Francisco J. Montes

Prediction of kLa in yeast broths

Abstract Oxygen transfer rate, can play an important role in the scale-up and economy of many microbial processes and values of the volumetric oxygen transfer coefficient (kLa) for specific fermentation culture media need to be evaluated and correlated to obtain the appropriate design tools. The purpose of this work was to determinate the values of kLa in yeast broths (Trigonopsis variabilis) in a mechanically-stirred, sparger-aerated and baffled reactor, the most common fermenter type, over a wide range of superficial air velocities impeller rotational speeds and geometric parameters. Three different mixing vessels (2, 5 and 15 litres) were used in order to consider the effect of the fermenter scale-up on kLa. Once kLa data are obtained, several empirical and theoretical correlations were used to fit the experimental data. A new correlation is proposed k L a=3.2·10 −3 P V 0.35 U sg 0.41 based on the power input per unit volume of liquid (P/V) and the superficial gas velocity (Usg). The correlation improves the prediction of kLa values in culture media with respect to other generic correlations, mainly because early correlations were developed for strong coalescent and non-coalescent fluids, whereas the medium used in this work and in most the yeast broths behaves as a typical Newtonian, slightly non-coalescence fluid, due to the moderate presence of mineral salts.

Kinetics and heat-inactivation mechanisms of D-amino acid oxidase

Abstract A study was made of the stability of crude hog kidney d -amino acid oxidase ( d -AAO) under different experimental conditions of temperature, enzyme concentration, buffer, and in the presence of flavine adenine dinucleotide (FAD)_ and glycerol. A deactivation mechanism is proposed. The kinetic deactivation studies were performed in a buffer at pH over a temperature range of 277-327K (4–54°C). The activity for d -AAO at 1 U/ml at 277 K in potassium phosphate and potassium pyrophosphate buffer remains almost constant for 20 days. For d -AAO at 0·02 U/ml at 303 K (30°C) in phosphate buffer, the presence of FAD and glycerol causes the deactivation constant to decrease, while the initial activity and the half-life time increase, the latter doubling on passing from buffer alone to buffer with FAD and 10% glycerol. In the case of d -AAO at 0·2 U/ml, the stability increases considerably with respect to 0·02 U/ml. Both FAD and glycerol enhance this stabilization. For temperatures above 313 K (40°C), the deactivation of d -AAO at 0·2 U/ml showed values of the thermodynamic variables for the overall deactivation constant and for the deactivation constant due to the loss of FAD that indicate that the dissociation of FAD is the main deactivation mechanism. Finally, deactivation due to the loss of FAD is higher for d -AAO at 0·1 U/ml as compared with a concentration of 0·2 U/ml.

Inhibition ofd-amino acid oxidase by α-keto acids analogs of amino acids

The inhibition of D-amino acid oxidase by certain alpha-keto acids products of the reaction with D-amino acids, in particular alpha-keto acids that are analogs of the amino acids alanine, valine, leucine, phenylanaline, phenylglycine, tyrosine and tryptophan, is reported. All the alpha-keto acids assayed behaved as substrate competitive inhibitors of the enzyme. The relationship between the degree of inhibition and the structure of the inhibitor is discussed.

Investigation of transmembrane protein fused in lipid bilayer membranes supported on porous silicon

This article investigates a device made from a porous silicon structure supporting a lipid bilayer membrane (LBM)fused with Epithelial Sodium Channel protein. The electrochemically-fabricated porous silicon template had pore diameters in the range 0.2~2 µm. Membranes were composed of two synthetic phospholipids: 1,2-diphytanoyl-sn-glycero-3-phosphoserine and 1,2-diphytanoyl-sn-glycero-3-phosphoethanolamine. The LBMwas formed by means of the Langmuir-Blodgett and Langmuir-Schaefer techniques, at a monolayer surface tension of 26 m Nm−1 in room temperature and on a deionized water subphase, which resulted in an average molecular area of 0.68–0.73 nm2. Fusion of transmembrane protein was investigated using Atomic Force Microscopy. Initial atomic force microscopy results demonstrate the ability to support lipid bilayers fused with transmembrane proteins across a porous silicon substrate. However, more control of the membrane’s surface tension using traditional membrane fusion techniques is required to optimize protein incorporation.

Oxygen Kinetic and Metabolic Parameters for the Yeast Trigonopsis variabilis

The metabolic and kinetic parameters of oxygen consumption by the yeast Trigonopsis variabilis under conditions of induced and non-induced D-amino acid oxidase are described for the first time. These parameters can be calculated from the results of a single batch fermentation running at an oxygen-limiting condition. The values obtained for the parameters may be used as a basis for the calculation of the aeration and stirring requirements and optimal oxygen conditions for the growth of T. variabilis in batch, fed-batch or continuous fermentations.

Shape oscillating bubbles: hydrodynamics and mass transfer - a review

AbstractThe subject of bubble oscillations, the associated hydrodynamics and the effect of bubbles on mass transfer in gas–liquid contact equipment, is reviewed. The emphasis is on rising and shape oscillating bubbles (n>0 mode) with little or negligible apparent volume change, rather than on volume oscillations (n = 0 mode). Bubbles, as they move in liquid media, are subjected to forces that try to deform them as well as forces that try to keep them as individual entities, resulting in the fact that bubble contact area changes in time and so do the velocity profiles surrounding them. As a result, the concentration profiles are also affected, influencing the Sherwood number and the mass transfer rates from the gas phase to the liquid phase. The physical properties of the phases as well as bubble coalescence and breakup processes that occur within the equipment play an important role in defining the oscillation amplitude and decay. Thus, we summarise the main results and the theories behind bubble dynamics...

A GENETIC STRUCTURED MODEL IN RELATION TO D-AMINO ACID OXIDASE PRODUCTION IN TRIGONOPSIS VARIABILIS

ABSTRACT In this article, a genetic structured model regarding the synthesis of D-amino acid oxidase (DAO) by the yeast Trigonopsis variabilis growing under batch conditions is proposed for the first time. The basis of the model is a system of coupled ordinary differential equations (ODEs) accounting for the rate of messenger-ribonucleic acid (mRNA) transcription, the rate of DAO translation, and the rates of deactivation of both mRNA and DAO. The present model quantitatively represents the influence of methionine and ammonium on the synthesis of the enzyme. The values of the calculated parameters point to a repression in the transcription phase as responsible for the low levels of DAO observed in cells growing in culture media containing ammonium. The model reasonably explains the experimental data from this work in both the exponential and stationary phases of the cell growth.

A Metabolic Model Describing Growth and Substrate Uptake of Trigonopsis variabilis

Abstract As a part of the study on the production of the enzyme D -Amino acid oxidase (D-AAO) by the yeast Trigonopsis variabilis, a chemically structured model capable of explaining cellular growth and substrate uptake of T. variabilis is presented. The model makes use of a simple sequence of biochemical reactions produced inside the cell and is capable of simulating a range of metabolic responses obtained from the T. variabilis growth in discontinuous culture. The model can serve to understand the behavior of the yeast under different growth conditions and could be used as a basis for the design of an industrial fermentor for D-AAO production. Since some modifications have been introduced to the basic metabolic model to provide even more generality, this new model can be applied to any yeast growing under discontinuous conditions.