Fluorescence activated cell-sorting principles and applications in microalgal biotechnology

Isolation and Selection of Protein-Rich Mutants of Chlorella vulgaris by Fluorescence-Activated Cell Sorting with Enhanced Biostimulant Activity to Germinate Garden Cress Seeds

Microalgae are a promising feedstock with proven biostimulant activity that is enhanced by their biochemical components (e.g., amino acids and phytohormones), which turns them into an appealing feedstock to reduce the use of fertilisers in agriculture and improve crop productivity and resilience. Thus, this work aimed to isolate protein-rich microalgal mutants with increased biostimulant activity. Random mutagenesis was performed with Chlorella vulgaris, and a selection of protein-rich mutants were sorted through fluorescence-activated cell sorting (FACS), resulting in the isolation of 17 protein-rich mutant strains with protein contents 19-34% higher than that of the wildtype (WT). Furthermore, mutant F4 displayed a 38%, 22% and 62% higher biomass productivity, growth rate and chlorophyll content, respectively. This mutant was then scaled up to a 7 L benchtop reactor to produce biomass and evaluate the biostimulant potential of this novel strain towards garden cress seeds. Compared to water (control), the germination index and the relative total growth increased by 7% and 19%, respectively, after the application of 0.1 g L-1 of this bioproduct, which highlights its biostimulant potential.

Bioprospecting of Chlamydomonas reinhardtii for boosting biofuel-related products production based on novel aggregation-induced emission active extracellular polymeric substances nanoprobes

Biofuel production from microalgae has been greatly restricted by low biomass productivity and long-term photosynthetic efficacy. Here, a novel strategy for selecting high-growing, stress-resistant algal strains with high photosynthetic capacity was proposed based on biocompatible extracellular polymeric substances (EPS) probes with aggregation-induced emission (AIE) properties. Specifically, AIE active EPS probes were synthesized for in-situ long-term monitoring of the EPS productivity at different algal growth stages. By coupling the AIE-based fluorescent techniques, algal cells were classified into four diverse populations based on their chlorophyll and EPS signals. Mechanistic studies on the sorted algal cells revealed their remarkable stress resistance and high expression of cell division, biopolymer production and photosynthesis-related genes. The sorted and subcultured algal cells consistently exhibited relatively higher growth rates and photosynthetic capacities, resulting in an increased (1.2 to 1.8-fold) algal biomass production, chlorophyll, and lipids. This study can potentially open new strategies to boost microalgal-based biofuel production.

Passive microfluidic devices for cell separation

The separation of specific cell populations is instrumental in gaining insights into cellular processes, elucidating disease mechanisms, and advancing applications in tissue engineering, regenerative medicine, diagnostics, and cell therapies. Microfluidic methods for cell separation have propelled the field forward, benefitting from miniaturization, advanced fabrication technologies, a profound understanding of fluid dynamics governing particle separation mechanisms, and a surge in interdisciplinary investigations focused on diverse applications. Cell separation methodologies can be categorized according to their underlying separation mechanisms. Passive microfluidic separation systems rely on channel structures and fluidic rheology, obviating the necessity for external force fields to facilitate label-free cell separation. These passive approaches offer a compelling combination of cost-effectiveness and scalability when compared to active methods that depend on external fields to manipulate cells. This review delves into the extensive utilization of passive microfluidic techniques for cell separation, encompassing various strategies such as filtration, sedimentation, adhesion-based techniques, pinched flow fractionation (PFF), deterministic lateral displacement (DLD), inertial microfluidics, hydrophoresis, viscoelastic microfluidics, and hybrid microfluidics. Besides, the review provides an in-depth discussion concerning cell types, separation markers, and the commercialization of these technologies. Subsequently, it outlines the current challenges faced in the field and presents a forward-looking perspective on potential future developments. This work hopes to aid in facilitating the dissemination of knowledge in cell separation, guiding future research, and informing practical applications across diverse scientific disciplines.

