240 Chapter 8 8. 4 Amino acid fermentation wild strains Many micro-organisms accumulate amino acids in culture media. Indeed wild strains have proved to be effective producers of amino acids like alanine, glutamic acid and valine Since amino acids are used as essential components of the microbial cells and their biosynthesis is regulated to maintain an optimal level, they are normally synthesised in limited amounts and are subject to negative feedback control. The main problem using wild strains is, therefore, the production of minor amounts of amino acids at an early tage in the fermentation, giving rise to feedback control To achieve overproduction of amino acids the follo improvement of the uptake of the raw material(starting materiaL); hindrance of the side reactions stimulation of the enzymes that are involved in the synthesis inhibition of the degradation of the desired amino acid; stimulation of excretion of the amino acid that is produce ategies for The most successful way to achieve overproduction is to make use of mutants. Another rproducton way to overcome feedback regulation is to make use of a kind of semi-fermentation process called precursor addition fermentation; this will be considered later in this chapte Amino acids produced by fermentation on an industrial scale are listed in table 8.3 Ino acids tonnes/year ppllcatlons ca8,000 westener) synthesis of alan glutamic acid ca.270,00 flavours, pharmaceuticals ca.90,000 ca.8,000 aspartame(sweetener) ca.500 dietary ca.100 pharmaceuticals, dietary Table 8.3 Amino acids industrially produced by fermentation ∏ Examine the list of procedures to achieve overproduction(shown above)and identify which ones could be achieved by mutation of a wild strain. Since all the procedures listed involve enzymes they all could be achieved by mutation This emphasises the potential of using mutation for amino acid production240 Chapter 8 8.4 Amino acid fermentation wild strains Many micro-organisrns accumulate amino acids in culture media. Indeed, wild strains have proved to be effective producers of amino acids like alanine, glutamic acid and valine. Since amino acids are used as essential components of the microbial cells and their biosynthesis is regulated to maintain an optimal level, they are normally synthesised in limited amounts and are subject to negative feedback control. The main problem using wild strains is, therefore, the production of minor amounts of amino acids at an early stage in the fermentation, giving rise to feedback control. To achieve overproduction of amino acids the following procedures can be used: 0 improvement of the uptake of the raw material (starting material); 0 hindrance of the side reactions; tzgz mw 0 stimulation of the enzymes that are involved in the synthesis; 0 inhibition of the degradation of the desired amino acid; 0 stimulation of excretion of the amino acid that is produced. The most successful way to achieve overproduction is to make use of mutants. Another way to overcome feedback rrgulation is to make use of a kind of semi-fermentation process called precursor addition fermentation; this will be considered later in this chapter. Amino acids produced by fermentation on an industrial scale are listed in Table 8.3. smegies br overpcoddm amino aclds tonneelyear aspartic acid ca. 8,000 glutamic acid lysine phenylalanine threonine tryptophan ca. 270,000 ca. 90,000 ca. 8,000 ca. 500 ca. 100 applications aspartame (sweetener) enzymatic synthesis of alanine and phenylanine flavours, pharmaceuticals dietary aspartame (sweetener) dietary pharmaceuticals, dietary Table 8.3 Amino adds industrially produced by fermentation. Examine the list of p'ocedures to achieve overproduction (shown above) and n idenbfy which ones could be achieved by mutation of a wild strain. Since all the procedures listed involve enzymes they all could be achieved by mutation. This emphasises the potential of using mutation for amino acid production