Generalization of monod kinetics for analysis of growth data with substrate inhibition

The inhibitory effect of butanol on yeast growth has been studied for the strain Candida utilis ATCC 8205 growing aerobically on butanol under batch conditions. A mathematical expression was then proposed to fit the kinetic pattern of butanol inhibition on the specific growth rate: \documentclass{article}\pagestyle{empty}\begin{document}$$ \mu = \frac{{\mu _m S}}{{K_s + S}}\left[{1 - \frac{S}{{S_m }}} \right];n $$\end{document}The maximum allowable butanol concentration above which cells do not grow was predicted to be 9.16g/L. The proposed model appears to accurately represent the experimental data obtained in this study and the literature data developed for a variety of batch culture systems at widely ranging substrate concentrations.     

Cell immobilization in kappa-carrageenan for ethanol production

A combination of extended Monod kinetics and the diffusional equation was used for evaluating the effectiveness factor of entrapped immobilized cells. Based on the kinetics of Zymomonas mobilis reported in the literature, the numerical results have revealed that the problem of mass transfer diffusional restrictions can be neglected by using small beads (1 mm in diameter) with a corresponding cell loading up to 276 g/L gel. On the basis of the numerical results obtained, the application of immobilized cells for continuous ethanol production was investigated. The kappa-carrageenan method was utilized to entrap Z. mobilis CP4, a potential ethanol producer. A two stage fermentation process has also been developed for ethanol production by the Z. mobilis carrageenan-bound cells. About 90 g/L ethanol was produced by immobilized cells at a total residence time of 1.56 h. The ethanol yield was estimated to be 93% of theoretical. The results obtained in this study also indicated that the control of optimum pH in an immobilized cell column is necessary to enhance the rate of ethanol production.     

Kinetics of ethanol inhibition in alcohol fermentation

The inhibitory effect of ethanol on yeast growth and fermentation has been studied for the strain Saccharomyces cerevisiae ATCC No. 4126 under anaerobic batch conditions. The results obtained reveal that there is no striking difference between the response of growth and ethanol fermentation. Two kinetic models are also proposed to describe the kinetic pattern of ethanol inhibition on the specific rates of growth and ethanol fermentation: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {\frac{{\mu _i }}{{\mu _0 }} = 1{\rm } - {\rm }\left( {\frac{P}{{P_m }}} \right);\alpha } \hfill & {\left( {{\rm for}\ {\rm growth}} \right)} \hfill \\ {\frac{{\nu _i }}{{\nu _0 }} = 1{\rm } - {\rm }\left( {\frac{P}{{P'_m }}} \right);\beta } \hfill & {\left( {{\rm for}\ {\rm ethanol}\ {\rm production}} \right)} \hfill \\ \end{array}$$\end{document} The maximum allowable ethanol concentration above which cells do not grow was predicted to be 112 g/L. The ethanol-producing capability of the cells was completely inhibited at 115 g/L ethanol. The proposed models appear to accurately represent the experimental data obtained in this study and the literature data.     

Monitoring glutamine in animal cell cultures using a chemiluminescence fiber optic biosensor

Together with flow injection analysis (FIA), a chemiluminescence (CL) fiber optic biosensor system has been developed for determining glutamine in animal cell cultures. Glutaminase (GAH) and glutamate oxidase (GLO) were onto separate porous aminopropyl glass beads via glutaraldehyde activation and packed to form an enzyme column. These two enzymes acted in sequence on glutamine to produce hydrogen peroxide, which was then reacted with luminol in the presence of ferricyanide to produce a light signal. An anion exchanger was introduced on-line to eliminate interfering endogenous glutamate in view of its negative charge at pH above 3.22 (isoelectric pH). Among several resins tested, the acetate form was most effective, and this type of ion exchanger also effectively adsorbed uric acid, acetaminophen, and aspartic acid.There was an excellent linear relationship between the CL response and standard glutamine concentration in the range 1 to 100 muM. A complete analysis could be performed in 2 min, including sampling and washing with a good reproducibility (+/- 4.4%). Both the bi-enzymic and ion exchange columns were useful for at least 500 analyses when the biosensor system was applied for the glutamine determination in murine hybridoma cell cultures and insect cell cultures. The values obtained compared well with those of HPLC, thus validating the applicability of the CL fiber optic system. (c) 1993 John Wiley & Sons, Inc.     

Sequences and Evolution of Human and Squirrel Monkey Blue Opsin Genes

The sequences of the entire blue opsin gene in the squirrel monkey (Saimiri boliviensis) and the five introns of the human blue opsin gene were obtained. Intron 3 of these genes contains an Alu sequence and intron 4 contains a partial mer13 sequence. A comparison of the squirrel monkey opsin sequence with published mammalian opsin sequences shows that features believed to be functionally critical are all conserved. However, the blue opsin has evolved twice as fast as rhodopsin and is only as conservative as the β globin, which has evolved at the average rate of mammalian proteins. Interestingly, the interhelical loops are, on average, actually more conservative than the transmembrane α helical regions. The introns of the blue opsin gene have evolved at the average rate of introns in primate genes. Received: 5 August 1996 / Accepted: 2 October 1996     

Estimating the maintenance energy and biomass concentration of Saccharomyces cerevisiae by continuous calorimetry