Random mutagenesis of Phaeodactylum tricornutum using ultraviolet, chemical, and X-radiation demonstrates the need for temporal analysis of phenotype stability

We investigated two non-ionising mutagens in the form of ultraviolet radiation (UV) and ethyl methanosulfonate (EMS) and an ionising mutagen (X-ray) as methods to increase fucoxanthin content in the model diatom Phaeodactylum tricornutum. We implemented an ultra-high throughput method using fluorescence-activated cell sorting (FACS) and live culture spectral deconvolution for isolation and screening of potential pigment mutants, and assessed phenotype stability by measuring pigment content over 6 months using high-performance liquid chromatography (HPLC) to investigate the viability of long-term mutants. Both UV and EMS resulted in significantly higher fucoxanthin within the 6 month period after treatment, likely as a result of phenotype instability. A maximum fucoxanthin content of 135 ± 10% wild-type found in the EMS strain, a 35% increase. We found mutants generated using all methods underwent reversion to the wild-type phenotype within a 6 month time period. X-ray treatments produced a consistently unstable phenotype even at the maximum treatment of 1000 Grays, while a UV mutant and an EMS mutant reverted to wild-type after 4 months and 6 months, respectively, despite showing previously higher fucoxanthin than wild-type. This work provides new insights into key areas of microalgal biotechnology, by (i) demonstrating the use of an ionising mutagen (X-ray) on a biotechnologically relevant microalga, and by (ii) introducing temporal analysis of mutants which has substantial implications for strain creation and utility for industrial applications.

Microfluidic based single cell or droplet manipulation: Methods and applications

The isolation of single cell or droplet is first and crucial step to single-cell analysis, which is important for cancer research and diagnostic methods. This review provides an overview of technologies that are currently used or in development to realize the isolation. Microfluidic based manipulation is an emerging technology with the distinct advantages of miniaturization and low cost. Therefore, recent developments in microfluidic isolated methods have attracted extensive attention. We introduced herein five strategies based on microfluid: trap, microfluidic discrete manipulation, bioprinter, capillary and inertial force. For every technology, their basic principles and features were discussed firstly. Then some modified approaches and applications were listed as the extension. Finally, we compared the advantages and drawbacks of these methods, and analyzed the trend of the manipulation based on microfluidics.

Current Fungal Taxonomy and Developments in the Identification System

A functional identification system is the core and basis of fungal taxonomy, which provides sufficient diagnostic characteristics for species delimitation. Phenotype-based identification systems have exhibited significant drawbacks, such as being laborious and time-consuming. Thus, a molecular-based identification system (rDNA, DNA fingerprint, etc.) is proposed for application to fungi that lack reliable morphological characteristics. High Throughput Sequencing also makes great contributions to fungal taxonomy. However, the formal naming of nonculturable fungi from environmental sequencing is a significant challenge. Biochemical profile-based identification systems have outstanding value in fungal taxonomy and can occasionally be indispensable. This method utilizes biomarker metabolites and proteins that are expected to be unequivocal and stable. Of these, Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry has become the method of choice for chemotaxonomy. In sum, these described identification systems cannot solve all problems of species delimitation, and considerable attention to the updating of fungal nomenclature, standardization of techniques, knowledge sharing, and dissemination will be necessary.

Droplet Detection and Sorting System in Microfluidics: A Review

Since being invented, droplet microfluidic technologies have been proven to be perfect tools for high-throughput chemical and biological functional screening applications, and they have been heavily studied and improved through the past two decades. Each droplet can be used as one single bioreactor to compartmentalize a big material or biological population, so millions of droplets can be individually screened based on demand, while the sorting function could extract the droplets of interest to a separate pool from the main droplet library. In this paper, we reviewed droplet detection and active sorting methods that are currently still being widely used for high-through screening applications in microfluidic systems, including the latest updates regarding each technology. We analyze and summarize the merits and drawbacks of each presented technology and conclude, with our perspectives, on future direction of development.

