Development of an on-line biosensor for optimization and control of continuous bioreactor process

During the operation of any bioreactor process two of the most crucial elements are the microbial biomass products and their metabolic state of growth. One of the major inhibiting factors in the development and implementation of effective bioreactor control regimes has been the lack of suitable on-line sensors for measuring such parameters and variables. The aim of the work is to develop and evaluate an on-line biosensor for a continuous bioreactor based on the light emission capabilities of the recombinant host cell culture. The cells have been genetically engineered to include the luz gene operon, originally isolated from bioluminescent marine bacteria, such as Vibrio fischeri. The lux gene codes for products that lead to the bioluminescence phenomenon. The focus of this work is to derive an on-line growth and biomass estimation scheme based on the intensity of emitted light. Experimental data is presented, and it appears that bioluminescence level corresponds to the relative dilution rate which is equal to the growth rate at steady state. It was found that higher dilution rate leads to higher bioluminescence level. It confirmed the batch experimental results that bioluminescence is a reflection of the relative rate of growth rather than the absolute amount of biomass.