Structure, Regulation, and Significance of Cyanobacterial and Chloroplast Adenosine Triphosphate Synthase in the Adaptability of Oxygenic Photosynthetic Organisms

In cyanobacteria and chloroplasts (in algae and plants), ATP synthase plays a pivotal role as a photosynthetic membrane complex responsible for producing ATP from adenosine diphosphate and inorganic phosphate, utilizing a proton motive force gradient induced by photosynthesis. These two ATP synthases exhibit similarities in gene organization, amino acid sequences of subunits, structure, and functional mechanisms, suggesting that cyanobacterial ATP synthase is probably the evolutionary precursor to chloroplast ATP synthase. In this review, we explore the precise synthesis and assembly of ATP synthase subunits to address the uneven stoichiometry within the complex during transcription, translation, and assembly processes. We also compare the regulatory strategies governing ATP synthase activity to meet varying energy demands in cyanobacteria and chloroplasts amid fluctuating natural environments. Furthermore, we delve into the role of ATP synthase in stress tolerance and photosynthetic carbon fixation efficiency in oxygenic photosynthetic organisms (OPsOs), along with the current researches on modifying ATP synthase to enhance carbon fixation efficiency under stress conditions. This review aims to offer theoretical insights and serve as a reference for understanding the functional mechanisms of ATP synthase, sparking innovative ideas for enhancing photosynthetic carbon fixation efficiency by utilizing ATP synthase as an effective module in OPsOs.

Arthrospira promotes plant growth and soil properties under high salinity environments

Salt stress detrimentally impacts plant growth, imperiling crop yield and food quality. Ameliorating plant resilience and productivity in saline environments is critical for global food security. Here, we report the positive effect of Arthrospira (Spirulina) on plant growth and salt tolerance in Arabidopsis and sweet sorghum. Arthrospira application greatly promotes seed germination and seedling growth in both species under salt stress conditions in a dosage-dependent manner. Application of 6 mg Arthrospira per plate significantly enhances K+/Na+ equilibrium and reactive oxygen species (ROS) scavenging in Arabidopsis, reducing salt-induced toxicity. The primary root length, survival rate, chlorophyll content, photosynthesis, plant height, biomass and yield were all improved in both species. Concurrently, Arthrospira demonstrated the synthesis of compatible solutes, such as trehalose (Tre) and glucosylglycerol (GG), contributing to heightened stress tolerance when co-cultivated with Arabidopsis on plates. Transcriptome analysis revealed dramatic up-/down- regulation of genes involved in phytohormone signal transduction, chlorophyll and photosynthesis metabolism, and phenylpropanoid metabolism in Arabidopsis. Furthermore, the application of Arthrospira exerted a positive influence on the rhizosphere bacteriome structure in sweet sorghum, crucial for nutrient cycling and soil health enhancement. Our findings uncovered the underlying mechanisms of algae-plants interaction in saline soil, proposing strategies to enhance crop productivity and soil quality, thereby addressing the urgent need for sustainable agriculture practices to mitigate salinity's repercussions amidst climate change challenges.

Culture-free identification of fast-growing cyanobacteria cells by Raman-activated gravity-driven encapsulation and sequencing

By directly converting solar energy and carbon dioxide into biobased products, cyanobacteria are promising chassis for photosynthetic biosynthesis. To make cyanobacterial photosynthetic biosynthesis technology economically feasible on industrial scales, exploring and engineering cyanobacterial chassis and cell factories with fast growth rates and carbon fixation activities facing environmental stresses are of great significance. To simplify and accelerate the screening for fast-growing cyanobacteria strains, a method called Individual Cyanobacteria Vitality Tests and Screening (iCyanVS) was established. We show that the 13C incorporation ratio of carotenoids can be used to measure differences in cell growth and carbon fixation rates in individual cyanobacterial cells of distinct genotypes that differ in growth rates in bulk cultivations, thus greatly accelerating the process screening for fastest-growing cells. The feasibility of this approach is further demonstrated by phenotypically and then genotypically identifying individual cyanobacterial cells with higher salt tolerance from an artificial mutant library via Raman-activated gravity-driven encapsulation and sequencing. Therefore, this method should find broad applications in growth rate or carbon intake rate based screening of cyanobacteria and other photosynthetic cell factories.