Trait drift in microalgae and applications for strain improvement

Microalgae are increasingly used to generate a wide range of commercial products, and there is growing evidence that microalgae-based products can be produced sustainably. However, industrial production of microalgal biomass is not as developed as other biomanufacturing platform technologies. In addition, results of bench-scale research often fail to translate to large-scale or mass production systems. This disconnect may result from trait drift and evolution occurring, through time, in response to unique drivers in each environment, such as cultivation regimes, weather, and pests. Moreover, outdoor and indoor cultivation of microalgae has the potential to impose negative selection pressures, which makes the maintenance of desired traits a challenge. In this context, this review sheds the light on our current understanding of trait drift and evolution in microalgae. We delineate the basics of phenotype plasticity and evolution, with a focus on how microalgae respond under various conditions. In addition, we review techniques that exploit phenotypic plasticity and evolution for strain improvement in view of industrial commercial applications, highlighting associated advantages and shortcomings. Finally, we suggest future research directions and recommendations to overcome unwanted trait drift and evolution in microalgae cultivation.

Fluorescent Imaging and Sorting of High-Lipid-Content Strains of Green Algae by Using an Aggregation-Induced Emission Luminogen

Microalgae-based biofuels are receiving attention at the environmental, economic, and social levels because they are clean, renewable, and quickly produced. The green algae Chlorella vulgaris has been extensively studied in research laboratories and the biofuel industry as a model organism to increase lipid production to be cost-effective in commercial production. In this work, we utilized a lipid-droplet-specific luminogen with aggregation-induced emission (AIE) characteristics to increase the lipid production of C. vulgaris by fluorescent imaging and sorting of those algal cells with large and rich lipid droplets for subculturing. The AIE-active TPA-A enabled real-time monitoring of the size and number of lipid droplets in C. vulgaris during their growth period so that we can identify the best time for harvesting. Furthermore, the algae cells with high lipid content were identified and collected for subculturing by the technique of fluorescence-activated cell sorting (FACS). The lipid production in the generation of two successive selections was almost doubled compared to the generation with natural selection. This work demonstrated that the technologies of AIE and FACS could be applied together to improve the production of a third-generation biofuel.

Acoustofluidic cell micro-dispenser for single cell trajectory control

The precise manipulation of individual cells is a key capability for the study of single cell physiological characteristics or responses to stimuli. Currently, only large cell populations can be transferred with certainty using expensive and laborious flow cytometry platforms. However, when approaching small populations of cells, this task becomes increasingly challenging. Here, we report an effective acoustofluidic micro-dispenser, utilising surface acoustic waves (SAWs), with the ability to trap and release cells on demand, which when combined with an external valve can guide the trajectory of individual cells. We demonstrate single cell trap and release with a single cell trapping effectiveness of 74%, enabling the capability of dispensing a highly controlled amount of cells without any harmful effects. This device has the potential to be easily integrated into a wide range of analytical platforms for applications such as single cell fluorescent imaging and single cell proteomic studies.

Bioprospecting microalgae and cyanobacteria for biopharmaceutical applications

Microalgae and cyanobacteria have sparked a lot of interest due to their potential in various industries like biorefineries, biopharmaceuticals, food supplements, nutraceuticals, and other high-value products. Polysaccharides, vitamins, proteins, enzymes, and steroids are valuable products isolated from microalgae and cyanobacteria and potentially used in health and biomedical applications. Bioactive compounds derived from microalgae and cyanobacteria exhibit various pharmaceutical properties like antibacterial, anticancer, antiviral, antialgal, and antioxidant. From the properties listed above, the research for novel antibiotics has become particularly appropriate. In addition, the possible emergence of resistance against pathogens, as well as the potential decline in antibiotic efficacy, has prompted researchers to look for a new source of antibiotics. Microalgae and cyanobacteria have indicated a great and unexplored potential among these sources. For this reason, microalgae and cyanobacteria have been highlighted for their efficiency in different industrial sectors, as well as for their potential uses in the betterment of human and environmental health. This review gives an overview of bioactive compounds and metabolites with several biological properties isolated from microalgae and cyanobacteria for treating different animal and human diseases.

