||Abstract: "The excess oxygen concentration within the plesiomorphic cyanobacterium Gloeobactor violaceus is only 0.025 μM, or four orders of magnitude lower than the oxygen concentration in air-saturated water." P.1885 right column bottom paragraph: "Gloeobacter violaceus: This cyanobacterium does not contain thylakoid membranes. Instead, its plasmic membrane contains all the proteins needed for oxygenic photosynthesis (ref 46). [Investigators] assume that the plasmic membrane is similar to the thylakoid membrane, with Pt = 8 cm/s. Combining this with Eqs. 6, 7, and 14, [they] obtain an oxygen concentration of C(R) = 0.024 μM + C0 on the outside surface of the cell and a concentration difference across the photosynthetic membrane of ΔC = 6 × 10^−4 μM. Thus, the oxygen concentration within the cell will be only 0.025 μM higher than the average concentration C0 in the surrounding water." P.1886 right column bottom paragraph: "For all modeled photosynthetic single cells, the excess oxygen concentration within the cell is negligible compared with the oxygen concentration of 230µM, which is typical for air-saturated water. As expected, the most primitive known cyanobacterium, Gloeobacter violaceus, generates the lowest excess oxygen level of 0.025µM or ~0.01% of ambient oxygen concentration."