COMPARATIVE STUDY OF GLUTAMIC ACID PRODUCTION BY WILD-TYPE AND MUTANT STRAINS OF CORYNEBACTERIUM GLUTAMICUM
CHAPTER ONE
1.0Â Â INTRODUCTION
1.1Â Â Â Â Â Â Â Â Background of the Study
Corynebacterium glutamicum is a rod-shaped Gram-positive aerobic bacterium, which can be found in soil, sewages, vegetables, and fruits (Eggeling and Bott, 2005). This bacterium is capable of utilizing various sugars as well as organic acids (Blombach and Seibold, 2010). Among others, C. glutamicum has the ability to metabolize glucose, fructose, and sucrose as well as lactate, pyruvate, and acetate (Blombach and Seibold, 2010); additionally, C. glutamicum has the ability to grow on mixtures of different carbon sources with a monoauxic growth (Wendisch et al., 2000) as opposed to diauxic growth observed for many other microorganisms such as Escherichia coli and Bacillus subtilis. Only a few exceptions have been reported as in the case of glucose-ethanol or acetate-ethanol mixtures, where preferential substrate utilization was observed (Zahoor et al., 2012). Since its discovery, C. glutamicum has become an indispensable microorganism for the biotechnological industry (Wendisch, 2014). With the development of amino acid market, a new era for the production of these amino acids by many companies and academic associations have enthusiastically arisen with the start of research and development in this field to increase the rate of amino acid production. This technological race has expedited the expansion of amino acid production by various methods. Thus, almost all the amino acids can be produced by any of the four methods which include; chemical synthesis, protein hydrolysis, enzymatic synthesis and fermentation.
However, industrially, the most advantageous and economical method used for amino acids manufacture is microbial method, that is fermentation (Ikeda, 2003). For almost fifty years, amino acids have been produced through fermentation (Rastegari et al., 2013). Out of ten non-essential amino acids, glutamic acid is second to alanine in priority due to that it stands first in the list as it is commercially very important amino acid used as flavor enhancer in foods (Javaid et al., 2012).
Among all biochemical methods, fermentation is the most economical, practical and eco-friendly means of producing glutamic acid, with low temperature requirement and the possibility of using cheaper carbon sources such as agricultural residues (Ekwealor and Obeta, 2005).
Microorganisms have regulatory mechanisms to control the quantities and qualities of enzymes that are involved in the synthesis of amino acids. Therefore, it is necessary to use these regulatory mechanisms in order to get the mass production of the target amino acid. Moreover the titre of amino acid increases if the enzymes involved in the production of the required amino acid are found in large amounts under workable situations. For this purpose, strains of microorganisms are improved using several techniques to make this process possible (Kothari, 2009).
Microorganisms employed for amino acid production are categorized into four groups; including the wild-type, auxotrophic, regulatory and auxotrophic regulatory mutants. The species of Corynebacterium or Brevibacterium are widely used for glutamic acid production (Choi et al., 2004). Similarly, their mutant strains that are auxotrophic or resistant to certain chemicals result in enhanced production of glutamic acid (Anastassiadis, 2007).
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COMPARATIVE STUDY OF GLUTAMIC ACID PRODUCTION BY WILD-TYPE AND MUTANT STRAINS OF CORYNEBACTERIUM GLUTAMICUM
