate the protein-protein interaction between Rubisco and essential pyrenoid component 1 (EPYC1), a linker protein required for Rubisco aggregation. We showed that EPYC1 interacts with the small subunit of Rubisco (SSU) from Chlamydomonas and that EPYC1 has at least five SSU interaction sites. Interaction is crucially dependent on the two surface-exposed α-helices of the Chlamydomonas SSU. EPYC1 could be localized to the chloroplast in higher plants and was not detrimental to growth when expressed stably in Arabidopsis with or without a Chlamydomonas SSU. Although EPYC1 interacted with Rubisco in planta, EPYC1 was a target for proteolytic degradation. Plants expressing EPYC1 did not show obvious evidence of Rubisco aggregation. Nevertheless, hybrid Arabidopsis Rubisco containing the Chlamydomonas SSU could phase separate into liquid droplets with purified EPYC1 in vitro, providing the first evidence of pyrenoid-like aggregation for Rubisco derived from a higher plant., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

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.

A phase-separated, liquid-like organelle called the pyrenoid mediates CO 2 fixation in the chloroplasts of nearly all eukaryotic algae. While most algae have 1 pyrenoid per chloroplast, here we describe a mutant in the model alga Chlamydomonas that has on average 10 pyrenoids per chloroplast. Characterization of the mutant leads us to propose a model where multiple pyrenoids are favored by an increase in the surface area of the starch sheath that surrounds and binds to the liquid-like pyrenoid matrix. We find that the mutant's phenotypes are due to disruption of a gene, which we call StArch Granules Abnormal 1 ( SAGA1 ) because starch sheath granules, or plates, in mutants lacking SAGA1 are more elongated and thinner than those of wild type. SAGA1 contains a starch binding motif, suggesting that it may directly regulate starch sheath morphology. SAGA1 localizes to multiple puncta and streaks in the pyrenoid and physically interacts with the small and large subunits of the carbon-fixing enzyme Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), a major component of the liquid-like pyrenoid matrix. Our findings suggest a biophysical mechanism by which starch sheath morphology affects pyrenoid number and CO 2 -concentrating mechanism function, advancing our understanding of the structure and function of this biogeochemically important organelle. More broadly, we propose that the number of phase-separated organelles can be regulated by imposing constraints on their surface area., Competing Interests: The authors declare no conflict of interest., (Copyright © 2019 the Author(s). Published by PNAS.)

Background: Tracking and predicting the growth performance of plants in different environments is critical for predicting the impact of global climate change. Automated approaches for image capture and analysis have allowed for substantial increases in the throughput of quantitative growth trait measurements compared with manual assessments. Recent work has focused on adopting computer vision and machine learning approaches to improve the accuracy of automated plant phenotyping. Here we present PS-Plant, a low-cost and portable 3D plant phenotyping platform based on an imaging technique novel to plant phenotyping called photometric stereo (PS)., Results: We calibrated PS-Plant to track the model plant Arabidopsis thaliana throughout the day-night (diel) cycle and investigated growth architecture under a variety of conditions to illustrate the dramatic effect of the environment on plant phenotype. We developed bespoke computer vision algorithms and assessed available deep neural network architectures to automate the segmentation of rosettes and individual leaves, and extract basic and more advanced traits from PS-derived data, including the tracking of 3D plant growth and diel leaf hyponastic movement. Furthermore, we have produced the first PS training data set, which includes 221 manually annotated Arabidopsis rosettes that were used for training and data analysis (1,768 images in total). A full protocol is provided, including all software components and an additional test data set., Conclusions: PS-Plant is a powerful new phenotyping tool for plant research that provides robust data at high temporal and spatial resolutions. The system is well-suited for small- and large-scale research and will help to accelerate bridging of the phenotype-to-genotype gap., (© The Author(s) 2019. Published by Oxford University Press.)

The rapid and widespread adoption of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas technologies has allowed genetic editing in plants to enter a revolutionary new era. In this mini review, we highlight the current CRISPR/Cas tools available in plants and the use of Arabidopsis thaliana as a model to guide future improvements in crop yields, such as enhancing photosynthetic potential. We also outline the current socio-political landscape for CRISPR/Cas research and highlight the growing need for governments to better facilitate research into plant genetic-editing technologies., (© 2019 Scandinavian Plant Physiology Society.)

