Production of Poly (3-Hydroxybutyric Acid) by Ralstonia eutropha in a Biocalorimeter and its Thermokinetic Studies

A novel rotating wide gap annular bioreactor (Taylor-Couette type flow) for polyhydroxybutyrate production by Ralstonia eutropha using carob pod extract

An annular bioreactor (ABR) with wide gap was used for PHB production from Ralstonia eutropha. Hydrodynamic studies demonstrated the uniform distribution of fluid in the ABR due to the Taylor-Couette flow. Thereafter, the ABR was operated at different agitation and sparging rates to study its effect on R. eutropha growth and PHB production. The ABR operated at 500 rpm with air sparge rate of 0.8 vvm yielded a maximum PHB concentration of 14.89 g/L, which was nearly 1.4 times that obtained using a conventional stirred-tank bioreactor (STBR). Furthermore, performances of the bioreactors were compared by operating the reactors under fed-batch mode. At the end of 90 h of operation, the ABR resulted in a very high PHB production of 70.8 g/L. But STBR resulted in a low PHB concentration of 44.2 g/L. The superior performance was due to enhanced oxygen and nutrient mass transfer in the ABR.

Biokinetics of fed-batch production of poly (3-hydroxybutyrate) using microbial co-culture

A novel fed-batch strategy based on carbon/nitrogen (C/N) ratio in a microbial co-culture production medium broth was carried out in a biocalorimeter for improved production of poly (3-hydroxybutyrate) (PHB). Shake flask study suggested that the C/N ratio of 10 increased the yield of PHB by 2.8 times. Online parameters monitored during the C/N ratio of 10 in biocalorimeter (BioRC1e) indicated that the heat profile was maintained in the fed-batch mode resulting in a PHB yield of 30.3 ± 1.5 g/L. The oxy-calorific heat yield coefficient during the fed-batch strategy was found to be 394.24 ± 18.71 kJ/O₂ due to the oxidative metabolism of glucose. The reported heat-based model adapted for PHB concentration prediction in the present fed-batch mode. The heat-based model has a Nash-Sutcliffe efficiency of 0.9758 for PHB prediction. PHB obtained by fed-batch-mode was characterized using gas chromatography-mass spectrometry (GC-MS) for the monomer-acid analysis, Thermogravimetric analysis (TGA) for thermal stability of PHB, and Fourier transform infrared spectroscopy (FT-IR) for confirmation of functional groups. Here, we establish a favorable C/N ratio for achieving optimal PHB yield and a predictive heat-based model to monitor its production.

Effect of aeration and agitation on yeast inulinase production: a biocalorimetric investigation

Air flow rate and agitation speed for inulinase production by Kluyveromyces marxianus were optimized based on metabolic heat release profiles. Shear stress and oxygen transfer (k_La) values were compared to assess the effects of aeration and agitation. At agitation rates of ≤ 100 rpm, the oxygen mass transfer rates were small and eventually led to less inulinase production, but at agitation rates > 150 rpm, loss of biomass resulted in less inulinase activity. Bio-reaction calorimeter (BioRc1e) experiment with aeration rates ≤ 0.5 lpm showed low k_La while at 1.5 lpm frothing of reactor contents caused loss of biomass and inulinase activity. The optimum conditions for aeration and agitation rate for K. marxianus in BioRc1e were 1 lpm and 150 rpm. Heat yield values obtained for the substrate, product and biomass reinstated the ongoing metabolic process. The heat release pattern could be a promising tool for optimization of bioprocess and in situ monitoring, with a possibility of interventions during the biotransformation process. At optimized aeration and agitation conditions, a two-fold increase in inulinase activity could be noticed.

Water Splitting-Biosynthetic Hybrid System for CO2 Conversion using Nickel Nanoparticles Embedded in N-Doped Carbon Nanotubes

CO₂ reduction has drawn increasing attention owing to the concern of global warming. Water splitting-biosynthetic hybrid systems are novel and efficient approaches for CO₂ conversion. Intimate coupling of electrocatalysts and biosynthesis requires the catalysts possess both high catalytic performance and excellent biocompatibility, which is a bottleneck of developing such catalysts. Here, a complex of Ni nanoparticles embedded in N-doped carbon nanotubes (Ni@N-C) is synthesized as a hydrogen evolution reaction electrocatalyst and is coupled with a hydrogen oxidizing autotroph, Cupriavidus necator H16, to convert CO₂ to poly-β-hydroxybutyrate. In Ni@N-C, the Ni nanoparticles are encapsulated in N-C nanotubes, which prevents bacteria from direct contact with Ni and inhibits Ni²⁺ leaching. As a result, Ni@N-C exhibits excellent biocompatibility and stability. This work demonstrates that electrocatalysts and biosynthesis can be intimately coupled through rational catalyst design.

Modeling of exo-inulinase biosynthesis by Kluyveromyces marxianus in fed-batch mode: correlating production kinetics and metabolic heat fluxes

A metabolic heat-based model was used for estimating the growth of Kluyveromyces marxianus, and the modified Luedeking-Piret kinetic model was used for describing the inulinase production kinetics. For the first time, a relationship was developed to relate inulinase production kinetics directly to metabolic heat generated, which corroborated well with the experimental data (with R ² values of above 0.9). It also demonstrated the predominantly growth-associated nature of the inulinase production with Luedeking-Piret parameters α and β, having values of 0.75 and 0.033, respectively, in the exponential feeding experiment. MATLAB was used for simulating the inulinase production kinetics which demonstrated the model's utility in performing real-time prediction of inulinase concentration with metabolic heat data as input. To validate the model predictions, a biocalorimetric (Bio RC1e) experiment for inulinase production by K. marxianus was performed. The inulinase concentration (IU/mL) values acquired from the model in were validated with the experimental values and the metabolic heat data. This modeling approach enabled the optimization, monitoring, and control of inulinase production process using the real-time biocalorimetric (Bio RC1e) data. Gas chromatography and mass spectrometry analysis were carried out to study the overflow metabolism taking place in K. marxianus inulinase production.