Effects Of Culture Conditions On The Production Of ALA By Recombinant E.coli

5-aminolevulinic acid (ALA) is the biosynthetic precursor of the tetrapyrroles, such as porphyrin, heme, chlorophyll (CHL), and vitamin B12. The ability of ALA to generate photosensitization derivatives in human bodies, insects and certain plant species make it possible to be used as an antitumor medicine, herbicide, insecticide, as well as growth promoting factor and stress tolerance improver for plants. In December 1999 ALA was authorized by FDA as a photodynamic medicine to treat skin cancer in prophase. And it is drawing more and more attentions of scientists to apply it in the treatment of various epidermis cancers. Recently, ALA has been applied to the treatment of acne vulgaris and the suppression of the inflammatory response to coronary and iliac injuries. As the second generation of photodynamic medicine, its outstanding advantages include less side effect, better curative effect and penetrability, lower price, etc. As an agricultural chemical, ALA at least has the advantage of being biodegradable and having no accumulation in environment.A recombinant Escherichia coli BL21 (DE3) harboring hemA gene from Agrobacterium radiobacter, which was created in our previous work, is used for the extra-cellular production of 5-Aminolevulinic acid (ALA). The influence of varied physiological factors such as the concentrations of precursors (glycine, succinic acid and D-glucose) and the inhibitor of 5-aminolevulinate dehydratase (levulinic acid) on the accumulation of ALA in fermentation broth was investigated both in shake flasks and in a jar fermenter. Among these precursors, glycine exhibited the strongeast inhibition on cell growth, while glucose inhibited mainly ALA formation. Optimum initial concentrations of glycine, succinic acid and D-glucose were found to be 2.0, 10.0 and 2.0 g/L, respectively. 30 mM levulinic acid (LA) was fed to the fermentation broth at the end of the exponential cell growth phase (about 8 h), and intracellular activity of ALA dehydratase was efficaciously suppressed. Repeating the optimum composition of medium in a stirred tank fermenter, 1.49 g/L ALA was achieved. Furthermore, fed-batch of precursors and inhibitor can further increase the ALA production up to 3.01 g/L.