Engineering Cyanobacterial Cell Factories for Photosynthetic Production of Fructose

Fructose is an important monosaccharide product widely applied in the food, medicine, and chemical industries. Currently, fructose is mainly manufactured with plant biomass-sourced polysaccharides through multiple steps of digestion, conversion, separation, and purification. The development of cyanobacterial metabolic engineering provides an attractive alternative route for the one-step direct production of fructose utilizing carbon dioxide and solar energy. In this work, we developed a paradigm for engineering cyanobacterial chassis cells into efficient cell factories for the photosynthetic production of fructose. In a representative cyanobacterial strain, Synechococcus elongatus PCC 7942, knockout of fructokinase effectively activated the synthesis and secretion of fructose in hypersaline conditions, independent of any heterologous transporters. The native sucrose synthesis pathway was identified as playing a primary role in fructose synthesis. Through combinatory optimizations on the levels of metabolism, physiology, and cultivation, the fructose yield of the Synechococcus cell factories was stepwise improved to 3.9 g/L. Such a paradigm was also adopted to engineer another Synechococcus strain, the marine species Synechococcus sp. PCC 7002, and facilitated an even higher fructose yield of over 6 g/L. Finally, the fructose synthesized and secreted by the cyanobacterial photosynthetic cell factories was successfully extracted and prepared from the culture broth in the form of products with 86% purity through multistep separation-purification operations. This work demonstrated a paradigm for systematically engineering cyanobacteria for photosynthetic production of desired metabolites, and it also confirmed the feasibility and potential of cyanobacterial photosynthetic biomanufacturing as a simple and efficient route for fructose production.

Unlocking the potentials of cyanobacterial photosynthesis for directly converting carbon dioxide into glucose

Glucose is the most abundant monosaccharide, serving as an essential energy source for cells in all domains of life and as an important feedstock for the biorefinery industry. The plant-biomass-sugar route dominates the current glucose supply, while the direct conversion of carbon dioxide into glucose through photosynthesis is not well studied. Here, we show that the potential of Synechococcus elongatus PCC 7942 for photosynthetic glucose production can be unlocked by preventing native glucokinase activity. Knocking out two glucokinase genes causes intracellular accumulation of glucose and promotes the formation of a spontaneous mutation in the genome, which eventually leads to glucose secretion. Without heterologous catalysis or transportation genes, glucokinase deficiency and spontaneous genomic mutation lead to a glucose secretion of 1.5 g/L, which is further increased to 5 g/L through metabolic and cultivation engineering. These findings underline the cyanobacterial metabolism plasticities and demonstrate their applications for supporting the direct photosynthetic production of glucose.

Engineered hypermutation adapts cyanobacterial photosynthesis to combined high light and high temperature stress

Photosynthesis can be impaired by combined high light and high temperature (HLHT) stress. Obtaining HLHT tolerant photoautotrophs is laborious and time-consuming, and in most cases the underlying molecular mechanisms remain unclear. Here, we increase the mutation rates of cyanobacterium Synechococcus elongatus PCC 7942 by three orders of magnitude through combinatory perturbations of the genetic fidelity machinery and cultivation environment. Utilizing the hypermutation system, we isolate Synechococcus mutants with improved HLHT tolerance and identify genome mutations contributing to the adaptation process. A specific mutation located in the upstream non-coding region of the gene encoding a shikimate kinase results in enhanced expression of this gene. Overexpression of the shikimate kinase encoding gene in both Synechococcus and Synechocystis leads to improved HLHT tolerance. Transcriptome analysis indicates that the mutation remodels the photosynthetic chain and metabolism network in Synechococcus. Thus, mutations identified by the hypermutation system are useful for engineering cyanobacteria with improved HLHT tolerance.

Engineering cyanobacteria for converting carbon dioxide into isomaltulose

Isomaltulose is a promising functional sweetener with broad application prospects in the food industry. Currently, isomaltulose is mainly produced through bioconversion processes based on the isomerization of sucrose, the economic feasibility of which is influenced by the cost of sucrose feedstocks, the biocatalyst preparation, and product purification. Cyanobacterial photosynthetic production utilizing solar energy and carbon dioxide represents a promising route for the supply of sugar products, which can promote both carbon reduction and green production. Previously, some cyanobacteria strains have been successfully engineered for synthesis of sucrose, the main feedstock for isomaltulose production. In this work, we introduced different sucrose isomerases into Synechococcus elongatus PCC 7942 and successfully achieved the isomaltulose synthesis and accumulation in the recombinant strains. Combinatory expression of an Escherichia coli sourced sucrose permease CscB with the sucrose isomerases led to efficient secretion of isomaltulose and significantly elevated the final titer. During a 6-day cultivation, 777 mg/L of isomaltulose was produced by the engineered Synechococcus cell factory. This work demonstrated a new route for isomaltulose biosynthesis utilizing carbon dioxide as the substrate, and provided novel understandings for the plasticity of cyanobacterial photosynthetic metabolism network.

