Photosynthetic bacteria have a potential doubling rate that ranges from minutes to a few hours, depending on their biology and on chemical and physical factors in the environment in which the cells are growing.  Under natural conditions CO₂ consumption rates by phytoplankton of 0.312 g CO₂ g^-1 cell mass h^-1 have been recorded.  Based on this theoretical understanding, an experimental bioreactor was designed and constructed to measure the CO₂ consumption activity of photosynthetic bacteria. The reactor was equipped with sensors to measure media pH and electrical conductivity and controlled CO₂ gas intake.  It was also equipped with a gas sampling chamber containing sensors that measured humidity, pressure and CO₂ gas exhausted from the reactors. These data were used to calculate CO₂ fixation by the bacteria.  In total, six experiments were carried out, with incubation periods ranging from two days to seven days. This study measured photosynthetic rates for one purple non sulfur bacteria and one green non sulfur bacteria. This research measured CO₂ consumption rates similar to those reported for growth under natural conditions. For Rodospeudomonas palustris, the CO₂ uptake rates were from 0.543 g CO₂ g^-1 cell mass h^-1 to 1.038 g CO₂ g^-1 cell mass h^-1, and for Rodobacter capsulatus the CO₂ uptake was 0.359 g CO₂ g^-1 cell mass h^-1.                                     R. Paul Voroney, (519) 824-4120, pvoroney.@uoguelph.ca