Abstract:The capacity of inducing a H2-uptake hydrogenase under free-living heterotrophic condition was examined in strain MXDI6 of Rhizobium of Desmodium intortum, and the effect of some factors such as gas phase, pH values and nickel on the expression of hydrogenase in strain MXDI6 has been investigated. It has been found that: (1) The optimum concentration of O2 and H2 for hydrogenase expression of strain MXDI6 are 4% and 15% respectively, while carbon dioxide has no obvious effect. (2)Favourable pH values for expression of hydrogenase of strain MXDI6 are 5. 0-6. 0.(3) THe H2-up take activities in strain MXDI6 are enhanced markedly by adding a lower concentration (<1 μmol/L)of NiCl2, whereas it is inhibited by a higher concentration (> 1 μmol/L) of NiC12. When NiCl2 concentration is 0. 5 μmol/L, the H2-uptake activities are increased to 3. 4 times.