Manipulating the Expression of Glycogen Phosphorylase in Synechococcus elongatus PCC 7942 to Mobilize Glycogen Storage for Sucrose Synthesis

Cyanobacteria are a promising photosynthetic chassis to produce biofuels, biochemicals, and pharmaceuticals at the expense of CO₂ and light energy. Glycogen accumulation represents a universal carbon sink mechanism among cyanobacteria, storing excess carbon and energy from photosynthesis and may compete with product synthesis. Therefore, the glycogen synthesis pathway is often targeted to increase cyanobacterial production of desired carbon-based products. However, these manipulations caused severe physiological and metabolic impairments and often failed to optimize the overall performance of photosynthetic production. Here, in this work, we explored to mobilize the glycogen storage by strengthening glycogen degradation activities. In Synechococcus elongatus PCC 7942, we manipulated the abundances of glycogen phosphorylase (GlgP) with a theophylline dose-responsive riboswitch approach, which holds control over the cyanobacterial glycogen degradation process and successfully regulated the glycogen contents in the recombinant strain. Taking sucrose synthesis as a model, we explored the effects of enhanced glycogen degradation on sucrose production and glycogen storage. It is confirmed that under non-hypersaline conditions, the overexpressed glgP facilitated the effective mobilization of glycogen storage and resulted in increased secretory sucrose production. The findings in this work provided fresh insights into the area of cyanobacteria glycogen metabolism engineering and would inspire the development of novel metabolic engineering approaches for efficient photosynthetic biosynthesis.

[Engineering the glycogen metabolism in cyanobacterial photosynthetic cell factories: a review]

Cyanobacteria are important photosynthetic autotrophic microorganisms and are considered as one of the most promising microbial chassises for photosynthetic cell factories. Glycogen is the most important natural carbon sink of cyanobacteria, playing important roles in regulating its intracellular carbon distributions. In order to optimize the performances of cyanobacterial photosynthetic cell factories and drive more photosynthetic carbon flow toward the synthesis of desired metabolites, many strategies and approaches have been developed to manipulate the glycogen metabolism in cyanobacteria. However, the disturbances on glycogen metabolism usually cause complex effects on the physiology and metabolism of cyanobacterial cells. Moreover, the effects on synthesis efficiencies of different photosynthetic cell factories usually differ. In this manuscript, we summarized the recent progress on engineering cyanobacterial glycogen metabolism, analyzed and compared the physiological and metabolism effects caused by engineering glycogen metabolism in different cyanobacteria species, and prospected the future trends of this strategy on optimizing cyanobacterial photosynthetic cell factories.

Engineering a Controllable Targeted Protein Degradation System and a Derived OR-GATE-Type Inducible Gene Expression System in Synechococcus elongatus PCC 7942

Cyanobacteria are important model organisms for exploring the mechanisms of photosynthesis and are considered as promising microbial platforms for photosynthetic biomanufacturing. The development of efficient cyanobacteria cell factories requires efficient and convenient tools to dynamically regulate and manipulate target proteins, modules, and pathways. Targeted protein degradation is important to achieve rapid responses of cellular metabolic networks to artificial or environmental signals, and there are currently limited approaches to induce protein degradation in cyanobacteria. In this work, we developed an Escherichia coli sourced ssrA-tagging system in an important cyanobacteria strain, Synechococcus elongatus PCC 7942, to achieve inducible degradation of target proteins. A modified version of the E. coli ssrA tag (ssrA_DAS) proved to be immune to the native ClpXP system in Synechococcus elongatus PCC 7942, while induced expression of the E. coli sourced adaptor SspB and ClpXP resulted in effective degradation of the tagged proteins. Compared to the previously developed down-regulation approaches, the inducible ssrA_DAS-SspB-ClpXP_Ec system facilitated the smart and rapid degradation of target proteins in PCC7942 cells at different growth stages. Furthermore, when used to regulate the degradation of LacI, the repressor element of LacO-LacI transcription regulation system, an efficient and stringent inducible gene expression system was obtained based on an OR-GATE type genetic circuit design. The tools developed in this work expanded the cyanobacteria synthetic biology toolbox and will facilitate the success of future dynamic metabolic engineering.

Phase I result of ICP-192 (gunagratinib), a highly selective irreversible FGFR inhibitor, in patients with advanced solid tumors harboring FGFR pathway alterations

