Effect of sulfur supply on sulfate uptake, and alkaline sulfatase activity in free-living and symbiotic bradyrhizobia
O'Hara, G.W., Franklin, M. and Dilworth, M.J. (1987) Effect of sulfur supply on sulfate uptake, and alkaline sulfatase activity in free-living and symbiotic bradyrhizobia. Archives of Microbiology, 149 (2). pp. 163-167.
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The effect of sulfur limitation on sulfate transport and metabolism was studied in four bradyrhizobia strains using sulfur-limited and sulfur-excess chemostat cultures. Characteristics of bradyrhizobia associated with sulfurlimitation were determined and these parameters used to bioassay the sulfur status of bacteroids in nodules on sulfur adequate or sulfur deficient soybean and peanut plants. Sulfur-limited cells took up sulfate 16- to 100-fold faster than sulfur-rich cells. The sulfate-uptake system appeared similar in all strains with apparent Km values ranging from 3.1 μM to 20 μM sulfate with maximum activities between 1.6 and 10 nmol·min-1·mg-1 protein of cells. Sulfate-limited cells of all strains derepressed the enzyme alkaline sulfatase in parallel with the derepression of the sulfate transport system. Similarly, the initial enzyme of sulfate assimilation (ATP sulfurylase) was fully derepressed in sulfur-limited cultures. Bacteroids isolated from sulfur adequate and sulfur deficient soybean and peanut possessed very limited sulfate uptake activity and low levels of activity of ATP sulfurylase as well as lacking alkaline sulfatase activity. These results indicate bacteriods have access to adequate sulfur to meet their requirements even when the host plant is sulfur-deficient.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||School of Environmental and Life Sciences|
|Copyright:||© 1987 Springer-Verlag|
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