Two CO₂ uptake systems in cyanobacteria: four systems for inorganic carbon acquisition in Synechocystis sp. strain PCC6803

Mari Shibata, Hiroshi Ohkawa, Hirokazu Katoh, Masaya Shimoyama and Teruo Ogawa

Abstract

The cyanobacterium Synechocystis sp. strain PCC6803 possesses two CO₂ uptake systems; one constitutive, dependent on NdhD3/NdhF3/CupA (Sll1734), and one low-CO₂ inducible, dependent on NdhD4/NdhF4/CupB (Slr1302). Homologues of these genes are present in pairs in most cyanobacterial strains. Synechocystis PCC6803 also possesses two types of HCO₃^– transporters; an ATP-binding cassette (ABC)-type transporter encoded by the cmp operon, and a novel sodium-dependent transporter encoded byslr1512(sbtA) that plays a central role in HCO₃^– uptake. Mutants impaired for one of these four inorganic-carbon acquisition systems did not show mutant phenotype. Mutants inactivated for both CO₂ uptake systems were unable to grow at pH 7.0 in air, although they grew normally at pH 9.0 in air. Additional inactivation of the SbtA-type HCO₃^– transporter abolished growth at pH 9.0 in air. A fragment containing the promoter region of ndhF3 fused to the coding region of luxAB was inserted into a neutral site of the ΔndhD4 mutant to construct apF3-lux/ ΔndhD4 strain. The luminescence intensity of this strain was low in high-CO₂ grown cells, and was increased about 100 times after acclimation to air. Inactivation of the pF3-lux/ ΔndhD4 strain with a transposon-tagging library enabled us to isolate mutants incapable of acclimation to low CO₂.

Keywords: CO2 uptake system, cyanobacteria, HCO3– transporter, low-CO2 induction, Synechocystis.

Functional Plant Biology 29(3) 123 - 129 (2002) doi:10.1071/PP01188