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Background: ICP-192 (gunagratinib), developed by InnoCare Pharma, is a novel pan-FGFR (fibroblast growth factor receptors) inhibitor that potently and selectively inhibits FGFR activities irreversibly by covalent binding. Preclinical data showed that gunagratinib overcomes the acquired resistance to the first-generation reversible FGFR inhibitors, e.g., infigratinib. ICP-CL-00301 is a phase I, first-in-human, clinical study which includes a dose escalation followed by dose expansion. The safety and tolerability as well as pharmacokinetics/pharmacodynamics (PK/PD) of gunagratinib were evaluated in patients with advanced solid tumors, and the preliminary anti-tumor activity was evaluated by RECIST1.1 in patients with FGF/FGFR gene aberrations. Methods: In the dose-escalation stage, patients with advanced solid tumors with or without FGF/FGFR alterations were treated with escalating doses (2, 4, 8, 10, 12, 14, 16 mg etc.) of gunagratinib once daily in 21-day cycles until disease progression or unacceptable toxicity. During the dose-expansion stage, patients with cholangiocarcinoma harboring FGFR2 gene fusion/translocation received the treatment of gunagratinib daily at 12 mg continuously. Results: As of February 2021, a total of 30 patients had received the treatment of gunagratinib. The median age of the treated patients was 55.0 (range: 28 to 75 years) with 56.7% male and ECOG performance status between 0-1. The maximum tolerated dose (MTD) had not been reached. The most common treatment-related adverse events (TRAEs) ( > 20%) included hyperphosphatemia, hypercalcemia, increased ALT or AST, diarrhea and hypertriglyceridemia. Hyperphosphatemia is a commonly reported AE from other trials targeting FGFR and here serves as a PD biomarker of FGFR inhibition. This PD biomarker was observed in 73.3% of the patients treated with gunagratinib at all dose levels and was consistently observed at doses of 8 mg QD and above. Hyperphosphatemia was well managed with oral phosphate binders when necessary. The plasma exposure increased proportionally to the oral dosage levels of gunagratinib. Among the 12 patients with FGF/FGFR gene aberrations who have completed at least one tumor assessment, the overall response rate (ORR) was 33.3%, including 1 patient (8.3%) of cholangiocarcinoma with complete response (CR) and 3 patients (25%) with partial response (PR). The disease control rate (DCR) was 91.7% (11 of 12 patients). Conclusions: Gunagratinib is safe and well-tolerated in patients with advanced solid tumors. Anti-tumor activity was demonstrated in patients with FGF/FGFR gene aberrations in multiple tumor types, including cholangiocarcinoma (NCT03758664). Better response is expected with the increase of treatment durations. Clinical trial information: NCT03758664.

Rapidly Improving High Light and High Temperature Tolerances of Cyanobacterial Cell Factories Through the Convenient Introduction of an AtpA-C252F Mutation

Photosynthetic biomanufacturing is a promising route for green production of biofuels and biochemicals utilizing carbon dioxide and solar energy. Cyanobacteria are important microbial platforms for constructing photosynthetic cell factories. Toward scaled outdoor cultivations in the future, high light and high temperature tolerances of cyanobacterial chassis strains and cell factories would be determinant properties to be optimized. We proposed a convenient strategy for rapidly improving high light and high temperature tolerances of an important cyanobacterial chassis Synechococcus elongatus PCC 7942 and the derived cell factories. Through introduction and isolation of an AtpA-C252F mutation, PCC 7942 mutants with improved high light and high temperature tolerances could be obtained in only 4 days with an antibiotics-free mode. Adopting this strategy, cellular robustness and sucrose synthesizing capacities of a PCC 7942 cell factory were successfully improved.

Systematic Identification of Target Genes for Cellular Morphology Engineering in Synechococcus elongatus PCC7942

Cyanobacteria are serving as promising microbial platforms for development of photosynthetic cell factories. For enhancing the economic competitiveness of the photosynthetic biomanufacturing technology, comprehensive improvements on industrial properties of the cyanobacteria chassis cells and engineered strains are required. Cellular morphology engineering is an up-and-coming strategy for development of microbial cell factories fitting the requirements of industrial application. In this work, we performed systematic evaluation of potential genes for cyanobacterial cellular morphology engineering. Twelve candidate genes participating in cell morphogenesis of an important model cyanobacteria strain, Synechococcus elongatus PCC7942, were knocked out/down and overexpressed, respectively, and the influences on cell sizes and cell shapes were imaged and calculated. Targeting the selected genes with potentials for cellular morphology engineering, the controllable cell lengthening machinery was also explored based on the application of sRNA approaches. The findings in this work not only provided many new targets for cellular morphology engineering in cyanobacteria, but also helped to further understand the cell division process and cell elongation process of Synechococcus elongatus PCC7942.

[Cyanobacteria based photosynthetic production of sucrose: development and prospect]

Biorefinery technologies provide promising solutions to achieve sustainable development facing energy and environment crisis, while abundant sugar feedstock is an essential basis for biorefinery industries. Photosynthetic production of sucrose with cyanobacteria is an alternative sugar feedstock supply route with great potentials. Driven by solar energy, cyanobacteria photosynthetic cell factory could directly convert carbon dioxide and water into sucrose, and such a process could simultaneously reduce carbon emissions and supply sugar feedstocks. Here we introduced the history and updated the state-of-the-art on development of cyanobacteria cell factories for photosynthetic production of sucrose, summarized the progress and problems on mechanisms of sucrose synthesis, metabolic engineering strategies and technology expansions, and finally forecasted the future development direction in this area.

