PSAE-MEDIATED AND NDHF-MEDIATED ELECTRON-TRANSPORT AFFECT BICARBONATETRANSPORT RATHER THAN CARBON-DIOXIDE UPTAKE IN THE CYANOBACTERIUM SYNECHOCOCCUS SP PCC7002

The wild-type and three deletional interposon mutants (psaE, ndhF, psa E/ndhF) of Synechococcus sp. PCC7002 were analysed with respect to the ir ability to induce the CO2-concentrating mechanism (CCM). The respon se of the ndhF mutant was similar to that of the control with normal a daptation of CO2 and HCO3- transport at low CO2. In contrast, the psaE mutant was unable to grow normally at 20 mu L . L(-1) and could not i nduce high-affinity HCO3- uptake. The double mutant showed an even gre ater degree of impaired growth than the psaE mutant, even at 350 mu L . L(-1) CO2. It also showed a relatively specific defect in the abilit y of the cells to induce high-affinity HCO3--uptake, although when gro wth was severely restricted at 20 mu L . L(-1) CO2 there may also have been some effect on the induction of CO2 transport. Our results indic ate a key role for psaE-mediated, and to a lesser extent ndhF-mediated electron transport in efficient utilisation of HCO; under low inorgan ic carbon in Synechococcus sp. PCC7002.