Stable competitive coexistence in a continuous fermentor with size-selective properties.

Area of Science:

• Biotechnology and Bioprocessing
• Microbial Ecology
• Chemical Engineering

Background:

• Achieving stable coexistence of microbial species with different growth rates in continuous culture is challenging.
• Traditional continuous culture systems often lead to the washout of slower-growing species.
• Size-based separation offers a potential strategy for managing mixed microbial populations.

Purpose of the Study:

• To develop and evaluate a size-selective reactor for enabling stable coexistence of Escherichia coli and Saccharomyces cerevisiae.
• To investigate the mechanisms of size-based cell retention and removal in a mixed culture.
• To analyze the stability conditions for microbial coexistence in the developed reactor system.

Main Methods:

• Construction of a continuous culture reactor with an inclined side-arm for enhanced cell sedimentation and recycling.
• Utilizing differential cell size between Saccharomyces cerevisiae (larger) and Escherichia coli (smaller) for separation.
• Performing stability analysis based on net removal rates as a function of cell concentration.
• Experimental measurement of the net removal rate function using a separate system.

Main Results:

• The size-selective reactor successfully maintained a stable mixed culture of E. coli and S. cerevisiae.
• Larger yeast cells were preferentially retained and recycled, while smaller, faster-growing bacteria were removed.
• Stability was achieved when the net yeast removal rate function was concave up, observed with growth in the settler at low biomass.

Conclusions:

• Size-selective reactors can effectively manage mixed microbial cultures with different characteristics.
• Enhanced sedimentation in an inclined side-arm facilitates preferential retention of larger cells.
• Microbial growth within the settler can contribute to the stability of coexistence steady states in continuous culture.