自生条件下根瘤菌固氮酶活性的表达

EXPRESSION OF NITROGENASE ACTIVITY IN FREE-LIVING RHIZOBIUM

在自生条件下,测定从四种热带豆科植物中分离得到的七株根瘤菌乙炔还原能力,获得四株根瘤具有固氮活性。南洋楹菌株8638L、8638M、8638S和四棱豆菌株PS,其中菌株8638L和PS表现较高的固氮活性。结果表明,在培养基中含有低浓度氮源(谷氨酰胺)、两种碳水化合物(阿拉伯糖和琥珀酸钠)及低浓度的氧,是根瘤菌表达较高固氮酶活性所必需的。菌株8638L和PS固氮酶表达最适氧浓度为1％,谷氨酰胺浓度分别为2mMol/L或3mMol/L,最适pH范围在5.6～6.0之间.

Seven free-living strains of RhiRiobium, isolated from the nodules of four species of tropical leguminous plants, have been studied for their adility of acetylene reduction. Four strains of Rhtizobium, viz. 8638L 8638M and 8638S, Albizia falcataria, and strain PS Psophocarpus tetrago-nolobus produced more than trace amounts of acetylene reduction activity. Among them, Rhizobium sp. strains 8638L and PS yield higher nitrogenase activity. A medium containing a low-level source of nitrogen (Glutamine), a conbination of two carbohydrate (Arabinose and Succinate) and low oxygen tension appears necessary for the expression of high level of nitrogenase activity.The results showed that the optimal concentrations of oxygen for both strains 8638L and PS, were 1%, while the concentrations of Glutamine for the strains 8638L and PS were 2 mMol/L or mMol/L, respectively. The nitrogenase activity of both strains cultured on the medium being hi-hger under pH 5.6-6.0.