Some enzymes acids have been produced in Japan by bacterial fermentation. Their biosynthesis is now possible by genetically manipulating and physiologically altering the microorganism. Corynebacterium glutamicum and Brevibacteriumflavum are involved in the synthesis of L-lysine and L-theronine from a common intermediate, aspartic acid. The regulatory mutants of bacteria lysine in sufficient amount. Such bacteria eliminate the dependence of enzyme formation on inducer addition.
Generally , E.coli and Enterobacter aerogenes are used the formation of diaminopalmelic acid and for the decarboxylation of the diaminopalmelic acid by an enzyme DAP decarboxylase . E. aeregenes is an auxotroph requires L- homoserine of a mixture of L- theronine and L- methionine. The lysine- histidine, double auxotrophic mutant of E. coli produces diaminopalmelic acid on a molasses medium with a yield of 19-24 g/litre. The entire information solution including the cell material is subsequently incubated with E. aerogenes at 35°C. After 20h, the DAP is quantitatively decarboxylated to L-lysine.
The fermentation media consist of glycerol, corn steep liquor, ammonium sulphate.In addition calcium carbonate is employed in the production medium.The pH is left neutral and incubation is carried out for 72h at 28°C with high aeration. The yield of lysine is as high as 30gm/litre, earlier was produced by two stage processes using two different organisms. But now a days single stage process using mutants of Corynebacterium, Brevibacterium etc. are grown on a synthetic medium containing glucose, an inorganic nitrogen source and a small concenteration of either homoserine, methionine etc. in addition to a small concenteration of biotin.
Although, lysine is bound in the cell but due to mutantions in the producing strains, it is secreted out and recovered.
L- glutamic acid is produced by using bacterial isolate, Micrococcus glutamicus (syn: Corynebacterium glutamicum). Although, this organismis is not an auxotroph but requires biotin in the medium for growth. This amino acid is present both intracellulerly as well as leaked out in the medium subjected to optimum biotin level available for fermentative production of L-glutamic acid. If excess of biotin is present in the medium there is heavy cell growth, but lactic acid production starts.
Some microorganisms such as Corynebacterium herculis, C. lilium, Arthrobacter globiformis, Microbacterium salicinovorum, Bervibacterium divaricatum, B. aminogenes, B. flavum, B. megaterium are other glutamic acid producing species. Modifications of the permeability of a microorganism is provided by the glutamic acid fermentation. The permeability of Corynebacterium glutamicum may be controlled by the composition of the culture medium.
The medium contains glucose, ammonium acetate, molasses, potassium hydrogen phosphate, potassium sulphate, manganese sulphate, antifoam agent in one liter distilled water. The size of the inoculum remain 6 percent. The fermentative organism is Brevibacterium divaricatum. The incubation was carried out for 16 hours at 35°C. At the beginning of the fermentation 0.65 ml per litre of olive oil is added. The pH is set at 8.5 with ammonia and is automatically maintained at 7.8 during fermentation. After beginning of growth of the culture, the temperature is increased from 32-28°C. The glucose feeding is done until the fermentation is completed.
The glutamic acid content is analysed hourly. The fermentation is stopped after 30-35 hours with a yield of 100 g per litre. If molasses from starch saccharification is substituted for glucose, the glutamic acid yield is 94 gm per litre after 36 hours.
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