Open AccessRole of bacterial polysaccharides in the derepression of ex‐planta nitrogenase activity with rhizobia
Author(s) -
Jain D.K.,
Prévost D.,
Bordeleau L.M.
Publication year - 1990
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.1990.tb03937.x
Subject(s) - nitrogenase , rhizobia , polysaccharide , bradyrhizobium japonicum , derepression , biochemistry , chemistry , incubation , food science , bradyrhizobium , strain (injury) , biology , rhizobiaceae , rhizobium , microbiology and biotechnology , nitrogen fixation , bacteria , symbiosis , psychological repression , gene expression , gene , genetics , anatomy
Since bacterial polysaccharides may limit the availability of oxygen to the cells, we have investigated the role of rhizobial extracellular polysaccharides (EPS) and the non‐rhizobial polyscharide, xanthan, in the depression of ex‐planta nitrogenase activity with rhizobia in liquid medium. Two rhizobial strains known to exhibit ex‐planta nitrogenase activity on solid media were used; the slow‐growing Bradyrhizobium japonicum USDA 110 and the arctic Rhizobium strain N31, both being prolific EPS producers. In low nitrogen mannitol (LNM) liquid medium strain N31 exhibited nitrogenase activity only after 15 days, when sufficient EPS had accumulated in the medium, and activity was correlated with EPS production. When rhizobial EPS from an old culture was added to the LNM medium, nitrogenase activity was detected after 48 h incubation, indicating that EPS of the medium decreased oxygen diffusion to cells to a level that depressed nitrogenase activity. In modified LNM medium with xanthan nitrogenase activity was readily depressed. In both strains activity increased with increased xanthan concentration, but decreased sharply at higher concentrations. Strain N31 exhibited a narrower range of polysaccharide concentration for nitrogenase activity than the slow strain USDA 110. Thus, the condition for derepression of nitrogenase might be a careful balancing of the oxygen concentration surrounding the cells, and this condition is met when a balancing of polsaccharide, either synthesized by the rhizobia or added to the medium, can permit oxygen diffusion to within the narrow range required for the depression and expression of nitrogenase.