Oxygen mass transfer and gas holdup in a bubble column bioreactor with biosynthesis liquids

The influence of the rheology of some antibiotic biosynthesis liquids produced by Streptomyces aureofaciens, Nocardia mediterranei and Penicillium chrysogenum on the volumetric liquid phase oxygen transfer coefficient, k_La, and gas holdup, ε_G, together with the influence of superficial gas velocity, were studied in a bubble column bioreactor, using samples of fermentation liquids taken from industrial stirred tank fermenters, at 30-hour intervals during fermentation batch. The results were compared to those of previous studies from literature on non-Newtonian homogeneous fluids, such as CMC-Na, xanthan and starch solutions, respectively. In the heterogeneous broths, ε_G and k_La decreased with increasing apparent viscosity of the broth and increased with increasing superficial velocity. The experimental data were correlated using non-linear regression with correlation coefficients above 0.85.     

Letter: The magnitude of intramolecular DNA optical absorbance with variation in (Na+) and GC base composition: for special application to DNA reassociation studies.

The magnitude of intramolecular DNA optical absorbance is presented as a function of [Na⁺] and GC composition of the DNA. The data are presented as a ratio of absorbances A₀/A₀ for the DNA at the denaturing temperature (T_d) and renaturing temperature (T_r) under the given conditions. All ratios were determined for T_r corresponding to the temperature optimum (T_m ? T_r = 25°C) in DNA reassociation rate. This fact, coupled with the convenient A₀/A₀ ratio representation, permits the quick estimation of the magnitude of this optical effect in DNA reassociation reactions over a wide range of experimental conditions.     

Dynamic and structural scalings of the complexation between pDNA and bPEI in semidilute and low‐salt solutions

Using a combination of static and dynamic laser light scattering, we investigated the complexation of a supercoiled plasmid DNA (pDNA, 10⁴ bp) and a branched polyethyleneimine (bPEI, M_w = 25 kD) in semidilute and low‐salt aqueous solutions. Our results unearth some scaling laws for dynamic and structural properties of the resultant complexes (polyplexes) with different bPEI:pDNA (N:P) molar ratios. Namely, the average scattering intensity (<I>) and the average linewidth of the Rayleigh peak (<Γ>) are scaled to the scattering vector (q) as <I> ∝ q or <Γ> ∝ q, where α_S and α_D are two N:P dependent scaling exponents. The N:P ratio strongly affects the complexation. When N:P < 2.0, the motions of the negatively charged and extended pDNA chains and the polyplexes are highly correlated so that they behave like a transient network with a fractal dimension. As the N:P ratio increases, nearly all of pDNA chains condensed and the overall charge of the polyplexes reverses to slightly positive, resulting in a turbid dispersion of large loose aggregates made of smaller, but more compact, polyplexes. Further increase of N:P finally disrupts large loose aggregates, leading to a homogeneous transparent dispersion of the polyplexes. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 571–577, 2010. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

Studies on mass transfer characteristics of a modified airlift fermenter

An approach to modify external loop airlift bioreactor is presented that examines its performance with respect to mass transfer. There are various designs of airlift fermenter [1]. In the proposed system [2] the riser has been replaced by a tube of irregular geometry, in the form of converging-diverging sections (CDT-ALF), so that better mass transfer may be obtained due to better liquid mixing caused by the bubble flow, pulsation effect and early transition to turbulence. Mass transfer characteristics of the modified airlift fermenter CDT-ALF were studied and compared with those of a conventional one, UT-ALF. Overall volumetric mass transfer coefficient,K _L a, was determined by sulfite oxidation method.K _L a was determined with respect toU _G for differenth _i. HigherK _L a was always observed in CDT-ALF compared to that in UT-ALF under any operating condition ofh _i andU _G. If theK _L a values are compared in both the systems under their optimum conditions ofh _i andU _G, CDT-ALF showed 122.5% higher values ofK _L a compared to UT-ALF. However, when both the systems were operated at the lowest experimental conditions ofU _G, thek _L a in CDT-ALF was found to be 170% higher. In UT-ALF while with the decrease ofU _G,k _L a decreased, in CDT-ALF the reverse was observed i.e. at lowU _G,K _L a was higher. However with the increase ofh _i,K _L a decreased in both the systems. To predict volumetric mass transfer coefficientK _L a, empirical correlations were developed by dimensional analysis for both the reactors. The correlations were experimentally verified to determine their reliability to predict mass transfer coefficient and the deviation was found within reasonable limit.List of abbreviations ALF Airlift Fermenter - UT-ALF Uniform Tube Airlift Fermenter - CDT-ALF Converging-diverging Tube Airlift Fermenter     

