Metabolic heat and respirometric responses of kluyveromyces marxianus and saccharomyces cerevisiae during carboxypeptidase production

Abstract

Microorganisms maintain constant internal entropy by exporting the entropy as heat to the environment produced during substrate consumption. This energy release is directly proportional to microbial growth, substrate and oxygen consumption and metabolite formation. Though any change in the process directly influences the heat rate, the heat rate measured by biocalorimeter can be used extensively in bioprocess monitoring and control. newlineKluyveromyces marxianus and Saccharomyces cerevisiae were industrially potential strains for the production of carboxypeptidase Y (CPDY) enzyme, The scope and objectives of the present research are two-fold, First, to investigate the heat evolution pattern for the enhanced CPDY enzyme production by K.marxianus and compare it with the well-known CPDY producing yeast S.cerevisiae in a bioreaction calorimeter. The second objective is to generate the bio kinetic data of CPDY production, which is not available so far. Biokinetic data would assist further in the scale-up of the product. To fulfill the above objectives, shake flask and biocalorimetric optimizations and respirometric measurements were carried out with offline parameters such as pH, biomass and CPDY production during different phases of the bioprocess. Shake flask studies of K.marxianus showed higher CPDY enzyme activity of 6 IU/mL with DCW of 3.5 g/L. The reduction in CPDY enzyme activity and total protein beyond 12th h is due to pH change, product accumulation, and sporulation. Metabolic heat responses during CPDY production by K.marxianus was estimated by optimizing the aeration and agitation rates. 1 LPM and 150 RPM were found to be optimum for maximum CPDY production in a 2 litre capacity bioreaction calorimeter. Biokinetic constants, KLa and total metabolic heat released were estimated for CPDY production. For the first time, biocalorimetry coupled respirometric studies have given a maximum CPDY yield making it attractive for commercial applications. Biocalorimetric studies favored in identifying ethanol production and consumption. Biocalorimetric investigation combined with respirometric studies suggested that the rate of heat evolution was directly linked to DCW, enzyme activity, and the consumption of substrates. Further, a heat-based model and the bioprocess monitoring control can be developed from this study for the bioprocess scale-up. The maximum yield obtained for K.marxianus was 14 IU/mL, which was three-fold higher than the shake flask experiment. newline