Random Mutagenesis as a Promising Tool for Microalgal Strain Improvement towards Industrial Production

Microalgae have become a promising novel and sustainable feedstock for meeting the rising demand for food and feed. However, microalgae-based products are currently hindered by high production costs. One major reason for this is that commonly cultivated wildtype strains do not possess the robustness and productivity required for successful industrial production. Several strain improvement technologies have been developed towards creating more stress tolerant and productive strains. While classical methods of forward genetics have been extensively used to determine gene function of randomly generated mutants, reverse genetics has been explored to generate specific mutations and target phenotypes. Site-directed mutagenesis can be accomplished by employing different gene editing tools, which enable the generation of tailor-made genotypes. Nevertheless, strategies promoting the selection of randomly generated mutants avoid the introduction of foreign genetic material. In this paper, we review different microalgal strain improvement approaches and their applications, with a primary focus on random mutagenesis. Current challenges hampering strain improvement, selection, and commercialization will be discussed. The combination of these approaches with high-throughput technologies, such as fluorescence-activated cell sorting, as tools to select the most promising mutants, will also be discussed.

Strain Development in Microalgal Biotechnology-Random Mutagenesis Techniques

Microalgal biomass and metabolites can be used as a renewable source of nutrition, pharmaceuticals and energy to maintain or improve the quality of human life. Microalgae’s high volumetric productivity and low impact on the environment make them a promising raw material in terms of both ecology and economics. To optimize biotechnological processes with microalgae, improving the productivity and robustness of the cell factories is a major step towards economically viable bioprocesses. This review provides an overview of random mutagenesis techniques that are applied to microalgal cell factories, with a particular focus on physical and chemical mutagens, mutagenesis conditions and mutant characteristics.

High-throughput characterization of the filamentous cyanobacterium Anabaena sp. using flow cytometry

In stirred-tank photobioreactors agitation causes fragmentation of filamentous cyanobacteria. Here, we introduce a flow cytometric approach for high-throughput measurements of trichome dimensions, heterocysts and metabolic activity of Anabaena sp. cultures. The longest characterized trichome had 1135 μm chain length. This technology could potentially be used for monitoring and control purposes.

Recent advances in acoustic microfluidics and its exemplary applications

Acoustic-based microfluidics has been widely used in recent years for fundamental research due to its simple device design, biocompatibility, and contactless operation. In this article, the basic theory, typical devices, and technical applications of acoustic microfluidics technology are summarized. First, the theory of acoustic microfluidics is introduced from the classification of acoustic waves, acoustic radiation force, and streaming flow. Then, various applications of acoustic microfluidics including sorting, mixing, atomization, trapping, patterning, and acoustothermal heating are reviewed. Finally, the development trends of acoustic microfluidics in the future were summarized and looked forward to.

Marine microbial bioprospecting: Exploitation of marine biodiversity towards biotechnological applications-a review

The increase in the human population causes an increase in the demand for nutritional supplies and energy resources. Thus, the novel, natural, and renewable resources became of great interest. Here comes the optimistic role of bioprospecting as a promising tool to isolate novel and interesting molecules and microorganisms from the marine environment as alternatives to the existing resources. Bioprospecting of marine metabolites and microorganisms with high biotechnological potentials has gained wide interest due to the variability and richness of the marine environment. Indeed, the existence of extreme conditions that increases the adaptability of marine organisms, especially planktons, allow the presence of interesting biological species that are able to produce novel compounds with multiple health benefits and high economical value. This review aims to provide a comprehensive overview of marine microbial bioprospecting as a growing field of interest. It emphasizes functional bioprospecting that facilitates the discovery of interesting metabolites. Marine bioprospecting was also discussed from a legal aspect for the first time, focusing on the shortcomings of international law. We also summarized the challenges facing bioprospecting in the marine environment including economic feasibility issues.

