Fast induction of high-affinity HCO₃^-transport in cyanobacteria

The induction of a high-affinity state of the CO₂-concentration mechanism was investigated in two cyanobacterial species, Synechococcus sp. strain PCC7002 and Synechococcus sp. strain PCC7942. Cells grown at high CO₂ concentrations were resuspended in low-CO₂ buffer and illuminated in the presence of carbonic anhydrase for 4 to 10 min until the inorganic C compensation point was reached. Thereafter, more than 95% of a high-affinity CO₂-concentration mechanism was induced in both species. Mass-spectrometric analysis of CO₂ and HCO₃^- fluxes indicated that only the affinity of HCO₃^- transport increased during the fast-induction period, whereas maximum transport activities were not affected. The kinetic characteristics of CO₂ uptake remained unchanged. Fast induction of high-affinity HCO₃^- transport was not inhibited by chloramphenicol, cantharidin, or okadaic acid. In contrast, fast induction of high-affinity HCO₃^- transport did not occur in the presence of K252a, staurosporine, or genistein, which are known inhibitors of protein kinases. These results show that induction of high-affinity HCO₃^- transport can occur within minutes of exposure to low-inorganic-C conditions and that fast induction may involve posttranslational phosphorylation of existing proteins rather than de novo synthesis of new protein components.