RANDOM INSERTIONAL MUTAGENESIS USED IN THE GENERATION OF MUTANTS OF THE MARINE CYANOBACTERIUM SYNECHOCOCCUS SP STRAIN PCC7002 WITH AN IMPAIRED CO2 CONCENTRATING MECHANISM

Random insertional mutagenesis (gene tagging) has been used to generat e ten kanamycin resistant mutants of the marine cyanobacterium, Synech ococcus sp. strain PCC7002, defective in components of the CO, concent rating mechanism (CCM). Three mutants had physiological characteristic s consistent with defects in carboxysome functioning such as the abili ty to over-accumulate inorganic carbon (Ci) but make Little use of thi s pool for photosynthesis. Another group of mutants could not survive at 20 mu L CO2 L-1 (low Ci) even though they were able to induce high- affinity CO2 and HCO3- transport systems within 6 h of acclimation to low Ci, albeit at reduced maximum rates compared to wild type (WT) cel ls. A third class of mutant grew more slowly at 20 mu L CO2 L-1 (pH 8. 2) than WT cells and failed to grow at pH 7.0 under the same CO2 condi tions. Besides inhibition of Ci transport rates in low-Ci cells and sm all internal Ci pools, these mutants had only partly developed a high- affinity HCO3- uptake system and had completely failed to induce a hig h-affinity CO2 transport system. Physiological characteristics of thes e mutants are discussed along with prospects for isolating the genes a ffected in these mutants.