In the rapidly evolving landscape of synthetic glycobiology, the identification of optimal microbial hosts, or chassis strains, is the cornerstone of successful industrial bioproduction. Traditional screening methods, often reliant on manual selection or low-throughput chromatography, create a significant bottleneck when navigating the vast genetic diversity of engineered libraries. CD BioGlyco addresses this challenge by providing a sophisticated fluorescence-activated cell sorting (FACS)-based chassis strain screening service.
By integrating high-speed flow cytometry with precise genetic engineering, we enable the isolation of superior glycan-producing variants from populations exceeding 108 cells. Our platform leverages fluorescent reporters and biosensors to link intracellular metabolic activity with a detectable signal, allowing for the rapid identification of strains with enhanced titer, yield, and physiological robustness. This high-throughput (HTP) approach compresses development timelines, ensuring that only the most promising candidates proceed to fermentation scale-up.
Key Technologies
1. Genetically Encoded Fluorescent Biosensors
To screen for non-fluorescent glycans or metabolites, CD BioGlyco develops and implements custom biosensors. These consist of transcription factors (TFs) or riboswitches that respond specifically to a target molecule, driving the expression of a fluorescent protein such as green fluorescent protein (GFP). This technology converts a metabolic state into a sortable optical signal, enabling the HTS of libraries for complex glycan production.
2. Droplet Microfluidics Integration
For products that are secreted rather than retained intracellularly, we utilize droplet microfluidics. By encapsulating cells within picoliter-volume aqueous droplets, we create "micro-reactors" that prevent the diffusion of secreted glycans. These droplets are then analyzed and sorted via FACS, allowing us to screen for extracellular enzyme activity or secreted polysaccharide production with unparalleled precision.
Accelerating Discovery: From Massive Mutant Libraries to Elite Production Chassis
At CD BioGlyco, our service scope is designed to bridge the gap between large-scale genetic diversification and industrial application. When researchers utilize gene editing tools to generate millions of variants, the ability to find the "needle in the haystack", the single strain with optimal post-translational modification (PTM) capabilities, requires more than just speed; it requires high-resolution selection. Our service primarily focuses on the systematic screening and isolation of microbial chassis, including Escherichia coli, Saccharomyces cerevisiae, and Pichia pastoris, optimized for glycan-related substances. We provide a suite of methodologies:
Intracellular Glycan Accumulation Screening: For strains engineered to produce intracellular polysaccharides or glycoproteins, we utilize direct fluorescent labeling or internal biosensors to sort cells based on accumulation levels.
Surface Display Screening: By utilizing yeast or bacterial surface display, we attach target glycans or enzymes to the cell wall. Fluorescently labeled antibodies or lectins are then used to detect and sort strains based on the density and structural fidelity of the displayed glycans.
Enzyme Activity Evolution: For clients focused on glycosyltransferases or glycosidases, we screen for improved catalytic efficiency or altered substrate specificity using fluorogenic substrates within microfluidic droplets.
We implement these services by first consulting with clients to define the "selection pressure." Whether the goal is maximizing yield or ensuring a specific glycosylation pattern, we tailor the FACS gating strategy to meet those exact parameters. Our platform handles everything from initial library transformation to the final validation of sorted "hits," providing a seamless transition to bioprocess optimization.
Workflow
Library Construction and Preparation
We begin by receiving or generating a diverse library of mutant strains. This may involve site-directed mutagenesis, genome editing, or combinatorial pathway assembly. We ensure the library is properly integrated with the necessary fluorescent reporters or biosensor circuits.
Sample Preparation and Fluorescent Labeling
Cells are cultured to the appropriate growth phase to ensure stable reporter expression. If the target is a surface-bound glycan, we perform high-affinity staining with fluorophore-conjugated lectins or antibodies. For secreted products, cells are encapsulated into monodisperse microfluidic droplets.
High-Speed Flow Cytometry Analysis
The heterogeneous population is processed through our state-of-the-art flow cytometers. We analyze multiple parameters simultaneously, including forward scatter (FSC) for size, side scatter (SSC) for granularity, and multiple fluorescence channels to evaluate metabolic health and product titer.
Precision FACS Sorting
Based on a predefined gating strategy, the "elite" subpopulation is physically isolated. Our sorters process up to 50,000 events per second, allowing us to screen a library of 107 variants in just a few hours. We typically perform multiple rounds of sorting to achieve ultra-high purity (>99%).
Recovery and Clonal Expansion
Sorted cells are collected into growth media or onto agar plates. We ensure gentle handling to maintain high viability. Each "hit" is then expanded into a clonal population for downstream analysis.
