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Photosynthetic bacterium, with original light synthetic system, is one of the earliest lives on the Earth. Under anaerobic condition, they can use light as an energy source and use natural organic material, sulfide, ammonia and other chemicals as hydrogen or carbon source for the photosynthesis. Photosynthetic bacteria are widely distributed in the soil, paddy fields, marshes, lakes and rivers etc., mainly in the anoxic zone of the aquatic environment where light can be transmitted. Now photosynthetic bacteria have been widely study in agriculture, environmental protection and medicine etc because of their distinctive mode of life.28 strains of photosynthetic bacteria were enriched and isolated from different samples. By combining the utilization of the carbon source and nitrogen source with 16S rDNA analysis, these strains were classified into five categories, The 16S rDNA of 8 strains from these five categories were sequenced and the phylogenetic tree of the 16S rDNAs were constructed. Among them, four types of photosynthetic bacteria were identified as Rubrivivax gelatinosus, Rhodobacter capsulate, Rhodobacter spheroids and Rhodopseudomonas palutris, respectively.Rubrivivax gelatinosus can excrete extracellular proteases. Selected Rubrivivax gelatinosus HI strain from the isolated Photosynthetic bacteria was used as the research object to investigate effects of the culture conditions on the production of the extracellular proteases, and investigated the biochemical characteristics of the extracellular protease. Under oxygen and dark condition, no extracellular protease activity was detected; indicating that in the oxygen and dark condition strain H1 can not produce extracellular protease. But under the light condition, in the logarithmic growth phase the extracellular protease activity increased rapidly with the multiplication of bacteria. After cultured for 132 h, the cell optical density was the highest, and the protease activity reached the maximum. Then the culture enters into the decline phase with reduced protease activity.Malic acid and glutamine are the best carbon source and nitrogen source, respectively, for the strain to pruduce extracellular protease.The characterization of the protease by using crude enzyme showed that the optimum pH and temperature for the protease are pH8.0 and 40℃respectively, the serine protease inhibitor PMSF almost completely inhibited the actibity of the extracellular proteolytic enzyme, while other serine protease inhibitors, metal ion-type protease inhibitors and cysteine or serine protease inhibitor leupeptin did not inhibit it. These results showed that the protease could belong to serine protease family.In addition, the enzyme indicated strong resistance to many organic solvents and denaturants.
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