Advances in automated real-time flow cytometry for monitoring of bioreactor processes

Flow cytometry and its technological possibilities have greatly advanced in the past decade as analysis tool for single cell properties and population distributions of different cell types in bioreactors. Along the way, some solutions for automated real-time flow cytometry (ART-FCM) were developed for monitoring of bioreactor processes without operator interference over extended periods with variable sampling frequency. However, there is still great potential for ART-FCM to evolve and possibly become a standard application in bioprocess monitoring and process control. This review first addresses different components of an ART-FCM, including the sampling device, the sample-processing unit, the unit for sample delivery to the flow cytometer and the settings for measurement of pre-processed samples. Also, available algorithms are presented for automated data analysis of multi-parameter fluorescence datasets derived from ART-FCM experiments. Furthermore, challenges are discussed for integration of fluorescence-activated cell sorting into an ART-FCM setup for isolation and separation of interesting subpopulations that can be further characterized by for instance omics-methods. As the application of ART-FCM is especially of interest for bioreactor process monitoring, including investigation of population heterogeneity and automated process control, a summary of already existing setups for these purposes is given. Additionally, the general future potential of ART-FCM is addressed.

Improved high-throughput screening technique to rapidly isolate Chlamydomonas transformants expressing recombinant proteins

Abstract

The single-celled eukaryotic green alga Chlamydomonas reinhardtii has long been a model system for developing genetic tools for algae, and is also considered a potential platform for the production of high-value recombinant proteins. Identifying transformants with high levels of recombinant protein expression has been a challenge in this organism, as random integration of transgenes into the nuclear genome leads to low frequency of cell lines with high gene expression. Here, we describe the design of an optimized vector for the expression of recombinant proteins in Chlamydomonas, that when transformed and screened using a dual antibiotic selection, followed by screening using fluorescence activated cell sorting (FACS), permits rapid identification and isolation of microalgal transformants with high expression of a recombinant protein. This process greatly reduces the time required for the screening process, and can produce large populations of recombinant algae transformants with between 60 and 100% of cells producing the recombinant protein of interest, in as little as 3 weeks, that can then be used for whole population sequencing or individual clone analysis. Utilizing this new vector and high-throughput screening (HTS) process resulted in an order of magnitude improvement over existing methods, which normally produced under 1% of algae transformants expressing the protein of interest. This process can be applied to other algal strains and recombinant proteins to enhance screening efficiency, thereby speeding up the discovery and development of algal-derived recombinant protein products.

Key points

• A protein expression vector using double-antibiotic resistance genes was designed

• Double antibiotic selection causes fewer colonies with more positive for phenotype

• Coupling the new vector with FACS improves microalgal screening efficiency > 60%

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11790-9.

Carotenoid biosynthetic gene expression, pigment and n-3 fatty acid contents in carotenoid-rich Tetraselmis striata CTP4 strains under heat stress combined with high light

In this study, two carotenoid-rich strains of the euryhaline microalga Tetraselmis striata CTP4 were isolated by random mutagenesis combined with selection via fluorescence activated cell sorting and growth on norflurazon. Both strains, ED5 and B11, showed an up to 1.5-fold increase in carotenoid contents as compared with the wildtype, independent of the growth conditions. More specifically, violaxanthin, β-carotene and lutein contents reached as high as 1.63, 4.20 and 3.81 mg g^-1 DW, respectively. Genes coding for phytoene synthase, phytoene desaturase, lycopene-β-cyclase and ε-ring hydroxylase involved in carotenoid biosynthesis were found to be upregulated in ED5 and B11 cells as compared to the wildtype. Both strains showed higher contents of eicosapentaenoic acid as compared with those of the wildtype, reaching up to 4.41 and 2.88 mg g^-1 DW, respectively. Overall, these results highlight the complexity of changes in carotenoid biosynthesis regulation that are required to improve pigment contents in microalgae.

Make microalgal cultures axenic again - a fast and simple workflow utilizing fluorescence-activated cell sorting

Since the removal of contaminations in microalgal cultures is extremely laborious and time-consuming, we developed a rapid workflow to obtain axenicity by a combination of fluorescence-activated cell sorting (FACS) and plate spreading. During method development, several cyanobacteria and green algae strains were successfully made axenic. At the end, method transferability to another FACS device was demonstrated. Our workflow offers great time-savings with less hands-on laboratory work compared to conventional isolation techniques.