Adopting a Theophylline-Responsive Riboswitch for Flexible Regulation and Understanding of Glycogen Metabolism in Synechococcus elongatus PCC7942

Cyanobacteria are supposed to be promising photosynthetic microbial platforms that recycle carbon dioxide driven into biomass and bioproducts by solar energy. Glycogen synthesis serves as an essential natural carbon sink mechanism, storing a large portion of energy and organic carbon source of photosynthesis. Engineering glycogen metabolism to harness and rewire carbon flow is an important strategy to optimize efficacy of cyanobacteria platforms. ADP-glucose pyrophosphorylase (GlgC) catalyzes the rate-limiting step for glycogen synthesis. However, knockout of glgC fails to promote cell growth or photosynthetic production in cyanobacteria, on the contrary, glgC deficiency impairs cellular fitness and robustness. In this work, we adopted a theophylline-responsive riboswitch to engineer and control glgC expression in Synechococcus elongatus PCC7942 and achieved flexible regulation of intracellular GlgC abundance and glycogen storage. With this approach, glycogen synthesis and glycogen contents in PCC7942 cells could be regulated in a range from about 40 to 300% of wild type levels. In addition, the results supported a positive role of glycogen metabolism in cyanobacteria cellular robustness. When glycogen storage was reduced, cellular physiology and growth under standard conditions was not impaired, while cellular tolerance toward environmental stresses was weakened. While when glycogen synthesis was enhanced, cells of PCC7942 displayed optimized cellular robustness. Our findings emphasize the significance of glycogen metabolism for cyanobacterial physiology and the importance of flexible approaches for engineering and understanding cellular physiology and metabolism.

Systematic identification of a neutral site on chromosome of Synechococcus sp. PCC7002, a promising photosynthetic chassis strain

Cyanobacteria based photosynthetic biomanufacturing is supposed to be one of the alternative routes for sustainable production of biofuels and biochemicals. Synechococcus sp. PCC 7002 is a promising cyanobacterial chassis strain possessing desired properties for scaled cultivation in future. Development of cyanobacterial cell factories requires modifications of PCC7002 chromosome to expand the photosynthesis-based metabolism networks. Therefore, mining genomic neutral sites for stable integration of heterologous genes and pathways would be of great significance for expanding the toolbox for PCC7002 genome engineering. Here we demonstrate a paradigm for identification of potential neutral sites from chromosome of PCC7002 based on genomic and transcriptomics data. By refining the massive omics information from database, 51 putative sites with no significant physiological or metabolism effects were extracted as candidates. Combining genomic context analysis, a locus termed as NS0027 between two neighboring putative neutral genes was selected and evaluated as a neutral site for genetic integration. In addition, an ethanol synthesis pathway was introduced into the NS0027 site to assess the functionality of this site. The sites we identified and the strategy we adopted in this work would benefit the development of effective genetic toolbox and efficient photosynthetic cell factories based on PCC7002.

[Cyanobacteria cell factories for ethanol photosynthetic production: development and prospect]

Bioethanol is one of the most promising and representative biofuel products. Photosynthetic production of ethanol using CO₂ and solar energy based on cyanobacteria is of great significance for research and application, due to the potential to reduce CO₂ emission and to provide renewable energy simultaneously. Here we review the history and updated development of cyanobacteria cell factories for ethanol photosynthetic production, the progress and problems in pathway optimization, chassis selection, and metabolic engineering strategies, and finally indicate the future development in this area.

Rescuing ethanol photosynthetic production of cyanobacteria in non-sterilized outdoor cultivations with a bicarbonate-based pH-rising strategy

BACKGROUND

Ethanol photosynthetic production based on cyanobacteria cell factories utilizing CO₂ and solar energy provides an attractive solution for sustainable production of green fuels. However, the scaling up processes of cyanobacteria cell factories were usually threatened or even devastated by biocontaminations, which restricted biomass or products accumulations of cyanobacteria cells. Thus it is of great significance to develop reliable biocontamination-controlling strategies for promoting ethanol photosynthetic production in large scales.

RESULTS

The scaling up process of a previously developed Synechocystis strain Syn-HZ24 for ethanol synthesis was severely inhibited and devastated by a specific contaminant, Pannonibacter phragmitetus, which overcame the growths of cyanobacteria cells and completely consumed the ethanol accumulation in the cultivation systems. Physiological analysis revealed that growths and ethanol-consuming activities of the contaminant were sensitive to alkaline conditions, while ethanol-synthesizing cyanobacteria strain Syn-HZ24 could tolerate alkaline pH conditions as high as 11.0, indicating that pH-increasing strategy might be a feasible approach for rescuing ethanol photosynthetic production in outdoor cultivation systems. Thus, we designed and evaluated a Bicarbonate-based Integrated Carbon Capture System (BICCS) derived pH-rising strategy to rescue the ethanol photosynthetic production in non-sterilized conditions. In lab scale artificially simulated systems, pH values of BG11 culture medium were maintained around 11.0 by 180 mM NaHCO₃ and air steam, under which the infection of Pannonibacter phragmitetus was significantly restricted, recovering ethanol production of Syn-HZ24 by about 80%. As for outdoor cultivations, ethanol photosynthetic production of Syn-HZ24 was also successfully rescued by the BICCS-derived pH-rising strategy, obtaining a final ethanol concentration of 0.9 g/L after 10 days cultivation.