On-line estimation of kLa by an analog computer

A new method was developed for estimating the volumetric oxygen transfer coefficient, k_La, in a fermentor. Various methods were investigated for the on-line estimation of k_La with an analog computer employing a steepest-descent calculation technique. The method by which k_La is estimated (by minimizing the error residue of the model) was found to be very applicable. A method for the simultaneous estimation of the volumetric oxygen transfer coefficient and respiration rate in biological systems is also presented.     

Effects of hydrocarbon additions on gas-liquid mass transfer coefficients in biphasic bioreactors

The effects of aliphatic hydrocarbons (n-hexadecane andn-dodecane) on the volumetric oxygen mass transfer coefficient (k _L a) were studied in flat alveolar airlift reactor and continuous stirred tank reactors (CSTRs). In the flat alveolar airlift reactor, high aeration rates (>2 vvm) were required in order to obtain efficient organic-aqueous phase dispersion and reliablek _L a measurements. Addition of 1% (v/v)n-hexadecane orn-dodecane increased thek _l a 1.55-and 1.33-fold, respectively, compared to the control (superficial velocity: 25.8×10⁻³ m/s, sparger orifice diameter: 0.5 mm). Analysis of the gas-liquid interfacial areaa and the liquid film mass transfer coefficientk _L suggests that the observedk _L a increase was a function of the media's liquid film mass transfer. Addition of 1% (v/v)n-hexadecane orn-dodecane to analogous setups using CSTRs led to ak _L a increase by a factor of 1.68 and 1.36, respectively (superficial velocity: 2.1×10⁻³ m/s, stirring rate: 250 rpm). These results propose that low-concentration addition of oxygen-vectors to aerobic microbial cultures has additional benefit relative to incubation in purely aqueous media.     

Relation of amino acid composition and the Moffitt parameters to the secondary structure of proteins

A statistical analysis of the relation between the amino acid composition of proteins and the amount of helical secondary structure as characterized by the Moffitt b₀ parameter has shown a high degree of correlation of the b₀ parameter with those amino acids whose homopolymers can form helical structures. Using the data for 107 proteins, a linear relation was found between b₀ and the sum of the residue percentages of alanine, arginine, aspartic acid, cysteine, glutamic acid, leucine, andlysine. A statistical analysis of the Moffitt a₀ parameter, on the other hand, showed no statistically significant grouping of amino acids in relation to the amount of secondary β structure in a protein. A plot of b₀ versus a₀–a, where a represents the a⁰ parameter for a fully denatured protein, for 55 proteins showed distinct nonlinearity. This nonlinearity was postulated to be due to presence of β structure, and a nomagram was constructed which allowed a semiquantitative estimate of the amount of helical and β-type secondary structures from the b₀ versus a₀–a plot.     

A population genetic study of the Banks and Torres Islands (Vanuatu) and of the Santa Cruz Islands and polynesian outliers (Solomon Islands)

