FIG 4 .
Expression of uptake hydrogenase improves O2 tolerance of nitrogenase. (A) Effect of O2 on nitrogen fixation activity of the TSyNif-2 strain. (B) Schematic showing the insertion of uptake hydrogenase genes hupSL and hupW from Cyanothece 51142 into the chromosome of the TSyNif-2 strain. (C) Comparison of nitrogen fixation activities under different micro-oxic conditions. Samples were collected from cultures under 12-h light/12-h dark conditions in BG110 medium. Nitrogen fixation activity was assayed by acetylene reduction, and error bars represent the standard deviations of results from at least three independent experiments.