CONCLUSIONS

In this work, a novel product-consuming biocontamination pattern in cyanobacteria cultivations, causing devastated ethanol photosynthetic production, was identified and characterized. Physiological analysis of the essential ethanol-consuming contaminant directed the design and application of a pH-rising strategy, which effectively and selectively controlled the contamination and rescued ethanol photosynthetic production. Our work demonstrated the importance of reliable contamination control systems and strategies for large scale outdoor cultivations of cyanobacteria, and provided an inspiring paradigm for targeting effective solutions.

Inhibition of the small GTPase Cdc42 in regulation of epileptic-seizure in rats

Altered expression of neuronal cytoskeletal proteins are known to play an important role in hyper-excitability of neurons in patients and animal models of epilepsy. Our previous work showed that cell division cycle 42 GTP-binding protein (Cdc42), a small GTPase of the Rho-subfamily, is significantly increased in the brain tissue of patients with temporal lobe epilepsy (TLE) and in the brain tissues of the epileptic model of rats. However, whether inhibition of Cdc42 can modify epileptic seizures has not been investigated. In this study, using a pilocarpine-induced epileptic model, we found that pretreatment with ML141, a specific inhibitor of Cdc42, reduces seizure severity. Whole-cell patch-clamp recording on CA1 pyramidal neurons in hippocampal slices from pilocarpine-induced epileptic model demonstrated that ML141 significantly inhibits the frequency of action potentials (APs), increases the amplitude and frequency of miniature inhibitory postsynaptic currents (mIPSCs), and increases the amplitude of evoked inhibitory postsynaptic currents (eIPSCs). However, ML141 did not have an impact on the miniature excitatory postsynaptic currents (mEPSCs). Our results are the first to indicate that Cdc42 plays an important role in the onset and progression of epileptic-seizures by regulating synaptic inhibition.

Combinatory strategy for characterizing and understanding the ethanol synthesis pathway in cyanobacteria cell factories

BACKGROUND

Photosynthetic production of chemicals and fuels by recycling CO2 in cyanobacteria is a promising solution facing energy shortage and resource declination. Ethanol is an attractive and demonstrative biofuel product, and ethanol synthesis in cyanobacteria has been achieved by assembling of a pathway consisting of pyruvate decarboxylase (PDCzm) and alcohol dehydrogenase II (slr1192). For enabling more powerful ethanol photosynthetic production, an optimized and balanced catalyzing route was required. In this work, we provided a paradigm for systematically characterizing and optimizing the PDCzm-slr1192 pathway from engineered cyanobacteria strains, combining in vitro reconstitution, genetic engineering and feeding-cultivation.

RESULTS

We reconstituted the PDCzm-slr1192 pathway in vitro and performed specific titration assays for enzymes, substrates, cofactors, and metal ions. In the in vitro system, K 50 of PDCzm was 0.326 μM, with a V max of 2.074 μM/s; while for slr1192, the values were 0.109 μM and 1.722 μM/s, respectively. Titration response discrepancy indicated that PDCzm rather than slr1192 was the rate-limiting factor for ethanol synthesis. In addition, a 4:6 concentration ratio of PDCzm-slr1192 would endow the reaction with a maximal specific catalytic activity. Titration assays for other components were also performed. K m values for NADPH, pyruvate, TPP, Mg(2+) and acetaldehyde were 0.136, 6.496, 0.011, 0.104, and 0.393 mM, respectively. We further constructed Synechocystis mutant strains with diverse PDCzm-slr1192 concentrations and ratios, and compared the growth and ethanol synthesis performances. The results revealed that activities of PDCzm indeed held control over the ethanol generation capacities. We performed pyruvate-feeding treatment with the newly developed Syn-YQ4 strain, and confirmed that improvement of pyruvate supply would direct more carbon flow to ethanol formation.

CONCLUSIONS

We systematically characterized and optimized the PDCzm-slr1192 pathway in engineered cyanobacteria for ethanol production. Information gained from in vitro monitoring and genetic engineering revealed that for further enhancing ethanol synthesis capacities, PDCzm activities needed enhancement, and the PDCzm-slr1192 ratio should be improved and held to about 1:1.5. Considering actual metabolites concentrations of cyanobacteria cells, enhancing pyruvate supply was also a promising strategy for further updating the current ethanol photosynthetic cell factories.

