Mutation of ndh genes leads to inhibition of CO₂ uptake rather than HCO₃^- uptake in Synechocystis sp. strain PCC 6803

Six mutants (B1 to B6) that grew poorly in air on BG11 agar plates buffered at pH 8.0 were rescued after mutations were introduced into ndhB of wild-type (WT) Synechocystis sp. strain PCC 6803. In these mutants and a mutant (M55) lacking ndhB, CO₂ uptake was much more strongly inhibited than HCO₃^- uptake, i.e., the activities of CO₂ and HCO₃^- uptake in B1 were 9 and 85% of those in the WT, respectively. Most of the mutants grew very slowly or did not grow at all at pH 6.5 or 7.0 in air, and their ability to grow under these conditions was correlated with CO₂ uptake capacity. Detailed studies of B1 and M55 indicated that the mutants grew as fast as the WT in liquid at pH 8.0 under air, although they grew poorly on agar plates. The contribution of CO₂ uptake appears to be larger on solid medium. Five mutants were constructed by inactivating each of the five ndhD genes in Synechocystis sp. strain PCC 6803. The mutant lacking ndhD3 grew much more slowly than the WT at pH 6.5 under 50 ppm CO₂, although other ndhD mutants grew like the WT under these conditions and showed low affinity for CO₂ uptake. These results indicated the presence of multiple NAD(P)H dehydrogenase type I complexes with specific roles.