High-Throughput Raman Flow Cytometry and Beyond

Flow cytometry is a powerful tool with applications in diverse fields such as microbiology, immunology, virology, cancer biology, stem cell biology, and metabolic engineering. It rapidly counts and characterizes large heterogeneous populations of cells in suspension (e.g., blood cells, stem cells, cancer cells, and microorganisms) and dissociated solid tissues (e.g., lymph nodes, spleen, and solid tumors) with typical throughputs of 1,000-100,000 events per second (eps). By measuring cell size, cell granularity, and the expression of cell surface and intracellular molecules, it provides systematic insights into biological processes. Flow cytometers may also include cell sorting capabilities to enable subsequent additional analysis of the sorted sample (e.g., electron microscopy and DNA/RNA sequencing), cloning, and directed evolution. Unfortunately, traditional flow cytometry has several critical limitations as it mainly relies on fluorescent labeling for cellular phenotyping, which is an indirect measure of intracellular molecules and surface antigens. Furthermore, it often requires time-consuming preparation protocols and is incompatible with cell therapy. To overcome these difficulties, a different type of flow cytometry based on direct measurements of intracellular molecules by Raman spectroscopy, or "Raman flow cytometry" for short, has emerged. Raman flow cytometry obtains a chemical fingerprint of the cell in a nondestructive manner, allowing for single-cell metabolic phenotyping. However, its slow signal acquisition due to the weak light-molecule interaction of spontaneous Raman scattering prevents the throughput necessary to interrogate large cell populations in reasonable time frames, resulting in throughputs of about 1 eps. The remedy to this throughput limit lies in coherent Raman scattering methods such as stimulated Raman scattering (SRS) and coherent anti-Stokes Raman scattering (CARS), which offer a significantly enhanced light-sample interaction and hence enable high-throughput Raman flow cytometry, Raman imaging flow cytometry, and even Raman image-activated cell sorting (RIACS). In this Account, we outline recent advances, technical challenges, and emerging opportunities of coherent Raman flow cytometry. First, we review the principles of various types of SRS and CARS and introduce several techniques of coherent Raman flow cytometry such as CARS, multiplex CARS, Fourier-transform CARS, SRS, SRS imaging flow cytometry, and RIACS. Next, we discuss a unique set of applications enabled by coherent Raman flow cytometry, from microbiology and lipid biology to cancer detection and cell therapy. Finally, we describe future opportunities and challenges of coherent Raman flow cytometry including increasing sensitivity and throughput, integration with droplet microfluidics, utilizing machine learning techniques, or achieving in vivo flow cytometry. This Account summarizes the growing field of high-throughput Raman flow cytometry and the bright future it can bring.

Improved fucoxanthin and docosahexaenoic acid productivities of a sorted self-settling Tisochrysis lutea phenotype at pilot scale

This work aimed to select a Tisochrysis lutea phenotype with higher biomass and fucoxanthin productivities using fluorescence-activated cell sorting (FACS). A novel phenotype was obtained after 2 rounds of selection, based on high-fucoxanthin fluorescence. The resulting phenotype forms cell aggregates, has no flagella, and was stable after 15 months. Optimal temperature (30 °C) and light (300 µmol m^-2 s^-1) were obtained at laboratory scale, identical to the original strain. The biomass productivity was higher than the original strain: 1.9× at laboratory scale (0.4 L), and 4.5× under outdoor conditions (190 L). Moreover, compared to the original strain, the productivity of fucoxanthin increased 1.6-3.1× and docosahexaenoic acid 1.5-1.9×. These are the highest ever reported outdoor productivities, obtained with a robust new phenotype from a T. lutea monoculture isolated with FACS without genetic manipulation. The resulting phenotype shows high potential for industrial production.

