Quantification of Cyanobacterial Biomass

Cell dry weight concentrations were measured directly as ash- free dry weight (AFDW) (Pinchuk et al., 2010 (link)) and compared in a standard curve to the indirect OD₇₃₀ measurements obtained using a Genesys 20 visible spectrophotometer (Thermo Scientific, Rockford, IL). Protein was quantitated using BCA protein reagent (Thermo Scientific). Chl a and phycocyanin concentrations were estimated using a previously described method that corrects the effect of scatter on absorbance from whole-cell suspensions (see Supplemental Methodologies) (Myers, 1980 ; Burns et al., 2006 (link)). Dissolved O₂ concentration in the reactor was measured with a Clark O₂ electrode (InPro^® 6800Series, Mettler Toledo International Inc., Columbus, OH). O₂ production rates as a function of “white light” irradiance (tungsten incandescent) were measured inside an oxygraph chamber (Hansatech, Norfolk, UK).