Phenotypic and Genotypic Validation
The final stage involves verifying the performance of the selected chassis. We utilize next-generation sequencing (NGS) to identify the beneficial mutations and perform small-scale fermentation trials to confirm that the high-fluorescence phenotype correlates with superior industrial performance.
Publication Data
DoI: 10.3390/ijms22063041
Journal: International Journal of Molecular Sciences
IF: 4.9
Published: 2021
Results: This study develops a high-throughput FACS-based screening system for directed evolution of Bacillus licheniformis chitinase A (ChiA) to enhance chitin degradation. The chiA gene was cloned into E. coli BL21(DE3) and a mutant library generated via error-prone polymerase chain reaction (PCR). A fluorogenic substrate (4MUTC) was used, but its hydrophobic product (4MU) diffused from emulsion compartments, solved by adding 2-hydroxypropyl-β-cyclodextrin (HCD) to retain 4MU, plus HRP/H2O2 in the external phase to oxidize leaked 4MU. ChiA's toxicity to E. coli was addressed by limiting expression to 4 h. Twelve mutants (2-8 mutations each) were identified, with the most active (DH08) showing 2-fold higher activity than wild-type. Mutations localized to loops/secondary structure edges (not active sites), suggesting improved folding/stability. This system advances ultrahigh-throughput screening for chitinases, aiding eco-friendly chitin waste recycling.
Fig.1 FACS analysis of 4MU and 4MU+HCD. (Menghiu, et al., 2021)
Applications
Recombinant Glycoprotein Production
Screening mammalian or yeast chassis for optimized N-glycosylation patterns, ensuring the production of therapeutic antibodies with enhanced effector functions and reduced immunogenicity.
Industrial Enzyme Evolution
Identifying glycosyltransferase variants with improved thermal stability and higher turnover rates is essential for the cost-effective synthesis of human milk oligosaccharides (HMOs) and specialty carbohydrates.
Metabolic Pathway Optimization
Fine-tuning multi-gene pathways in E. coli or B. subtilis to maximize the flux toward nucleotide sugar precursors, facilitating the high-yield production of heparin or chondroitin-like polysaccharides.
Synthetic Organelle Engineering
Selecting strains with optimized "glyco-compartments" or modified Golgi-like vesicles that improve the efficiency of complex glycan assembly while minimizing cellular metabolic burden and toxicity.
Advantages
Ultra-High Throughput Capacity
CD BioGlyco's FACS service enables the screening of libraries exceeding 108 variants in a single day, offering a million-fold increase in speed compared to traditional microtiter plate-based assays.
Multiparametric Selection Logic
We don't just sort by "brightness." Our system analyzes size, complexity, and multiple fluorescent signals simultaneously to distinguish high-producers from cells that are merely stressed or abnormally large.
Custom Biosensor Development
Our expert synthetic biologists design bespoke TF-based biosensors, allowing us to apply FACS screening to virtually any glycan or metabolite, even those without inherent optical properties.
Exceptional Sorting Purity
We consistently achieve post-sort purities of over 98%, ensuring that clients receive the most robust and high-performing candidates for their specific glycobiological applications and downstream processing.
Frequently Asked Questions
Customer Review
"The throughput of CD BioGlyco's FACS screening platform is truly impressive. We were able to screen a library of a million yeast variants for optimized O-glycosylation in a fraction of the time it would have taken using conventional methods. The purity of the isolated hits was excellent, and the top candidate showed a 4-fold increase in titer during scale-up."
– A.S., Principal Scientist
"We struggled for months to find a biosensor-FACS setup that worked for our specific bacterial polysaccharide project. The team at CD BioGlyco not only designed a custom sensor for us but also optimized the sorting gates to handle our high-density cultures."
– Q.T., Senior Researcher
"Working with CD BioGlyco was a seamless experience. Their integrated workflow allowed us to hit our milestones ahead of schedule. The technical support was proactive, and the data package provided at the end was thorough and ready for our internal reports."
By combining massive parallel processing with the precision of fluorescent biosensing, CD BioGlyco empowers our clients to break through the "screening bottleneck" and identify the next generation of elite production hosts. Whether you are developing complex glycoproteins, novel enzymes, or specialty polysaccharides, our platform delivers the speed, accuracy, and reliability needed to move your project from the lab to the market. Please feel free to contact us to help you design the optimal screening strategy for your unique goals.
Reference
Menghiu, G.; et al. A high-throughput screening system based on fluorescence-activated cell sorting for the directed evolution of chitinase A. International Journal of Molecular Sciences. 2021, 22: 3041. (Open Access)
For research use only. Not intended for any clinical use.
Fig.1 FACS analysis of 4MU and 4MU+HCD. (Menghiu, et al., 2021)