Microfluidics for microalgal biotechnology

Microalgae have expanded their roles as renewable and sustainable feedstocks for biofuel, smart nutrition, biopharmaceutical, cosmeceutical, biosensing, and space technologies. They accumulate valuable biochemical compounds from protein, carbohydrate, and lipid groups, including pigments and carotenoids. Microalgal biomass, which can be adopted for multivalorization under biorefinery settings, allows not only the production of various biofuels but also other value-added biotechnological products. However, state-of-the-art technologies are required to optimize yield, quality, and the economical aspects of both upstream and downstream processes. As such, the need to use microfluidic-based devices for both fundamental research and industrial applications of microalgae, arises due to their microscale sizes and dilute cultures. Microfluidics-based devices are superior to their competitors through their ability to perform multiple functions such as sorting and analyzing small amounts of samples (nanoliter to picoliter) with higher sensitivities. Here, we review emerging applications of microfluidic technologies on microalgal processes in cell sorting, cultivation, harvesting, and applications in biofuels, biosensing, drug delivery, and nutrition.

Light spectra as triggers for sorting improved strains of Tisochrysis lutea

It is known that microalgae respond to different light colors, but not at single-cell level. This work aimed to assess if different light colors could be used as triggers to sort over-producing cells. Six light spectra were used: red + green + blue (RGBL), blue (BL), red (RL), green (GL), blue + red (BRL) and blue + green (BGL). Fluorescence-activated cell sorting method was used to analyse single-cell fluorescence and sort cells. BGL and RGBL lead to the highest fucoxanthin production, while RL showed the lowest. Therefore, it was hypothesized that hyper-producing cells can be isolated efficiently under the adverse condition (RL). After exposure to all light colors for 14 days, the top 1% fucoxanthin producing cells were sorted. A sorted strain from RL showed higher (16-19%) growth rate and fucoxanthin productivity. This study showed how light spectra affected single-cell fucoxanthin and lipid contents and productivities. Also, it supplied an approach to sort for high-fucoxanthin or high-lipid cells.

Development overview of Raman-activated cell sorting devoted to bacterial detection at single-cell level

Understanding the metabolic interactions between bacteria in natural habitat at the single-cell level and the contribution of individual cell to their functions is essential for exploring the dark matter of uncultured bacteria. The combination of Raman-activated cell sorting (RACS) and single-cell Raman spectra (SCRS) with unique fingerprint characteristics makes it possible for research in the field of microbiology to enter the single cell era. This review presents an overview of current knowledge about the research progress of recognition and assessment of single bacterium cell based on RACS and further research perspectives. We first systematically summarize the label-free and non-destructive RACS strategies based on microfluidics, microdroplets, optical tweezers, and specially made substrates. The importance of RACS platforms in linking target cell genotype and phenotype is highlighted and the approaches mentioned in this paper for distinguishing single-cell phenotype include surface-enhanced Raman scattering (SERS), biomarkers, stable isotope probing (SIP), and machine learning. Finally, the prospects and challenges of RACS in exploring the world of unknown microorganisms are discussed. KEY POINTS: • Analysis of single bacteria is essential for further understanding of the microbiological world. • Raman-activated cell sorting (RACS) systems are significant protocol for characterizing phenotypes and genotypes of individual bacteria.

Production and high throughput quantification of fucoxanthin and lipids in Tisochrysis lutea using single-cell fluorescence

This work aimed to investigate the accumulation of fucoxanthin and lipids in Tisochrysis lutea during growth (N+) and nitrogen-starvation (N-) and to correlate these products with single-cell emissions using fluorescence-activated cell sorting (FACS). Fucoxanthin content decreased 52.94% from N+ to N- in batch cultivation; increased 40.53% as dilution rate changed from 0.16 to 0.55 d^-1 in continuous cultivation. Total lipids (N-) were constant (~250 mg/g), but the abundance of neutral lipids increased from 4.87% to 40.63%. Nile red can stain both polar and neutral lipids. However, in vivo, this differentiation is limited due to an overlapping of signals between 600 and 660 nm, caused by neutral lipids concentrations above 3.48% (W/W). Chlorophyll autofluorescence (720 nm) was reported for the first time as a proxy for fucoxanthin (R² = 0.90) and polar lipids (R² = 0.98). FACS can be used in high throughput quantification of pigments and lipids and to select and sort cells with high-fucoxanthin/lipids.

