Showing papers by "Douglas B. Kell published in 1987"

The passive electrical properties of biological systems: their significance in physiology, biophysics and biotechnology

Abstract: The following topics are discussed: a summary of dielectric theory; amino acids, peptides, proteins and DNA; bound water in biological systems; biological electrolytes; membranes and cells; tissues.

Determination of biomass

Abstract: Apparatus for the determination of biomass in a suspension and its use in a fermentation apparatus. The apparatus comprises electrodes to be placed in the suspension and the following other components: a) means for applying an alternating voltage between the electrodes; b) means for providing a current signal indicative of the current in the current electrode circuit; c) means for providing a voltage signal indicative of the voltage between the voltage electrodes; and d) means for determining the ratio between the value of the voltage signal and the value of a quadrature component of the current signal, or vice versa, to provide a capacitance dependent signal.

Matrix method for determining steps most rate‐limiting to metabolic fluxes in biotechnological processes

Abstract: The metabolic control theory developed by Kacser, Burns, Heinrich, and Rapoport is briefly outlined, extended, and transformed so as optimally to address some biotechnological questions. The extensions include (i) a new theorem that relates the control of metabolite concentrations by enzyme activities to flux ratios at branches in metabolic pathways; (ii) a new theorem that does the same for the control of the distribution of the flux over two branches; (iii) a method that expresses these controls into properties (the so-called elasticity coefficients) of the enzymes in the pathway; and (iv) a theorem that relates the effects of changes in metabolite concentrations on reaction rates to the effects of changes in enzyme properties on the same rates. Matrix equations relating the flux control and concentration control coefficients to the elasticity coefficients of enzymes in simple linear and branched pathways incorporating feedback are given, together with their general solutions and a numerical example. These equations allow one to develop rigorous criteria by which to decide the optimal strategy for the improvement of a microbial process. We show how this could be used in deciding which property of which enzyme should be changed in order to obtain the maximal concentration of a metabolite or the maximal metabolic flux.

The Roles of Osmotic Stress and Water Activity in the Inhibition of the Growth, Glycolysis and Glucose Phosphotransferase System of Clostridium pasteurianum

Abstract: Growth of Clostridium pasteurianum was inhibited in media of high solute content. At equal osmolarities, ‘permeant’ solutes (glycerol and acetamide) were much less growth-inhibitory than ‘non-permeant’ solutes (KC1 and xylitol). Glycolysis by washed cell suspensions was inhibited by these solutes in parallel with growth. However, in their inhibition of glucose 6-phosphate dissimilation by permeabilized cells the distinction between ‘permeant’ and ‘impermeant’ solutes was significantly less marked. The glucose phosphotransferase system (PTS) of intact cells was much more strongly inhibited by ‘non-permeant’ than by ‘permeant’ solutes. It was concluded that the predominant inhibitory effects on this organism of media of high solute content are due not to the low water activity of such media per se, but to the creation of an osmotic pressure across the bacterial cytoplasmic membrane, which acts to inhibit the glucose PTS by which the organism effects glucose uptake. Parallel measurements of the effects of xylitol on both glycolysis and the activity of the glucose PTS suggested that despite this correlation between the osmotic inhibition of growth, glycolysis and the PTS, the flux-control coefficient of the PTS on glycolysis did not exceed 0.2 under the conditions used.

Forces, Fluxes and the Control of Microbial Growth and Metabolism: The Twelfth Fleming Lecture

