Random Insertional Mutagenesis Used in the Generation of Mutants of the Marine Cyanobacterium Synechococcus sp. Strain PCC7002 With an Impaired CO₂ Concentrating Mechanism

Abstract

Random insertional mutagenesis (gene tagging) has been used to generate ten kanamycin resistant mutants of the marine cyanobacterium, Synechococcus sp. strain PCC7002, defective in components of the CO₂ concentrating mechanism (CCM). Three mutants had physiological characteristics consistent with defects in carboxysome functioning such as the ability to over-accumulate inorganic carbon (Ci) but make little use of this pool for photosynthesis. Another group of mutants could not survive at 20 mL 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) cells. A third class of mutant grew more slowly at 20 mL CO₂ L^-1 (pH 8.2) than WT cells and failed to grow at pH 7.0 under the same CO₂ conditions. Besides inhibition of Ci transport rates in low-Ci cells and small internal Ci pools, these mutants had only partly developed a high-affinity HCO₃^- uptake system and had completely failed to induce a high-affinity CO₂ transport system. Physiological characteristics of these mutants are discussed along with prospects for isolating the genes affected in these mutants.