As part of a multidisciplinary survey of populations in the Banks and Torres Islands of Vanuatu and the Southern and Central Districts of the Solomon Islands, nearly 2,400 persons have been tested for ABO blood groups and a number of serum protein and red cell enzyme genetic marker systems. For the ABO system, the populations are characterized in general by high gene O and low gene B frequencies except in two of the Polynesian Outlier Islands, Rennell and Bellona, which have high frequencies of B. Among the serum proteins, several alleles have distributions indicating significant movement of people between islands. These include Albumin ^{New Guinea} and the transferrin alleles Tf, and Tf, and Tf. Similar specific alleles for red cell enzymes also show distributions reflecting interisland population movement as well as contact with persons from outside the southern Pacific region. Examples are ACP in the acid phosphatase system, PGM and PGM, PGM and PGM, PGK⁴ and also HbJ^Tongariki. The data available for 11 polymorphic systems were used to generate genetic distances. Of the four Polynesian Outlier Islands, Anuta is most remote genetically, with Rennell and Bellona also relatively isolated. The fourth Polynesian Outlier, Tikopia, occupies a position genetically close to the Melanesian populations of the Banks and Torres Islands and the southern Solomons. The history of early European contact and voyaging in the Pacific, as well as archaeological and linguistic evidence and local legends, indicate that significant movements of people occurred between islands and provided opportunities for genes to be introduced from Europeans, Africans, and Asians. The genetic marker studies give evidence for genes from all these sources, though at a low level. Despite this admixture, the Polynesian Outlier and Melanesian populations have preserved their own distinctive genetic patterns.     

Rheological behaviour of some antibiotic biosynthesis liquids

This paper prsents the results of teh study of rheological behaviour of antibiotic biosynthesis liquids obtained by submerged aerobic cultivation of microorganisms belonging to the actinomycete and fungi classes, in stirred tank bioreactors with turbine impellers. These liquids have a non-Newtonian behaviour which follows the power-law rhcological model with a correlation index of over 0.95. The studied liquids are pseudoplastic, and alter their rheological properties, such as consistency index, (K), flow index, (n), apparent viscosity, (η_a), maximum Newtonian viscosity (η₀), with the culture age, microrganism strain and batch conditions. Also, these liquids are time dependent, exhibiting thixotropy. The most viscous liquids are produced by Streptomyces aureofaciens and Streptomyces rimosus cultivation, while that produced by Streptomyces griseus is the least viscous. A higher pseudoplasticity appears after 30 hours culture age. Since all these biosynthesis are aerobic, a careful observation of the rhelogical behaviour dynamics is necessary to avoid the oxygen culture supply limitation and the decrease of the bioreactor performance during biosynthesis.     

Microcalorimetric investigations of the metabolism of yeasts. growth in batch and chemostat cultures on ethanol medium

Summary In the presence of protein, Hansenula polymorpha cultivation medium exhibits a maximum volumetric mass transfer coefficient, k_La, as function of the employed antifoam agents (soy oil and Desmophen 3600). With diminishing superficial gas velocity this maximum disappeas.Symbols E_G Relative gas holdup - k_La Volumetric mass transfer coefficient (s^–1) - w_SL Superficial liquid velocity (cm s^–1) - w_SG Superficial gas velocity (cm s^–1)     

Venturi aeration and thermophilic aerobic sewage sludge digestion in small-scale reactors

Summary The aeration performance of two venturi aeration reactors (operating volumes 381 and 251) was studied for an air-water system. It was found that the mass transfer coefficient (k _la) could be described in terms of the superficial gas velocity (V _s) alone by the simple expressionk _La=aV _infb ^supS with constantsa=0.313,b=0.579 for the 38-1 reactor anda=0.214,b=0.534 for the 25-1 reactor. A similar relationship was obeyed when the 38-1 reactor was aerated with a diffuser tile (a=17.0,b=1.52). A linear relationship betweenk _La and gas hold-up was observed for the 38-1 reactor with both venturi and diffuser aeration. The 25-1 reactor was used successfully for the thermophilic aerobic digestion of sewage sludge. A mean sludge temperature rise of 30°C was observed. Chemical oxygen demand, pH, and total solids content of the digested sludge differed significantly from the feed sludge and were similar to values obtained for full-scale thermophilic aerobic digestion. No significant differences between inorganic solids content, dissolved oxygen concentration, or redox potential were observed between feed and digested sludge.     