Engineering cellular robustness of microbes by introducing the GroESL chaperonins from extremophilic bacteria

The cellular robustness is a big concern for efficient microbial production of biofuels and biochemicals. In this study, the groESL genes from extremophilic bacteria were found to serve as transplantable stress-response elements to improve diverse types of stress-tolerances of other microbes. By overexpressing the groESL from the solvent-tolerant Pseudomonas putida in Escherichia coli, its thermo-tolerance and ethanol-tolerance were significantly increased. Meanwhile, the groESL from the thermophilic Thermoanaerobacter tengcongensis endowed Clostridium acetobutylicum with improved corn cob hydrolysates (CCH)-tolerance as well as elevated butanol productivity. The chaperonins GroESL have been widely considered as cellular stress-response proteins and overexpression of native groESL has been proven to improve cellular tolerances facing various stresses. Here we found that the groESL genes from extremophilic bacteria were superior to the native ones, possibly because they have adapted to the environmental stresses during long-term natural evolution. Moreover, our results also revealed that different extreme groESL genes performed quite different in different microbes. Thus the relation and compatibility between the extremophiles and the host must be considered for selection of the proper groESL for engineering microbial robustness.

Developing controllable hypermutable Clostridium cells through manipulating its methyl-directed mismatch repair system

Development of controllable hypermutable cells can greatly benefit understanding and harnessing microbial evolution. However, there have not been any similar systems developed for Clostridium, an important bacterial genus. Here we report a novel two-step strategy for developing controllable hypermutable cells of Clostridium acetobutylicum, an important and representative industrial strain. Firstly, the mutS/L operon essential for methyldirected mismatch repair (MMR) activity was inactivated from the genome of C. acetobutylicum to generate hypermutable cells with over 250-fold increased mutation rates. Secondly, a proofreading control system carrying an inducibly expressed mutS/L operon was constructed. The hypermutable cells and the proofreading control system were integrated to form a controllable hypermutable system SMBMutC, of which the mutation rates can be regulated by the concentration of anhydrotetracycline (aTc). Duplication of the miniPthl-tetR module of the proofreading control system further significantly expanded the regulatory space of the mutation rates, demonstrating hypermutable Clostridium cells with controllable mutation rates are generated. The developed C. acetobutylicum strain SMBMutC2 showed higher survival capacities than the control strain facing butanol-stress, indicating greatly increased evolvability and adaptability of the controllable hypermutable cells under environmental challenges.

Genome replication engineering assisted continuous evolution (GREACE) to improve microbial tolerance for biofuels production

BACKGROUND

Microbial production of biofuels requires robust cell growth and metabolism under tough conditions. Conventionally, such tolerance phenotypes were engineered through evolutionary engineering using the principle of "Mutagenesis followed-by Selection". The iterative rounds of mutagenesis-selection and frequent manual interventions resulted in discontinuous and inefficient strain improvement processes. This work aimed to develop a more continuous and efficient evolutionary engineering method termed as "Genome Replication Engineering Assisted Continuous Evolution" (GREACE) using "Mutagenesis coupled-with Selection" as its core principle.

RESULTS

The core design of GREACE is to introduce an in vivo continuous mutagenesis mechanism into microbial cells by introducing a group of genetically modified proofreading elements of the DNA polymerase complex to accelerate the evolution process under stressful conditions. The genotype stability and phenotype heritability can be stably maintained once the genetically modified proofreading element is removed, thus scarless mutants with desired phenotypes can be obtained.Kanamycin resistance of E. coli was rapidly improved to confirm the concept and feasibility of GREACE. Intrinsic mechanism analysis revealed that during the continuous evolution process, the accumulation of genetically modified proofreading elements with mutator activities endowed the host cells with enhanced adaptation advantages. We further showed that GREACE can also be applied to engineer n-butanol and acetate tolerances. In less than a month, an E. coli strain capable of growing under an n-butanol concentration of 1.25% was isolated. As for acetate tolerance, cell growth of the evolved E. coli strain increased by 8-fold under 0.1% of acetate. In addition, we discovered that adaptation to specific stresses prefers accumulation of genetically modified elements with specific mutator strengths.

CONCLUSIONS

We developed a novel GREACE method using "Mutagenesis coupled-with Selection" as core principle. Successful isolation of E. coli strains with improved n-butanol and acetate tolerances demonstrated the potential of GREACE as a promising method for strain improvement in biofuels production.

Surgical treatment of intractable epilepsy combined with bipolar electrocoagulation on functional cortex

OBJECTIVE

Resecting epileptogenic foci combined with bipolar electrocoagulation of functional cortex has been successfully used to treat intractable epilepsy.

METHOD

124 cases with intractable epilepsy have been treated from 1996 to 1999, 75 cases with temporal lobe epilepsy and 48 cases with extra-temporal lobe epilepsy, and one case with infantile hemiplegia. Electrocorticography (ECoG) was used pre- and postoperatively. 108 cases were followed-up from one to three years.

RESULTS

The general efficiency of bipolar electrocoagulation on functional cortex (BCFC) for epilepsy is 91.7%. The pathological features indicate that the damage by coagulation of the cortex is only in the supra- and infra-granular layers, similar to multiple subpial transection (MST).

CONCLUSION

When the epileptogenic foci are located in functional cortex, the method of resecting the foci combined with BCFC has been effective and improves the results greatly. BCFC is safe and easy to use.

