Distinct constitutive and low-[CO.sub.2]-induced [CO.sub.2] uptake systems in cyanobacteria: Genes involved and their phylogenetic relationship with homologous genes in other organisms

Cyanobacteria possess a [CO.sub.2]-concentating mechanism that involves active [CO.sub.2] uptake and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] transport. For [CO.sub.2] uptake, we have identified two systems in the cyanobacterium Synechocystis sp. strain PCC 6803, one induced at low [CO.sub.2] and one constitutive. The low [CO.sub.2]-induced system showed higher maximal activity and higher affinity for [CO.sub.2] than the constitutive system. On the basis of speculation that separate NAD(P)H dehydrogenase complexes were essential for each of these systems, we reasoned that inactivation of one system would allow selection of mutants defective in the other. Thus, mutants unable to grow at pH 7.0 in air were recovered after transformation of a [Delta] ndhD3 mutant with a transposon-bearing library. Four of them had tags within slr1302 (designated cupB), a homologue of sll1734 (cupA), which is cotranscribed with ndhF3 and ndhD3. The [Delta] cupB, [Delta] ndhD4, and [Delta] ndhF4 mutants showed [CO.sub.2]-uptake characteristics of the low [CO.sub.2]-induced system observed in wild type. In contrast, mutants [Delta] cupA, [Delta] ndhD3, and [Delta] ndhF3 showed characteristics of the constitutive [CO.sub.2]-uptake system. Double mutants impaired in one component of each of the systems were unable to take up [CO.sub.2] and required high [CO.sub.2] for growth. Phylogenetic analysis indicated that the ndhD3/ ndhD4-, ndhF3/ndhF4-, and cupA/cupB-type genes are present only in cyanobacteria. Most of the cyanobacterial strains studied possess the ndhD3/ndhD4-, ndhF3/ndhF4-, and cupA/cupB-type genes in pairs. Thus, the two types of NAD(P)H dehydrogenase complexes essential for low [CO.sub.2]-induced and constitutive [CO.sub.2]-uptake systems associated with the NdhD3/NdhF3/CupA-homologues and NdhD4/NdhF4/CupB-homologues, respectively, appear to be present in these cyanobacterial strains but not in other organisms. NAD(P)H dehydrogenase | constitutive [CO.sub.2] uptake | affinity to [CO.sub.2] | [CO.sub.2]-concentrating mechanism