Study On The Biosynthesis Of 5-Aminolevulinic Acid By Photobacteria And Recombinant E.coli GT48

5-aminolevulinic acid (ALA) is the biosynthetic precursor of the tetrapyrroles, such as porphyr'in, heme, chlorophyll (CHL), and vitamin B12. It is reported that ALA has no toxicity, to either huraanbeing or animals, is degradable easily, and has no accumulation in environment; therefore, it is a green agricultural chemical. ALA can also be served as a pharmaceutical therapy fighting against cancer, and used as a chemical for detecting blood plumbum content. 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. As the second generation of photodynamic medicine, its outstanding advantages include less side effect, better curative effect and penetrability, lower price, etc.Some techniques to synthesize ALA by chemical and biological processes have been proposes abroad, however, they are still blankness in China.In this work, the biological synthesis of ALA was studied. At first, the screen and mutating of photobacteria were performed to obtain high productive strain for ALA synthesizing, and the medium composition and fermentation conditions were optimized. Next, a strain of recombinant, E. coh' GT48, was applied for ALA production.Four strains of photobacterium were screened from active sludge in a local wastewater treatment factory using van Niel medium. A strain with the highest ALA productivity among four strains was selected for further studied, which belongs to Rhodopseudomonas by an identification procedure. Treated by N-methyl-N' -nitro-N-nitrosoguanidine and ultraviolete, a mutant, C-2, was obtained with ALA productivity of 21.2 mg/L. After preliminary optimization in medium composition and cultivation conditions, the ALA productivity increased to 38. 9 mg/L.A recombinant strain, E. coli GT48 was applied for ALA production, in which, a gene of ALA synthetase was cloned into a plasraid. The initial productivity of ALA was about 19.8mg/L. After preliminary optimization in medium composition and cultivation conditions, the ALA productivity increased to 47. 8mg/L in batch fermentation.In order to improve the cell density and ALA productivity, The fed-batch fermentation was studied in 5L BET fermentor. The effects of medium composition in feed and dissolved oxygen on ALA production were evaluated, and the ALA productivity was increased up to 72. 9mg/L.Although it is only a preliminary study of biological synthesis of ALA and the productivity is not as high as expected, this work lays the foundation for the further improvement in ALA production.