中文摘要：

对从不同生态环境中分离得到的20株光合细菌，进行5-氨基乙酰丙酸（5-ALA）的产量检测，结果显示一株分离自广州市云溪公园池塘底泥的菌株R5，其5-ALA产量最高，达4．92mg／L．根据GenBank上公布的5-氨基乙酰丙酸合成酶hemA基因序列，设计引物进行hemA基因的克隆．结果表明，菌株R5的hemA基因序列长1230bp，不含HindⅢ酶切位点，G＋C为64．68％，编码一个409个氨基酸的酶蛋白，分子质量为44．9ku，与Rhodopseudomonas palustris KUGB306菌株的hemA基因序列相似性为98．6％，氨基酸序列相似性为100％．系统发生树显示，菌株R5与Rhodopseudomonas palmtris处在一个分支，显示菌株R5可能是Rhodopseudomonas palustris，这与微生物鉴定实验的结果一致．本研究克隆的高产5-氨基乙酰丙酸菌株的hemA基因，为后期获取高产5-ALA的基因工程菌打下基础．

英文摘要：

5-aminolevulinic acid （5-ALA） is a derivative of 5-carbon amino acid and is found in most living organisms with photosynthetic bacteria having the highest extra-cellular production of 5-ALA. In this study, the productions of 5-ALA by 20 photosynthetic bacteria strains from different habitats were determined. Strain R5 isolated from the bottom mud of a pond in Yunxi park, Guangzhou, had the highest production of 5-ALA （4. 92 mg/L）. 5-aminolevulinate synthase （ALAS）, the first enzyme of the heme biosynthesis pathway, is encoded from hemA gene in photosynthetic bacteria. The full-length sequence of hemA from Strain R5 was 1230 bp, with G ＋ C content of 64.68% and no Hind m restriction enzyme site. It encoded an enzyme of 409 amino acids with a predicted molecular mass of 44.9 kDa. The strain R5 showed 98.6% similarity of nucleotide acid sequence and 100% identity of deduced amino acid sequence with Rhodopseudomonas palustris KUGB306. A phylogenetic tree constructed by the Neighbour-Joining method based on the sequence of ALAS amino acid sequence showed that strain R5 was clustered with Rhodopseudomonas palustris with homology being 100%. Strain R5 with the highest production of 5- ALA should therefore be classified in the genus of microbiological identification. The work lays the overproduction of 5-ALA. Rhoclopseudomonas, which was accordance with the result the foundation for obtaining genetic engineering strains for