PsaE- and NdhF-mediated electron transport affect bicarbonate transport rather than carbon dioxide uptake in the cyanobacterium Synechococcus sp. PCC7002

The wild-type and three deletional interposon mutants (psaE, ndhF, psaE/ndhF) of Synechococcus sp. PCC7002 were analysed with respect to their ability to induce the CO₂-concentrating mechanism (CCM). The response of the ndhF mutant was similar to that of the control with normal adaptation of CO₂ and HCO₃/^- transport at low CO₂. In contrast, the psaE mutant was unable to grow normally at 20 μL·L^-1 and could not induce high-affinity HCO₃/^- uptake. The double mutant showed an even greater degree of impaired growth than the psaE mutant, even at 350 μl·L^-1 CO₂. It also showed a relatively specific defect in the ability of the cells to induce high- affinity HCO₃/^--uptake, although when growth was severely restricted at 20 μL.L^-1 CO₂ there may also have been some effect on the induction of CO₂ transport. Our results indicate a key role for psaE-mediated, and to a lesser extent ndhF-mediated, electron transport in efficient utilisation of HCO₃/^- under low inorganic carbon in Synechococcus sp. PCC7002.