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Title: The examination of organic acid production during the growth of Streptomyces lividans TK24
Author: Madden, Ernestine Anne
ISNI:       0000 0001 3616 0848
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 1996
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Organic acid excretion by Streptomyces lividans TK24 lowers the culture medium pH and may interfere with growth and recombinant product integrity. The acids excreted were identified by HPLC and enzymic assays as pyruvate and α-ketoglutarate. Acid excretion occurred during growth on glucose in defined medium, but was dependent on the nitrogen source employed. With nitrate as the sole nitrogen source, high levels of pyruvate and traces of α-ketoglutarate were detected. Carbon from D-[U-14C]glucose was converted to both acids. With a selected amino acid as the sole nitrogen source, less pyruvate and more α-ketoglutarate was excreted. The sum of maximum acid levels was greater than in glucose-nitrate media. Carbon from both labelled glucose and amino acids was converted to the acids. With ammonium as the sole nitrogen source, no acids were produced. Cultures supplied with mixed organic and inorganic nitrogen sources exhibited a reversion of the acid production pattern as if the organic source were absent. Experiments with alternative carbon sources showed that starch, maltose and glycerol supported acid production. Levels of excreted acids were higher when the carbon sources were combined with an organic nitrogen source compared to nitrate. Fructose, sucrose and dextrin did not support high growth or any detectable acid over-production. Acid accumulation occurred in complex MEP medium (1% malt extract broth, 1% peptone, 2% glycerol), and in media containing the constituent carbon sources, malt extract and malt extract broth, with defined nitrogen sources. The acid production patterns were generally equivalent to the most similar defined combinations. It was concluded that acid production was supported by the principal carbon sources and influenced by the amino acids in the peptones. An ammonium supplement reduced acid production by 85%. In most media, acids were reassimilated towards the end of rapid growth and during the stationary phase. Conversion of consumed carbon to undesirable acid byproducts was greater in defined media (around 11%) than complex media (around 6%).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Recombinant product sysnthesis; Culture medium