Abstract: It is an interesting fact (Macfarlane, 1984) that 58 years elapsed between the publication of the studies of Burdon Sanderson and of Lister showing the antibacterial action of members of the genus Penicillium (Burdon Sanderson, 187 1 ; Lister, 187 1) and Fleming’s somewhat more celebrated paper (Fleming, 1929) to the same effect. Coincidentally enough, a similar period links this latter date with the present year. When seeking to account for Fleming’s apparent ignorance of the prior art, Macfarlane (1984) notes that Papacostas & Gat6 (1928) had just published a book which contained a 60 page section, headed ‘Antibiosis’, on the extensive subject of bacterial inhibition by moulds and by other bacteria, devoted to previously published observations on this phenomenon and with seuerul hundred historical references! The evident moral to be drawn from this tale is that the state of the art as perceived by the co:lective consciousness (or its foremost representatives) often differs markedly from what has actually been widely recorded in the literature. Thus, given the impossibility of being allpervasive, one must often, and especially in an overview of the present type, concentrate upon the crucial principles at the expense of the details. I state this by way of an excuse for doing that very thing in what follows, since I shall be seeking, in the most eclectic manner, to summarize my own analysis of several areas of what constitutes a huge field of enquiry: the question of what controls the growth and metabolic rates of bacteria. Now, the first distinction which we make when we seek to analyse the mechanisms by which bacteria contrive to control the rates at which they grow or metabolize is that between catabolism and anabolism, which are of course linked predominantly by means of the adenine nucleotide system (Fig. 1). Here we see, in a formal sense, the conceptual separation between the provision and utilization of free energy in the living bacterial cell, so that the cell is modelled as a non-equilibrium thermodynamic energy converter. The negative of the free energy change per extent of reaction for the catabolic reactions constitutes the input force (or affinity; see e.g. Prigogine, 1967; Welch, 1985a) to the adenine nucleotide system, whilst the output force is represented by the free energy change (per extent of reaction) for the formation of biomass. The relevant fluxes are constituted by the rates at which the catabolic and anabolic processes take place. It is particularly important to note that not all the free energy that is generated by catabolism is actually used to drive anabolism, and this is represented formally as an uncoupled ATP hydrolase reaction. To quantify this contribution in particular, we must define the efficiency of microbial growth.

The physiology of Clostridium sporogenes NCIB 8053 growing in defined media

Abstract: The physiology of Clostridium sporogenes was investigated in defined, minimal media. In batch culture, the major end products of glucose dissimilation were acetate, ethanol and formate. When L-proline was present as an electron acceptor, acetate production was strongly enhanced at the expense of ethanol. As judged by assay of the relevant enzymes, glucose was metabolized via the Embden-Meyerhof-Parnas pathway. The growth energetics of Cl. sporogenes were investigated in glucose- or L-valine-limited chemostat cultures. In the former case, the addition of L-proline to the medium caused a significant increase in the molar growth yield (as calculated by extrapolation to infinite dilution rate). This finding adds weight to the view that the reduction of L-proline by Cl. sporogenes is coupled to the conservation of free energy.

The growth and nutrition of Clostridium sporogenes NCIB 8053 in defined media.

Abstract: Various defined and minimal media are described for the growth of Clostridium sporogenes NCIB 8053. The organism requires 10 amino acids and one vitamin for growth, whilst three other vitamins are growth stimulatory. L-alpha-hydroxy acid analogues can replace eight, and fatty acid analogues four, of these amino acids. The organism may generate free energy by a variety of Stickland reactions. Most Stickland acceptors, but not glycine, stimulate the growth of this organism on glucose. Nonetheless, cells grown in the presence of glycine will reductively deaminate it. The media described support the growth of several other strains of this species. The simplified growth media which we have developed permit quantitative studies of the physiology of this organism.

Effects of pCO2 on the growth and metabolism of Clostridium sporogenes NCIB 8053 in defined media

Abstract: The effects of the partial pressure of carbon dioxide (pCO2) on the growth rate of Clostridium sporogenes NCIB 8053 in batch culture were investigated in defined minimal media. Depending upon the growth medium, CO2 was stimulatory or inhibitory to growth. The absolute CO2 requirement for growth displayed by Cl. sporogenes in certain media was shown to be due to the involvement of CO2 in the synthesis of branched-chain amino acids. High concentrations of CO2 were growth inhibitory except in complex media. In media where an optimal pCO2 was observed it was approximately 0˙45 atm. The pattern of fermentation end-products displayed by this organism was also modified by the pCO2. The equilibria of the different species of ‘CO2’ present in microbiological media are described. Finally, the metabolic control theory of Kacser, Burns, Heinrich and Rapoport has been applied to the results obtained, to provide a quantitative description of the effects of pCO2 on the growth rate of Cl. sporogenes.