Recent advances in synthetic biology research have been underpinned by an exponential increase in available genomic information and a proliferation of advanced DNA assembly tools. The adoption of plasmid vector assembly standards and parts libraries has greatly enhanced the reproducibility of research and the exchange of parts between different labs and biological systems. However, a standardized modular cloning (MoClo) system is not yet available for cyanobacteria, which lag behind other prokaryotes in synthetic biology despite their huge potential regarding biotechnological applications. By building on the assembly library and syntax of the Plant Golden Gate MoClo kit, we have developed a versatile system called CyanoGate that unites cyanobacteria with plant and algal systems. Here, we describe the generation of a suite of parts and acceptor vectors for making (1) marked/unmarked knock-outs or integrations using an integrative acceptor vector, and (2) transient multigene expression and repression systems using known and previously undescribed replicative vectors. We tested and compared the CyanoGate system in the established model cyanobacterium Synechocystis sp. PCC 6803 and the more recently described fast-growing strain Synechococcus elongatus UTEX 2973. The UTEX 2973 fast-growth phenotype was only evident under specific growth conditions; however, UTEX 2973 accumulated high levels of proteins with strong native or synthetic promoters. The system is publicly available and can be readily expanded to accommodate other standardized MoClo parts to accelerate the development of reliable synthetic biology tools for the cyanobacterial community., (© 2019 American Society of Plant Biologists. All Rights Reserved.)

A memory clinic used two key approaches in developing a patient and family handbook: partnership with people with memory loss and strengths-based social work practice. Social worker coeditors of the handbook intentionally sought guidance from people with mild to moderate memory loss regarding handbook content, design, and overall tone. A focus group, three sessions of a review group, e-mails, and personal interviews were used to solicit and review input from participants. The editors also incorporated content contributions in the form of essays, quotations, and an original poem from people with memory loss, alongside contributions from clinic staff, university faculty, and community service providers. People with memory loss provided input in five areas: response to a new diagnosis, coping with memory loss, messages to other newly diagnosed people and health care professionals, available community resources, and recommendations for handbook design. The development process reinforced a key message of the handbook: People with memory loss exhibit ongoing strengths, which help them participate in life. The process also ensured that the handbook content and design would be relevant and applicable to its users. The handbook is now regularly distributed as a primary patient education tool in the memory clinic and community programs.

Background: Improvements in high-throughput phenotyping technologies are rapidly expanding the scope and capacity of plant biology studies to measure growth traits. Nevertheless, the costs of commercial phenotyping equipment and infrastructure remain prohibitively expensive for wide-scale uptake, while academic solutions can require significant local expertise. Here we present a low-cost methodology for plant biologists to build their own phenotyping system for quantifying growth rates and phenotypic characteristics of Arabidopsis thaliana rosettes throughout the diel cycle., Results: We constructed an image capture system consisting of a near infra-red (NIR, 940 nm) LED panel with a mounted Raspberry Pi NoIR camera and developed a MatLab-based software module (iDIEL Plant) to characterise rosette expansion. Our software was able to accurately segment and characterise multiple rosettes within an image, regardless of plant arrangement or genotype, and batch process image sets. To further validate our system, wild-type Arabidopsis plants (Col-0) and two mutant lines with reduced Rubisco contents, pale leaves and slow growth phenotypes ( 1a3b and 1a2b ) were grown on a single plant tray. Plants were imaged from 9 to 24 days after germination every 20 min throughout the 24 h light-dark growth cycle (i.e. the diel cycle). The resulting dataset provided a dynamic and uninterrupted characterisation of differences in rosette growth and expansion rates over time for the three lines tested., Conclusion: Our methodology offers a straightforward solution for setting up automated, scalable and low-cost phenotyping facilities in a wide range of lab environments that could greatly increase the processing power and scalability of Arabidopsis soil growth experiments.

Growth and productivity in important crop plants is limited by the inefficiencies of the C3 photosynthetic pathway. Introducing CO2-concentrating mechanisms (CCMs) into C3 plants could overcome these limitations and lead to increased yields. Many unicellular microautotrophs, such as cyanobacteria and green algae, possess highly efficient biophysical CCMs that increase CO2 concentrations around the primary carboxylase enzyme, Rubisco, to enhance CO2 assimilation rates. Algal and cyanobacterial CCMs utilize distinct molecular components, but share several functional commonalities. Here we outline the recent progress and current challenges of engineering biophysical CCMs into C3 plants. We review the predicted requirements for a functional biophysical CCM based on current knowledge of cyanobacterial and algal CCMs, the molecular engineering tools and research pipelines required to translate our theoretical knowledge into practice, and the current challenges to achieving these goals., (© The Author 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Introducing components of algal carbon concentrating mechanisms (CCMs) into higher plant chloroplasts could increase photosynthetic productivity. A key component is the Rubisco-containing pyrenoid that is needed to minimise CO 2 retro-diffusion for CCM operating efficiency. Rubisco in Arabidopsis was re-engineered to incorporate sequence elements that are thought to be essential for recruitment of Rubisco to the pyrenoid, namely the algal Rubisco small subunit (SSU, encoded by rbcS) or only the surface-exposed algal SSU α-helices. Leaves of Arabidopsis rbcs mutants expressing 'pyrenoid-competent' chimeric Arabidopsis SSUs containing the SSU α-helices from Chlamydomonas reinhardtii can form hybrid Rubisco complexes with catalytic properties similar to those of native Rubisco, suggesting that the α-helices are catalytically neutral. The growth and photosynthetic performance of complemented Arabidopsis rbcs mutants producing near wild-type levels of the hybrid Rubisco were similar to those of wild-type controls. Arabidopsis rbcs mutants expressing a Chlamydomonas SSU differed from wild-type plants with respect to Rubisco catalysis, photosynthesis and growth. This confirms a role for the SSU in influencing Rubisco catalytic properties., (© 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.)

