Substrate inhibition kinetics of Saccharomyces cerevisiae in fed-batch cultures operated at constant glucose and maltose concentration levels

Physico-Chemical Characteristics and Amino Acid Content Evaluation of Citric Acid by-Product Produced by Microbial Fermentation as a Potential Use in Animal Feed

The production of citric acid produces 70% waste product or by-product. This by-product is produced by microbial fermentation which could be used as an alternative raw material for animal feed because it still contains citric acid, which could help to reduce pathogenic bacteria. The objective of this study is to evaluate the physical and chemical value of citric acid by-product from rice (CABR) to compare the properties with those of rice bran and broken rice and to determine its potential as an alternative energy source in animal feed. The chemical composition of CABR was calculated using proximate analysis. The color of CABR was darker, and the bulk density value was 549.65 (g/L) (p < 0.05). With free flow, the angle of repose was 40°, and the particle size had less polygonal starch granules. CABR had a low pH of 4.77 and contained 19.80% crude protein, 11.97% crude fiber, and 4005.72 kcal/kg of energy. CABR had a higher crude protein value than broken rice and rice bran and a higher gross energy value than broken rice but less than rice bran. It also had a higher crude fiber value (p > 0.05). The results suggest that CABR could be utilized as an energy and protein source for animal feed formulations.

Real-time and on-line monitoring of ethanol fermentation process by viable cell sensor and electronic nose

In this study, introduction of a viable cell sensor and electronic nose into ethanol fermentation was investigated, which could be used in real-time and on-line monitoring of the amount of living cells and product content, respectively. Compared to the conventional off-line biomass determination, the capacitance value exhibited a completely consistent trend with colony forming units, indicating that the capacitance value could reflect the living cells in the fermentation broth. On the other hand, in comparison to the results of off-line determination by high-performance liquid chromatography, the ethanol concentration measured by electronic nose presented an excellent consistency, so as to realize the on-line monitoring during the whole process. On this basis, a dynamic feeding strategy of glucose guided by the changes of living cells and ethanol content was developed. And consequently, the ethanol concentration, productivity and yield were enhanced by 15.4%, 15.9% and 9.0%, respectively. The advanced sensors adopted herein to monitor the key parameters of ethanol fermentation process could be readily extended to an industrial scale and other similar fermentation processes.

Perfusion Microfermentor Integrated into a Fiber Optic Quasi-Elastic Light Scattering Sensor for Fast Screening of Microbial Growth Parameters

This research presents a microfermentor integrated into an optical fiber sensor based on quasi-elastic light scattering (QELS) to monitor and swiftly identify cellular growth kinetic parameters. The system uses a 1310 nm laser light that is guided through single-mode silica optical fibers to the interior of perfusion chambers, which are separated by polycarbonate membranes (470 nm pores) from microchannels, where a culture medium flows in a constant concentration. The system contains four layers, a superior and an inferior layer made of glass, and two intermediate poly(dimethylsiloxane) layers that contain the microchannels and the perfusion chambers, forming a reversible microfluidic device that requires only the sealing of the fibers to the inferior glass cover. The QELS autocorrelation decay rates of the optical signals were correlated to the cells counting in a microscope, and the application of this microsystem to the monitoring of alcoholic fermentation of Saccharomyces cerevisiae resulted in the kinetic parameters of K_M = 4.1 g/L and μ_m = 0.49 h⁻¹. These results agree with both the data reported in the literature and with the control batch test, showing that it is a reliable and efficient biological monitoring system.

Polymer-based controlled-release fed-batch microtiter plate - diminishing the gap between early process development and production conditions

BACKGROUND

Fed-batch conditions are advantageous for industrial cultivations as they avoid unfavorable phenomena appearing in batch cultivations. Those are for example the formation of overflow metabolites, catabolite repression, oxygen limitation or inhibition due to elevated osmotic concentrations. For both, the early bioprocess development and the optimization of existing bioprocesses, small-scale reaction vessels are applied to ensure high throughput, low costs and prompt results. However, most conventional small-scale procedures work in batch operation mode, which stands in contrast to fed-batch conditions in large-scale bioprocesses. Extensive expenditure for installations and operation accompany almost all cultivation systems in the market allowing fed-batch conditions in small-scale. An alternative, more cost efficient enzymatic glucose release system is strongly influenced by environmental conditions. To overcome these issues, this study investigates a polymer-based fed-batch system for controlled substrate release in microtiter plates.

RESULTS

Immobilizing a solid silicone matrix with embedded glucose crystals at the bottom of each well of a microtiter plate is a suitable technique for implementing fed-batch conditions in microtiter plates. The results showed that the glucose release rate depends on the osmotic concentration, the pH and the temperature of the medium. Moreover, the applied nitrogen source proved to influence the glucose release rate. A new developed mathematical tool predicts the glucose release for various media conditions. The two model organisms E. coli and H. polymorpha were cultivated in the fed-batch microtiter plate to investigate the general applicability for microbial systems. Online monitoring of the oxygen transfer rate and offline analysis of substrate, product, biomass and pH confirmed that fed-batch conditions are comparable to large-scale cultivations. Furthermore, due to fed-batch conditions in microtiter plates, product formation could be enhanced by the factor 245 compared to batch cultivations.

CONCLUSIONS

The polymer-based fed-batch microtiter plate represents a sophisticated and cost efficient system to mimic typical industrial fed-batch conditions in small-scale. Thus, a more reliable strain screening and early process development can be performed. A systematical scale-down with low expenditure of work, time and money is possible.

Intrinsic kinetic parameters of Thermococcus onnurineus NA1 strains and prediction of optimum carbon monoxide level for ideal bioreactor operation

This study determines and compares the intrinsic kinetic parameters (Ks and Ki) of selected Thermococcus onnurineus NA1 strains (wild-type (WT), and mutants MC01, MC02, and WTC156T) using the substrate inhibition model. Ks and Ki values were used to find the optimum dissolved CO (CL) conditions inside the reactor. The results showed that in terms of the maximum specific CO consumption rates (qCO(max)) of WT, MC01, MC02, and WTC156T the optimum activities can be achieved by maintaining the CL levels at 0.56mM, 0.52mM, 0.58mM, and 0.75mM, respectively. The qCO(max) value of WTC156T at 0.75mM was found to be 1.5-fold higher than for the WT strain, confirming its superiority. Kinetic modeling was then used to predict the conditions required to maintain the optimum CL levels and high cell concentrations in the reactor, based on the kinetic parameters of the WTC156T strain.

Dynamic flux balance analysis of batch fermentation: effect of genetic manipulations on ethanol production

In silico optimization of bioethanol production from lignocellulosic biomasses is investigated by combining process systems engineering approach and systems biology approach. Lignocellulosic biomass is an attractive sustainable carbon source for fermentative production of bioethanol. For enhanced ethanol production, metabolic engineering of wild-type strains-that can metabolize both hexose and pentose sugars or microbial consortia consisting of substrate-selective microbes-may be advantageous. This study presents a detailed in silico analysis of bioethanol production from glucose-xylose mixtures of various compositions by batch mono-culture and co-culture fermentation of specialized microbes. Dynamic flux balance models based on available genome-scale reconstructions of the microorganisms have been used to analyze bioethanol production, and the maximization of ethanol productivity is addressed by computing optimal aerobic-anaerobic switching times. Effects of ten metabolic engineering strategies that have been suggested in the literature for ethanol overproduction, have been evaluated for their efficiency in enhancing the ethanol productivity in the context of batch mono-culture and co-culture processes.