A Continuous Culture Millifluidic Device for the Study of Escherichia coli under Low and Fluctuating Nutrient Conditions
July 7th, 2026
We present a protocol for the millifluidic continuous culture device (MCCD), which allows the cultivation of bacterial populations under constant low-nutrient conditions (down to hundreds of nanomolar concentrations) or temporal nutrient fluctuations on a minute timescale.
My research focuses on examining how bacteria adapt physiologically to low and fluctuating nutrient conditions typical of natural environments. Conventional cultivation systems poorly replicate low dynamic nutrient conditions, whereas our system enables cultivation under these environmental relevant conditions. Prepare the overnight culture the day before the experiment.
Prepare a pre-culture by adding six microliters of the overnight culture to a tube containing six milliliters of full-rich defined media, or RDM. Divide the mixture equally into two 15-milliliter culture tubes and label them as A and B.Incubate both tubes at 37 degrees Celsius, with shaking at 200 RPM. Monitor the optical density at 600 nanometers using tube B, and do not proceed until the optical density reaches approximately 0.5.
During incubation, prepare the Low RDM medium, and allocate the total volume across bottles for different time points. Then seal each bottle with caps fitted with three tubes. Connect the third-widest silicone tube to a 0.2-micrometer vent filter for sterile air exchange.
Attach one end of each peristaltic tube fitted with male Luer lock connectors to the smaller-diameter silicone tubes. Leave the aluminum foil cover on the free male Luer lock fitting at the other end of the peristaltic tubes until the experiment begins to prevent contamination. Place the bottles and peristaltic pump into an incubator set to 37 degrees Celsius.
Secure all peristaltic tubing into the channels of the same pump head, ensuring identical flow rates across all filters. Dilute the pre-culture at a ratio of one to 10 by adding 600 microliters of culture into a tube containing 5.4 milliliters of Low RDM. Using a one-milliliter pipette, introduce one milliliter of diluted culture into each of six 0.45-micrometer polyvinylidene fluoride, or PVDF filters.
After rinsing one-way check valves with autoclaved ultra-pure water, attach them to each end of the filters. Remove the aluminum foil covers from tubing fittings. Connect each filter to the peristaltic tubing fittings.
Set the flow rate to two milliliters per minute on the peristaltic pump. Place a waste receptacle below the filters to collect outflow, and start the flow. After two hours, unplug one of the filters connected to the one liter bottle, unscrew the one-way check valves, and place the filter into a 50-milliliter centrifuge tube with the inlet facing downward.
Centrifuge at 2, 000 G for two minutes. Using a sterilized pipe cutter, apply gentle pressure at the outlet end of the plastic casing to open the filter. Release the inner cylinder and discard the membrane-containing section.
Rinse the inner walls of the filter casing with the collected culture medium. Measure the total collected volume using a five-milliliter serological pipette. Take three 100-microliter aliquots from the sample and fix them with glutaraldehyde to a final concentration of 1.5%Unplug the corresponding filters at subsequent time points and repeat the collection procedure.
Label the collected samples according to their respective time points. Label the samples with the fluorescent DNA dye, and count the cells using flow cytometry. Over time, the log 10 transformed cell counts followed linear trajectories, indicating exponential growth in all conditions.
The growth rates were approximately 0.88 per hour for the 0.5%RDM condition, 0.64 per hour for the 0.25%condition, and 0.18 per hour for the 0.01%condition. The cell counts reached up to one billion cells per sample, demonstrating that the millifluidic continuous culture device, or MCCD, supports both exponential growth, and high biomass yield at nanomolar to micromolar nutrient concentrations. Cells grown in 0.5%RDM had a greater mean cell length than cells grown in 0.01%RDM.
The main challenge during low nutrient cultivation is maintaining adequate cell densities to prevent clogging, pressure buildup, and nutrient depletion. Following this procedure, cells can be harvested for other downstream analysis, including proteomics, metabolomics, and other omics approaches. Future studies can investigate microbial adaptation to nutrient limitation and fluctuations by integrating this protocol with a quantitative omic analysis.
View the full transcript and gain access to thousands of scientific videos
Overview
This article introduces the millifluidic continuous culture device (MCCD), a novel platform designed to study microbial responses to both stable and fluctuating nutrient conditions. The MCCD overcomes limitations of traditional culturing methods by enabling precise control of nutrient concentrations and temporal fluctuations, closely mimicking natural microbial habitats. The protocol details the operation of the MCCD for cultivating bacteria such as Escherichia coli under ecologically relevant, low-nutrient environments.