Continuous calorimetry has been applied to monitoring the heat evolution of Saccharomyces cerevisiae grown on d-glucose. The heat evolution, together with the energy and carbon balances, was used to evaluate the energetic efficiency of biomass, by-product biosynthesis, fermentative heat evolution as well as the maintenance energy of S. cerevisiae in ‘aerobic fermentation’ and ‘aerobic respiration’. In aerobic fermentation, under catabolite repression, the fraction of substrate energy converted to heat evolution, maintenance requirement, and biomass decreased with the increase of d-glucose concentration. The fraction of substrate energy converted to ethanol is the highest value and it could contribute up to 70% of the total substrate energy. In aerobic respiration, 43% of the total substrate energy was evolved as heat. While 50% of the total substrate energy was converted into biomass, only 7% of the total substrate energy was used for maintenance functions. The maintenance energy coefficient of S. cerevisiae was determined to be 0.427 MJ kg^?1 cell h^?1 (0.102 kcal g^?1 cell h^?1). For the first time, heat evolution together with yield-maintenance energy was used to predict biomass concentration during the fed-batch cultivation of S. cerevisiae.     

Development of a biosensor for assaying postmortem nucleotide degradation in fish tissues

An enzyme sensor system has been developed to assess the freshness level in fish tissue. The system was designed to measure the K value, the concentration ratio of [Hx + HxR] and [Hx + HxR + IMP], where Hx, HxR, and IMP are hypoxanthine, inosine and inosine-5'-monophosphate, respectively. The [Hx + HxR] concentration in tissue extract was measured by nucleoside phosphorylase and xanthine oxidase immobilized on a preactivated nylon membrane and attached to the tip of a polarographic electrode. The electrode amperometrically detected the products of degradation, hydrogen peroxide and uric acid. For determination of [IMP + HxR + Hx], IMP was first converted to HxR by nucleotidase immobilized on the wall of a polystyrene tube. The enzyme electrode consisting of nucleoside phosphorylase and xanthine oxidase provided excellent reproducible results for at least 40 repeated assays and immobilized nucleotidase was good for at least 40 assays as well. The K value for each sample could be determined in ca. 10 min. When applied to K value measurements in several fish meats, the results obtained agreed well with those obtained by the conventional enzymatic method.     

Golden bananas in the field: elevated fruit pro‐vitamin A from the expression of a single banana transgene

Vitamin A deficiency remains one of the world's major public health problems despite food fortification and supplements strategies. Biofortification of staple crops with enhanced levels of pro‐vitamin A (PVA) offers a sustainable alternative strategy to both food fortification and supplementation. As a proof of concept, PVA‐biofortified transgenic Cavendish bananas were generated and field trialed in Australia with the aim of achieving a target level of 20 μg/g of dry weight (dw) β‐carotene equivalent (β‐CE) in the fruit. Expression of a Fe'i banana‐derived phytoene synthase 2a (MtPsy2a) gene resulted in the generation of lines with PVA levels exceeding the target level with one line reaching 55 μg/g dw β‐CE . Expression of the maize phytoene synthase 1 (ZmPsy1) gene, used to develop ‘Golden Rice 2’, also resulted in increased fruit PVA levels although many lines displayed undesirable phenotypes. Constitutive expression of either transgene with the maize polyubiquitin promoter increased PVA accumulation from the earliest stage of fruit development. In contrast, PVA accumulation was restricted to the late stages of fruit development when either the banana 1‐aminocyclopropane‐1‐carboxylate oxidase or the expansin 1 promoters were used to drive the same transgenes. Wild‐type plants with the longest fruit development time had also the highest fruit PVA concentrations. The results from this study suggest that early activation of the rate‐limiting enzyme in the carotenoid biosynthetic pathway and extended fruit maturation time are essential factors to achieve optimal PVA concentrations in banana fruit.     

Cognitive and socio-emotional deficits in platelet-derived growth factor receptor-β gene knockout mice

Platelet-derived growth factor (PDGF) is a potent mitogen. Extensive in vivo studies of PDGF and its receptor (PDGFR) genes have reported that PDGF plays an important role in embryogenesis and development of the central nervous system (CNS). Furthermore, PDGF and the β subunit of the PDGF receptor (PDGFR-β) have been reported to be associated with schizophrenia and autism. However, no study has reported on the effects of PDGF deletion on mice behavior. Here we generated novel mutant mice (PDGFR-β KO) in which PDGFR-β was conditionally deleted in CNS neurons using the Cre/loxP system. Mice without the Cre transgene but with floxed PDGFR-β were used as controls. Both groups of mice reached adulthood without any apparent anatomical defects. These mice were further examined by conducting several behavioral tests for spatial memory, social interaction, conditioning, prepulse inhibition, and forced swimming. The test results indicated that the PDGFR-β KO mice show deficits in all of these areas. Furthermore, an immunohistochemical study of the PDGFR-β KO mice brain indicated that the number of parvalbumin (calcium-binding protein)-positive (i.e., putatively γ-aminobutyric acid-ergic) neurons was low in the amygdala, hippocampus, and medial prefrontal cortex. Neurophysiological studies indicated that sensory-evoked gamma oscillation was low in the PDGFR-β KO mice, consistent with the observed reduction in the number of parvalbumin-positive neurons. These results suggest that PDGFR-β plays an important role in cognitive and socioemotional functions, and that deficits in this receptor may partly underlie the cognitive and socioemotional deficits observed in schizophrenic and autistic patients.