Combining 3D sidewall electrodes and contraction/expansion microstructures in microchip promotes isolation of cancer cells from red blood cells

Cell sorting from heterogeneous organisms and tissues composed of multi-type cells is of great importance in biological and clinical applications. As promising cell sorting methods, dielectrophoresis (DEP) and hydrodynamics are attracting much attention in recent years. In this paper, we report a novel strategy by coupling DEP unit (3D sidewall electrodes) and hydrodynamic unit (microchannels with contraction/expansion structures) together in one microfluidic chip. Depending on the relative positions of 3D sidewall electrodes and contraction/expansion structure, three microchips (full-coupling, semi-coupling and non-coupling) are developed and their cell sorting performance are compared by isolating lung cancer cells (PC-9 cells) from red blood cells (RBCs). Both finite element simulation and practical cell sorting prove that high cell sorting efficiency (recovery of PC-9 cells: 90.21%, recovery of RBCs: 94.35%) can be achieved in full-coupling microchip, mainly owing to the synergistic effects between DEP sorting and hydrodynamic sorting. i.e., the positive DEP force generated by 3D sidewall electrodes can simultaneously act as an additional shear gradient lift force and thus trigger secondary flow even at low flow velocity. Live/dead cell staining, hemolysis ratio, fluorescence images and CCK-8 assay prove that RBCs and PC-9 cells show no significance difference in cell viability before and after cell sorting. The proposed coupling platform for cell sorting brings on a new pathway to construct integrated microfluidic chips for effective cell sorting and separation.

The Detailed Comparison of Cell Death Detected by Annexin V-PI Counterstain Using Fluorescence Microscope, Flow Cytometry and Automated Cell Counter in Mammalian and Microalgae Cells

The evaluation of cell wellness is an important task for molecular biology research. This mainly comprises the assessment for morphology and viability of culturing cells. Annexin V-Propidium iodide counterstaining has been currently one of the common and easy methods to discriminate apoptotic and necrotic cell profiles. The method is operated by fluorescence-based detection of counterstain via laser beam-employed instruments including flow cytometer, fluorescence microscope and automated cell counter. The detection is primarily conducted based on the same principle; however the efficiency of instruments may vary. Here we evaluated the efficiency of those instruments for the clear-cut detection of cell death through various mammalian and microalgae cell lines. To the best of our knowledge, this is the first study revealing comparative analyses of apoptotic and necrotic cells in mammalian and microalgae cells using Annexin V-PI counterstain detected by flow cytometer, fluorescence microscope and automated cell counter. Fluorescence microscope and cell counter instruments were also tested and compared for the traditional trypan blue-based cell viability detection performance. For these, cell death was induced by UV-irradiation and/or bee venom for mammalian (pancreatic cancer, metastatic breast cancer and mouse fibroblasts) and microalgae cells (Chlorella vulgaris), respectfully. Findings postulated that automated cell counter and fluorescence microscopy revealed similar patterns for the detection by both counterstain and trypan blue in mammalian cells. Interestingly, flow cytometry did provide an accurate and significant detection for only one mammalian cell line when UV-treatment was followed by routine Annexin V-Propidium iodide counterstaining. Unlike, only flow cytometry revealed a significant change in the detection of death of microalgae cells by Annexin V-Propidium iodide method, but both Annexin and conventional trypan blue methods were not applicable for the automated cell counter and microscopic detections for microalgae cells. The related outputs propose that the obtaining reliable quantitation strongly depends on cell type and instruments used. These suggest the necessity of optimization and validation endeavors before any cell death detection initiative. The analytical outcomes present insights into detailed assessment of cell death detection of eukaryotic cells and provide a direction to researchers to consider.