Organisms for Growth

The possibility of indirectly measuring cell biomass and growth rate by computer-aided on-line substrate balancing was first mentioned in a publication by Humphrey (11). The method is discussed in detail in a review by Humphrey (1). The technique operates by noting that the difference in amount of a particular component in and out of the vessel is equal to that used by the organism for growth and maintenance if no appreciable secondary metabolites are formed. Mathematically this can be stated as... 

Ignoring the small amount of sugars used by the organisms for growth and maintenance, the theoretical maximum yield of fermentation ethanol from the pentose sugars is 51.14 wt % of the sugars fermented, the same as the theoretical maximum yield from the hexose sugars. 

Hiscox, J. A., Thomas, D. J. (1995). Genetic modification and selection of micro-organisms for growth on Mars. Journal of the British Interplanetary Society, 48, 419. 

Folic acid and its derivatives (mostly the tri-and heptaglutamyl peptides) are widespread in nature. It is a specific growth ctor for certain micro-organisms, but in animals the intestinal bacteria provide the small quantities needed for growth. The coenzyme forms are actually... 

Physiological Role of Citric Acid. Citric acid occurs ia the terminal oxidative metabolic system of virtually all organisms. This oxidative metabohc system (Fig. 2), variously called the Krebs cycle (for its discoverer, H. A. Krebs), the tricarboxyUc acid cycle, or the citric acid cycle, is a metaboHc cycle involving the conversion of carbohydrates, fats, or proteins to carbon dioxide and water. This cycle releases energy necessary for an organism s growth, movement, luminescence, chemosynthesis, and reproduction. The cycle also provides the carbon-containing materials from which cells synthesize amino acids and fats. Many yeasts, molds, and bacteria conduct the citric acid cycle, and can be selected for thek abiUty to maximize citric acid production in the process. This is the basis for the efficient commercial fermentation processes used today to produce citric acid. 

Aerobe An organism that requires free oxygen for growth. 

In more recent times chemically defined basal media have been elaborated, on which the growth of various lactic acid bacteria is luxuriant and acid production is near-optimal. The proportions of the nutrients in the basal media have been determined which induce maximum sensitivity of the organisms for the test substance and minimize the stimulatory or inhibitory action of other nutrilites introduced with the test sample. Assay conditions have been provided which permit the attainment of satisfactory precision and accuracy in the determination of amino acids. Experimental techniques have been provided which facilitate the microbiological determination of amino acids. On the whole, microbiological procedures now available for the determination of all the amino acids except hydroxy-proline are convenient, reasonably accurate, and applicable to the assay of purified proteins, food, blood, urine, plant products, and other types of biological materials. On the other hand, it is improbable that any microbiological procedure approaches perfection and it is to be expected that old methods will be improved and new ones proposed by the many investigators interested in this problem. 

The stoichiometry of growth and metabolism can also be described by elemental material balances. This approach can provide an insight into the potential of the organism for biomass or product production, and thus the scope for process improvement. 

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