79 Advances in Biochemical Engineering / Biotechnology Managing Editor: T. Scheper Editorial Board: W. Babel. H. W. Blanch. I. Endo. S.-O. Enfors A. Fiechter • M. Hoare • B. Mattiasson • H. Sahm K. Schiigerl • G. Stephanopoulos • U. yon Stockar G. T. Tsao. J. ViUadsen • C. Wandrey • J.-J. Zhong Springer Berlin Heidelberg New York Hong Kong London Milan Paris Tokyo Microbial Production of L-Amino-Acids Volume Editors: Robert Faurie • Jiirgen Thommel With contributions by B. Bathe, V. G. Debabov, S. Huebner, M. Ikeda, E. Kimura, A. Marx, B. M6ckel, U. Mueller, W. Pfefferle ~ Springer Advances in Biochemical Engineering/Biotechnology reviews actual trends in modern biotechnology. Its aim is to cover all aspects of this interdisciplinary technology where knowledge, methods and expertise are required for chemistry, biochemistry, micro- biology, genetics, chemical engineering and computer science. Special volumes are dedi- cated to selected topics which focus on new biotechnological products and new pro- cesses for their synthesis and purification. They give the state-of-the-art of a topic in a comprehensive way thus being a valuable source for the next 3- 5 years. It also discusses new discoveries and applications. In general, special volumes are edited by well known guest editors. The managing editor and publisher wilt however always be pleased to receive suggestions and supplementary information. Manuscripts are accepted in English. In references Advances in Biochemical Engineering/Biotechnology is abbreviated as Adv Biochem Engin/Biotechnot as a journal. Visit the ABE home page at http://link.springer.de/series/abe/ http://hnk.Springer-ny.com/series/abe/ ISSN 0724-6145 ISBN 3-540-43383-X Springer-Verlag Berlin Heidelberg New York Library of Congress Catalog Card Number 72-152360 This work is subject to copyright. 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Save 15 % We recommend a standing order for the series to ensure you automatically receive all volumes and all supplements and save 15% on the list price. Preface It was in 1908, when Prof. Kinue Ikeda, grandfather of Dr. T. Ikeda, a Japanese chemist discovered glutamic acid as a flavoring component in seaweed ("Kon- bu") and soy hydrolysates. After neutralization with caustic soda, he isolated Mono Sodium Glutamate (MSG), a flavor enhancer that represented the initial product for the company Ajinomoto. The company's name is synonymous with its first product and MSG was setting the stage for large scale production of amino acids. MSG is still today's most important amino acid and flavor enhancer. This was not only the birth of the first industrial scale amino acid production from natural raw material hydrolysates but also the fundamental process for the isolation of other amino acids. Several proteins derived from soy, corn or wheat contain only approximately 10-20% glutamic acid and glutamine whereas the residues contain many other amino acids, such as the essential ones (leucine, isoleucine, valine, threonine, methionine, lysine, phenylalanine and tryptophan) and the semi essential ones (arginine, cyst(e)ine, histidine and tyrosine). It is, however, very difficult to separate and purify all these components from the crude initial hydrolysate and therefore not surprising that the market price for those amino acids was comparably high. In order to meet the growing demand of MSG worldwide which was especially used in instant food and developing seasoning blends and to reduce production costs, the German companies Degussa AG/Frankfurt and the Amino GmbH/ Frellstedt produced the MSG from vinasses or from beet sugar molasses. This was done by alkaline hydrolysis of the pyrrolidonic carboxylic acid (PCA) extracted in large amounts from these cheap vegetable by-products. The real breakthrough was however achieved in the late 1960s and early 1970s when Kyowa Hakko and Ajinomoto applied a completely new technology and thus circumvented the expensive technology of protein hydrolysis and subse- quent by-products recovery as a source of amino acids using highly sophisticat- ed separation technologies. It was the birth of modern biotechnology when two Japanese scientists, Dr. Kinoshita and Dr. Udaka, at the research labs of Kyowa Hakko Kogyo dis- covered in 1957 that a certain strain of the Gram-positive soil bacterium "Corynebacterium" was able to excrete significant amounts of glutamic acid under certain conditions. This corynebacterium was exploited for large scale fermentation of glutamic acid for MSG production and the world market prices dropped dramatically from over US$ 8 to below US$ 2. Today MSG represents X Preface the commercially dominating amino acid with an annual production rate of more than 800,000 tons worldwide. The application of fermentation technology did not remain limited to MSG production. By natural screening accompanied by shot gun mutagenesis many Corynebacterum derived strains and also Gram-negative bacteria such as E. coti were discovered and proven to be suitable for amino acid breeding. However, the upcoming efforts of modern molecular biology offered new sophisticated tools such as the revolutionary enzyme engineering technology in the late 1970s. Enzyme engineering represents the fundamental tool for modern metabolic engineering. These techniques made it possible to modify individual key enzymes of the amino acid anabolism by site-directed mutagenesis in order to optimize their turn over and/or by knocking out feedback inhibition. The next milestone was the introduction of Polymerase Chain Reaction (PCR) combined with high throughput sequencing that made it possible to deci- pher complete organism genomes. The complete 3 million base pair genome of Corynebacterium glutamicurn is known today and on the way to being commer- cially exploited by companies like BASF and Degussa AG. What is the commercial interest behind this research in the field of amino acid biotechnology.~ Besides the use of MSG and some other amino acids as flavoring substances, the largest market for amino acids is the feed market showing outstanding growth rates.While the market for amino acids in general is said to double every decade, the market for L-lysine being the most important and best selling bio- technological produced feed amino acid demonstrated a tremendous growth by a factor of twenty during the last two decades. L-Lysine has reached the large output of the chemically produced D,z-methionine with approximately 400,000 tons per year. The significance of these amino acids on the world market is derived from their physiological essentiality and that their limited content in many tradition- al animal feed sources such as soy and corn. This fact is usually visualized by the so called "barrel model" to demonstrate the nutritive value of certain feedstuffs. This means that the value of the total proteins present is limited by the intrinsic content of the essential amino acid present at the lowest level. Methionine, e.g., is the value limiting Amino Acid in soy protein. By fortifying proteins by addition of only small amounts of the lim- iting amino acid the total efficacy of the individual feed product increases dra- matically. The addition of only one part of D,z-methionine allows the substitu- tion of 15 times the amount of soy at identical biological value and therefore to reduce cost of pig growing for dramatically. D,z-Methionine and ~.-lysine represent the dominating feed amino acids. In a ranking of limiting Amino Acids and in dependence of the feeding raw material used, L-threonine, L-tryptophan and the so called "Branched Chain Amino Acids" (BCAA) e-isoleucine, z-valine and z-leucine are the next amino acids to follow. z-Threonine has been marketed for several years in the feed market and seems to be the new star with an annual production rate of more than 15,000 tons.