Bubble coalescence behaviour in biological media

Summary A twin bubble column was used to measure the k_La values for oxygen in model and cultivation media using the steady state method described previously (Adler et al. 1980). Desmophen and soy oil were used as antifoam agents together with model and/or cultivation media for Chaetomium cellulotyticum, Trichoderma reesei, Hansenula polymorpha, Saccharomyces cerevisiae and Escherichia coli. The bubble coalescence behavior is mainly influenced by antifoam agents and somewhat by protein and alcohol additives. In the range investigated (0.01 to 0.1%.), the k_La values are not influenced by the Desmophen concentration and only slighthly by the soy oil concentration (0.5 to 1.5%.). The coalescence behaviour was characterized by the ratio m_corr=(k_La)_corr/(k_La)_ref. A nutrient salt solution with Desmophen was used as a reference. The k_La measured in the investigated media were corrected by considering the differences in k_La's in the investigated and reference media. These m_corr values can directly be used for bubble columns close to the optimum aeration rate.Symbols a Specific gas/liquid interfacial area - c Concentration - k_L Mass transfer coefficient - k_La Volumetric mass transfer coefficient - W_SG Superficial gas velocity - E_G Relative gas hold-up     

Novel mononuclear η-pentamethylcyclopentadienyl complexes of platinum group metals bearing pyrazolylpyridazine ligands: Syntheses and spectral studies

Condensation of 3,6-dichloropyridazine with 3,5-dimethylpyrazole in 1:1 ratio yielded one side substituted pyrazolylpyridazine ligand 3-chloro-6-(3,5-dimethylpyrazolyl)pyridazine (L) while condensation of 3,6-dichloropyridazine with substituted pyrazoles in 1:2 ratio yielded both side substituted pyrazolylpyridazine ligands such as 3,6-bis(pyrazolyl)pyridazine (L1), 3,6-bis(3-methylpyrazolyl)pyridazine (L2) and 3,6-bis(3,5-dimethylpyrazolyl)pyridazine (L3). A new series of cationic mononuclear complexes of the type [(η⁵-Cp)M_a(L)(PPh₃)]PF₆, [(η⁵-Cp*)M_b(L)Cl]PF₆, [(η⁵-Cp*)Ru(L′)(PPh₃)]PF₆ and [(η⁵-Cp*)M_b(L′)Cl]⁺ (where M_a = Ru, Os; M_b = Rh, Ir and L′ = L1, L2, L3) bearing pyrazolylpyridazine and η⁵-cyclopentadienyl ligands are reported. The complexes have been completely characterized by spectral studies. The molecular structures of representative complexes have been determined by single crystal X-ray crystallography.     

A new dynamic model for highly efficient mass transfer in aerated bioreactors and consequences for kLa identification

Gas–liquid mass transfer is often rate‐limiting in laboratory and industrial cultures of aerobic or autotrophic organisms. The volumetric mass transfer coefficient k_La is a crucial characteristic for comparing, optimizing, and upscaling mass transfer efficiency of bioreactors. Reliable dynamic models and resulting methods for parameter identification are needed for quantitative modeling of microbial growth dynamics. We describe a laboratory‐scale stirred tank reactor (STR) with a highly efficient aeration system (k_La ≈ 570 h^?1). The reactor can sustain yeast culture with high cell density and high oxygen uptake rate, leading to a significant drop in gas concentration from inflow to outflow (by 21%). Standard models fail to predict the observed mass transfer dynamics and to identify k_La correctly. In order to capture the concentration gradient in the gas phase, we refine a standard ordinary differential equation (ODE) model and obtain a system of partial integro‐differential equations (PIDE), for which we derive an approximate analytical solution. Specific reactor configurations, in particular a relatively short bubble residence time, allow a quasi steady‐state approximation of the PIDE system by a simpler ODE model which still accounts for the concentration gradient. Moreover, we perform an appropriate scaling of all variables and parameters. In particular, we introduce the dimensionless overall efficiency κ, which is more informative than k_La since it combines the effects of gas inflow, exchange, and solution. Current standard models of mass transfer in laboratory‐scale aerated STRs neglect the gradient in the gas concentration, which arises from highly efficient bubbling systems and high cellular exchange rates. The resulting error in the identification of κ (and hence k_La) increases dramatically with increasing mass transfer efficiency. Notably, the error differs between cell‐free and culture‐based methods of parameter identification, potentially confounding the determination of the “biological enhancement” of mass transfer. Our new model provides an improved theoretical framework that can be readily applied to aerated bioreactors in research and biotechnology. Biotechnol. Bioeng. 2012; 109: 2997–3006. © 2012 Wiley Periodicals, Inc.     