Many algae use a biophysical carbon concentrating mechanism for active accumulation and retention of inorganic carbon within chloroplasts, with CO2 fixation by RuBisCO within a micro-compartment, the pyrenoid. Engineering such mechanisms into higher plant chloroplasts is a possible route to augment RuBisCO operating efficiency and photosynthetic rates. Significant progress has been made recently in characterising key algal transporters and identifying factors responsible for the aggregation of RuBisCO into the pyrenoid. Several transporters have now also been successfully incorporated into higher plant chloroplasts. Consistent with the predictions from modelling, regulation of higher plant plastidic carbonic anhydrases and some form of RuBisCO aggregation will be needed before the mechanism delivers potential benefits. Key research priorities include a better understanding of the regulation of the algal carbon concentrating mechanism, advancing the fundamental characterisation of known components, evaluating whether higher plant chloroplasts can accommodate a pyrenoid, and, ultimately, testing transgenic lines under realistic growth conditions., (Copyright © 2016. Published by Elsevier Ltd.)

Many eukaryotic green algae possess biophysical carbon-concentrating mechanisms (CCMs) that enhance photosynthetic efficiency and thus permit high growth rates at low CO2 concentrations. They are thus an attractive option for improving productivity in higher plants. In this study, the intracellular locations of ten CCM components in the unicellular green alga Chlamydomonas reinhardtii were confirmed. When expressed in tobacco, all of these components except chloroplastic carbonic anhydrases CAH3 and CAH6 had the same intracellular locations as in Chlamydomonas. CAH6 could be directed to the chloroplast by fusion to an Arabidopsis chloroplast transit peptide. Similarly, the putative inorganic carbon (Ci) transporter LCI1 was directed to the chloroplast from its native location on the plasma membrane. CCP1 and CCP2 proteins, putative Ci transporters previously reported to be in the chloroplast envelope, localized to mitochondria in both Chlamydomonas and tobacco, suggesting that the algal CCM model requires expansion to include a role for mitochondria. For the Ci transporters LCIA and HLA3, membrane location and Ci transport capacity were confirmed by heterologous expression and H(14) CO3 (-) uptake assays in Xenopus oocytes. Both were expressed in Arabidopsis resulting in growth comparable with that of wild-type plants. We conclude that CCM components from Chlamydomonas can be expressed both transiently (in tobacco) and stably (in Arabidopsis) and retargeted to appropriate locations in higher plant cells. As expression of individual Ci transporters did not enhance Arabidopsis growth, stacking of further CCM components will probably be required to achieve a significant increase in photosynthetic efficiency in this species., (© 2015 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.)

The balance between carbon assimilation, storage and utilisation during photosynthesis is dependent on partitioning of photoassimilate between starch and sucrose, and varies in response to changes in the environment. However, the extent to which the capacity to modulate carbon partitioning rapidly through short-term allosteric regulation may contribute to plant performance is unknown. Here we examine the physiological role of fructose 2,6-bisphosphate (Fru-2,6-P2 ) during photosynthesis, growth and reproduction in Arabidopsis thaliana (L.). In leaves this signal metabolite contributes to coordination of carbon assimilation and partitioning during photosynthesis by allosterically modulating the activity of cytosolic fructose-1,6-bisphosphatase. Three independent T-DNA insertional mutant lines deficient in 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (F2KP), the bifunctional enzyme responsible for both the synthesis and degradation of Fru-2,6-P2 , lack Fru-2,6-P2 . These plants have normal steady-state rates of photosynthesis, but exhibit increased partitioning of photoassimilate into sucrose and have delayed photosynthetic induction kinetics. The F2KP-deficient plants grow normally in constant environments, but show reduced growth and seed yields relative to wildtype plants in fluctuating light and/or temperature. We conclude that Fru-2,6-P2 is required for optimum regulation of photosynthetic carbon metabolism under variable growth conditions. These analyses suggest that the capacity of Fru-2,6-P2 to modulate partitioning of photoassimilate is an important determinant of growth and fitness in natural environments., (© 2015 The Authors The Plant Journal © 2015 John Wiley & Sons Ltd.)

