Isolation of high-CO_2 requiring mutants through the systematic gene disruption system in a cyanobacterium, Synechocystis sp. PCC6803

摘要

Aquatic photosynthetic organisms, such as a cyanobacterium, Synechocystis sp. PCC6803, induce a set of genes for a carbon concentrating mechanism (CCM) to acclimate to CO_2-limiting stress (Price 1998, Kaplan 1999). This mechanism elevates the CO_2concentration around the active site of ribulose-1,5-bisphosphate carboxylase / oxygenase (Rubisco) and thereby enables efficient CO_2 fixation despite the low affinity and selectivity of their Rubisco for CO_2. Analyses of high-CO_2 requiring mutants and low-CO_2 inducible genes have shown that several genes such as icfA coding for carbonic anhydrase (Fukuzawa 1992), ccmKLM for carboxysome components (Price 1993), ictB for putative regulator (Bonfil 1998), cmpABCD for ABC-type bicarbonate transporter (Omata 1999) and ndhD for NADH dehydrogenase subunit (Ohkawa 2000), play roles in the CCM. Nevertheless no high-CO_2 requiring mutants defective in essential Ci transporters have been identified to date. Taken with the fact that the profound effect of theictB mutation on HCO_3~--transporting activity is incompatible with the presumed occurrence of multiple HCO_3~- transporters and that the disruptant of cmpABCD did not show high-CO_2 requiring phenotype, it is assumed that other transporters are operating in the Ci uptake processes.