[Clinical study on treatment of secondary epilepsy caused by intracranial inflammatory granuloma by removing the lesion and bipolar coagulation]

OBJECTIVE

To study the clinical effects of treatment of secondary epilepsy caused by intracranial inflammatory granuloma by resection of the local focus and resection of local focus combined with bipolar coagulation.

METHODS

Twenty-five cases of secondary epilepsy caused by intracranial inflammatory granuloma that were treated from January 1992 to June 1996 (the first group) underwent operation of resection of intracranial granuloma. Pathological examination of the specimens resected during operation was made. Twenty-three cases treated from July 1996 to December 1999 (the second group) underwent operation of the same style and low power thermal cauterization of the surface of multiple cerebral cortex. Specific antibiotic treatment lasted one month after operation for both groups. Antiepileptics were used at least for two years.

RESULTS

In the first group, eighteen cases had been followed up, five cases of which showed unsatisfying control of symptoms of epilepsy; and 7 cases were lost to follow-up. In the second group, twenty cases had been followed up and their symptoms of epilepsy were controlled satisfying except in one case.

CONCLUSION

Low power thermal cauterization of the horizontal fibers among the neurons in cerebral cortex under pia mater is one of the essential measures for treatment of secondary epilepsy caused by intracerebral inflammatory granuloma. It is of equal importance as resection of local lesion.

[18F-FDG PET cerebral imaging for localizing epileptogenic foci and its relation to predicting operative outcome]

OBJECTIVE

To find out the relationship between FDG PET image pattern and epileptogenic focus localization and predict prognosis by comparing pre- and post-surgical FDG images with operative effects.

METHODS

72 patients with epilepsy who underwent surgery (49M, 23F, aged 24.3 years on average) were studied with pre-surgical FDG PET cerebral imaging and followed up (av. 15 months, 3-24 months) for assessment of seizure control. 20 of them were studied with post-surgical FDG PET. The accuracy of localization of epileptogenic foci of FDG PET was compared with that of VEEG and MRI. The relationship between pre- and post-surgical FDG metabolic image pattern and surgical outcome was evaluated.

RESULTS

(1) 71 patients showed pre-surgical interictal focal hypometabolism. 1 patient with continuous seizure showed ictal hypermetabolic focus. (2) FDG PET could localize the seizure foci in patients whose EEG showed bilateral or no definite epileptoform discharge. The rate of detection of epileptogenic foci with FDG PET was much higher than that with MRI. Since hypometabolic foci were non-specific, not all hypometabolic foci were epileptogenic. The correlation between postoperative FDG PET and surgical effect could help determine the nature of metabolic focus. (3) Hypometabolism of ipsilateral thalamus and/or contralateral cerebellum with temporal lobe lesion was secondary functional change. (4) The patternization of cerebral images was helpful to surgical planning and helped predict operative outcome.

CONCLUSION

Comparison of pre-surgical with post-surgical FDG PET images help determine the nature of hypometabolic foci. The patternization of FDG PET images help the surgeon select patients, plan type of operation and predict surgical effect.

Retrograde transvenous neuroperfusion: a back door treatment for stroke

BACKGROUND AND PURPOSE

Stroke is the third leading cause of death and the leading cause of adult disability in the United States. The clot-lysis drug tissue plasminogen activator is the only treatment that has been effective for acute stroke patients, yet there are significant limitations to its use and effectiveness. In this study retrograde transvenous neuroperfusion (RTN) was evaluated for its efficacy in reversing acute ischemia, preventing paralysis, and limiting pathological evidence of infarction in baboons.

METHODS

Ten adult male baboons underwent 3.5 hours of reversible middle cerebral artery occlusion (MCAO) under isoflurane (0.25% to 1.5%) anesthesia. Five randomly chosen animals received RTN treatment 1 hour after start of MCAO. Somatosensory evoked potentials were recorded during MCAO. Animals were assigned daily neurological scores. Animals were killed 6 days after MCAO, and brains were quantitatively analyzed for infarct volume.

RESULTS

Within 1 hour after RTN was started, treated animals showed significantly improved somatosensory evoked potentials (103.3% versus 75% of baseline; P<0.01). Likewise, the combined neurological score for the RTN-treated group was 99.2, while the combined mean score for the untreated group was 66.4 (P<0.015). The mean infarction volume was 8.8+/-3.1% (of contralateral hemisphere) for the control group and 0.3+/-0.2% for the RTN-treated group (P<0.01). No increased mortality was seen in the RTN-treated group.

CONCLUSIONS

We conclude that RTN treatment during MCAO effectively reverses the pathophysiological sequelae of ischemia, even when the treatment is initiated 1 hour after the onset of ischemia. Although the infarct volume in the control group was variable when quantitatively assessed 6 days after 3.5 hours of MCAO, virtually no evidence of infarcts was seen in the RTN-treated group.