Maximizing the productivity of catalytic biofilms on solid supports in membrane aerated reactors

A new solid support membrane aerated biofilm reactor was designed for the synthesis of enantiopure (S)‐styrene oxide utilizing Pseudomonas sp. strain VLB120ΔC growing in a biofilm as biocatalyst. In analogy to traditional packed bed systems, maximizing the volumetric oxygen mass transfer capability (k_La) was identified as the most critical issue enabling a consistent productivity, as this parameter was shown to directly influence biofilm growth and biotransformation performance. A microporous ceramic unit was identified as an ideal microenvironment for biofilm growth and for efficient oxygen transfer. A uniform and dense biofilm developed on this matrix. Due to this dual function, the reactor configuration could be significantly simplified by eliminating additional packing materials, as used in traditional packed bed reactors. Up to now, a maximum productivity of 28 g L day^?1 was achieved by integrating an in situ substrate feed and an in situ product recovery technique based on a silicone membrane. The system was stable for more than 30 days before it was actively terminated. Biotechnol. Bioeng. 2010;106: 516–527. © 2010 Wiley Periodicals, Inc.     

An Unbalanced Mixed Model with Random Effects Having Unequal Variances

Consider the mixed model where x_ijk's are known constants, β_k are unknown parameters and a_i, e_ij are random variables independently and normally distributed with zero means and variances σd_i and σ² respectively, where it is assumed that the d_i's are known (d_i >0). This paper presents procedures for estimating the variance components σ, σ², for testing the hypothesis σ = 0, and for making transformations to random variables with uncorrelated errors and constant variances in order to estimate as well as to test hypothesis concerning the β_k's in the model.     

Photoinduced electron transfer in cytochrome bc1: Dynamics of rotation of the Iron-sulfur protein during bifurcated electron transfer from ubiquinol to cytochrome c1 and cytochrome bL

The electron transfer reactions within wild-type Rhodobacter sphaeroides cytochrome bc₁ (cyt bc₁) were studied using a binuclear ruthenium complex to rapidly photooxidize cyt c₁. When cyt c₁, the iron?sulfur center Fe₂S₂, and cyt b_H were reduced before the reaction, photooxidation of cyt c₁ led to electron transfer from Fe₂S₂ to cyt c₁ with a rate constant of k_a = 80,000 s^?1, followed by bifurcated reduction of both Fe₂S₂ and cyt b_L by QH₂ in the Q_o site with a rate constant of k₂ = 3000 s^?1. The resulting Q then traveled from the Q_o site to the Q_i site and oxidized one equivalent each of cyt b_L and cyt b_H with a rate constant of k₃ = 340 s^?1. The rate constant k_a was decreased in a nonlinear fashion by a factor of 53 as the viscosity was increased to 13.7. A mechanism that is consistent with the effect of viscosity involves rotational diffusion of the iron?sulfur protein from the b state with reduced Fe₂S₂ close to cyt b_L to one or more intermediate states, followed by rotation to the final c₁ state with Fe₂S₂ close to cyt c₁, and rapid electron transfer to cyt c₁.     

Characteristic parameters and polydispersity elimination factors for hydrodynamic quantities of semirigid polymers, especially of DNA

Relations are given allowing the calculation of intrinsic viscosity, diffusion constant, and related molecular weights of monodisperse subfractions of polydisperse samples from the measured averages of the hydrodynamic quantities and the individual (reduced) sedimentation constant distribution. The peculiarities resulting from the special behavior of semirigid polymers like DNA are treated. Expressions are derived which describe the dependence of the exponents a_s(a_ηs = a_η/a_s), and a_η of the relations s^o = k_sM^as [η] = k_ηs(s^o)^aηs, and [η] = k_ηM^aη on s^o and [η], respectively, and which are useful for practical and theoretical discussions of the wormlike chain. Furthermore, a generalized exponent rule for a_η and a_s has been suggested, considering the dependence of the Mandelkern-Flory-Scheraga parameter β(?Φ^1/3P^?1) on molecular weight. The results of this paper are applied extensively in the following paper to molecular weight and hydrodynamic properties of homogeneous DNA.