Medical social workers have needs for training in ethics that is specific to dilemmas that arise while providing service to patients who are very ill, mentally compromised, or in a terminal condition. A social work department developed a continuing education training to educate social workers in bioethics related to determining decisional capacity and understanding standards of ethical decision making. Case studies are used to illustrate ethical conflicts and the role of social workers in resolving them. The benefits of case study training are discussed.

Vascular plant bio-photovoltaics (VP-BPV) is a recently developed technology that uses higher plants to harvest solar energy and the metabolic activity of heterotrophic microorganisms in the plant rhizosphere to generate electrical power. In the present study, electrical output and maximum power output variations were investigated in a novel VP-BPV configuration using the crop plant rice (Oryza sativa L.) or an associated weed, Echinochloa glabrescens (Munro ex Hook. f.). In order to compare directly the physiological performances of these two species in VP-BPV systems, plants were grown in the same soil and glasshouse conditions, while the bio-electrochemical systems were operated in the absence of additional energy inputs (e.g. bias potential, injection of organic substrate and/or bacterial pre-inoculum). Diurnal oscillations were clearly observed in the electrical outputs of VP-BPV systems containing the two species over an 8-day growth period. During this 8-day period, O. sativa generated charge ∼6 times faster than E. glabrescens. This greater electrogenic activity generated a total charge accumulation of 6.75 ± 0.87 Coulombs for O. sativa compared to 1.12 ± 0.16 for E. glabrescens. The average power output observed over a period of about 30 days for O. sativa was significantly higher (0.980 ± 0.059 GJ ha(-1) year(-1)) than for E. glabrescens (0.088 ± 0.008 GJ ha(-1) year(-1)). This work indicates that electrical power can be generated in both VP-BPV systems (O. sativa and E. glabrescens) when bacterial populations are self-forming. Possible reasons for the differences in power outputs between the two plant species are discussed.

Buddhism has grown in the United States in the past 50 years. Immigrants come following long traditions. American converts are more eclectic. The first Buddhist precept prohibiting harm to living things, the virtue of compassion, and the goal of a peaceful death provide guidance for ethical decision making regarding organ donation, withholding and withdrawing life-sustaining treatment, voluntary cessation of eating, physician aid in dying, and euthanasia. Concepts and views from three Buddhist traditions and views of master practitioners are presented. Case examples illustrate some of the differences within Buddhism. Suggestions for social workers are provided.

Bio-photovoltaic cells (BPVs) are a new photo-bio-electrochemical technology for harnessing solar energy using the photosynthetic activity of autotrophic organisms. Currently power outputs from BPVs are generally low and suffer from low efficiencies. However, a better understanding of the electrochemical interactions between the microbes and conductive materials will be likely to lead to increased power yields. In the current study, the fresh-water, filamentous cyanobacterium Pseudanabaena limnetica (also known as Oscillatoria limnetica) was investigated for exoelectrogenic activity. Biofilms of P. limnetica showed a significant photo response during light-dark cycling in BPVs under mediatorless conditions. A multi-channel BPV device was developed to compare quantitatively the performance of photosynthetic biofilms of this species using a variety of different anodic conductive materials: indium tin oxide-coated polyethylene terephthalate (ITO), stainless steel (SS), glass coated with a conductive polymer (PANI), and carbon paper (CP). Although biofilm growth rates were generally comparable on all materials tested, the amplitude of the photo response and achievable maximum power outputs were significantly different. ITO and SS demonstrated the largest photo responses, whereas CP showed the lowest power outputs under both light and dark conditions. Furthermore, differences in the ratios of light : dark power outputs indicated that the electrochemical interactions between photosynthetic microbes and the anode may differ under light and dark conditions depending on the anodic material used. Comparisons between BPV performances and material characteristics revealed that surface roughness and surface energy, particularly the ratio of non-polar to polar interactions (the CQ ratio), may be more important than available surface area in determining biocompatibility and maximum power outputs in microbial electrochemical systems. Notably, CP was readily outperformed by all other conductive materials tested, indicating that carbon may not be an optimal substrate for microbial fuel cell operation.

A new configuration of the fluid dynamic gauging technique for measuring soft layers on surfaces was used to monitor the growth of a cyanobacterium, Synechococcus sp. WH 5701, on stainless steel (SS), glass and an indium tin oxide (ITO) on a polyethylene terephthalate (PET) substratum. The biofilm thickness increased steadily over 4 weeks and exhibited noticeable changes in microstructure and strength. The biofilms all exhibited a two-layer structure, with a compact layer next to the substratum and a loose layer above. Biofilms on ITO or SS exhibited cohesive failure when removed by fluid shear whereas those on glass exhibited adhesive failure. The technique is able to elucidate various aspects of biofilm behaviour, as illustrated by the action of a biocide (NaOCl) on a mature biofilm.