Key Study Components
Area of Science
- Microbiology
- Microbial ecology
- Biotechnology
Background
- Natural microbial habitats feature low, mixed nutrient concentrations, spatial heterogeneity, and temporal fluctuations.
- Traditional batch cultures and chemostats do not adequately replicate these environmental conditions.
- Microfluidic systems allow dynamic environments but do not yield sufficient biomass for population-level analyses.
- There is a need for culturing platforms that enable controlled, low-nutrient, and fluctuating environments for microbial studies.
Purpose of Study
- To develop and demonstrate a continuous culture device capable of maintaining stable or fluctuating low-nutrient conditions.
- To provide a protocol for operating the MCCD in both constant and fluctuating nutrient modes.
- To enable studies of bacterial growth and physiology under conditions that closely resemble natural habitats.
Methods Used
- Design and use of the MCCD with a Sterivex filter (0.45 μm PVDF membrane) to house bacterial populations.
- Continuous flow of media to sustain stable culture conditions and prevent nutrient depletion.
- Implementation of a three-way solenoid valve system, controlled by custom Matlab software, for precise nutrient fluctuation control.
- Protocols for culturing E. coli under both constant and fluctuating low-nutrient conditions.
Main Results
- E. coli achieved exponential growth in mixtures of amino acids and nucleobases at nanomolar concentrations.
- Cell densities reached approximately 109 cells/mL under these low-nutrient conditions.
- The MCCD successfully recreated key features of natural microbial environments in a controlled laboratory setting.
- The system is suitable for studying other microbial species beyond E. coli.
Conclusions
- The MCCD enables detailed studies of microbial growth and physiology under ecologically relevant, low-nutrient, and fluctuating conditions.
- This platform addresses major limitations of traditional culturing methods for environmental microbiology research.
- The device facilitates new experimental approaches for understanding microbial adaptation and behavior in natural-like environments.
Frequently Asked Questions
Executive Industry Relevance
Discovery-stage microbial research often fails to replicate the low and fluctuating nutrient environments found in nature, limiting predictive confidence for translational applications. The millifluidic continuous culture device (MCCD) enables controlled, scalable studies of bacterial growth and physiology under ecologically relevant conditions, supporting robust target validation and mechanistic de-risking. This platform enhances the reliability of early-stage findings for downstream biopharma R&D pipelines.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables interrogation of microbial adaptation and metabolic pathways under physiologically relevant nutrient conditions.
- Supports functional target validation by maintaining stable or fluctuating low-nutrient environments.
- Improves predictive confidence for microbial system behavior in complex, real-world scenarios.
Screening & Assay Development
- Facilitates preparation of validated microbial cultures for downstream omics and phenotypic assays.
- Delivers reproducible, quantitative outputs by precisely controlling nutrient concentrations and fluctuations.
- Enables assay standardization and scalability for high-throughput screening of microbial responses.
Translational & Preclinical Research
- Aligns in vitro microbial studies with disease-relevant or environmental biomarker conditions.
- Provides continuity from early discovery through preclinical validation by mimicking natural microbial habitats.
- Supports risk-adjusted advancement decisions by reducing mechanistic ambiguity in microbial models.
Pipeline & Workflow Integration
The MCCD fits within the discovery-to-preclinical continuum, bridging early hypothesis testing and downstream functional validation for microbial systems.
- Discovery Biology: Enables hypothesis testing and pathway clarification under controlled, low-nutrient conditions.
- Screening: Provides assay-ready, reproducible cultures for quantitative evaluation of microbial phenotypes.
- Analytics: Supports population-level omic analyses with sufficient biomass and precise environmental control.
- Translational Research: Facilitates alignment with natural or disease-relevant microbial environments for preclinical studies.
- Enterprise Reuse: Offers a reusable platform adaptable to various microbial species and experimental designs.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence and reduces mechanistic ambiguity in microbial target validation.
- Operational Value: Standardizes culture conditions and enables reproducible, scalable workflows.
- Strategic Value: Improves go/no-go decisions and capital efficiency by providing robust early-stage data.
- Portfolio Impact: Supports risk-adjusted prioritization and advancement of microbial targets and models.
Implementation Considerations
- Requires expertise in microbial culturing and fluidic system operation.
- Needs instrumentation for continuous flow control and programmable nutrient delivery.
- Demands cross-team standardization for reproducibility across experiments and sites.
- Adaptable to different microbial species with consideration of membrane compatibility and nutrient requirements.
- Limited to studies where sufficient biomass and precise environmental control are critical for downstream analyses.
