| Abstract | Application of on-line sensors (flow calorimeter, fluorescence probe, dissolved oxygen and CO₂ probes) was assessed to monitor microbial biomass and physiological state of cells during a biological process. Two systems were studied; diauxic growth of Pseudomonas putida ATCC 11172 on glycerol and phenol, and the aerobic growth of Saccharomyces cerevisiae ATCC 18824 on glucose. The results showed that the cells produced a heat output which could be quantitatively related to the various phases of the growth cycle. The initial stage of enzymatic induction and substrate mobilization during the diauxic growth of P. putida was easily detected, and a clear oscillation phenomenon was observed during enzymatic rearrangement in shifting from phenol to glycerol metabolism. Glucose oxidation in ethanol and then in acetate was also clearly delineated from the growth of S cerevisiae. NADH (fluorescence probe) measurements gave a strong correlation with various biomass indicators such as optical density, dry weight, ATP content and cellular protein. The fluorescence signal appeared to be very sensitive to the quenching effect of the culture medium and of the cells themselves. The fluorescence emitted from the NADH molecules in a culture medium can be reduced from 30–70% depending on the chemical composition and the optical density. |
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